BIOCHAR FROM CELLULOSE FOR MICROPOLLUTION ELIMINATION WHITE PAPER OCTOBER 2023
OUR AIM IS TO USE THE BIOCHAR PRODUCED FROM CELLULOSE AS SUPPORTING MATERIAL IN SO-CALLED CONSTRUCTED WETLANDS (CWS), A NATURE-BASED SOLUTION FOR WASTEWATER TREATMENT, WITH THE SPECIFIC AIM TO REMOVE MICROPOLLUTANTS FROM EFFLUENT WASTEWATER.
AUTHORS Joachim Hansen, Silvia Venditti, Irene Salmeron Garcia – University of Luxembourg John Gallagher – Trinity College Inka Hobus – Wupperverbandsgesellschaft für integrale Wasserwirtschaft
INTRODUCTION The most obvious resource from sewage… yes.. toilet paper or cellulose. Yearly 6,5 million tonnes of toilet paper ends up in the sewer system and finally in our wastewater treatment plants. 4,5 million tonnes of this toilet paper can be recovered. This theoretically equals 14 million trees per year. With cellulose sievings, we can already make biochar, acetic acid and bio-oil. Now, we took a next step and activated the biochar into activated carbon for elimination of micropollutants at small and medium sewage treatment plants. This material then can be used in constructed wetlands as an additional step after the conventional treatment. This application opens possibilities for new markets. This whitepaper contains the following chapters: 1. EXPLANATION OF THE GENERAL PRINCIPLE OF AC PRODUCTION FROM RESIDUAL STREAMS 2. BIOCHAR FROM CELLULOSE - MANUFACTURING PROCESS AND POSSIBLE APPLICATION 3. ELIMINATION OF POLLUTANTS USING BIOCHAR FROM CELLULOSE IN CONSTRUCTED WETLANDS 4. CONSTRUCTED WETLANDS WITH BIOCHAR - CASE STUDY FOR A SMALL CATCHMENT AREA 5. CIRCULARITY MEASUREMENT & ASSESSMENT METHODOLOGY 6. FUTURE CHALLENGES
ENJOY READING! This whitepaper gives an overview of (part of) the results of the Interreg NWE project WOW! - Wider business Opportunities for raw materials from Wastewater. More information about this project can be found on the website of WOW!
1. Explanation of the general principle of AC production from residual streams The average person uses around 85 rolls of toilet paper (mainly consisting of cellulose) per year, meaning that a huge amounts of paper – ca. 4 Mio tons per year in EU 27 - ends up in the wastewater treatment plants (WWTPs) through the sewage. Said that we aimed to recover that cellulose to be used as raw material to produce biochar for pollution mitigation; The intention is to bridge large Sewage Treatment Plants (STPs) seen as factories of valuable material with rural areas, boosting in that way territorial cohesion and inclusive growth, according to the Interreg North-West Europe (NWE) program.
BIOCHAR’S MULTIPLE APPLICATIONS
Biochar is defined by the International Biochar Initiative (IBI, 2015) as the solid material obtained from the thermochemical conversion of biomass in an oxygen-limited environment. This material is considered to have multiple applications environmentally advantageous, such as 1) catalyst in the transesterification and esterification process of waste oil for biodiesel
production 2) soil additive to enhance its fertility 3) alternative fuel because of its high calorific value 4) additive for compost to accelerate the process 5) Greenhouse emissions controller in air purification for CO2 capture and finally 6) adsorbent of pollutants from water and wastewater.
OUR AIM
Our aim is to use the biochar produced from cellulose as supporting material in so-called Constructed Wetlands (CWs), a nature-based solution for wastewater treatment, with the specific aim to remove Micropollutants from effluent wastewater.
2. Biochar from Cellulose - manufacturing process and possible application
Figure 1 : a) RBF sieve b) recovered cellulose from toilet paper c) raw cellulose
The production of biochar from recovered Cellulose can be summarized by the following subsequent steps:
1. SIEVING AND DEWATERING
For capturing cellulosic screenings from the wastewater stream, rotating belt fine sieves (RBF) were used in the mechanical treatment step of STP Ede (NL), constructed by Dutch Company CirTec B.V.. RBF combines two processes in one unit - solids separation and solids thickening (see fig. 1), thus can replace conventional screens and primary sedimentation. The filtrate (free water) is collected behind the filter mesh (of 350 microns) and is discharged, while the solids are recovered from the filter mesh by means of a tailored designed cleaning system, using low pressure air.
Figure 2: dried pellets
Figure 3.a. pellets of 100 % cellulose
2. DRYING AND PELLETIZATION
The pressed material is dried in a curtain dryer by a mixture of air and flue gas, leaving the dryer at a temperature of 60°C and a dry content of 65-70%. Then, it is converted into pellets with a diameter of 6 mm and transported to a secondary drying unit. The secondary dryer is fed with a mixture of flue gas and air at 120°C. The hot gases flow countercurrent through the column and leave the dryer at 40-45°C. The process is controlled by an infrared temperature sensor and the regulation of a ventilator. Pellets leave the secondary dryer with 90% of dry matter (see fig. 2). To guarantee the suitability of biochar for biological activation, the recovered cellulose can be mixed with straw or wood chips before pelletization (fig. 3).
Figure 3.b. pellets of 50 % cellulose – 50 % straw
Figure 3.c. pellets of 50 % cellulose – 50 % wood
3. CARBONIZATION
Carbonization is carried out in a continuous mode in modern carbonization plants. The temperature is between 600 and 800°C and the residence time in the reactor can be regulated, being usually from 2 to 6 hours. All process is developed in the absence of air. The product can be seen in fig. 4.
BIOLOGICAL ACTIVATION
The substrate is activated via an anaerobic fermentation by Klimafarmer (Germany). For this purpose, the biochar obtained in the previous step is mixed with minerals, a nutrient substrate and microorganisms, as bacteria and yeast. The mixture is fermented at a temperature between 25 and 35 °C for a time period of 2 - 4 weeks. Figure 4: biochar after pellets carbonization
3. Elimination of pollutants using Biochar from cellulose in Constructed Wetlands The NWE zone is composed of rural areas with a high percentage of small and medium STPs discharging in sensitive rivers where pollution mitigation is of utmost importance to achieve and maintain good (chemical and) ecological conditions in surface water according to the Water Frame Directive (WFD). When released from small STPs located in rural areas, micropollutants (MPs) (i.e. pharmaceuticals, pesticides and herbicides) can lead to critical concentrations in the receiving waters mainly due to the limited dilution factor and eventually to the more vulnerable hydrology of the rivers. In the last twenty years the need to minimize MP emissions has found a consensus in the upgrade of STPs with a post-treatment step (additionally to the conventional mechanical-biological treatment) because of the incapability of conventional activated sludge treatment in the removal of most MPs. Till now, the majority of STPs apply common technologies such as Activated Carbon Filtration (both powdered, PAC and granulated, GAC ) and ozone which are however not affordable to be applied to small STPs because of operational and economic reasons. Nature-based solutions (NBS) have been considered as a potential alternative for MPs removal in rural settlements when the upgrade is needed.
The application of biochar produced from cellulose recovered from large STPs and activated by fermentation as admixture (supporting material to enhance the processes in the soil) in NBS was tested for MPs’s treatment adopted in rural areas. Due to their low investment and operation cost combined with good effluent quality, CWs in vertical flow configuration are the NBS selected for the application of Wow-AC as admixture. In pre-tests carried out at University of Luxembourg, the biochar produced from a mixture of cellulose and straw (50% / 50%, so called WOWAC) has shown the best results. An experimental set up (fig. 5) was designed to assess the removal of the selected WOW-AC towards a list of MPs representative for small and medium sized STPs and relevant in a water quality perspective. The WOW-AC was compared with a similar biochar (namely EmiSûre - AC) produced from plant residues and activated biologically via fermentation in the same way of the WOW-AC. This biochar has been previously tested from Uni.Lu and Klimafarmer in the frame of the Interreg GR funded projects, EmiSûre and CoMinGreat.
Phragmites australis Iris pseudacorusm
Figure 5: Laboratory set-up
Two 20 L reactors M1 and M2 were built and filled with 10 cm of drainage material (6 cm of coarse 4-8 mm and 4 cm of fine 2-8 mm gravel) and 20 cm of substrate as following: • M1: 95 % Sand + 5 % EmiSûre biochar produced from plant residues and activated biologically via fermentation (EmiSûre -AC) • M2: 95 % Sand + 5 % Wow biochar produced from cellulose/straw and activated biologically via fermentation (WOW -AC)
(Luxembourg) and treating 72,000 population equivalents (PE). Generally, removal rate exceeded 80% for most compounds (see fig. x), with the only exception of the betablocker Atenolol and the flame retardant TCPP. These results are in line with those of the previous projects where flame retardants were poorly removed (< 30 %) and found still in relevant effluent concentrations (around 3 µ/L)
Both reactors were planted with Phragmites australis and Iris pseudacorusm (macrophytes typical of CWs and applied in previous projects), operated in down flow mode and fed simultaneously and intermittently at the same flow rate, with the same wastewater. This mode of operandi is typical of a vertical flow configuration which ensures continuous aeration of the substrate and well-established aerobic conditions favoring biological degradation of persistent compounds. The wastewater is pumped at Hydraulic Loading Rate (HLR) of 0.023 m3 of water/m2 irrigated surface for 30 min, 2 times per day. To mimic natural sunlight and to enable photodegradation, UV lamps are installed to provide 8 h per day of light (10 a.m. to 6 p.m.). 28 compounds were selected taking into account: a) those known to be excreted in the highest amount (in the case of pharmaceuticals: antibiotics, beta-blockers, analgesics etc), b) those known with the highest eco-toxicity (i.e. cytostatics), c) those known to be underobservation (i.e. macrolides) or with legal obligations (i.e. isoproturon, diuron), d) those known to be especially relevant for the Greater Region. 12 out of 28 compounds were considered relevant for the real wastewater used for the experiments, collected from STP Beringen operated by SIDERO
Figure 6: average removal efficiencies of the 12 relevant MPs
In the last years, some countries have set up more strict national discharge standards, started to plan and implement additional treatment steps for MP-removal identifying urban areas which are significant point sources in the river basin they are located in. Luxembourg released a guideline (Administration de Gestion de l’eau, 2020) for those STPs that have been selected to be upgraded with a post-treatment. The effluent quality has to achieve 80 % cumulative removal for four mandatory compounds namely anti-inflammatory drug diclofenac, anti-epileptic drug carbamazepine, antibiotic clarithromycin and corrosion inhibitor benzotriazole with the option of
adding to the permit substances that are relevant for the respective STP when measured above Environmental Quality Standards (EQSs) in the receiving surface waters. The 80 % reduction has to be calculated between the STP influent concentration and the one discharged after the post-treatment step is applied.
admixture in a CW allows to comply with the 80 % removal threshold for the four mandatory compounds (Luxembourg legislation).
When the removal contributions of the two treatments steps (conventional mechanical- biological in STP and additional M1 or M2 (see Figure x)) to the overall elimination of the selected compounds is plotted, the CW (M1 or M2) resulted to be: • the dominant treatment in the elimination of those compounds that are known to be persistent and hardly removed in conventional activated sludge treatment such as lidocaine, carbamazepine; • a strong contributor in the elimination of antibiotics (i.e. clarithromycin and ciprofloxacin); • a non-significant contributor in the elimination of those compounds highly degraded from the STP (i.e. ibuprofen, DEET etc). The results depicted in Figure x have been widely demonstrated in the previous projects at different STPs. Since there are not significant differences between EmiSûre -AC and WOW-AC performances, it is robust to affirm that as for EmiSûre -AC the use of CW with WOW-AC as an
Figure 7: relative contribution of the CW with cellulose biochar and the WWTP to the overall global average removal efficiencies
Results show that the WOW-AC proved to be suitable as admixture in CW for the removal of MPs (post-treatment step) with performances similar to those of previous Activated Biochar (produced from plants) with more than 80 % elimination for most relevant MPs.
4. Constructed Wetlands with biochar Case study for a small catchment area The investigations were carried out for the catchment area of the Blies river. The river rises in France and flows into the Saar in Germany. The catchment area is rural with a large number of small wastewater treatment plants. The receiving waters of the wastewater treatment plants are relatively small and some discharge their effluents close to the source area. This results in high micro pollution concentration in the river. For an improvement of the water quality, technically simple solutions with a low operating expense are required for the small wastewater treatment plants. The case study aims to show how circular solutions for the production of biochar from wastewater and the use of the produced biochar in
constructed wetlands can be implemented for a small river basin. Two variants were investigated: • Variant 1: Integration of constructed wetlands at three small wastewater treatment plants that have the greatest impact on the concentration of micro-pollution in the river catchment area (capacity of 7,783 PE). • Variant 2: Integration of constructed wetlands at all small WWTPs where it is technical feasible (9 WWTPs with a capacity of 13.863 PE) For this purpose, fine sieve with a cellulose washer and press were considered for variant 1 at three WWTPs with a connected population of 32,000 PE und for variant 2 at five WWTPs with a connected population of 61,400 PE.
up to 1,08 Mio. t for variant 1 and 1,98 Mio. t/a for variant 2. In addition to the recovery of cellulose, the integration of a fine sieve results in a reduction of the inlet load to the biological stage and thus also a reduction of the required air flow by 20 %. Furthermore, this results in free capacities for the connection of further inhabitants.
Figure 8: River catchment of the river blies (German part) and location of the WWTPs (Schmitt et al., 2019)
For the installation of the fine sieves, WWTPs were selected on which no primary clarifier and no sludge digestion are installed. The cellulose produced is dried and then pyrolyzed together with straw to produce WOW-biochar. With a specific cellulose load of 32 g/PE/d (WOW, 2022), the same amount of straw and a loss of 80% due to the pyrolysis the produced WOW-biochar sums
The produced WOW-Biochar is used at small WWTPs with a connection size between 500 – 3,100 population equivalents to reduce the micro pollutant concentration. The surface area for the constructed wetland was determined using a maximum hydraulic surface loading of 400 l/ m²/d or a specific area of 0.4 m²/PE. The maximum surface area of both design rules is used for the layout of the constructed wetland. Due to the high infiltration water up to 75 % in the sewage system of the investigated WWTPs huge filter areas are required. For the design of the constructed wetlands, it was therefore assumed that the infiltration water is reduced to less than 20 %. The total area for the constructed wetlands sums up to 7,400 m² for Variant 1 and 13,545 m² for the Variant 2. In the picture below the design of a constructed wetland for WWTP Haupersweiler with a size of 3,033 PE is shown.
Figure 9: Capex of the installation of cellulose recovery and constructed wetlands with WOW biochar for variant 1 and variant 2
The Capex for the installation of the Cellulose recovery, the production of WOW-Biochar and for the construction of the constructed wetlands were estimated to 8,8 Mio. € per variant 1 and 19,8 Mio. € for variant 2. The main cost block is the production of the biochar and the construction of the filters. There is still a great potential for optimisation here. Investigation at a constructed wetland with activated carbon shows that the maximum hydraulic load could rise to 2,592 L/d*m² without clogging (Brunsch et al., 2020). In the graph below you can see the influence of the constructed wetlands with biochar on the diclofenac concentration. The elimination rate of the constructed wetlands with WOW biochar was conservatively set to 80 %, although the elimination rate of the pilot plants shows an elimination rate of up to 90 %. With the construction of three filters the Environmental Quality Standards (EQS)
for diclofenac can be met almost over the entire flow path for the Oster river, a branch of the Blies river. With the installation of constructed wetlands at all small WWTPs diclofenac concentration falls below the EQS.
Figure 10: Diclofenac concentration of the river Oster for the current conditions and for variant 1 and 2 (Schmitt et al.;2019)
In Figure 10 you can see the influence of the constructed wetlands with biochar on the diclofenac concentration. The elimination rate of the constructed wetlands with WOW biochar was conservatively set to 80 %, although the elimination rate of the pilot plants shows an elimination rate of up to 90 %. With the construction of three filters the Environmental Quality Standards (EQS) for diclofenac can be met almost over the entire flow path for the Oster river, a branch of the Blies river. With the installation of constructed wetlands at all small WWTPs diclofenac concentration falls below the EQS.
The case study show, that the combination of cellulose recovery with fine sieves in order to provide WOW Biochar for constructed wetlands for micro pollutant removal in a river catchment is possible. Although the load reduction from small WWTP in comparison to the whole load from all WWTP in the catchment is small, the impact on the river quality is high. For implementation further investigation into hydraulic load and invest costs is necessary.
Small scale models of contructed wetlands
5. Circularity Measurement & Assessment Methodology for Activated Biochar Production
Figure 11. Current structure and connectivity of ISO 59000 family of standards.
The production of activated biochar (AB) using cellulose extracted from the wastewater treatment cycle represents an opportunity to create a circular resource. Applying a circularity measurement and assessment (CMA) methodology, which follows one standard (ISO 59020) as part of a new family of ISOs provided in Figure 11, and can quantify the technical, economic, social, and environmental value of AB production. The case study for AB production using cellulose and its circular use in constructed wetlands for enhanced treatment of micropollutants (Hobus et al., 2023) provides an example within the WOW! project for applying this methodology when a complete dataset is compilated.
CIRCULARITY MEASUREMENT & ASSESSMENT FRAMEWORK
The CMA framework can be applied to a given system in focus. This system in focus may represent a product, service, or process, and sits within an economic system, and is connected to external social and environmental systems. The CMA process has three steps; (i) boundary setting in which the system in focus to be measured is defined; (ii) circularity measurement and data acquisition outlines the necessary data to quantify the CMA results; and (iii) circularity assessment and reporting translates the findings into relevant information for different stakeholders.
Boundary Setting: AB production using cellulose reflects the system in focus and the CMA process would provide findings of relevance to waterboards / water authorities as both the source of cellulose and user of AB, and companies producing AB from cellulose. The goal and scope of the study is best to consider a regional scale, reflecting one or multiple WWTPs as the sources of cellulose and users of AB. Constructed wetlands (CWs) are more suitable as a form of tertiary treatment for smaller WWTPs, therefore Saarland in Germany (region evaluated in (Hobus et al., 2023)) provides a suitable example for a CMA. This biochar can also be compared to activated carbon (AC) as an alternative feedstock for CWs. Lastly, the CMA is considered to have relevance at both organisational and product levels. Circularity measurement and data acquisition: Seven circularity indicators were selected for the evaluation of AB, with one core indicator i.e. lifetime of product relative to industry average, and six additional indicators capturing energy, water, economic and social factors. A complementary life cycle assessment can be applied (EF v3.0 method) to quantify the relevant environmental impacts of the AB production process and allow for a comparison to AC as an alternative CW feedstock for enhanced treatment. In addition, Sustainable Development Goals (SDGs) were
identified as having relevant value as AB production can ensure clean water and sanitation (#6), whilst supporting decent work and economic growth (#8), new industry, innovation and infrastructure (#9) and reduce inequalities (#10) in this new sector. Stage 3: Circularity assessment and reporting: The formulae and data requirements to quantify the selected circularity indicators are outlined in Table 1. These results set a benchmark for resource flows including energy and water, as well as economic and social performance for AB production using cellulose. The complementary LCA quantifies the environmental performance of AB, and the SDG assessment links its value to global sustainability metrics. With this knowledge, measures to improve its circularity performance, including environmental impacts and sustainability goals, can be achieved. This can also increase its competitive ness as compared to AB, with targeted outputs for relevant stakeholders in water authorities / waterboards and AB producers.
CONCLUSIONS
The CMA framework is presented to allow for a future analysis of the circular performance of the AB production process, once a complete dataset is collated. The appropriate boundaries of the system in focus, the most relevant indicators to capture the circular performance, and the relevant stakeholders in the AB value chain to benefit from these findings have been identified within the report. From this, the process can be applied to quantify the circularity of AB from cellulose, and providing a comparison with AC, that can be used in CWs to enhance the treatment of wastewater. More information on the circularity measurement and assessment methodology developed to assess AB production can be found in (Gallagher, 2023).
Table 1. Formulae and data requirements to quantify qircularity indicators for assessment the valorisation of activated biochar production from cellulose.
5. FUTURE CHALLENGES The Interreg NWE WOW! project provided many new insights in the recovery of cellulose with fine sieves on municipal wastewater treatment plants in order to provide activated carbon as supporting material for constructed wetlands for micropollutant removal in rural areas. Are we ready for fullscale production? Definitely, we would say. Technically it is possible to produce activated carbon from ingredients of incoming wastewater and use it for micropollutant removal on large scale. But of course there are also still some remaining challenges that need to be adressed: • • • •
Maximum hydraulic load to the constructed wetlands. Requirements and costs of smaller or medium size pyrolysis plants for biochar production must be further investigated in a scale-up with plant manufacturers. GHG-emissions in comparison with conventionally produced activated carbon. Long-term performance of the product.
Do you want to be involved in tackling these challenges or do you have ideas on how to overcome them? Do not hesitate to contact us.
REFERENCES Hobus, I.; Kolisch, G. (2023): Finding most suitable locations for AC-production (larger STP) and possible application in Constructed Wetlands -Case Study. Report: WOW-Project Gallagher, J. (2023): A circularity measurement and assessment methodology of resource recovery and reuse from sewage. Report: WOW-Project
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PROJECT PARTNERS WORKING ON AC
The WOW! project has been finished in October 2023. The project partners will keep continuing the research on PHA. More information about the project can be found on the website:
If you have specific questions please contact: Joachim Hansen Professor University of Luxembourg joachim.hansen@uni.lu For media inquiries, please contact the WOW! communications officer: Wendy van Rijsbergen w.vanrijsbergen@avans.nl
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