Methanepotentialofsewagesludge lourdesrodriguez

METHANE POTENTIAL OF SEWAGE SLUDGE TO INCREASE BIOGAS PRODUCTION

Lourdes Rodriguez

August 2011

TRITA-LWR Degree Project ISSN 1651-064X LWR-EX-11-22

Lourdes Rodriguez

TRITA LWR Degree Project 11:22

© Lourdes Rodriguez 2011 Degree Project at Masters Level Materials and Sensor Systems for Environmental Technologies (IMMSSET) Department of Land and Water Resources Engineering Royal Institute of Technology (KTH) SE-100 44 STOCKHOLM, Sweden Reference should be written as: Rodriguez, L (2011) “Methane potential of sewage sludge to increase biogas production” TRITA LWR Degree Project 11:22

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Methane potential of sewage sludge to increase biogas production

S UMMARY The current global environmental concern which revolves on the dependency of fossil fuels has caused a mayor impulse in alternative energies such as solar, wind, geothermal and biogas. Sludge is the only and most abundant residue that remains from waste water treatment plants. Sludge can be anaerobically digested and produces biogas, composed mainly of methane and carbon dioxide. This method reduces the volume of sludge for disposal and presents a positive energetic balance, recovering energy as electricity. This thesis was developed in Hammarby Sjöstadsverk research facility, with the specific aim to perform biochemical methane potential (BMP) test in the sludge in order to measure the anaerobic biodegradability of substrate and quantify the maximum methane producing capacity of the bacteria involved. Anaerobic digestion is the biological process in which organic material of a substrate is degraded by microorganisms in the absence of oxygen and it is the most used method used to stabilize sewage sludge. BMP tests are used to provide a measure of anaerobic degradability of a given substrate. This study describes a new BMP test procedure formulated by Bioprocess Control. The Automated Methane Potential Test System® (AMPTS) consists of a thermostatic water bath used for reactor incubation. In each reactor a small amount of substrate and inoculum are incubated at desired temperature and mixed by a slow rotating agitator. Biogas is produced in each reactor and passes to the next unit. This is a CO2 fixing step, the biogas goes through an individual vial containing an alkali solution (NaOH). Gases such as CO2 and H2S are removed by chemical reactions and CH4 passes to the next step which is the gas volume measuring device, CH4 is analyzed using a wet gas flow measuring device that works by the principle of liquid displacement. When a defined volume of gas is accumulated, the flow cell lifts open and the bubble of gas emerges through water. After the flow cell has opened and clicked back down, a digital pulse is generated and recorded in the computer. Each flow cell is connected to a data acquisition unit that together with a computer; records and displays the resulting methane production. In the experiments conducted, two different inoculums were used to seed the reactors. Inoculum 1 was taken from Sjöstadsverket’s reactor and Inoculum 2 was taken from Henriksdal’s digestion chambers to make a reliable comparison. The substrate used throughout all the experiments was the incoming sludge to Sjöstadsverket’s reactor consisting in mainly primary sludge. Two experiments were performed, experiment 1: was using an Inoculum/Substrate ratio of 2:1 based on VS content. Experiment 2: was using I/S ratio of 1:1 based on volumes. For experiment 1, VS% of inoculum and substrate were calculated in order to determine the amount of volumes to mix. After recollection of data from the AMPTS, the methane potential was calculated in normalized volume of CH4 produced per gram VS of substrate added (NL/gVS). After 20 days of incubation samples S1 and H2 in experiment 1 resulted in 1.06 and 0.88 NL of CH4, respectively. A mean value of accumulated gas in the blanks was subtracted and a methane potential of 0.29 and 0.33 NL/gVS was determined. For experiment 2, the same procedure was conducted and samples Control S1 and Control H2 resulting in 1.08 and 0.96 NL of CH4, respectively and a methane potential of 0.31 and 0.29 NL/gVS was determined. For both experiments the first 2-3 days iii

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represented the maximum percentage of accumulated gas (around 4020% of the total gas production). Results demonstrated that both samples containing inoculum 1, produced a larger volume of total accumulated gas, however the methane potential which is calculated in Normal Liters per gram of VS added, is higher for sample H2 than S1. Therefore this means that samples containing inoculum 1, after converting all the organic material available from the substrate started to produce methane from the inoculum itself. This may suggest that inoculum 1, originating from SjÜstadsverket’s digester, can operate at a higher organic load rate. It can also mean that methanogenic bacteria in the sludge have great adaptability and grew rapidly. After analyzing the AD process system of SjÜstadsverket it can be concluded that disposing of the dewatered sludge coming from the digester would mean a removal of potential organic material that can be converted to methane. Therefore the recycling and reintegration of the dewatered sludge back to the digester could mean an increase in the methane yield of the process, in the meantime decreasing the HRT and increasing the SRT. This moreover means an increase in capacity and process efficiency.

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Methane potential of sewage sludge to increase biogas production

S AMMANFATTNING Nuvarande globala miljöproblem som till stor del handlar om beroendet av fossila bränslen har skapat en stor drivkraft för utveckling av alternativa energikällor som sol, vind, jordvärme och biogas. Avloppsslam är den enda och viktigaste resten från avloppsreningsverk. Slam kan anaerobt rötas, vilket ger biogas som huvudsakligen består av metan och koldioxid. Anaerob rötning reducerar volymen av slam för destruktion, ger en positiv energibalans och energin kan återvinnas som elektricitet. Denna avhandling har gjorts vid Hammarby Sjöstadsverk forskningsanläggning, med det specifika syftet att utföra biokemiska metanpotentialtester (BMP) av slammet för att mäta den anaeroba nedbrytbarheten för substrat och kvantifiera den maximala metankapaciteten att för bakterierna. Anaerob rötning är en biologisk process där organiskt material i ett substrat bryts ned av mikroorganismer i frånvaro av syre och är den mest använda metoden för att stabilisera avloppsslam. BMP tester används för att ge ett mått på anaerob nedbrytbarhet för ett visst substrat. Denna studie beskriver en ny BMP testförfarande som utvecklats av Bioprocess Control. Automated Metan Potential Test System ® (AMPTS) består av termostatvattenbad som används för reaktorinkubation. I varje reaktor inkuberas en liten mängd av substrat med inokulum vid önskad temperatur och blandas med en långsam roterande omrörare. Biogas produceras i varje reaktor och leds till nästa enhet. Detta är en CO2 fixerande steg där biogas går genom en flaska som innehåller en alkalisk lösning (NaOH). Gaser som CO2 och H2S avlägsnas genom kemiska reaktioner och CH4 passes till nästa steg där gasvolymen mäts med hjälp av en våt gasflödesmätare, som verkar genom principen om flytande deplacement. När en definierad volym gas samlats, lyfter flödescellen och öppnas och gasbubbla går upp genom vattnet. Efter att flödescellen har öppnat och klickat tillbaka, genereras en digital puls som registreras i datorn. Varje flödescell är ansluten till en datainsamlingsenhet som tillsammans med en dator, registrerar och visar den resulterande metanproduktionen. I experiment har två olika inoculum använts till reaktorerna. Inokulum 1 togs från Sjöstadsverket rötkammare och inokulum 2 togs från Henriksdals rötkammare. Substratet används i alla försöken var inkommande slam till Sjöstadsverket rötkammare som i huvudsak består av primärslam. Två försök utfördes: Försök 1 använde inokulum/substrat i förhållandet 2:1 baserat på VS innehåll. Försök 2 använde inokulum/substrat i förhållandet 1:1 baserat på volymer. För försök 1, beräknades VS% av inokulum och substrat för att fastställa vilka volymerna som skall blandas. Efter uppsamling av data från AMPTS, beräknades metanpotentialen i normaliserade volym CH4 producerat per gram VS av tillfört substrat (NL/gVS). Efter 20 dagars inkubation gav proverna S1 och H2 i försök 1 i 1.06 respektive 0.88 NL av CH4,. Ett medelvärde av ackumulerade gas i blankprov med enbart inokulum subtraheras varvid metanpotentialerna 0.29 respektive 0.33 NL/gVS erhölls. För försök 2 genomfördes samma förfarande och proverna S1 och proverna H2 gav 1.08 respektive 0.96 NL av CH4, och metanpotentialerna 0.31 respektive 0.29 NL/gVS erhölls. För båda experimenten gav de första 2-3 dagarna den högsta procentandel av ackumulerad gas (ca 40-20% av den totala gasproduktionen).

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Resultaten visade att proverna med inokulum 1, producerade en större volym totalt ackumulerade gas, men metanpotential beräknat i Normalliter per gram VS l, är högre för prov H2 än S1. Detta innebär att prover som innehåller inokulum 1, efter konvertering allt organiska material som finns I substratet började tillverka metan från själva inokulum. Detta kan tyda på att inokulum 1, med ursprung från Sjöstadsverkets rötkammare, kan fungera på en högre organisk belastning. Det kan också betyda att metanbildande bakterier i slammet hade stor anpassningsförmåga och växte snabbt. Efter att ha analyserat den anaeroba rötningsprocessen vid Sjöstadsverket kan man dra slutsatsen att användning av avvattnat slam från rötkammaren kan ytterliggare reducera organiskt material som kan omvandlas till metan. Återvinning och cirkulering av avvattnat slam tillbaka rötkammaren kan ge en ökning av metanutbytet av processen genom att minska HRT (hydrauliska uppehållstiden) och öka SRT (slamuppehållstiden). Detta innebär dessutom en ökning av kapaciteten och processeffektivitet.

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A CKNOWLEDGMENTS My greatest gratitude goes to my family; my parents and sisters who have always been there for me, guiding my steps, giving me their support and always having a word of encouragement. I also wish to express my gratitude to my supervisor Erik Levlin, for giving me the opportunity to perform this thesis and guiding me with insightful comments and explanations. To Lars Bengtsson and all the people from Hammarby Sjรถstadsverk for opening their doors and letting me learn more about anaerobic digestion and making my time in the plant more fun. Furthermore, I would like to thank the Erasmus Mundus Programmme for providing economical support throughout this master and to my professors from the Royal Institute of Technology and the University of Bologna for all their shared knowledge. I would also like to thank all my friends for their unconditional support, for cheering me on and enjoying with me all the great moments and experiences I have had during these past two amazing years.

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Methane potential of sewage sludge to increase biogas production

T ABLE OF CONTENT Summary Sammanfattning Acknowledgments Table of content Abbreviations Abstract 1. Introduction 2. Background 2.1

Sewage sludge 2.1.1 2.1.2

2.2

4

Microbiology in anaerobic digestion Process parameters in anaerobic digestion

Methane potential test

3.4 3.5

4.

Sample preparation CO2 fixing BMP setup

12 13 13

Methane production Anaerobic degradability

Results and Discussion 4.1 4.2 4.3

5. 6. 7.

Methane potential tests Biodegradability Inoculum to substrate ratio

Conclusions Future research References 7.1

7 8 9 10 10 11 12

Experimental design Inoculum and substrate Batch digestion tests 3.3.1 3.3.2 3.3.3

4 5

9

Materials and Methods 3.1 3.2 3.3

8.

2 3

Hammarby SjĂśstadsverk treatment process Henriksdal treatment process Technologic advances and investigations 2.5.1

3.

Types of sludge Recycling and disposal of sludge

Anaerobic digestion 2.2.1 2.2.2

2.3 2.4 2.5

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Other references

Appendix I – Raw data from the AMPTS program

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14 14 14 14 17 18 18 20 20 22 I

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A BBREVIATIONS AD AMPTS BMP CSTR HRT NL OLR SRT STP TS VFA VS VSR WWTP

Anaerobic Digestion Automated Methane Potential Test System Biochemical Methane Potential Continuous Stirred Tank Reactor Hydraulic Retention Time Normal Liter Organic Load Rate Solids Retention Time Standard Temperature-Pressure Total Solids Volatile Fatty Acids Volatile Solids Volatile Solids Reduction Waste Water Treatment Plant

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Methane potential of sewage sludge to increase biogas production

A BSTRACT Sewage sludge is treated with the biological process of anaerobic digestion in which organic material of a substrate is degraded by microorganisms in the absence of oxygen. The result of this degradation is biogas, a mixture mainly of methane and carbon dioxide. Biochemical Methane Potential tests are used to provide a measure of the anaerobic degradability of a given substrate. This study aims to determine the methane potential in Sjöstadsverket’s sludge this will moreover determine the viability of recycling the digested sludge back into the anaerobic system for further digestion. Batch digestion tests were performed in both Sjöstadsverket’s (S1) and Henriksdal’s (H2) sludge, for a reliable comparison. An inoculum to substrate ratio of 2:1 based on VS content was used and BMP tests presented results that S1 and H2 in the 20 days of incubation produced 0.29 NLCH4/gVS and 0.33 NLCH4/gVS respectively. A second experiment considering the same amount of substrate (200ml) and inoculum (200ml) for each sample, showed that Control S1 had a higher methane potential than Control H2, 0.31 NL/gVS and 0.29 NL/gVS respectively. All the samples containing Sjöstadsverket’s inoculum presented a higher volume of total accumulated gas (measured in Normal Liters), however methane potentials are low. Results demonstrated that methane production in samples S1 and Control S1 was originating from the grams of VS in the inoculum itself after depletion of all the soluble organic material in the substrate. This suggested that Sjöstadsverket’s sludge can endure a higher organic load rate and that the digested sludge still has potential to produce biogas, hence the recycling of this can enhance the biogas production in the digestion system. Key words: Anaerobic digestion; Methane potential; Biogas production; Sewage sludge; BMP.

1. I NTRODUCTION The current global environmental concern focuses on two important aspects: the increase in the emission of greenhouse gases, which is attributed to cause climate change; and the energy crisis. This outlines the importance of studying alternative energies as a result of the negative impacts of production and use of fossil fuels as well as the dependence on the global economy towards them. This has caused a major impulse to a wide range of alternative energies, such as solar, wind, geothermal and biogas. Sludge is the only and most abundant residue that remains from wastewater treatment plants. Sewage sludge can be anaerobically digested and its product is biogas, composed mainly of methane and carbon dioxide. This process moreover minimizes the volume of sludge, which decreases the also growing problem of exponential generation of waste. Anaerobic digestion helps break down biodegradable organic fraction present in municipal solid waste sludge, turning it into biogas with high methane content, therefore, having a high energy use and a stabilized final waste with a high rate of destruction of pathogenic microorganisms, which can be alternatively used as soil fertilizer. Hence, anaerobic digestion presents a positive energetic balance allowing both pollution prevention and recovery of sustainable energy (De Baere, 2000). Anaerobic digestion of sludge not only offers the possible use of biogas for electricity but the growing interest of upgrading biogas for fuel, makes this alternative all the more stimulating and attractive. Hammarby Sjöstadsverk is a leading research & development facility in wastewater purification technologies and currently involved in a project 1

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destined to increase the biogas production from sewage sludge treatment in their pilot anaerobic reactor. The overall goal is to increase the degree of digestion to over 60%, reducing the hydraulic retention time from 20 days to 10 days and simultaneously increasing the organic load rate. The following thesis was developed within this project, testing the biodegradability and methane potential in the sludge of the digestion process. The specific aim of this thesis is to investigate and perform biochemical methane potential (BMP) test in the sludge of the anaerobic digester operating in Sjรถstadsverket, in order to measure the anaerobic biodegradability of substrate and quantify the maximum methane producing capacity by the group of organisms present in the sludge, and the rate of biodegradability. BMP tests as well as being used for monitoring the quality of the sludge in anaerobic reactors, is a tool that evaluates the behavior of biomass and determines the maximum organic load rate that can be applied to the system, ensuring stability and degradability of the substrates enhancing the overall biogas production. BMP tests will moreover determine the viability of recycling the dewatered sludge back to the digester. Furthermore, a comparison with the sludge from Henriksdal Wastewater Treatment Plant (WWTP) and the biogas potential therein is also investigated in order to present a reliable and stable comparison. The necessity to perform this study is based on developing an alternative use to the volume of dewatered sludge generated after the digestion process and enhance the overall biogas production.

2. B ACKGROUND This chapter gives an introduction to the literature review done in the thesis work. It starts with the description of types of sludge and the possible methods of disposition. Following with a theoretical background of the general steps involved in the anaerobic digestion process and the description of the parameters that affect the process. Finishing with a quick overview of the treatment methods of wastewater used in Hammarby Sjรถstadsverket and Henriksdal Wastewater Treatment Plant as well as the technological advances in the anaerobic digestion of sludge.

2.1

Sewage sludge As the only residue produced from waste water treatments, the handling of sewage sludge has become of growing awareness. The disposal of sludge accounts up to 60% of the total costs for wastewater treatment plants (Ahmed et al, 2008). The increasing production of sludge and the risk it may have to the environment and human health have made a necessity to find efficient ways to handle it and reduce its volume. Many studies have proven that the process of anaerobic digestion is an efficient, economic and sustainable method to treat sewage sludge.

2.1.1

Types of sludge The characteristic of the sludge depends mostly on the origin (treatment of industrial, domestic or drinking water) and technical parameters used in each treatment. Sewage sludge can be divided into different types according to the conventional treatment process it has been through. Primary sludge comes after the primary treatment, generally physical or chemical processes to retain suspended particles, large and/or dense particles (solids, grease and scum). It removes 50-70% of suspended 2

Methane potential of sewage sludge to increase biogas production

solids (El-Hadj 2006). And it has a low level of Volatile Solids content (VS around 55% to 60%). This type of sludge ferments very easily. Secondary sludge is generated from the biological treatment of wastewater, it uses a mixture of living microorganisms, mainly bacteria, that break down the organic material and contaminants that remain after the primary treatment. It is also called activated sludge. Mixed sludge is a combination of primary and secondary sludge that can be mixed prior to sludge treatment. Digested sludge is secondary or mixed sludge that has gone through a biological stabilizing process called digestion. This digestion can be done under different temperatures (mesophillic or thermophillic) and in aerobic or anaerobic conditions. Digested sludge is less odorous, reduced in mass, reduced in pathogens and is more easily dewatered (Bitton, 1999).

2.1.2

Recycling and disposal of sludge The production of sewage sludge is always increasing with growing population and effective ways of its handling must be carried out. There are 3 main routes for recycling and disposing of sludge in the European Union. Agriculture Agricultural application is a way to recycle the agricultural value (macro and micronutrients) that is present in the stabilized or treated sludge and incorporate it to land. It may be the cheapest route; however; it has many constraints and regulations to be followed. Many concerns in potential risks to human health and the environment have lead to directives and regulations, such as Directive 86/278/EEC, that assure sludge quality and microbiological standards. In Sweden the use of sludge in agriculture has had to gain acceptance and trust. The Swedish Environmental Protection Agency (SEPA) has implemented more rigorous directives and regulations that ban the usage of sewage sludge on pastureland and it controls all the necessary analysis for contaminants in sludge and soil. Also, Sweden has adopted other regulations concerning different aspects such as permissible concentrations of toxic elements is sewage sludge, management of fertilizers, requirements and permissions for waste water treatment plants, deposit of sludge and sludge quality assurance (Gendebien et al, 2010). Incineration This technique is significantly increasing when an agricultural application is banned or excluded. Sludge can be incinerated and produces residual ash which is usually disposed in a landfill, and a flue gas. This alternative is a potential source of renewable energy, there is the possibility of energy recovery in the form of heat, which in turn can be used in various stages throughout the process. The main heat recovered comes from the flue gases after the combustion process (David et al, 2010). However, incineration is more costly than agriculture application and the gases released into the atmosphere may cause impacts on greenhouse gas emissions. Landfilling The landfilling of sludge is decreasing and relatively small in overall. The multiple regulations for landfilling sewage sludge and the high taxes imposed in these have made the necessity to come up with more efficient and economic alternatives. The Landfill Directive 99/31/EC sets a compulsory target to reduce the biodegradable waste in landfills 3

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(Gendebien et al, 2010); therefore limiting the landfilling of sewage sludge when there is no other route possible. Nevertheless, this technique is widely used in some countries.

2.2

Anaerobic digestion Anaerobic digestion (AD) in the most used method to treat or stabilize sewage sludge before it can be recycled or disposed (Gendebien et al, 2010). Anaerobic digestion is a biological process in which organic material of a substrate is degraded by microorganisms in the absence of oxygen. The result of this degradation is a mixture of methane, carbon dioxide and some small quantities of H2S, H2 and NH3. The composition of the biogas is dependent on the type of digested material and the functioning parameters of the process.

2.2.1

Microbiology in anaerobic digestion The anaerobic digestion process is characterized by four different phases in the substrate degradation. Each phase is carried out by different groups of bacteria that relate to each other. In fact many of these reactions occur simultaneously (Fig.1). Hydrolysis The first step in anaerobic digestion is the hydrolysis of high molecular weight compounds, lipids, proteins, polysaccharides and nucleic acids into soluble compounds that are easier to degrade such as sugars, amino acids and fatty acids (Appels et al, 2008). Hydrolytic bacteria involved in this phase hydrolyze the substrate with extracellular enzymes making them available for transportation between cell membranes and can then be degraded in the next phase. The degree of hydrolysis and the speed of the process depend on many elements that include pH, temperature, concentration of hydrolytic biomass and particulate size (Soto et al, 1993; Parawira et al., 2005). Hydrolysis of some complex compounds is the limiting step of their anaerobic digestion, while if the substrate is readily degradable, the limiting step is acetogenesis and methanogenesis (Bjรถrnsson et al., 2001). Acidogenesis

Fig 1. Degradation steps of the anaerobic digestion process. Modified from (Appels et al, 2008). 4

Methane potential of sewage sludge to increase biogas production

The soluble compounds obtained from hydrolysis are metabolized by fermentative bacteria and are converted into more simple compounds which include volatile fatty acids (VFA), acetate, ammonia, alcohols, lactate, H2, CO2, and other by-products. The bacteria responsible for this fermentation are both facultative and obligate anaerobes (Schink, 1997). Acetogenesis While some products of the fermentation process can be metabolized directly by methanogens, other intermediate compounds produced such as high organic acids and alcohols need to be further digested in order to be available for methanogens in the next phase. Acetogens are the bacteria that convert the intermediate compounds into mainly acetic acid as well as H2 and CO2 (Appels et al, 2008). The conversion in acetogenic reactions is mainly controlled by a low partial pressure of H2 in the mixture (Schink, 1997). Methanogenesis In this final phase, methanogenic archae convert the acetic acid, H2 and CO2 into CH4 (methane) and CO2. The methanogenic bacteria are divided into two groups; the first group is aceticlastic methanogens which degrade acetic acid to form CH4 and CO2. This path is responsible for up to 70% of the methane produced in normal anaerobic digesters (Coates, 1996). The second group is hydrogenotrophic methanogens and use hydrogen as electron donor and carbon dioxide as acceptor to produce methane (Appels et al, 2008).

2.2.2 Process parameters in anaerobic digestion Anaerobic digestion is a complex biochemical process; therefore it is necessary to maintain optimal conditions that can allow both the chemical reactions that need to take place, as well as the intracellular biochemical reactions required for the microorganisms to live. In order to create a stabilized system there are many environmental parameters to consider and monitor along the entire process. Temperature In general, at high temperatures the rates of chemical and biological reactions are faster than at low temperatures. Reaction speed of biological processes depends on the speed of growth of the microorganisms, which in turn is dependent on the temperature. AD is produced in nature in a wide range of temperatures from psychrophilic (below 20 ) to mesophillic (between 25-45 ) and thermophillic (between 45-65 )(Van Lier et al 1993). Temperature has many effects on the degradation process, it influences the partial pressure of H2 in the digester and the growth rate and metabolism of microorganisms, therefore the population dynamics (Appels et al, 2008). High temperatures have many advantages for instance an increase of solubility of organic compounds, enhanced biological and chemical reaction rates, increased death rate of pathogens especially in thermophillic environments and an increased degradation of VFAs and other intermediate compounds (Boe, 2006). However, high temperature can increase the fraction of free ammonia and can be inhibiting for some microorganisms (Appels et al, 2008). Temperature control plays a defining role in the anaerobic process and maintaining a stable temperature in the digester is of vital importance since sharp fluctuations of temperature can affect the bacteria behavior, particularly in methanogens.

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pH The organisms involved in each phase are different and need different pH ranges to achieve an optimum environment to live in. Therefore equilibrium between production and consumption of acids must be established so bacteria can coexist inside the digester in appropriate conditions. The change in pH can be both an indicator, and the cause of process imbalance. Methanogenic archea function in an optimal range of 6.5 – 8.0 (Boe, 2006) and fermentative bacteria in a wider pH range of 4 to 8.5 (Hwang et al., 2004). If a drastic pH change occurs, methanogens are interrupted and cause accumulation of VFAs; hence a decrease of pH in the reactor and an overall inhibition of the process. Monitoring of pH change and establishing the right pH is crucial to control and establish a stable operating system. Nutrients Sufficient nutrients and trace elements are required for an adequate microbial activity. Carbon, nitrogen, phosphorous, sulphur, potassium, calcium, nickel, zinc, cobalt, iron and copper are necessary for optimal performance of anaerobic microorganisms (Boe, 2006). Most nutrients can also be inhibitory to the process if they are present in high concentrations. Wastewater may contain high levels of the nutrients such as nitrogen and phosphorus. Generally in swine and cow manure all the nutrients needed are present in enough quantities. Mixing Mixing of anaerobic digesters has many objectives. These can be summarized in: forming a continual contact between substrate and the microbial population; preventing the formation of surface layers and foaming, as well as sedimentation in the digester; eliminating thermal stratification, sustaining a uniform temperature throughout the entire reactor and preventing the formation of dead spaces that would reduce the effective volume of the digester (Noone, 1990). The velocity of the mixing in a digester is a parameter than can influence greatly in the development of the digestion. Studies (McMahon et al, 2001) have discovered that a reactor with minimized mixing can tolerate a higher organic load than a reactor with intensive mixing, a higher rate of mixing resulted in acidification of the system. High mixing velocities can interrupt the formation of bacterial aggregates and the oxidation of VFA therefore slightly decreasing the biogas production. Organic Load Rate The organic load rate (OLR) is the ratio of the amount of organic material for each cubic meter of digester volume (i.e. kg VS/m3 per day). The adequate OLR of a system is directly dependent on the digester design, substrate concentration and retention time. High organic loads lead to a higher biogas production but also to higher instability due to an accumulation of VFA (Ahring et al, 1995). A low organic load prevents overloading and process failure, however results in low methane yield and is uneconomical to not use the maximum capacity of the digester. Therefore it is vital to determine an efficient OLR to maximize biogas production for each AD system. Retention Times Retention time is a very important parameter that mainly depends on the type of reactor to be used and the type of substrate. There can be two different ways to measure retention time. The first one is by hydraulic 6

Methane potential of sewage sludge to increase biogas production

retention time (HRT) which is the average time a liquid volume resides inside the digester; the second is by solids retention time (SRT) which is the average time the solid matter resides inside the digester. The fraction of organic material degraded increases with higher retention times, however the methane production will decrease after it exceeds the optimum. The digestion process needs of methanogenic bacteria. These are relatively slow reproducing bacteria and need sufficient time to reproduce. If the rate of bacteria leaving the digester with the effluent exceeds the growth rate of the bacteria, the population inside the digester will be washed out of the system. It is therefore necessary to determine sufficient solids retention time and hydraulic retention time that are adequate for the system and optimize the process. Toxicity There are many substances that can result inhibiting to the growth of anaerobic microorganisms, these can be already in the influent or can be produced during the AD process. VFA are the main intermediates in the AD process and along with acetate, H2 and methanol they become strong inhibitors for anaerobic sludge if they are present in high concentrations (Angelidaki et al, 2006). Ammonia is a common inhibitor, it is produced during the degradation process of nitrogenous matter mainly proteins. Ammonia toxicity increases at elevated pH and temperature due to a higher concentration of free ammonia which can penetrate through cell membranes and cause proton imbalance and potassium deficiency. The concentration of oxidized sulphur compounds can also be inhibitory in the process. Sulphate-reducing bacteria compete with methanogenic and acetogenic bacteria for many substrates like alcohol, organic acid and others and therefore decrease the amount of methane in the biogas produced. (Appels et al, 2008). Heavy metals are also found in industrial and domestic wastewater and sludge. Some heavy metals such as nickel and copper at low concentrations (below 10-4 M) are necessary nutrients for many enzymes, but at high concentrations can cause toxic effects to microorganisms (Boe, 2006).

2.3

Hammarby Sjöstadsverk treatment process

The following thesis was done at Hammarby Sjöstadsverket facilities. The water treatment designed in Sjöstadsverket is a conventional Swedish wastewater treatment with the following steps: pre-precipitation, sedimentation, six stages of biological treatment, secondary sedimentation and sand filtration. The pilot anaerobic reactor in Sjöstadsverket is supplied with both primary and secondary sludge coming from the sedimentation in different process lines in the plant. The sewage sludge used to perform the experiments in this thesis came from Sjöstadsverket pilot anaerobic reactor. In Sweden most of the anaerobic reactors are continuously blended where the liquid phase is not separated from the solid phase, therefore having a HRT and SRT of same duration. Sjöstadsverket aims to increase the biogas production in the anaerobic digester and reduce the normal HRT of 20 days to 10 days and increase the SRT by recycling the organic material in the digested sludge back to the reactor. The anaerobic digestion system works in the following way (Fig.2): primary and secondary sludge (sedimentation from line 1, 2 and 3) are pumped and mixed in a thickener which is then pumped to the digester. The anaerobic digester is a 10 cubic meter reactor that operates at a mesophillic temperature of around 37 °C ± 0.5 °C. The recycling of the sludge consists of dewatering the digested sludge by using a centrifuge 7

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Fig 2. Sludge pathway in the anaerobic digestion system at Sjรถstadsverket. and adding a polymer to separate the organic matter. The dewatered sludge is then introduced back directly into the digester; this recirculation will increase the residence time of organic material resulting in increased biogas production and efficiency. Moreover, the amount of sludge requiring disposal is reduced and the system becomes less sensitive to slow growing methanogens, since these can have an adequate time to grow even if the HRT is low.

2.4

Henriksdal treatment process The Henriksdal WWTP is the largest one in Stockholm, with an average incoming flow of about 240,000 m3 / d (Hellstedt et al, 2010). The treatment process consists of mechanical, chemical, biological treatment and a final stage in which the water passes through a sand filter before it reaches the final waterway destination (Fig.3). The sludge that is produced during the treatment process is collected and pumped into seven digesters located throughout the plant, adding to a total volume of about 38,400 m3. These digesters are continuously stirred tank reactors (CSTR) in which three different fractions are treated: primary sludge, excess biological sludge and external organic material (sludge collected from grease separators in the food and beverage industry). After AD, the digested sludge is dewatered and disposed. The biogas produced in the anaerobic digesters is collected in a gas dome and utilized for fuel in electricity production and heating and most importantly for the upgrading to vehicle fuel (biomethane) (Hellstedt et al, 2010).

8

Methane potential of sewage sludge to increase biogas production

Fig 3. A schematic view of Henriksdal’s wastewater treatment process. (Taken from stockholmvatten.se).

2.5

Technologic advances and investigations

Anaerobic digestion is one of the oldest and proven processes used for the stabilization of sludge resulting from domestic and industrial wastewater treatment. India, during the 60’s noticeably promoted the biogas production from cattle manure. China followed in the 70’s with the construction of digesters; and during the 80’s Denmark made an effort to demonstrate the potential of AD in production of electricity (Angelidaki et al, 2006). Great investigations in the basic knowledge of AD as well as its technological aspects have been developed throughout the years. These developments have introduced several different methodologies for the assessment of the activity and methane potential of sewage sludge and of the anaerobic biodegradability of organic substrates in wastewater sludge. In the following section, a brief description of the used methodology in this thesis is described.

2.5.1 Methane potential test A Biochemical Methane Potential (BMP) test is the most used tool to provide a measure of the anaerobic degradability of a given substrate. This method is a simple and fast way to determine the suitability of a substrate for anaerobic digestion and the potential methane yield therein. It is also commonly used to evaluate the potential in the co-digestion of mixed wastes to enhance the digester performance. Moreover BMP tests can measure the residual organic material remaining after treatment that can still be used to convert to biogas and the non-degradable part remaining (Moody et al, 2009). The use of BMP tests provides a relatively inexpensive, simple and repeatable method to make comparisons of the anaerobic digestibility and potential biogas potential between different substrates (Owens et al, 1993). There are many batch methods used to determine the methane potential of sludge. The basic principle in BMP tests is to gather organic waste and blend it with inoculum, incubate it in a closed vial at a specific temperature and measure the gas production volume and composition. The inoculum is seed sludge that comes from an operating digester, this way it is guaranteed to have the necessary microbial populations to perform the AD of the substrate (Angelidaki et al, 2006). The duration of the test differs mostly on the biodegradability rate of the substrate, 9

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meaning when there is no more biogas production measured. The methane potential is expressed in terms of standard temperature and pressure (STP) ml CH4 per 1 g of VS added (mL CH4 / g VS) (Hansen et al, 2003). Many methods based on product formation measuring end product (biogas) have been published over the years. All carry out the basic principle, however, the technical approaches and experimental setups vary significantly. There exist many differences in the pre-treatment of sample, the inoculum, the incubation process and the gas measurement method (Hansen et al, 2003). The biogas production can be measured as an increase of volume under constant pressure (volumetric methods), measuring the increase in pressure in constant volume (manometric methods), or the measurement of methane formation by gas chromatography (Angelidaki et al, 2006). The above procedures require expensive laboratory equipment such as gas chromatography also the biogas produced and methane content can only be measured manually and periodically with gas tight syringes, making it time-consuming to obtain sufficient data to fully understand the degradation profile dynamics. This thesis describes the BMP test procedure used in Bioprocess Control’s Laboratory in Lund, Sweden. The BMP tests were performed with Bioprocess Control’s Automated Methane Potential Test System (AMPTS)® (described in more detail in section 3.1) This AMPTS is a simple and efficient way for the recording and analysis of high quality data which moreover provides a better understanding of the methane potential of specific biomass substrates and its degradation. It is developed for on-line measurements of ultra low biogas and bio-methane flows produced from the anaerobic digestion of any biological degradable substrate (both solid and liquid form) at laboratory scale.

3. M ATERIALS AND M ETHODS The following chapter describes the experimental setups and protocol used in the thesis, as well as a characterization of the inoculums and substrates used. The methane potential was studied using an automated methane potential test system (AMPTS). Batch digestion tests were performed to analyze two different types of sludge as inoculum. The experiments were conducted using each inoculum with different inoculum to substrate ratio in terms of volatile solids content and volume. The same substrate was used throughout all the experiments.

3.1

Experimental design The batch digestion tests for methane potential were carried out using Bioprocess Control’s AMPTS equipment. The instrument setup can be divided into four units (Fig. 4). Unit A is a thermostatic water bath used for reactor incubation. In each reactor a small amount of substrate and inoculum are incubated at desired temperature and mixed by a slow rotating agitator. Biogas is produced in each reactor and passes to the next unit. Unit B is a CO2 fixing step, the biogas produced in each reactor goes through an individual vial containing an alkali solution (NaOH). Gases such as CO2 and H2S are removed by chemical reactions and CH4 is the only gas that passes through unchanged. Unit C is the gas volume measuring device, after CH4 passes through the alkali solution it is analyzed using a wet gas flow measuring device. This flow cell measuring device works by the principle of liquid displacement. When a defined volume of gas is accumulated, the flow cell lifts open and the 10

Methane potential of sewage sludge to increase biogas production

Fig 4. Schematic view of the experimental setup. bubble of gas can be seen emerging through the water. After the flow cell has opened and clicked back down, a digital pulse is generated and recorded in the computer program. Each flow cell is connected to Unit D, this is a data acquisition unit that together with a computer; records, analyzes and displays the resulting methane production.

3.2

Inoculum and substrate During the experiment, two different inoculums were used to seed the reactors and obtain an adequate environment. Inoculum 1 was digested sludge taken from Sjöstadsverket pilot anaerobic digester. The sludge was used fresh from the digester and poured into the reactor. The digester is a 10 m3 CSTR operating at a temperature around 37 ± 0.5 °C and with a HRT of 9 days. The OLR currently being applied at the time of inoculum collection was 1.3 – 1.5 kg/m3 per day. Inoculum 2 used in the BMP tests was digested sludge taken from Henriksdal WWTP. The sludge was collected and used fresh from one of the digestion chamber of the plant. The digester works at a mesophillic temperature around 37 °C and has a HRT of 19.5 days. The OLR applied to the digester is 1.5 kg/m3 per day. The substrate used for all the experiments was the incoming sludge of Sjöstadsverket plant, consisting mainly of primary sludge from the sedimentation in the different process lines. All inoculums and substrate were characterized in duplicates and an average was calculated (Table 1). 11

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TRITA LWR Degree Project 11:22

Table 1. Characteristics of Inoculum 1, 2 and substrate. Sludge

TS (%)

VS (%) 3.12

Temperature (°C) 37

Inoculum 1

4.70

Inoculum 2 Substrate

pH 6.86

2.32

1.43

36

7.07

1.53

1.30

21

5.96

VS and TS content were analyzed according to Standard Methods (APHA, 1998). Temperature and pH values were measured with a pH meter 330i from WTW (Weilheim, Germany).

3.3

Batch digestion tests

Two experiments were performed with the AMPTS. The first digestion test was performed to measure the methane potential in each batch reactor using different inoculums: SjĂśstadsverket sludge (Inoculum 1) and Henriksdal sludge (Inoculum 2). The inoculum to substrate ratio (I/S) selected was 2:1, based on VS content, which is the ratio mostly used in literature. Inoculum and substrate were mixed in digesters. Both samples were performed in triplicates. The second experiment was performed to determine the methane potential in each batch reactor using an inoculum to substrate ratio of 1:1 based on the volume, this was determined to set an example closer to reality where certain parameters such as VS% may not measured (i.e. codigestion in a farm). Samples were inoculated with Inoculum 1 and others with Inoculum 2. Both samples were performed in duplicates. Blank tests for each inoculum were performed in order to determine the background methane production from the inoculum alone that can then be subtracted from the methane production obtained from the samples. Blank tests were performed in duplicates.

3.3.1 Sample preparation Setting up the tests, the first step is to determine the VS of the inoculum and of the substrate to be tested (Table 1). For the first experiment, the sludge volume added to the bottles was calculated using the VS concentration. A total volume of 400ml is selected to avoid problems if foaming occurs. The selected ratio I/S was 2:1: (Equation 3.1) (Equation 3.2) To calculate the amount of inoculum needed, the equations 3.1 and 3.2 need to be re-written, substituting 3.2 in 3.1 to result in the following equations: (Equation 3.3) (Equation 3.4) Applying the equations 3.3 and 3.4, all the volumes of inoculum (1 and 2) and substrate were determined (Table 2). Reactors containing inoculum 1 are called from here on S1 and reactors containing inoculum 2 are called H2. When measuring the amount of inoculum and substrate to be used it is assumed that the density is 1 g/ml so that the volume in ml is equal to the weight in grams. 12

Methane potential of sewage sludge to increase biogas production

Table 2. Volumes of inoculum and substrates added to reactors (2:1 ratio based on VS content). Name

Unit (g)

Blank S (Inoc. 1) 400.00

Total liquid amount I/S ratio

(VS/VS)

Inoculum (Blank) content Substrate content

S1 400.00

Blank H (Inoc. 2) 400.00

H2 400.00

0.0

2.0

0.0

2.0

(% VS)

3.12

3.12

1.43

1.43

(% VS)

0.00

1.30

0.00

1.30

Inoculum amount

(g)

400.00

181.82

400.00

258.06

Substrate amount

(g)

0.00

218.18

0.00

141.94

Inoculum

(gVS)

12.48

5.67

5.72

3.69

Substrate

(gVS)

0.00

2.84

0.00

1.85

For the second experiment, a ratio of 1:1 based on volume of inoculum and substrate were mixed in the reactor. Two reactors contained (200ml of inoculum 1 + 200ml of substrate), from here on called Control S1; and two reactors contained (200ml of inoculum 2 + 200ml of substrate), from here on called Control H2. After all reactor bottles have been filled with the determined volumes of inoculum and substrates each mix was characterized (Table 3) in order to calculate the VS reduction after the anaerobic digestion.

3.3.2 CO2 fixing Carbon dioxide fixing bottles are prepared in order to make gases such as CO2 and H2S to chemically react with an alkali solution and be separated from the remaining methane. The alkali solution is prepared with a 3M NaOH solution. A pH indicator (Thymophthalein) is added in each bottle to monitor the sufficient OH- concentration in order to effectively strip CO2 and H2S.

3.3.3 BMP setup The digestion tests were performed in 500ml glass bottles. After filling up the reactors with inoculum and substrate a rubber stopper with three openings is placed. One opening is to insert the bent mixing stick that is attached to a motor. The second opening is to flush the reactor. The third opening is for biogas flow. Then an aluminum screw cap seals the reactor. All reactors are marked and placed in the water bath with a temperature set to 37 °C ± 1°C. The gas flow opening is connected to a CO2 fixing bottle and then connected to a flow cell in the gas measuring device. After all the tubes are properly connected, each reactor is flushed with N2 for two minutes. The data logging program was started and the methane production was monitored during 20 days. The mixing interval in each reactor was 60 seconds on and 60 seconds off. Table 3. Characteristics of the input mixed sludge in reactor. Reactor

TS (%)

VS (%)

pH

S1

3.09

2.21

6.66

H2

1.96

1.35

7.01

Control S1

3.27

2.31

6.75

Control H2

1.72

1.25

6.97

13

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3.4

TRITA LWR Degree Project 11:22

Methane production The methane potential was calculated as the accumulated methane produced per gram of VS added in each reactor, determined as followed: (Equation 3.5) Where, MP (methane potential) is the normalized volume produced per gram VS of substrate added (NL/gVS). Vsubstrate & inoculum is the accumulated volume produced from the reactor with both inoculum and substrate mixed. Vinoculum is the mean value of the accumulated volume produced by the blanks. The data from the AMPTS was analyzed and mean values from the sample replicas were calculated for the accumulated methane production during the 20 days.

3.5

Anaerobic degradability During the digestion test the SRT was equal to the HRT of 20 days, however not all the organic material present inside the reactors may be degraded. The degree of organic degradation in the anaerobic reactors can be measured based on the VS reduction after the anaerobic digestion process. The Volatile Solids Reduction (VSR) can be calculated by mass balance equations (Bhattacharya et al, 1996). Having obtained the characterization of input and output sludge, the mean degradation of VS in each reactor in a given time is measured as followed: (Equation 3.6)

4. R ESULTS AND D ISCUSSION The following chapter presents the final results from the anaerobic batch reactors. Both experiments using different I/S ratios are discussed. (Appendix 1) shows the raw data from all the experiments.

4.1

Methane potential tests The BMP is the experimental value of the maximum quantity of methane produced per gram of volatile solid. Applying equation 3.5 explained before, the methane yield as a function of time was calculated for each reactor. The results for the batch digestions test (Fig. 5) shows the methane potential curve of both samples with an inoculum/substrate ratio of 2:1. Sample S1 uses inoculum of Sjöstadsverket’s digester and H2 inoculum from Henriksdal’s digester. After 20 days of incubation, sample S1 and H2 resulted in a mean accumulated gas volume of 1.06 and 0.88 Normal Liters respectively. A mean value of the accumulated gas volume from the respective inoculum blanks is then subtracted from the accumulated gas volume of each of the samples. The methane potential is calculated taking in consideration the grams of VS added in the substrate volume in each reactor, therefore expressed as Normal Liter per grams of volatile solids (NL/gVS). The maximum methane potential of S1 and H2 in the 20 days of incubation was 0.29 NL/gVS and 0.33 NL/gVS respectively. Theses results are in an average range compared to other literature results. 14

Methane potential of sewage sludge to increase biogas production

METHANE POTENTIAL Accumulated gas volume NL/gVS

0.35 0.3 0.25 0.2 S1

0.15

H2

0.1 0.05 0 0

5

10

15

20

Time (days)

Fig 5. Methane potential of sample S1 and H2 with an I/S ratio of 2:1 measured in Normal Liter per gram of Volatile Solids added. The accumulated gas volume percentage was calculated continuously in a daily basis (Fig. 6). For both samples the first two days presented the maximum percentage of accumulated gas volume which ranged from 4020% of the total gas volume produced in each reactor, this may be due to the substrate being readily available for the methanogenic bacteria.

ACCUMULATED GAS VOLUME % 50

Accumulated gas volume %

45 40 35 30 25

S1

20

H2

15 10 5 0 0

5

10

15

20

Time (days)

Fig 6. Accumulated gas volume percent per day of incubation for samples S1 and H2. 15

Lourdes Rodriguez

TRITA LWR Degree Project 11:22

METHANE POTENTIAL Accumulated gas volume NL/gVS

0.35 0.3 0.25 0.2 Control S1

0.15

Control H2

0.1 0.05 0 0

5

10

15

20

Time (days)

Fig 7. Methane potential of samples Control S1 and Control H2 measured in Normal Liter per gram of Volatile Solids added. For the second experiment, two control samples were analyzed to measure the gas production based on the volume of substrate added. In one pair of samples 200ml of inoculum 1 is mixed with 200ml of substrate. On the second pair of samples 200ml of inoculum 2 was mixed with 200ml of substrate. This corresponds to an inoculum to substrate ratio of 2.4:1 and 1.1:1 for Control H1 and Control S2 respectively. The mean value of accumulated gas volume for control S1 and control H2 was 1.08 and 0.96 NL respectively. The same procedure as for the first experiment was conducted subtracting the mean gas volume from the blanks and calculating the methane potential using equation 3.5 (Fig 7). The maximum methane potential of control S1 and control H2 in the 20 days of incubation was 0.31 NL/gVS and 0.29 NL/gVS respectively. The rate of methane production was measured as the accumulated gas volume percentage per day (Fig. 8). For both samples the first three days display the maximum percentage of accumulated gas volume which ranged from 37-20% of the total gas volume produced in each reactor. The slow increase in the methane production after 10 days could be due possibly to the depletion of soluble substrates within the first 10 days of digestion, hence meaning that the reactors were not overloaded. Throughout both experiments, all the samples containing inoculum 1 had a higher accumulated gas volume (measured in Normal Liters) then samples containing inoculum 2. On the other hand the methane potential (measured in Normal Liter per grams of volatile solids) was higher for sample H2 than S1 when based to a 2:1 I/S ratio. However it is key to remember that to consider a 2:1 ratio, defined volumes were calculated (Table 2); and sample H2 contained a larger amount of inoculum than sample S1. These results show that the high gas volume collected in samples with inoculum 1 may be due to organic material from the inoculum itself that are being converted into methane or a 16

Methane potential of sewage sludge to increase biogas production

ACCUMULATED GAS VOLUME % Accumulated gas volume %

40 35 30 25 20

Control S1

15

Control H2

10 5 0 0

5

10

15

20

Time (days)

Fig 8. Accumulated gas volume percent per day of incubation for samples Control S1 and Control H2. possible increase in the methanogenic population. This may suggest that inoculum 1 can endure a higher organic load.

4.2

Biodegradability The principle of anaerobic digestion is based on the growth of anaerobic biomass. Therefore, outlet sludge is composed of the recalcitrant matter in the sewage sludge and of the anaerobic biomass, proteins being the major constituent of the anaerobic biomass (Mottet et al, 2010). For the output sludge samples results showed a reduction in TS and organic material due to the fermentation during the anaerobic digestion (Table 4). Taking the initial and final concentration of VS in each sample and applying equation 3.6, the Volatile Solids Reduction (VSR) percentage was calculated (Fig. 9). The VSR % for sample S1, H2, Control S1, and Control H2 were 33%, 36%, 32% and 34% respectively. All samples carried out around the same VS removal efficiency ranging in 32-36%. The ranges of VS removal for mesophillic digesters varies among literature, however thermophillic digesters tend to have a better VS reduction (Appels et al, 2008). Table 4. Characteristics of the input and output mixed sludge in reactor. Initial parameters Sample

Final parameters

TS (%)

VS (%)

pH

TS (%)

VS (%)

pH

S1

3.09

2.21

6.66

2.25

1.47

7.03

H2

1.96

1.35

7.01

1.45

0.86

7.32

Control S1

3.27

2.31

6.75

2.43

1.58

7.08

Control H2

1.72

1.25

6.97

1.04

0.82

7.24

17

Lourdes Rodriguez

TRITA LWR Degree Project 11:22

VSR % 50

Volatile solids reduction %

45 40 35 30

S1

25

H2

20

Control S1

15

Control H2

10 5 0

Fig 9. Volatile Solids Reduction percent for all batch-digestion reactors. Because of the small amount of sludge tested and the imprecision in determining the final VS content; considering that the volatile solids concentration fluctuates with time; it was rather difficult to measure the degradability based on the VSR alone (James et al, 1990). For a more accurate VSR study, a larger sludge volume and longer retention time is preferable.

4.3

Inoculum to substrate ratio Although the inoculum/substrate ratios used in these experiments were in the similar range (1:1 – 2:1). Behera (2010) shows results that demonstrate that methane yields are highly influenced by the I/S ratio, i.e., the lower the I/S ratio, the lower the methane yield. This behavior might be related to a low methanogenic activity or an insufficient population of methanogens. This will cause an imbalance in the production and consumption rate of VFA hence in the accumulation of the VFA produced during the acidogenic step. High concentrations of VFA can cause inhibition in methanogens. The VFA concentrations were not measured in these experiments. However, the pH values of all the reactors were measured at the end of the experiments (Table 4). The final pH in the reactors for both experiments ranged from 7.03 to 7.32 indicating a neutral pH with no accumulation of VFA during the digestion process. This may establish that the reactors have a proper production and consumption of VFA, therefore were not overloaded. A VFA accumulation would result in a low pH value.

5. C ONCLUSIONS This chapter presents the concluding thoughts of the thesis work after the discussion and analysis of the experimental results and the literature findings. From the results obtained it can be concluded that digested sludge can be used as inoculum for anaerobic digestion in mesophillic environments and it is possible to measure the methane production of substrates 18

Methane potential of sewage sludge to increase biogas production

resulting in accumulated gas volumes of up to 1.06 Normal Liters of methane in 20 days of incubation. BMP tests were performed in batch laboratory scale reactors at a mesophillic environment of 37 ± 1 °C. Results demonstrated that both samples containing inoculum 1 (S1 and Control S1), produced a larger volume of total accumulated gas (measured in Normal Liters) then H2 and Control H2. However the methane potential which is calculated in Normal Liters per gram of VS added, is higher for sample H2 than S1. Therefore this means that samples containing inoculum 1, after converting all the organic material available from the substrate started to produce methane from the inoculum itself. This may suggest that inoculum 1, originating from Sjöstadsverket’s digester, can operate at a higher organic load rate and still perform efficient anaerobic digestion of organic material. It can also mean that methanogenic bacteria in the sludge have great adaptability and grew rapidly. After analyzing the AD process system of Sjöstadsverket it can be concluded that disposing of the dewatered sludge coming from the digester would mean a removal of potential organic material that can be converted to methane. Therefore the recycling and reintegration of the dewatered sludge back to the digester could mean an increase in the methane yield of the process, in the meantime decreasing the HRT and increasing the SRT. This moreover means an increase in capacity and process efficiency. The reactors with a higher VSR percentage corresponds to the reactors with higher methane potential, however because of the small amount of sludge tested and the imprecision in determining the final VS content; considering that the volatile solids concentration fluctuates with time; it is rather difficult to measure the degradability based on the VSR alone. The BMP test gave a more clear and precise degradation profile of the sludge reactors that was reproducible. All samples tested reached the maximum percentage of accumulated gas volume (around 40% of the total gas volume) during the first 3 days of incubation (Fig. 6 and 8). This suggests that no inhibition existed during the process and that the fast depletion of soluble substrates encourages a higher organic load rate in the operating digester. It was also considered that the final pH value in the reactors was a good indicator of an efficient anaerobic digestion, maintaining the reactor around a neutral pH value means that there is no VFA accumulation and the production and consumption of these are balanced, providing and effective methanogenic activity. The experimental batch reactors must be monitored and controlled frequently in order to capture and record the methane production as a function of time. The use of the Automated Methane Production Test System reduces the workload and allows a continuous recollection of data. This makes it easier to conduct BMP test with longer retention times and fully understand the degradation profile of a given substrate. Previous methods using pressure tight syringes and gas chromatography present efficient results and are commonly used. Nevertheless, the suggested protocol using the AMPTS is a more simple and detailed procedure that has a great potential in the studies of methane production and can furthermore determine the viability of pretreatment methods for enhanced anaerobic digestion and determine inhibition in methane potential for future research.

19

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TRITA LWR Degree Project 11:22

6. F UTURE RESEARCH Anaerobic digestion has the potential to effectively treat sewage sludge, and the use of anaerobic batch reactors at a laboratory-scale has been proved to produce qualitative results on determining the methane potential of substrates. This thesis has helped to develop a better understanding about the digestion process in the Sjรถstadsverket reactor. However, there are still many issues that should be further investigated. The following are several ideas or proposals for future research: Testing pretreatment methods of sludge can potentially increase the biogas production in a significant manner. Performing batch reactor tests can determine the most efficient method that can benefit the specific AD system being investigated. At the moment, there is no pretreatment done in the sludge entering the anaerobic digester in Sjรถstadsverket facilities. Therefore many methods, from enzyme addition to ozone treatment, can be tested in laboratory-scale reactors. The use of AMPTS can determine its feasibility and the potential in increased biogas production. Codigestion of different substrates is also an interesting alternative that can be researched. Codigestion of municipal sewage with agricultural waste has been a popular topic of investigation, resulting in significant increase in the biogas production (Ahring et al, 1992). However the codigestion of different types of substrates can develop many problems such as nutrient deficiency, low alkalinity, and excessive solids content. Implementing laboratory-scale reactors, the codigestion of substrates can be monitored and analyzed. This would represent an inexpensive way to increase biogas production. Inhibition tests are an excellent way to assess the origin and the degree of inhibitions that can be present or developed in the anaerobic process. Inhibition can be caused by a high concentration of intermediates products, alkali metals or toxic compounds that have a lethal effect on biomass (Angelidaki et al, 2006). Therefore, inhibition can be easily produced in AD and hence must be monitored closely. An additional objective of performing these tests is to assess the ability of the sludge to recover or adapt to an inhibitor.

7. R EF ERENCES Ahmed, S. & Henzea, M., (2008) Biological hydrolysis and acidification of sludge under anaerobic conditions: The effect of sludge type and origin on the production and composition of volatile fatty acids. Water Research, 42 (14), 3729-3738. Ahring, B.K., Sandberg, M. & Angelidaki, I., (1995) Volatile fatty acids as indicators of process imbalance in anaerobic digestors. Applied microbiological Biotechnology, 43 (3), 559-565. Ahring, B.K., Angelidaki, I. & Johansen, K., (1992) Anaerobic treatment of manure together with industrial waste. Water Science Technology, 25 (7), 311-318. Angelidaki I., Alves M., Campos L., Bolzonella D., Borzacconi L., Guwy A.J., Kalyuzhnyi S., Jenicek P. & Van Lier J.B., (2006) Anaerobic Biodegradation, Activity and Inhibition (ABAI). Institute of Environment & Resources Technical University of Denmark, 24.

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Methane potential of sewage sludge to increase biogas production

APHA, (1998) Standard Methods for Examination of Water and Wastewater, 20th ed. American Public Health Association, Washington, DC. Appels, L., Baeyens, J., Degreve, J. & Dewil, R., (2008) Principles and potential of the anaerobic digestion of waste-activated sludge. Progress in Energy and Combustion Science, 34, 755–781. Behera, S.K., Park, J.M., Kim, K.H. & Park, H.S., (2010) Methane production from food waste leachate in laboratory-scale simulated landfill. Waste Management, 30, 1502-1508. Bhattacharya, S.K., Madura, R., Walling, D. & Farrel, J., (1996) Volatile solids reduction in two-phase and conventional anaerobic sludge digestion. Water Research, 30 (5), 1041-1048. Bitton, G. (1999). Wastewater Microbiology, 2nd Edition. Wiley-Liss Inc. 578. Björnsson, L., Murto, M., Jantsch, T.G. & Mattiasson, B., (2001) Evaluation of new methods for the monitoring of alkalinity, dissolved hydrogen and the microbial community in anaerobic digestion. Water Research, 35 (12), 2833-2840. Boe, K., (2006) Online monitoring and control of the biogas process. Ph.D. Thesis. Institute of Environment and Resources, Technical University of Denmark (DTU), 47 Coates, J., Coughlanb, M. & Colleranb, E., (1996) Simple method for the measurement of the hydrogenotrophic methanogenic activity of anaerobic sludges. Journal of Microbiological Methods, 26, 237-246. David, B., Gendebien, A., Palfrey, R. & Middleton, J., (2010) Environmental, economic and social impact of the use of sewage sludge on land. Summary Report 2. Baseline scenario, analysis of risks and opportunities. Milieu Ltd, WRc, RPA. 1-76. De Baere,L. (2000) Anaerobic digestion of solid waste: state-of-the-art. Water Science And Technology, 41 (3), 283-290. El-Hadj, T. (2006) Biodegradation of organic micropollutants in thermophillic and mesophillic anaerobic digestion of sewage sludge. Universitat Barcelona. 215. Gendebien, A., David, B., Hobson, J., Palfrey, R., Pitchers, R., Rumbsy, P., Carlton-Smith, C. & Middleton, J., (2010) Environmental, economic and social impact of the use of sewage sludge on land. Summary Report 1, Assessment of Existing knowledge. Milieu Ltd, WRc, RPA. 1-51. Hansen, T.L., Schmidt, J.E., Angelidaki, Il, Marca, E., Jansen, J.C, Mosbaek, H. & Christensen, T.H., (2003) Method for determination of methane potentials of solid organic waste. Waste Management, 24 (4), 393-400. Hellstedt, C., Starberg, K., Olsson, L.E., Hellström, D., Jonsson, L. & Mossakowska, A., (2010) Increased biogas production at the Henriksdal Wastewater Treatment Plant (WWTP). Biogasmax, European Comission, 90. Hwang, M.H., Jang, N.J., Hyum, S.H. & Kim, I.S., (2004) Anaerobic biohydrogen production from ethanol fermentation: the role of pH. Journal of Biotechnology, 111 (3), 297-309. James, A., Chernicharo, C. & Campos, C., (1990) The development of a new methodology for the assessment of specific methanogenic activity. Water Research, 24 (7), 813-825. 21

Lourdes Rodriguez

TRITA LWR Degree Project 11:22

McMahon, K. D., Stroot, P. G., Mackie, R. I. & Raskin, L., (2001) Anaerobic co-digestion of municipal solid waste and biosolids under various mixing conditions- II: Microbial population dynamics. Water Research, 35 (7), 1817-1827. Moody, L., Burns, R., Wu-Hann, W. & Spajić, R., (2009) Use of Biochemical Methane Potential (BMP) Assays for Predicting and Enhancing Anaerobic Digester Performance. Agricultural Engineering, 44th Croatian & 4th International Symposium on Agriculture, 930-934. Mottet, A., Francois, E., Latrille, E., Steyer, J.P., Deleris, S., Vedrenne, F. & Carrere, H., (2010) Estimating anaerobic biodegradability indicator for waste activated sludge. Chemical Engineering Journal, 160, 488496. Noone, G.P., (1990) The treatment of domestic wastes. Anaerobic digestion: a waste treatment technology. Wheatley, A. (edited) Critical reports on applied chemistry, (31), 139-170. Owens, J.M. & Chynoweth, D.P., (1993) Biochemical methane potential of municipal solid-waste (MSW) components. Water Science & Technology, 27, 1-14. Parawira, W., Murto, M., Read,J.S. & Mattiasson, B., (2005) Profile of hydrolases and biogas production during two stage mesophillic anaerobic digestion of solid potato waste. Process Biochemistry, 40 (9), 2945-2952. Schink, B., (1997) Energetics of syntrophic cooperation in methanogenic degradation. Microbiology and Molecular Biology Reviews, 61 (2), 262-280. Soto, M., Mendez R. & Lema, J.M., (1993) Methanogenic and nonmethanogenic activity tests. Theoretical basis and experimental set up. Water Research, 27 (8), 1361-1376. Van Lier, J.B., Hulsbeek, J., Stams, A.J. & Lettinga, G., (1993) Temperature susceptibility of thermophilic methanogenic sludge: implication for reactor start-up and operation. Bioresource technology, 43, 227-235.

7.1

Other references Automated Methane Potential Test System® Manual by Bioprocess Control May 2011. Bengtsson, Lars: IVL/Hammarby Sjöstadsverk. Personal communication June 2011. Stockholm Water website: www.stockholmvatten.se. July 2011

22

Methane potential of sewage sludge to increase biogas production

8. A PPENDIX I – R AW DATA FROM THE AMPTS PROGRAM All results are expressed in unit: Normal Liter of CH4 Time (days)

Blank S1

Blank S2

S1

S2

S3

Blank H1

Blank H2

H1

H2

H3

Control S1

Control S2

Control H1

Control H2

0.008

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0.023

0

0

0

0

0

0

0

0

0

0.011

0

0

0

0

0.025

0

0

0

0

0

0

0

0

0.012

0.011

0

0

0

0

0.026

0

0

0

0

0

0

0

0.011

0.012

0.011

0

0

0

0

0.027

0

0

0

0

0

0

0

0.011

0.012

0.011

0

0.011

0

0

0.028

0

0

0

0

0

0

0

0.011

0.012

0.011

0.011

0.011

0

0

0.028

0

0

0

0.011

0

0

0

0.011

0.012

0.011

0.011

0.011

0

0

0.028

0

0

0

0.011

0.011

0

0

0.011

0.012

0.011

0.011

0.011

0

0

0.03

0

0

0

0.011

0.011

0

0

0.011

0.012

0.011

0.011

0.011

0.012

0

0.03

0

0

0

0.011

0.011

0

0

0.011

0.012

0.011

0.011

0.011

0.012

0.011

0.03

0

0

0.012

0.011

0.011

0

0

0.011

0.012

0.011

0.011

0.011

0.012

0.011

0.046

0

0

0.012

0.011

0.011

0

0

0.011

0.012

0.022

0.011

0.011

0.012

0.011

0.049

0

0

0.012

0.011

0.011

0

0

0.011

0.024

0.022

0.011

0.011

0.012

0.011

0.049

0

0

0.012

0.011

0.011

0.011

0

0.011

0.024

0.022

0.011

0.011

0.012

0.011

0.052

0

0

0.012

0.011

0.011

0.011

0

0.022

0.024

0.022

0.011

0.011

0.012

0.011

0.054

0

0

0.012

0.011

0.011

0.011

0

0.022

0.024

0.022

0.011

0.023

0.012

0.011

0.055

0

0

0.012

0.011

0.023

0.011

0

0.022

0.024

0.022

0.011

0.023

0.012

0.011

0.056

0

0

0.012

0.023

0.023

0.011

0

0.022

0.024

0.022

0.011

0.023

0.012

0.011

0.056

0

0

0.012

0.023

0.023

0.011

0

0.022

0.024

0.022

0.023

0.023

0.012

0.011

0.056

0

0

0.012

0.023

0.023

0.011

0.012

0.022

0.024

0.022

0.023

0.023

0.012

0.011

0.059

0

0

0.023

0.023

0.023

0.011

0.012

0.022

0.024

0.022

0.023

0.023

0.012

0.011

0.062

0

0

0.023

0.023

0.023

0.011

0.012

0.022

0.024

0.022

0.023

0.023

0.023

0.011

0.062

0

0

0.023

0.023

0.023

0.011

0.012

0.022

0.024

0.022

0.023

0.023

0.023

0.022

0.07

0

0

0.023

0.023

0.023

0.011

0.012

0.022

0.024

0.034

0.023

0.023

0.023

0.022

0.074

0

0

0.023

0.023

0.023

0.011

0.012

0.022

0.035

0.034

0.023

0.023

0.023

0.022

0.078

0

0

0.023

0.023

0.023

0.011

0.012

0.032

0.035

0.034

0.023

0.023

0.023

0.022

I

Lourdes Rodriguez

TRITA LWR Degree Project 11:22

0.08

0

0

0.023

0.023

0.023

0.011

0.012

0.032

0.035

0.034

0.023

0.034

0.023

0.022

0.081

0

0.011

0.023

0.023

0.023

0.011

0.012

0.032

0.035

0.034

0.023

0.034

0.023

0.022

0.082

0

0.011

0.023

0.023

0.023

0.011

0.012

0.032

0.035

0.034

0.034

0.034

0.023

0.022

0.082

0

0.011

0.023

0.023

0.034

0.011

0.012

0.032

0.035

0.034

0.034

0.034

0.023

0.022

0.082

0.011

0.011

0.023

0.023

0.034

0.011

0.012

0.032

0.035

0.034

0.034

0.034

0.023

0.022

0.084

0.011

0.011

0.023

0.034

0.034

0.011

0.012

0.032

0.035

0.034

0.034

0.034

0.023

0.022

0.088

0.011

0.011

0.035

0.034

0.034

0.011

0.012

0.032

0.035

0.034

0.034

0.034

0.023

0.022

0.093

0.011

0.011

0.035

0.034

0.034

0.023

0.012

0.032

0.035

0.034

0.034

0.034

0.023

0.022

0.094

0.011

0.011

0.035

0.034

0.034

0.023

0.012

0.032

0.035

0.045

0.034

0.034

0.023

0.022

0.095

0.011

0.011

0.035

0.034

0.034

0.023

0.012

0.032

0.035

0.045

0.034

0.034

0.035

0.022

0.096

0.011

0.011

0.035

0.034

0.034

0.023

0.012

0.032

0.035

0.045

0.034

0.034

0.035

0.033

0.099

0.011

0.011

0.035

0.034

0.034

0.023

0.012

0.032

0.047

0.045

0.034

0.034

0.035

0.033

0.104

0.011

0.011

0.035

0.034

0.034

0.023

0.012

0.043

0.047

0.045

0.034

0.034

0.035

0.033

0.108

0.011

0.011

0.035

0.034

0.034

0.023

0.012

0.043

0.047

0.045

0.034

0.046

0.035

0.033

0.11

0.011

0.011

0.035

0.034

0.046

0.023

0.012

0.043

0.047

0.045

0.034

0.046

0.035

0.033

0.11

0.011

0.011

0.035

0.034

0.046

0.023

0.012

0.043

0.047

0.045

0.046

0.046

0.035

0.033

0.11

0.011

0.011

0.035

0.034

0.046

0.023

0.024

0.043

0.047

0.045

0.046

0.046

0.035

0.033

0.112

0.011

0.011

0.035

0.046

0.046

0.023

0.024

0.043

0.047

0.045

0.046

0.046

0.035

0.033

0.118

0.011

0.011

0.035

0.046

0.046

0.023

0.024

0.043

0.047

0.056

0.046

0.046

0.035

0.033

0.118

0.011

0.011

0.047

0.046

0.046

0.023

0.024

0.043

0.047

0.056

0.046

0.046

0.035

0.033

0.125

0.011

0.011

0.047

0.046

0.046

0.023

0.024

0.043

0.059

0.056

0.046

0.046

0.035

0.033

0.13

0.011

0.011

0.047

0.046

0.046

0.023

0.024

0.043

0.059

0.056

0.046

0.046

0.047

0.033

0.13

0.011

0.011

0.047

0.046

0.046

0.023

0.024

0.043

0.059

0.056

0.046

0.046

0.047

0.044

0.131

0.011

0.011

0.047

0.046

0.046

0.023

0.024

0.054

0.059

0.056

0.046

0.046

0.047

0.044

0.135

0.011

0.011

0.047

0.046

0.046

0.023

0.024

0.054

0.059

0.056

0.046

0.057

0.047

0.044

0.136

0.011

0.011

0.047

0.046

0.046

0.023

0.024

0.054

0.059

0.056

0.057

0.057

0.047

0.044

0.137

0.011

0.011

0.047

0.046

0.057

0.023

0.024

0.054

0.059

0.056

0.057

0.057

0.047

0.044

0.139

0.011

0.011

0.047

0.057

0.057

0.023

0.024

0.054

0.059

0.056

0.057

0.057

0.047

0.044

0.143

0.011

0.011

0.047

0.057

0.057

0.023

0.024

0.054

0.059

0.067

0.057

0.057

0.047

0.044

0.144

0.011

0.011

0.047

0.057

0.057

0.034

0.024

0.054

0.059

0.067

0.057

0.057

0.047

0.044

0.148

0.011

0.011

0.059

0.057

0.057

0.034

0.024

0.054

0.059

0.067

0.057

0.057

0.047

0.044

II

Methane potential of sewage sludge to increase biogas production

0.151

0.011

0.011

0.059

0.057

0.057

0.034

0.024

0.054

0.071

0.067

0.057

0.057

0.047

0.044

0.157

0.011

0.011

0.059

0.057

0.057

0.034

0.024

0.065

0.071

0.067

0.057

0.057

0.047

0.044

0.161

0.011

0.011

0.059

0.057

0.057

0.034

0.024

0.065

0.071

0.067

0.057

0.069

0.047

0.044

0.163

0.011

0.011

0.059

0.057

0.057

0.034

0.024

0.065

0.071

0.067

0.069

0.069

0.047

0.044

0.163

0.011

0.011

0.059

0.057

0.057

0.034

0.024

0.065

0.071

0.067

0.069

0.069

0.047

0.056

0.164

0.011

0.011

0.059

0.057

0.057

0.034

0.024

0.065

0.071

0.067

0.069

0.069

0.058

0.056

0.165

0.011

0.011

0.059

0.057

0.069

0.034

0.024

0.065

0.071

0.067

0.069

0.069

0.058

0.056

0.166

0.011

0.011

0.059

0.068

0.069

0.034

0.024

0.065

0.071

0.067

0.069

0.069

0.058

0.056

0.166

0.023

0.011

0.059

0.068

0.069

0.034

0.024

0.065

0.071

0.067

0.069

0.069

0.058

0.056

0.167

0.023

0.011

0.059

0.068

0.069

0.034

0.024

0.065

0.071

0.079

0.069

0.069

0.058

0.056

0.167

0.023

0.011

0.059

0.068

0.069

0.034

0.036

0.065

0.071

0.079

0.069

0.069

0.058

0.056

0.169

0.023

0.023

0.059

0.068

0.069

0.034

0.036

0.065

0.071

0.079

0.069

0.069

0.058

0.056

0.177

0.023

0.023

0.07

0.068

0.069

0.034

0.036

0.065

0.071

0.079

0.069

0.069

0.058

0.056

0.178

0.023

0.023

0.07

0.068

0.069

0.034

0.036

0.065

0.082

0.079

0.069

0.069

0.058

0.056

0.183

0.023

0.023

0.07

0.068

0.069

0.034

0.036

0.075

0.082

0.079

0.069

0.069

0.058

0.056

0.188

0.023

0.023

0.07

0.068

0.069

0.034

0.036

0.075

0.082

0.079

0.069

0.08

0.058

0.056

0.19

0.023

0.023

0.07

0.068

0.069

0.034

0.036

0.075

0.082

0.079

0.08

0.08

0.058

0.056

0.192

0.023

0.023

0.07

0.08

0.069

0.034

0.036

0.075

0.082

0.079

0.08

0.08

0.058

0.056

0.192

0.023

0.023

0.07

0.08

0.069

0.034

0.036

0.075

0.082

0.09

0.08

0.08

0.058

0.056

0.193

0.023

0.023

0.07

0.08

0.08

0.034

0.036

0.075

0.082

0.09

0.08

0.08

0.058

0.056

0.196

0.023

0.023

0.07

0.08

0.08

0.034

0.036

0.075

0.082

0.09

0.08

0.08

0.058

0.067

0.198

0.023

0.023

0.07

0.08

0.08

0.034

0.036

0.075

0.082

0.09

0.08

0.08

0.07

0.067

0.201

0.023

0.023

0.07

0.08

0.08

0.046

0.036

0.075

0.082

0.09

0.08

0.08

0.07

0.067

0.204

0.023

0.023

0.07

0.08

0.08

0.046

0.036

0.075

0.094

0.09

0.08

0.08

0.07

0.067

0.207

0.023

0.023

0.082

0.08

0.08

0.046

0.036

0.075

0.094

0.09

0.08

0.08

0.07

0.067

0.211

0.023

0.023

0.082

0.08

0.08

0.046

0.036

0.086

0.094

0.09

0.08

0.08

0.07

0.067

0.216

0.023

0.023

0.082

0.08

0.08

0.046

0.036

0.086

0.094

0.09

0.08

0.092

0.07

0.067

0.217

0.023

0.023

0.082

0.08

0.08

0.046

0.036

0.086

0.094

0.101

0.08

0.092

0.07

0.067

0.217

0.023

0.023

0.082

0.08

0.08

0.046

0.036

0.086

0.094

0.101

0.091

0.092

0.07

0.067

0.22

0.023

0.023

0.082

0.091

0.08

0.046

0.036

0.086

0.094

0.101

0.091

0.092

0.07

0.067

0.223

0.023

0.023

0.082

0.091

0.092

0.046

0.036

0.086

0.094

0.101

0.091

0.092

0.07

0.067

III

Lourdes Rodriguez

TRITA LWR Degree Project 11:22

0.231

0.023

0.023

0.082

0.091

0.092

0.046

0.036

0.086

0.094

0.101

0.091

0.092

0.07

0.078

0.231

0.023

0.023

0.082

0.091

0.092

0.046

0.036

0.086

0.106

0.101

0.091

0.233

0.023

0.023

0.082

0.091

0.092

0.046

0.036

0.086

0.106

0.101

0.091

0.092

0.07

0.078

0.092

0.082

0.078

0.235

0.023

0.023

0.082

0.091

0.092

0.046

0.048

0.086

0.106

0.101

0.238

0.023

0.023

0.094

0.091

0.092

0.046

0.048

0.086

0.106

0.101

0.091

0.092

0.082

0.078

0.091

0.092

0.082

0.078

0.238

0.023

0.023

0.094

0.091

0.092

0.046

0.048

0.097

0.106

0.101

0.091

0.092

0.082

0.078

0.243

0.023

0.023

0.094

0.091

0.092

0.046

0.048

0.097

0.244

0.023

0.023

0.094

0.091

0.092

0.046

0.048

0.097

0.106

0.112

0.091

0.092

0.082

0.078

0.106

0.112

0.091

0.103

0.082

0.078

0.246

0.023

0.023

0.094

0.091

0.092

0.046

0.048

0.248

0.023

0.023

0.094

0.103

0.092

0.046

0.048

0.097

0.106

0.112

0.103

0.103

0.082

0.078

0.097

0.106

0.112

0.103

0.103

0.082

0.078

0.252

0.023

0.023

0.094

0.103

0.103

0.046

0.258

0.023

0.023

0.094

0.103

0.103

0.046

0.048

0.097

0.106

0.112

0.103

0.103

0.082

0.078

0.048

0.097

0.118

0.112

0.103

0.103

0.082

0.078

0.261

0.023

0.034

0.094

0.103

0.103

0.263

0.034

0.034

0.094

0.103

0.103

0.046

0.048

0.097

0.118

0.112

0.103

0.103

0.082

0.078

0.046

0.048

0.097

0.118

0.112

0.103

0.103

0.082

0.078

0.264

0.034

0.034

0.094

0.103

0.103

0.057

0.048

0.097

0.118

0.112

0.103

0.103

0.082

0.078

0.265

0.034

0.034

0.094

0.266

0.034

0.034

0.094

0.103

0.103

0.057

0.048

0.097

0.118

0.112

0.103

0.103

0.082

0.089

0.103

0.103

0.057

0.048

0.108

0.118

0.112

0.103

0.103

0.082

0.089

0.268

0.034

0.034

0.268

0.034

0.034

0.106

0.103

0.103

0.057

0.048

0.108

0.118

0.112

0.103

0.103

0.082

0.089

0.106

0.103

0.103

0.057

0.048

0.108

0.118

0.124

0.103

0.103

0.082

0.089

0.268

0.034

0.272

0.034

0.034

0.106

0.103

0.103

0.057

0.048

0.108

0.118

0.124

0.103

0.103

0.093

0.089

0.034

0.106

0.103

0.103

0.057

0.048

0.108

0.118

0.124

0.103

0.115

0.093

0.089

0.273 0.279

0.034

0.034

0.106

0.103

0.103

0.057

0.048

0.108

0.118

0.124

0.114

0.115

0.093

0.089

0.034

0.034

0.106

0.114

0.103

0.057

0.048

0.108

0.118

0.124

0.114

0.115

0.093

0.089

0.28

0.034

0.034

0.106

0.114

0.115

0.057

0.048

0.108

0.118

0.124

0.114

0.115

0.093

0.089

0.285

0.034

0.034

0.106

0.114

0.115

0.057

0.048

0.108

0.129

0.124

0.114

0.115

0.093

0.089

0.293

0.034

0.034

0.106

0.114

0.115

0.057

0.048

0.118

0.129

0.124

0.114

0.115

0.093

0.089

0.294

0.034

0.034

0.106

0.114

0.115

0.057

0.048

0.118

0.129

0.135

0.114

0.115

0.093

0.089

0.299

0.034

0.034

0.106

0.114

0.115

0.057

0.048

0.118

0.129

0.135

0.114

0.115

0.093

0.1

0.299

0.034

0.034

0.117

0.114

0.115

0.057

0.048

0.118

0.129

0.135

0.114

0.115

0.093

0.1

0.3

0.034

0.034

0.117

0.114

0.115

0.057

0.048

0.118

0.129

0.135

0.114

0.126

0.093

0.1

0.3

0.034

0.034

0.117

0.114

0.115

0.057

0.048

0.118

0.129

0.135

0.126

0.126

0.093

0.1

IV

Methane potential of sewage sludge to increase biogas production

0.304

0.034

0.034

0.117

0.114

0.115

0.057

0.048

0.118

0.129

0.135

0.126

0.126

0.105

0.1

0.305

0.034

0.034

0.117

0.114

0.115

0.057

0.06

0.118

0.129

0.135

0.126

0.126

0.105

0.1

0.309

0.034

0.034

0.117

0.114

0.126

0.057

0.06

0.118

0.129

0.135

0.126

0.126

0.105

0.1

0.31

0.034

0.034

0.117

0.125

0.126

0.057

0.06

0.118

0.129

0.135

0.126

0.126

0.105

0.1

0.311

0.034

0.034

0.117

0.125

0.126

0.057

0.06

0.118

0.141

0.135

0.126

0.126

0.105

0.1

0.319

0.034

0.034

0.117

0.125

0.126

0.057

0.06

0.118

0.141

0.146

0.126

0.126

0.105

0.1

0.321

0.034

0.034

0.117

0.125

0.126

0.057

0.06

0.129

0.141

0.146

0.126

0.126

0.105

0.1

0.327

0.034

0.034

0.117

0.125

0.126

0.057

0.06

0.129

0.141

0.146

0.137

0.126

0.105

0.1

0.328

0.034

0.034

0.117

0.125

0.126

0.057

0.06

0.129

0.141

0.146

0.137

0.138

0.105

0.1

0.33

0.034

0.034

0.129

0.125

0.126

0.057

0.06

0.129

0.141

0.146

0.137

0.138

0.105

0.1

0.333

0.034

0.034

0.129

0.125

0.126

0.069

0.06

0.129

0.141

0.146

0.137

0.138

0.105

0.1

0.334

0.034

0.034

0.129

0.125

0.126

0.069

0.06

0.129

0.141

0.146

0.137

0.138

0.105

0.111

0.337

0.034

0.034

0.129

0.125

0.138

0.069

0.06

0.129

0.141

0.146

0.137

0.138

0.105

0.111

0.339

0.034

0.034

0.129

0.125

0.138

0.069

0.06

0.129

0.153

0.146

0.137

0.138

0.105

0.111

0.34

0.034

0.034

0.129

0.125

0.138

0.069

0.06

0.129

0.153

0.146

0.137

0.138

0.117

0.111

0.342

0.034

0.034

0.129

0.137

0.138

0.069

0.06

0.129

0.153

0.146

0.137

0.138

0.117

0.111

0.345

0.034

0.034

0.129

0.137

0.138

0.069

0.06

0.129

0.153

0.157

0.137

0.138

0.117

0.111

0.349

0.034

0.034

0.129

0.137

0.138

0.069

0.06

0.14

0.153

0.157

0.137

0.138

0.117

0.111

0.354

0.034

0.034

0.129

0.137

0.138

0.069

0.06

0.14

0.153

0.157

0.149

0.138

0.117

0.111

0.356

0.034

0.034

0.129

0.137

0.138

0.069

0.06

0.14

0.153

0.157

0.149

0.149

0.117

0.111

0.361

0.034

0.034

0.141

0.137

0.138

0.069

0.06

0.14

0.153

0.157

0.149

0.149

0.117

0.111

0.365

0.034

0.034

0.141

0.137

0.149

0.069

0.06

0.14

0.153

0.157

0.149

0.149

0.117

0.111

0.366

0.034

0.034

0.141

0.137

0.149

0.069

0.06

0.14

0.165

0.157

0.149

0.149

0.117

0.111

0.369

0.034

0.034

0.141

0.137

0.149

0.069

0.06

0.14

0.165

0.157

0.149

0.149

0.117

0.122

0.37

0.034

0.046

0.141

0.137

0.149

0.069

0.06

0.14

0.165

0.157

0.149

0.149

0.117

0.122

0.37

0.046

0.046

0.141

0.137

0.149

0.069

0.06

0.14

0.165

0.157

0.149

0.149

0.117

0.122

0.371

0.046

0.046

0.141

0.137

0.149

0.069

0.06

0.14

0.165

0.169

0.149

0.149

0.117

0.122

0.374

0.046

0.046

0.141

0.148

0.149

0.069

0.06

0.14

0.165

0.169

0.149

0.149

0.117

0.122

0.376

0.046

0.046

0.141

0.148

0.149

0.069

0.06

0.14

0.165

0.169

0.149

0.149

0.128

0.122

0.377

0.046

0.046

0.141

0.148

0.149

0.069

0.06

0.151

0.165

0.169

0.149

0.149

0.128

0.122

0.38

0.046

0.046

0.141

0.148

0.149

0.069

0.06

0.151

0.165

0.169

0.16

0.149

0.128

0.122

V

Lourdes Rodriguez

TRITA LWR Degree Project 11:22

0.384

0.046

0.046

0.141

0.148

0.149

0.069

0.06

0.151

0.165

0.169

0.16

0.161

0.128

0.122

0.386

0.046

0.046

0.141

0.148

0.149

0.069

0.072

0.151

0.165

0.169

0.16

0.161

0.128

0.122

0.392

0.046

0.046

0.152

0.148

0.149

0.069

0.072

0.151

0.165

0.169

0.16

0.161

0.128

0.122

0.393

0.046

0.046

0.152

0.148

0.161

0.069

0.072

0.151

0.165

0.169

0.16

0.161

0.128

0.122

0.394

0.046

0.046

0.152

0.148

0.161

0.069

0.072

0.151

0.176

0.169

0.16

0.161

0.128

0.122

0.399

0.046

0.046

0.152

0.148

0.161

0.069

0.072

0.151

0.176

0.18

0.16

0.161

0.128

0.122

0.406

0.046

0.046

0.152

0.148

0.161

0.069

0.072

0.151

0.176

0.18

0.16

0.161

0.128

0.133

0.406

0.046

0.046

0.152

0.159

0.161

0.069

0.072

0.151

0.176

0.18

0.16

0.161

0.128

0.133

0.407

0.046

0.046

0.152

0.159

0.161

0.069

0.072

0.161

0.176

0.18

0.16

0.161

0.128

0.133

0.408

0.046

0.046

0.152

0.159

0.161

0.069

0.072

0.161

0.176

0.18

0.171

0.161

0.128

0.133

0.41

0.046

0.046

0.152

0.159

0.161

0.08

0.072

0.161

0.176

0.18

0.171

0.161

0.128

0.133

0.413

0.046

0.046

0.152

0.159

0.161

0.08

0.072

0.161

0.176

0.18

0.171

0.172

0.128

0.133

0.414

0.046

0.046

0.152

0.159

0.161

0.08

0.072

0.161

0.176

0.18

0.171

0.172

0.14

0.133

0.422

0.046

0.046

0.152

0.159

0.172

0.08

0.072

0.161

0.176

0.18

0.171

0.172

0.14

0.133

0.423

0.046

0.046

0.152

0.159

0.172

0.08

0.072

0.161

0.188

0.18

0.171

0.172

0.14

0.133

0.423

0.046

0.046

0.164

0.159

0.172

0.08

0.072

0.161

0.188

0.18

0.171

0.172

0.14

0.133

0.427

0.046

0.046

0.164

0.159

0.172

0.08

0.072

0.161

0.188

0.191

0.171

0.172

0.14

0.133

0.434

0.046

0.046

0.164

0.159

0.172

0.08

0.072

0.161

0.188

0.191

0.183

0.172

0.14

0.133

0.435

0.046

0.046

0.164

0.159

0.172

0.08

0.072

0.172

0.188

0.191

0.183

0.172

0.14

0.133

0.439

0.046

0.046

0.164

0.171

0.172

0.08

0.072

0.172

0.188

0.191

0.183

0.172

0.14

0.133

0.441

0.046

0.046

0.164

0.171

0.172

0.08

0.072

0.172

0.188

0.191

0.183

0.184

0.14

0.133

0.443

0.046

0.046

0.164

0.171

0.172

0.08

0.072

0.172

0.188

0.191

0.183

0.184

0.14

0.144

0.45

0.046

0.046

0.164

0.171

0.184

0.08

0.072

0.172

0.188

0.191

0.183

0.184

0.14

0.144

0.451

0.046

0.046

0.164

0.171

0.184

0.08

0.072

0.172

0.2

0.191

0.183

0.184

0.14

0.144

0.451

0.046

0.046

0.164

0.171

0.184

0.08

0.072

0.172

0.2

0.191

0.183

0.184

0.152

0.144

0.454

0.046

0.046

0.176

0.171

0.184

0.08

0.072

0.172

0.2

0.191

0.183

0.184

0.152

0.144

0.455

0.046

0.046

0.176

0.171

0.184

0.08

0.072

0.172

0.2

0.202

0.183

0.184

0.152

0.144

0.462

0.046

0.046

0.176

0.171

0.184

0.08

0.072

0.172

0.2

0.202

0.194

0.184

0.152

0.144

0.466

0.046

0.046

0.176

0.171

0.184

0.08

0.072

0.183

0.2

0.202

0.194

0.184

0.152

0.144

0.47

0.046

0.046

0.176

0.171

0.184

0.08

0.072

0.183

0.2

0.202

0.194

0.195

0.152

0.144

0.473

0.046

0.046

0.176

0.171

0.184

0.08

0.084

0.183

0.2

0.202

0.194

0.195

0.152

0.144

VI

Methane potential of sewage sludge to increase biogas production

0.473

0.046

0.046

0.176

0.182

0.184

0.08

0.084

0.183

0.2

0.202

0.194

0.195

0.152

0.144

0.479

0.046

0.046

0.176

0.182

0.195

0.08

0.084

0.183

0.2

0.202

0.194

0.195

0.152

0.144

0.481

0.046

0.046

0.176

0.182

0.195

0.08

0.084

0.183

0.2

0.202

0.194

0.195

0.152

0.155

0.481

0.046

0.046

0.176

0.182

0.195

0.08

0.084

0.183

0.212

0.202

0.194

0.195

0.152

0.155

0.482

0.046

0.046

0.176

0.182

0.195

0.08

0.084

0.183

0.212

0.214

0.194

0.195

0.152

0.155

0.484

0.057

0.046

0.176

0.182

0.195

0.08

0.084

0.183

0.212

0.214

0.194

0.195

0.152

0.155

0.486

0.057

0.046

0.188

0.182

0.195

0.08

0.084

0.183

0.212

0.214

0.194

0.195

0.152

0.155

0.489

0.057

0.057

0.188

0.182

0.195

0.08

0.084

0.183

0.212

0.214

0.194

0.195

0.152

0.155

0.49

0.057

0.057

0.188

0.182

0.195

0.08

0.084

0.183

0.212

0.214

0.194

0.195

0.163

0.155

0.491

0.057

0.057

0.188

0.182

0.195

0.08

0.084

0.183

0.212

0.214

0.206

0.195

0.163

0.155

0.494

0.057

0.057

0.188

0.182

0.195

0.092

0.084

0.183

0.212

0.214

0.206

0.195

0.163

0.155

0.496

0.057

0.057

0.188

0.182

0.195

0.092

0.084

0.194

0.212

0.214

0.206

0.195

0.163

0.155

0.5

0.057

0.057

0.188

0.182

0.195

0.092

0.084

0.194

0.212

0.214

0.206

0.207

0.163

0.155

0.506

0.057

0.057

0.188

0.194

0.195

0.092

0.084

0.194

0.212

0.214

0.206

0.207

0.163

0.155

0.508

0.057

0.057

0.188

0.194

0.207

0.092

0.084

0.194

0.212

0.214

0.206

0.207

0.163

0.155

0.511

0.057

0.057

0.188

0.194

0.207

0.092

0.084

0.194

0.223

0.214

0.206

0.207

0.163

0.155

0.511

0.057

0.057

0.188

0.194

0.207

0.092

0.084

0.194

0.223

0.225

0.206

0.207

0.163

0.155

0.519

0.057

0.057

0.199

0.194

0.207

0.092

0.084

0.194

0.223

0.225

0.206

0.207

0.163

0.155

0.52

0.057

0.057

0.199

0.194

0.207

0.092

0.084

0.194

0.223

0.225

0.206

0.207

0.163

0.167

0.52

0.057

0.057

0.199

0.194

0.207

0.092

0.084

0.194

0.223

0.225

0.217

0.207

0.163

0.167

0.527

0.057

0.057

0.199

0.194

0.207

0.092

0.084

0.204

0.223

0.225

0.217

0.207

0.163

0.167

0.53

0.057

0.057

0.199

0.194

0.207

0.092

0.084

0.204

0.223

0.225

0.217

0.218

0.163

0.167

0.531

0.057

0.057

0.199

0.194

0.207

0.092

0.084

0.204

0.223

0.225

0.217

0.218

0.175

0.167

0.539

0.057

0.057

0.199

0.194

0.218

0.092

0.084

0.204

0.223

0.225

0.217

0.218

0.175

0.167

0.54

0.057

0.057

0.199

0.194

0.218

0.092

0.084

0.204

0.223

0.236

0.217

0.218

0.175

0.167

0.542

0.057

0.057

0.199

0.205

0.218

0.092

0.084

0.204

0.223

0.236

0.217

0.218

0.175

0.167

0.542

0.057

0.057

0.199

0.205

0.218

0.092

0.084

0.204

0.235

0.236

0.217

0.218

0.175

0.167

0.55

0.057

0.057

0.199

0.205

0.218

0.092

0.084

0.204

0.235

0.236

0.229

0.218

0.175

0.167

0.554

0.057

0.057

0.211

0.205

0.218

0.092

0.084

0.204

0.235

0.236

0.229

0.218

0.175

0.167

0.558

0.057

0.057

0.211

0.205

0.218

0.092

0.084

0.215

0.235

0.236

0.229

0.218

0.175

0.167

0.561

0.057

0.057

0.211

0.205

0.218

0.092

0.084

0.215

0.235

0.236

0.229

0.218

0.175

0.178

VII

Lourdes Rodriguez

TRITA LWR Degree Project 11:22

0.561

0.057

0.057

0.211

0.205

0.218

0.092

0.084

0.215

0.235

0.236

0.229

0.23

0.175

0.178

0.57

0.057

0.057

0.211

0.205

0.218

0.092

0.084

0.215

0.235

0.247

0.229

0.23

0.175

0.178

0.57

0.057

0.057

0.211

0.205

0.218

0.092

0.096

0.215

0.235

0.247

0.229

0.23

0.175

0.178

0.571

0.057

0.057

0.211

0.205

0.23

0.092

0.096

0.215

0.235

0.247

0.229

0.23

0.175

0.178

0.572

0.057

0.057

0.211

0.205

0.23

0.092

0.096

0.215

0.235

0.247

0.229

0.23

0.187

0.178

0.572

0.057

0.057

0.211

0.205

0.23

0.092

0.096

0.215

0.247

0.247

0.229

0.23

0.187

0.178

0.577

0.057

0.057

0.211

0.216

0.23

0.092

0.096

0.215

0.247

0.247

0.229

0.23

0.187

0.178

0.581

0.057

0.057

0.211

0.216

0.23

0.092

0.096

0.215

0.247

0.247

0.24

0.23

0.187

0.178

0.588

0.057

0.057

0.223

0.216

0.23

0.092

0.096

0.215

0.247

0.247

0.24

0.23

0.187

0.178

0.588

0.057

0.057

0.223

0.216

0.23

0.103

0.096

0.215

0.247

0.247

0.24

0.23

0.187

0.178

0.59

0.057

0.057

0.223

0.216

0.23

0.103

0.096

0.226

0.247

0.247

0.24

0.23

0.187

0.178

0.594

0.057

0.057

0.223

0.216

0.23

0.103

0.096

0.226

0.247

0.247

0.24

0.241

0.187

0.178

0.599

0.057

0.057

0.223

0.216

0.23

0.103

0.096

0.226

0.247

0.259

0.24

0.241

0.187

0.178

0.602

0.057

0.057

0.223

0.216

0.23

0.103

0.096

0.226

0.247

0.259

0.24

0.241

0.187

0.189

0.603

0.057

0.057

0.223

0.216

0.241

0.103

0.096

0.226

0.247

0.259

0.24

0.241

0.187

0.189

0.603

0.057

0.057

0.223

0.216

0.241

0.103

0.096

0.226

0.259

0.259

0.24

0.241

0.187

0.189

0.606

0.069

0.057

0.223

0.216

0.241

0.103

0.096

0.226

0.259

0.259

0.24

0.241

0.187

0.189

0.613

0.069

0.057

0.223

0.228

0.241

0.103

0.096

0.226

0.259

0.259

0.24

0.241

0.187

0.189

0.613

0.069

0.057

0.223

0.228

0.241

0.103

0.096

0.226

0.259

0.259

0.251

0.241

0.187

0.189

0.615

0.069

0.057

0.223

0.228

0.241

0.103

0.096

0.226

0.259

0.259

0.251

0.241

0.199

0.189

0.619

0.069

0.068

0.223

0.228

0.241

0.103

0.096

0.226

0.259

0.259

0.251

0.241

0.199

0.189

0.622

0.069

0.068

0.223

0.228

0.241

0.103

0.096

0.237

0.259

0.259

0.251

0.241

0.199

0.189

0.624

0.069

0.068

0.234

0.228

0.241

0.103

0.096

0.237

0.259

0.259

0.251

0.241

0.199

0.189

0.627

0.069

0.068

0.234

0.228

0.241

0.103

0.096

0.237

0.259

0.259

0.251

0.253

0.199

0.189

0.629

0.069

0.068

0.234

0.228

0.241

0.103

0.096

0.237

0.259

0.27

0.251

0.253

0.199

0.189

0.634

0.069

0.068

0.234

0.228

0.241

0.103

0.096

0.237

0.27

0.27

0.251

0.253

0.199

0.189

0.637

0.069

0.068

0.234

0.228

0.253

0.103

0.096

0.237

0.27

0.27

0.251

0.253

0.199

0.189

0.645

0.069

0.068

0.234

0.228

0.253

0.103

0.096

0.237

0.27

0.27

0.251

0.253

0.199

0.2

0.648

0.069

0.068

0.234

0.228

0.253

0.103

0.096

0.237

0.27

0.27

0.263

0.253

0.199

0.2

0.651

0.069

0.068

0.234

0.239

0.253

0.103

0.096

0.237

0.27

0.27

0.263

0.253

0.199

0.2

0.655

0.069

0.068

0.234

0.239

0.253

0.103

0.096

0.247

0.27

0.27

0.263

0.253

0.199

0.2

VIII

Methane potential of sewage sludge to increase biogas production

0.658

0.069

0.068

0.234

0.239

0.253

0.103

0.096

0.247

0.27

0.27

0.263

0.253

0.21

0.2

0.659

0.069

0.068

0.234

0.239

0.253

0.103

0.096

0.247

0.27

0.281

0.263

0.253

0.21

0.2

0.662

0.069

0.068

0.246

0.239

0.253

0.103

0.096

0.247

0.27

0.281

0.263

0.253

0.21

0.2

0.663

0.069

0.068

0.246

0.239

0.253

0.103

0.096

0.247

0.27

0.281

0.263

0.264

0.21

0.2

0.665

0.069

0.068

0.246

0.239

0.253

0.103

0.096

0.247

0.282

0.281

0.263

0.264

0.21

0.2

0.673

0.069

0.068

0.246

0.239

0.264

0.103

0.096

0.247

0.282

0.281

0.263

0.264

0.21

0.2

0.675

0.069

0.068

0.246

0.239

0.264

0.103

0.108

0.247

0.282

0.281

0.263

0.264

0.21

0.2

0.682

0.069

0.068

0.246

0.239

0.264

0.103

0.108

0.247

0.282

0.281

0.274

0.264

0.21

0.2

0.689

0.069

0.068

0.246

0.239

0.264

0.103

0.108

0.258

0.282

0.281

0.274

0.264

0.21

0.2

0.689

0.069

0.068

0.246

0.239

0.264

0.103

0.108

0.258

0.282

0.281

0.274

0.264

0.21

0.211

0.689

0.069

0.068

0.246

0.239

0.264

0.103

0.108

0.258

0.282

0.292

0.274

0.264

0.21

0.211

0.69

0.069

0.068

0.246

0.251

0.264

0.103

0.108

0.258

0.282

0.292

0.274

0.264

0.21

0.211

0.691

0.069

0.068

0.246

0.251

0.264

0.115

0.108

0.258

0.282

0.292

0.274

0.264

0.21

0.211

0.697

0.069

0.068

0.246

0.251

0.264

0.115

0.108

0.258

0.294

0.292

0.274

0.264

0.21

0.211

0.699

0.069

0.068

0.246

0.251

0.264

0.115

0.108

0.258

0.294

0.292

0.274

0.276

0.21

0.211

0.702

0.069

0.068

0.258

0.251

0.264

0.115

0.108

0.258

0.294

0.292

0.274

0.276

0.21

0.211

0.703

0.069

0.068

0.258

0.251

0.264

0.115

0.108

0.258

0.294

0.292

0.274

0.276

0.222

0.211

0.709

0.069

0.068

0.258

0.251

0.276

0.115

0.108

0.258

0.294

0.292

0.274

0.276

0.222

0.211

0.72

0.069

0.068

0.258

0.251

0.276

0.115

0.108

0.258

0.294

0.304

0.274

0.276

0.222

0.211

0.721

0.069

0.068

0.258

0.251

0.276

0.115

0.108

0.258

0.294

0.304

0.286

0.276

0.222

0.211

0.722

0.069

0.068

0.258

0.251

0.276

0.115

0.108

0.269

0.294

0.304

0.286

0.276

0.222

0.211

0.73

0.069

0.068

0.258

0.251

0.276

0.115

0.108

0.269

0.306

0.304

0.286

0.276

0.222

0.211

0.732

0.069

0.068

0.258

0.262

0.276

0.115

0.108

0.269

0.306

0.304

0.286

0.276

0.222

0.211

0.734

0.069

0.068

0.258

0.262

0.276

0.115

0.108

0.269

0.306

0.304

0.286

0.276

0.222

0.222

0.739

0.069

0.068

0.258

0.262

0.276

0.115

0.108

0.269

0.306

0.304

0.286

0.287

0.222

0.222

0.745

0.069

0.068

0.27

0.262

0.276

0.115

0.108

0.269

0.306

0.304

0.286

0.287

0.222

0.222

0.746

0.08

0.068

0.27

0.262

0.276

0.115

0.108

0.269

0.306

0.304

0.286

0.287

0.222

0.222

0.748

0.08

0.068

0.27

0.262

0.276

0.115

0.108

0.269

0.306

0.304

0.286

0.287

0.234

0.222

0.75

0.08

0.08

0.27

0.262

0.276

0.115

0.108

0.269

0.306

0.304

0.286

0.287

0.234

0.222

0.75

0.08

0.08

0.27

0.262

0.287

0.115

0.108

0.269

0.306

0.304

0.286

0.287

0.234

0.222

0.751

0.08

0.08

0.27

0.262

0.287

0.115

0.108

0.269

0.306

0.315

0.286

0.287

0.234

0.222

IX

Lourdes Rodriguez

TRITA LWR Degree Project 11:22

0.756

0.08

0.08

0.27

0.262

0.287

0.115

0.108

0.28

0.306

0.315

0.286

0.287

0.234

0.222

0.76

0.08

0.08

0.27

0.262

0.287

0.115

0.108

0.28

0.306

0.315

0.297

0.287

0.234

0.222

0.763

0.08

0.08

0.27

0.262

0.287

0.115

0.108

0.28

0.317

0.315

0.297

0.287

0.234

0.222

0.774

0.08

0.08

0.27

0.262

0.287

0.115

0.108

0.28

0.317

0.315

0.297

0.299

0.234

0.222

0.775

0.08

0.08

0.27

0.273

0.287

0.115

0.108

0.28

0.317

0.315

0.297

0.299

0.234

0.222

0.78

0.08

0.08

0.27

0.273

0.287

0.115

0.108

0.28

0.317

0.315

0.297

0.299

0.234

0.233

0.784

0.08

0.08

0.27

0.273

0.287

0.115

0.108

0.28

0.317

0.326

0.297

0.299

0.234

0.233

0.79

0.08

0.08

0.27

0.273

0.287

0.115

0.108

0.29

0.317

0.326

0.297

0.299

0.234

0.233

0.79

0.08

0.08

0.281

0.273

0.287

0.115

0.108

0.29

0.317

0.326

0.297

0.299

0.234

0.233

0.792

0.08

0.08

0.281

0.273

0.287

0.115

0.12

0.29

0.317

0.326

0.297

0.299

0.234

0.233

0.792

0.08

0.08

0.281

0.273

0.299

0.115

0.12

0.29

0.317

0.326

0.297

0.299

0.234

0.233

0.794

0.08

0.08

0.281

0.273

0.299

0.115

0.12

0.29

0.317

0.326

0.297

0.299

0.245

0.233

0.799

0.08

0.08

0.281

0.273

0.299

0.126

0.12

0.29

0.317

0.326

0.297

0.299

0.245

0.233

0.799

0.08

0.08

0.281

0.273

0.299

0.126

0.12

0.29

0.329

0.326

0.297

0.299

0.245

0.233

0.8

0.08

0.08

0.281

0.273

0.299

0.126

0.12

0.29

0.329

0.326

0.309

0.299

0.245

0.233

0.818

0.08

0.08

0.281

0.273

0.299

0.126

0.12

0.29

0.329

0.337

0.309

0.299

0.245

0.233

0.82

0.08

0.08

0.281

0.285

0.299

0.126

0.12

0.29

0.329

0.337

0.309

0.299

0.245

0.233

0.822

0.08

0.08

0.281

0.285

0.299

0.126

0.12

0.29

0.329

0.337

0.309

0.31

0.245

0.233

0.824

0.08

0.08

0.281

0.285

0.299

0.126

0.12

0.301

0.329

0.337

0.309

0.31

0.245

0.233

0.826

0.08

0.08

0.281

0.285

0.299

0.126

0.12

0.301

0.329

0.337

0.309

0.31

0.245

0.244

0.835

0.08

0.08

0.281

0.285

0.31

0.126

0.12

0.301

0.329

0.337

0.309

0.31

0.245

0.244

0.837

0.08

0.08

0.281

0.285

0.31

0.126

0.12

0.301

0.341

0.337

0.309

0.31

0.245

0.244

0.838

0.08

0.08

0.293

0.285

0.31

0.126

0.12

0.301

0.341

0.337

0.309

0.31

0.245

0.244

0.841

0.08

0.08

0.293

0.285

0.31

0.126

0.12

0.301

0.341

0.337

0.309

0.31

0.257

0.244

0.843

0.08

0.08

0.293

0.285

0.31

0.126

0.12

0.301

0.341

0.337

0.32

0.31

0.257

0.244

0.853

0.08

0.08

0.293

0.285

0.31

0.126

0.12

0.301

0.341

0.349

0.32

0.31

0.257

0.244

0.859

0.08

0.08

0.293

0.285

0.31

0.126

0.12

0.312

0.341

0.349

0.32

0.31

0.257

0.244

0.866

0.08

0.08

0.293

0.296

0.31

0.126

0.12

0.312

0.341

0.349

0.32

0.31

0.257

0.244

0.867

0.08

0.08

0.293

0.296

0.31

0.126

0.12

0.312

0.341

0.349

0.32

0.322

0.257

0.244

0.873

0.08

0.08

0.293

0.296

0.31

0.126

0.12

0.312

0.341

0.349

0.32

0.322

0.257

0.255

0.874

0.092

0.08

0.293

0.296

0.31

0.126

0.12

0.312

0.341

0.349

0.32

0.322

0.257

0.255

X

Methane potential of sewage sludge to increase biogas production

0.877

0.092

0.08

0.293

0.296

0.31

0.126

0.12

0.312

0.353

0.349

0.32

0.322

0.257

0.255

0.88

0.092

0.08

0.293

0.296

0.322

0.126

0.12

0.312

0.353

0.349

0.32

0.322

0.257

0.255

0.887

0.092

0.08

0.293

0.296

0.322

0.126

0.12

0.312

0.353

0.349

0.331

0.322

0.257

0.255

0.888

0.092

0.08

0.305

0.296

0.322

0.126

0.12

0.312

0.353

0.349

0.331

0.322

0.257

0.255

0.889

0.092

0.08

0.305

0.296

0.322

0.126

0.12

0.312

0.353

0.349

0.331

0.322

0.269

0.255

0.891

0.092

0.08

0.305

0.296

0.322

0.126

0.12

0.312

0.353

0.36

0.331

0.322

0.269

0.255

0.896

0.092

0.08

0.305

0.296

0.322

0.126

0.12

0.323

0.353

0.36

0.331

0.322

0.269

0.255

0.896

0.092

0.091

0.305

0.296

0.322

0.126

0.12

0.323

0.353

0.36

0.331

0.322

0.269

0.255

0.91

0.092

0.091

0.305

0.296

0.322

0.126

0.12

0.323

0.353

0.36

0.331

0.331

0.269

0.255

0.915

0.092

0.091

0.305

0.306

0.322

0.126

0.12

0.323

0.353

0.36

0.331

0.331

0.269

0.255

0.915

0.092

0.091

0.305

0.306

0.322

0.126

0.131

0.323

0.353

0.36

0.331

0.331

0.269

0.255

0.918

0.092

0.091

0.305

0.306

0.322

0.137

0.131

0.323

0.353

0.36

0.331

0.331

0.269

0.255

0.918

0.092

0.091

0.305

0.306

0.322

0.137

0.131

0.323

0.363

0.36

0.331

0.331

0.269

0.255

0.92

0.092

0.091

0.305

0.306

0.322

0.137

0.131

0.323

0.363

0.36

0.331

0.331

0.269

0.265

0.926

0.092

0.091

0.305

0.306

0.332

0.137

0.131

0.323

0.363

0.36

0.331

0.331

0.269

0.265

0.929

0.092

0.091

0.305

0.306

0.332

0.137

0.131

0.323

0.363

0.369

0.331

0.331

0.269

0.265

0.931

0.092

0.091

0.305

0.306

0.332

0.137

0.131

0.323

0.363

0.369

0.341

0.331

0.269

0.265

0.934

0.092

0.091

0.305

0.306

0.332

0.137

0.131

0.332

0.363

0.369

0.341

0.331

0.269

0.265

0.936

0.092

0.091

0.305

0.306

0.332

0.137

0.131

0.332

0.363

0.369

0.341

0.331

0.279

0.265

0.941

0.092

0.091

0.315

0.306

0.332

0.137

0.131

0.332

0.363

0.369

0.341

0.331

0.279

0.265

0.957

0.092

0.091

0.315

0.306

0.332

0.137

0.131

0.332

0.363

0.369

0.341

0.343

0.279

0.265

0.961

0.092

0.091

0.315

0.306

0.332

0.137

0.131

0.332

0.374

0.369

0.341

0.343

0.279

0.265

0.963

0.092

0.091

0.315

0.317

0.332

0.137

0.131

0.332

0.374

0.369

0.341

0.343

0.279

0.265

0.968

0.092

0.091

0.315

0.317

0.332

0.137

0.131

0.332

0.374

0.38

0.341

0.343

0.279

0.265

0.969

0.092

0.091

0.315

0.317

0.332

0.137

0.131

0.332

0.374

0.38

0.341

0.343

0.279

0.276

0.973

0.092

0.091

0.315

0.317

0.332

0.137

0.131

0.342

0.374

0.38

0.341

0.343

0.279

0.276

0.976

0.092

0.091

0.315

0.317

0.343

0.137

0.131

0.342

0.374

0.38

0.341

0.343

0.279

0.276

0.977

0.092

0.091

0.315

0.317

0.343

0.137

0.131

0.342

0.374

0.38

0.352

0.343

0.279

0.276

0.984

0.092

0.091

0.315

0.317

0.343

0.137

0.131

0.342

0.374

0.38

0.352

0.343

0.29

0.276

0.994

0.092

0.091

0.327

0.317

0.343

0.137

0.131

0.342

0.374

0.38

0.352

0.343

0.29

0.276

1.004

0.092

0.091

0.327

0.317

0.343

0.137

0.131

0.342

0.386

0.38

0.352

0.343

0.29

0.276

XI

Lourdes Rodriguez

TRITA LWR Degree Project 11:22

1.006

0.092

0.091

0.327

0.317

0.343

0.137

0.131

0.342

0.386

0.38

0.352

0.354

0.29

0.276

1.009

0.092

0.091

0.327

0.317

0.343

0.137

0.131

0.342

0.386

0.392

0.352

0.354

0.29

0.276

1.014

0.092

0.091

0.327

0.329

0.343

0.137

0.131

0.342

0.386

0.392

0.352

0.354

0.29

0.276

1.014

0.103

0.091

0.327

0.329

0.343

0.137

0.131

0.342

0.386

0.392

0.352

0.354

0.29

0.276

1.015

0.103

0.091

0.327

0.329

0.343

0.137

0.131

0.353

0.386

0.392

0.352

0.354

0.29

0.276

1.017

0.103

0.091

0.327

0.329

0.343

0.137

0.131

0.353

0.386

0.392

0.352

0.354

0.29

0.287

1.022

0.103

0.091

0.327

0.329

0.343

0.137

0.131

0.353

0.386

0.392

0.364

0.354

0.29

0.287

1.024

0.103

0.091

0.327

0.329

0.355

0.137

0.131

0.353

0.386

0.392

0.364

0.354

0.29

0.287

1.033

0.103

0.091

0.327

0.329

0.355

0.137

0.131

0.353

0.386

0.392

0.364

0.354

0.302

0.287

1.047

0.103

0.091

0.327

0.329

0.355

0.149

0.131

0.353

0.386

0.392

0.364

0.354

0.302

0.287

1.047

0.103

0.091

0.338

0.329

0.355

0.149

0.131

0.353

0.386

0.392

0.364

0.354

0.302

0.287

1.049

0.103

0.091

0.338

0.329

0.355

0.149

0.131

0.353

0.398

0.392

0.364

0.354

0.302

0.287

1.05

0.103

0.091

0.338

0.329

0.355

0.149

0.131

0.353

0.398

0.403

0.364

0.354

0.302

0.287

1.05

0.103

0.102

0.338

0.329

0.355

0.149

0.131

0.353

0.398

0.403

0.364

0.354

0.302

0.287

1.052

0.103

0.102

0.338

0.329

0.355

0.149

0.143

0.353

0.398

0.403

0.364

0.354

0.302

0.287

1.054

0.103

0.102

0.338

0.329

0.355

0.149

0.143

0.353

0.398

0.403

0.364

0.366

0.302

0.287

1.059

0.103

0.102

0.338

0.329

0.355

0.149

0.143

0.364

0.398

0.403

0.364

0.366

0.302

0.287

1.065

0.103

0.102

0.338

0.34

0.355

0.149

0.143

0.364

0.398

0.403

0.364

0.366

0.302

0.287

1.067

0.103

0.102

0.338

0.34

0.355

0.149

0.143

0.364

0.398

0.403

0.364

0.366

0.302

0.298

1.067

0.103

0.102

0.338

0.34

0.355

0.149

0.143

0.364

0.398

0.403

0.375

0.366

0.302

0.298

1.074

0.103

0.102

0.338

0.34

0.366

0.149

0.143

0.364

0.398

0.403

0.375

0.366

0.302

0.298

1.082

0.103

0.102

0.338

0.34

0.366

0.149

0.143

0.364

0.398

0.403

0.375

0.366

0.314

0.298

1.093

0.103

0.102

0.338

0.34

0.366

0.149

0.143

0.364

0.398

0.414

0.375

0.366

0.314

0.298

1.096

0.103

0.102

0.338

0.34

0.366

0.149

0.143

0.364

0.409

0.414

0.375

0.366

0.314

0.298

1.102

0.103

0.102

0.35

0.34

0.366

0.149

0.143

0.364

0.409

0.414

0.375

0.366

0.314

0.298

1.104

0.103

0.102

0.35

0.34

0.366

0.149

0.143

0.364

0.409

0.414

0.375

0.377

0.314

0.298

1.105

0.103

0.102

0.35

0.34

0.366

0.149

0.143

0.375

0.409

0.414

0.375

0.377

0.314

0.298

1.113

0.103

0.102

0.35

0.34

0.366

0.149

0.143

0.375

0.409

0.414

0.387

0.377

0.314

0.298

1.117

0.103

0.102

0.35

0.34

0.366

0.149

0.143

0.375

0.409

0.414

0.387

0.377

0.314

0.309

1.118

0.103

0.102

0.35

0.351

0.366

0.149

0.143

0.375

0.409

0.414

0.387

0.377

0.314

0.309

1.125

0.103

0.102

0.35

0.351

0.377

0.149

0.143

0.375

0.409

0.414

0.387

0.377

0.314

0.309

XII

Methane potential of sewage sludge to increase biogas production

1.132

0.103

0.102

0.35

0.351

0.377

0.149

0.143

0.375

0.409

0.414

0.387

0.377

0.325

0.309

1.137

0.103

0.102

0.35

0.351

0.377

0.149

0.143

0.375

0.409

0.425

0.387

0.377

0.325

0.309

1.144

0.103

0.102

0.35

0.351

0.377

0.149

0.143

0.375

0.421

0.425

0.387

0.377

0.325

0.309

1.152

0.103

0.102

0.35

0.351

0.377

0.149

0.143

0.375

0.421

0.425

0.387

0.389

0.325

0.309

1.152

0.103

0.102

0.35

0.351

0.377

0.149

0.143

0.385

0.421

0.425

0.387

0.389

0.325

0.309

1.158

0.103

0.102

0.361

0.351

0.377

0.149

0.143

0.385

0.421

0.425

0.387

0.389

0.325

0.309

1.16

0.103

0.102

0.361

0.351

0.377

0.149

0.143

0.385

0.421

0.425

0.398

0.389

0.325

0.309

1.166

0.103

0.102

0.361

0.351

0.377

0.149

0.143

0.385

0.421

0.425

0.398

0.389

0.325

0.32

1.171

0.103

0.102

0.361

0.363

0.377

0.149

0.143

0.385

0.421

0.425

0.398

0.389

0.325

0.32

1.173

0.103

0.102

0.361

0.363

0.389

0.149

0.143

0.385

0.421

0.425

0.398

0.389

0.325

0.32

1.181

0.103

0.102

0.361

0.363

0.389

0.149

0.143

0.385

0.421

0.425

0.398

0.389

0.337

0.32

1.181

0.103

0.102

0.361

0.363

0.389

0.149

0.143

0.385

0.421

0.436

0.398

0.389

0.337

0.32

1.194

0.114

0.102

0.361

0.363

0.389

0.149

0.143

0.385

0.421

0.436

0.398

0.389

0.337

0.32

1.199

0.114

0.102

0.361

0.363

0.389

0.149

0.143

0.385

0.433

0.436

0.398

0.389

0.337

0.32

1.199

0.114

0.102

0.361

0.363

0.389

0.16

0.143

0.385

0.433

0.436

0.398

0.389

0.337

0.32

1.201

0.114

0.102

0.361

0.363

0.389

0.16

0.143

0.385

0.433

0.436

0.398

0.4

0.337

0.32

1.202

0.114

0.102

0.361

0.363

0.389

0.16

0.143

0.396

0.433

0.436

0.398

0.4

0.337

0.32

1.208

0.114

0.102

0.361

0.363

0.389

0.16

0.143

0.396

0.433

0.436

0.409

0.4

0.337

0.32

1.214

0.114

0.102

0.373

0.363

0.389

0.16

0.143

0.396

0.433

0.436

0.409

0.4

0.337

0.32

1.214

0.114

0.102

0.373

0.363

0.389

0.16

0.155

0.396

0.433

0.436

0.409

0.4

0.337

0.32

1.215

0.114

0.102

0.373

0.363

0.389

0.16

0.155

0.396

0.433

0.436

0.409

0.4

0.337

0.331

1.222

0.114

0.102

0.373

0.363

0.4

0.16

0.155

0.396

0.433

0.436

0.409

0.4

0.337

0.331

1.225

0.114

0.102

0.373

0.374

0.4

0.16

0.155

0.396

0.433

0.436

0.409

0.4

0.337

0.331

1.23

0.114

0.102

0.373

0.374

0.4

0.16

0.155

0.396

0.433

0.436

0.409

0.4

0.349

0.331

1.23

0.114

0.102

0.373

0.374

0.4

0.16

0.155

0.396

0.433

0.448

0.409

0.4

0.349

0.331

1.235

0.114

0.113

0.373

0.374

0.4

0.16

0.155

0.396

0.433

0.448

0.409

0.4

0.349

0.331

1.248

0.114

0.113

0.373

0.374

0.4

0.16

0.155

0.396

0.433

0.448

0.409

0.411

0.349

0.331

1.256

0.114

0.113

0.373

0.374

0.4

0.16

0.155

0.396

0.433

0.448

0.421

0.411

0.349

0.331

1.26

0.114

0.113

0.373

0.374

0.4

0.16

0.155

0.407

0.433

0.448

0.421

0.411

0.349

0.331

1.26

0.114

0.113

0.373

0.374

0.4

0.16

0.155

0.407

0.444

0.448

0.421

0.411

0.349

0.331

1.263

0.114

0.113

0.373

0.374

0.4

0.16

0.155

0.407

0.444

0.448

0.421

0.411

0.349

0.343

XIII

Lourdes Rodriguez

TRITA LWR Degree Project 11:22

1.267

0.114

0.113

0.385

0.374

0.4

0.16

0.155

0.407

0.444

0.448

0.421

0.411

0.349

0.343

1.272

0.114

0.113

0.385

0.374

0.412

0.16

0.155

0.407

0.444

0.448

0.421

0.411

0.349

0.343

1.278

0.114

0.113

0.385

0.385

0.412

0.16

0.155

0.407

0.444

0.448

0.421

0.411

0.349

0.343

1.279

0.114

0.113

0.385

0.385

0.412

0.16

0.155

0.407

0.444

0.448

0.421

0.411

0.36

0.343

1.286

0.114

0.113

0.385

0.385

0.412

0.16

0.155

0.407

0.444

0.459

0.421

0.411

0.36

0.343

1.297

0.114

0.113

0.385

0.385

0.412

0.16

0.155

0.407

0.444

0.459

0.421

0.423

0.36

0.343

1.305

0.114

0.113

0.385

0.385

0.412

0.16

0.155

0.407

0.444

0.459

0.432

0.423

0.36

0.343

1.312

0.114

0.113

0.385

0.385

0.412

0.16

0.155

0.407

0.444

0.459

0.432

0.423

0.36

0.354

1.319

0.114

0.113

0.385

0.385

0.423

0.16

0.155

0.407

0.444

0.459

0.432

0.423

0.36

0.354

1.323

0.114

0.113

0.396

0.385

0.423

0.16

0.155

0.407

0.444

0.459

0.432

0.423

0.36

0.354

1.324

0.114

0.113

0.396

0.385

0.423

0.16

0.155

0.417

0.444

0.459

0.432

0.423

0.36

0.354

1.326

0.114

0.113

0.396

0.385

0.423

0.16

0.155

0.417

0.456

0.459

0.432

0.423

0.36

0.354

1.327

0.114

0.113

0.396

0.385

0.423

0.16

0.155

0.417

0.456

0.459

0.432

0.423

0.372

0.354

1.331

0.114

0.113

0.396

0.397

0.423

0.16

0.155

0.417

0.456

0.459

0.432

0.423

0.372

0.354

1.345

0.114

0.113

0.396

0.397

0.423

0.16

0.155

0.417

0.456

0.47

0.432

0.423

0.372

0.354

1.345

0.114

0.113

0.396

0.397

0.423

0.16

0.155

0.417

0.456

0.47

0.432

0.434

0.372

0.354

1.353

0.114

0.113

0.396

0.397

0.423

0.16

0.155

0.417

0.456

0.47

0.443

0.434

0.372

0.354

1.36

0.114

0.113

0.396

0.397

0.423

0.16

0.155

0.417

0.456

0.47

0.443

0.434

0.372

0.365

1.368

0.114

0.113

0.396

0.397

0.423

0.171

0.155

0.417

0.456

0.47

0.443

0.434

0.372

0.365

1.369

0.114

0.113

0.396

0.397

0.435

0.171

0.155

0.417

0.456

0.47

0.443

0.434

0.372

0.365

1.375

0.114

0.113

0.396

0.397

0.435

0.171

0.155

0.417

0.456

0.47

0.443

0.434

0.383

0.365

1.376

0.114

0.113

0.408

0.397

0.435

0.171

0.155

0.417

0.456

0.47

0.443

0.434

0.383

0.365

1.38

0.126

0.113

0.408

0.397

0.435

0.171

0.155

0.417

0.456

0.47

0.443

0.434

0.383

0.365

1.385

0.126

0.113

0.408

0.408

0.435

0.171

0.155

0.417

0.456

0.47

0.443

0.434

0.383

0.365

1.391

0.126

0.113

0.408

0.408

0.435

0.171

0.167

0.417

0.456

0.47

0.443

0.434

0.383

0.365

1.392

0.126

0.113

0.408

0.408

0.435

0.171

0.167

0.428

0.456

0.47

0.443

0.434

0.383

0.365

1.393

0.126

0.113

0.408

0.408

0.435

0.171

0.167

0.428

0.456

0.47

0.443

0.446

0.383

0.365

1.396

0.126

0.113

0.408

0.408

0.435

0.171

0.167

0.428

0.468

0.47

0.443

0.446

0.383

0.365

1.404

0.126

0.113

0.408

0.408

0.435

0.171

0.167

0.428

0.468

0.47

0.455

0.446

0.383

0.365

1.408

0.126

0.113

0.408

0.408

0.435

0.171

0.167

0.428

0.468

0.481

0.455

0.446

0.383

0.365

1.41

0.126

0.113

0.408

0.408

0.435

0.171

0.167

0.428

0.468

0.481

0.455

0.446

0.383

0.376

XIV

Methane potential of sewage sludge to increase biogas production

1.418

0.126

0.113

0.408

0.408

0.446

0.171

0.167

0.428

0.468

0.481

0.455

0.446

0.383

0.376

1.424

0.126

0.113

0.408

0.408

0.446

0.171

0.167

0.428

0.468

0.481

0.455

0.446

0.395

0.376

1.429

0.126

0.113

0.42

0.408

0.446

0.171

0.167

0.428

0.468

0.481

0.455

0.446

0.395

0.376

1.433

0.126

0.125

0.42

0.408

0.446

0.171

0.167

0.428

0.468

0.481

0.455

0.446

0.395

0.376

1.441

0.126

0.125

0.42

0.419

0.446

0.171

0.167

0.428

0.468

0.481

0.455

0.446

0.395

0.376

1.443

0.126

0.125

0.42

0.419

0.446

0.171

0.167

0.428

0.468

0.481

0.455

0.457

0.395

0.376

1.457

0.126

0.125

0.42

0.419

0.446

0.171

0.167

0.428

0.468

0.481

0.466

0.457

0.395

0.376

1.459

0.126

0.125

0.42

0.419

0.446

0.171

0.167

0.428

0.468

0.481

0.466

0.457

0.395

0.387

1.463

0.126

0.125

0.42

0.419

0.446

0.171

0.167

0.439

0.468

0.481

0.466

0.457

0.395

0.387

1.468

0.126

0.125

0.42

0.419

0.458

0.171

0.167

0.439

0.468

0.481

0.466

0.457

0.395

0.387

1.471

0.126

0.125

0.42

0.419

0.458

0.171

0.167

0.439

0.48

0.481

0.466

0.457

0.395

0.387

1.474

0.126

0.125

0.42

0.419

0.458

0.171

0.167

0.439

0.48

0.492

0.466

0.457

0.395

0.387

1.474

0.126

0.125

0.42

0.419

0.458

0.171

0.167

0.439

0.48

0.492

0.466

0.457

0.407

0.387

1.481

0.126

0.125

0.431

0.419

0.458

0.171

0.167

0.439

0.48

0.492

0.466

0.457

0.407

0.387

1.493

0.126

0.125

0.431

0.419

0.458

0.171

0.167

0.439

0.48

0.492

0.466

0.469

0.407

0.387

1.496

0.126

0.125

0.431

0.431

0.458

0.171

0.167

0.439

0.48

0.492

0.466

0.469

0.407

0.387

1.508

0.126

0.125

0.431

0.431

0.458

0.171

0.167

0.439

0.48

0.492

0.477

0.469

0.407

0.387

1.509

0.126

0.125

0.431

0.431

0.458

0.171

0.167

0.439

0.48

0.492

0.477

0.469

0.407

0.398

1.519

0.126

0.125

0.431

0.431

0.469

0.171

0.167

0.439

0.48

0.492

0.477

0.469

0.407

0.398

1.524

0.126

0.125

0.431

0.431

0.469

0.171

0.167

0.439

0.48

0.492

0.477

0.469

0.418

0.398

1.534

0.126

0.125

0.443

0.431

0.469

0.171

0.167

0.439

0.48

0.492

0.477

0.469

0.418

0.398

1.542

0.126

0.125

0.443

0.431

0.469

0.171

0.167

0.45

0.48

0.492

0.477

0.469

0.418

0.398

1.543

0.126

0.125

0.443

0.431

0.469

0.171

0.167

0.45

0.48

0.492

0.477

0.48

0.418

0.398

1.544

0.126

0.125

0.443

0.431

0.469

0.171

0.167

0.45

0.48

0.504

0.477

0.48

0.418

0.398

1.551

0.126

0.125

0.443

0.442

0.469

0.171

0.167

0.45

0.48

0.504

0.477

0.48

0.418

0.398

1.551

0.126

0.125

0.443

0.442

0.469

0.171

0.167

0.45

0.491

0.504

0.477

0.48

0.418

0.398

1.551

0.126

0.125

0.443

0.442

0.469

0.183

0.167

0.45

0.491

0.504

0.477

0.48

0.418

0.398

1.56

0.126

0.125

0.443

0.442

0.469

0.183

0.167

0.45

0.491

0.504

0.477

0.48

0.418

0.409

1.56

0.126

0.125

0.443

0.442

0.469

0.183

0.167

0.45

0.491

0.504

0.489

0.48

0.418

0.409

1.569

0.126

0.125

0.443

0.442

0.48

0.183

0.167

0.45

0.491

0.504

0.489

0.48

0.418

0.409

1.574

0.137

0.125

0.443

0.442

0.48

0.183

0.167

0.45

0.491

0.504

0.489

0.48

0.418

0.409

XV

Lourdes Rodriguez

TRITA LWR Degree Project 11:22

1.574

0.137

0.125

0.443

0.442

0.48

0.183

0.167

0.45

0.491

0.504

0.489

0.48

0.43

0.409

1.584

0.137

0.125

0.443

0.442

0.48

0.183

0.179

0.45

0.491

0.504

0.489

0.48

0.43

0.409

1.585

0.137

0.125

0.455

0.442

0.48

0.183

0.179

0.45

0.491

0.504

0.489

0.48

0.43

0.409

1.594

0.137

0.125

0.455

0.442

0.48

0.183

0.179

0.45

0.491

0.504

0.489

0.492

0.43

0.409

1.608

0.137

0.125

0.455

0.453

0.48

0.183

0.179

0.45

0.491

0.504

0.489

0.492

0.43

0.409

1.611

0.137

0.125

0.455

0.453

0.48

0.183

0.179

0.45

0.491

0.504

0.489

0.492

0.43

0.42

1.614

0.137

0.125

0.455

0.453

0.48

0.183

0.179

0.45

0.491

0.504

0.5

0.492

0.43

0.42

1.618

0.137

0.125

0.455

0.453

0.48

0.183

0.179

0.45

0.491

0.515

0.5

0.492

0.43

0.42

1.621

0.137

0.125

0.455

0.453

0.492

0.183

0.179

0.45

0.491

0.515

0.5

0.492

0.43

0.42

1.624

0.137

0.125

0.455

0.453

0.492

0.183

0.179

0.46

0.491

0.515

0.5

0.492

0.43

0.42

1.624

0.137

0.125

0.455

0.453

0.492

0.183

0.179

0.46

0.491

0.515

0.5

0.492

0.441

0.42

1.638

0.137

0.125

0.466

0.453

0.492

0.183

0.179

0.46

0.491

0.515

0.5

0.492

0.441

0.42

1.638

0.137

0.125

0.466

0.453

0.492

0.183

0.179

0.46

0.503

0.515

0.5

0.492

0.441

0.42

1.646

0.137

0.125

0.466

0.453

0.492

0.183

0.179

0.46

0.503

0.515

0.5

0.503

0.441

0.42

1.65

0.137

0.136

0.466

0.453

0.492

0.183

0.179

0.46

0.503

0.515

0.5

0.503

0.441

0.42

1.662

0.137

0.136

0.466

0.453

0.492

0.183

0.179

0.46

0.503

0.515

0.5

0.503

0.441

0.431

1.668

0.137

0.136

0.466

0.465

0.492

0.183

0.179

0.46

0.503

0.515

0.5

0.503

0.441

0.431

1.673

0.137

0.136

0.466

0.465

0.503

0.183

0.179

0.46

0.503

0.515

0.5

0.503

0.441

0.431

1.675

0.137

0.136

0.466

0.465

0.503

0.183

0.179

0.46

0.503

0.515

0.5

0.503

0.453

0.431

1.677

0.137

0.136

0.466

0.465

0.503

0.183

0.179

0.46

0.503

0.515

0.512

0.503

0.453

0.431

1.689

0.137

0.136

0.478

0.465

0.503

0.183

0.179

0.46

0.503

0.515

0.512

0.503

0.453

0.431

1.697

0.137

0.136

0.478

0.465

0.503

0.183

0.179

0.46

0.503

0.526

0.512

0.503

0.453

0.431

1.699

0.137

0.136

0.478

0.465

0.503

0.183

0.179

0.46

0.503

0.526

0.512

0.514

0.453

0.431

1.713

0.137

0.136

0.478

0.465

0.503

0.183

0.179

0.46

0.503

0.526

0.512

0.514

0.453

0.442

1.713

0.137

0.136

0.478

0.465

0.503

0.183

0.179

0.471

0.503

0.526

0.512

0.514

0.453

0.442

1.725

0.137

0.136

0.478

0.465

0.503

0.183

0.179

0.471

0.503

0.526

0.512

0.514

0.465

0.442

1.727

0.137

0.136

0.478

0.465

0.515

0.183

0.179

0.471

0.503

0.526

0.512

0.514

0.465

0.442

1.729

0.137

0.136

0.478

0.465

0.515

0.183

0.179

0.471

0.515

0.526

0.512

0.514

0.465

0.442

1.73

0.137

0.136

0.478

0.476

0.515

0.183

0.179

0.471

0.515

0.526

0.512

0.514

0.465

0.442

1.741

0.137

0.136

0.49

0.476

0.515

0.183

0.179

0.471

0.515

0.526

0.512

0.514

0.465

0.442

1.742

0.137

0.136

0.49

0.476

0.515

0.194

0.179

0.471

0.515

0.526

0.512

0.514

0.465

0.442

XVI

Methane potential of sewage sludge to increase biogas production

1.743

0.137

0.136

0.49

0.476

0.515

0.194

0.179

0.471

0.515

0.526

0.523

0.514

0.465

0.442

1.759

0.137

0.136

0.49

0.476

0.515

0.194

0.179

0.471

0.515

0.526

0.523

0.526

0.465

0.442

1.763

0.137

0.136

0.49

0.476

0.515

0.194

0.179

0.471

0.515

0.526

0.523

0.526

0.465

0.453

1.775

0.137

0.136

0.49

0.476

0.515

0.194

0.179

0.471

0.515

0.526

0.523

0.526

0.476

0.453

1.779

0.137

0.136

0.49

0.476

0.515

0.194

0.179

0.471

0.515

0.537

0.523

0.526

0.476

0.453

1.785

0.137

0.136

0.49

0.476

0.526

0.194

0.179

0.471

0.515

0.537

0.523

0.526

0.476

0.453

1.792

0.148

0.136

0.49

0.476

0.526

0.194

0.179

0.471

0.515

0.537

0.523

0.526

0.476

0.453

1.795

0.148

0.136

0.501

0.476

0.526

0.194

0.179

0.471

0.515

0.537

0.523

0.526

0.476

0.453

1.796

0.148

0.136

0.501

0.487

0.526

0.194

0.179