Acceleration of Biogas Production in Cattle Dung Digestion through Jatropha Curcas Oil Cake as an Additive Sanjay L. Pal1, Atul P. Vanerkar2, Shanta Satyanarayan3 Assistant Professor, Department of Environmental Science, Sevadal Mahil Mahavidyalaya, Nagpur(M.S.) India.
1
Scientific Assistant, National Institute of Miners Health, Nagpur (M.S.) India
2
Retired. Scientist, National Environmental Engineering Research Institute, Nagpur (M.S.) India.
3
Drsanjaypal24@gmail.com; atvan123@gmail.com; dr_shantasa@rediffmail.com Abstract World is facing acute energy crisis. Attention is being directed towards other unconventional sources of energy. Recently more attempts are being made to produce biodiesel as an alternative source of ecofriendly energy using biomass of plant origin. One such biomass is Jatropha curcas. But during biodiesel production from 100 kgs of Jatropha seed only 30% of oil is extracted while 70% of de‐oiled cake is generated as a byproduct. Based on this fact work on enhancement of biogas by Jatropha amendment was studies in detail and studies showed that 20% amendment of Jatropha oil cake seems optimum with respect to gas production and volatile solids reduction. It is preferable to run the digester with optimal addition because addition of higher volume of Jatropha may pose a problem and may be rate limiting factor. Keywords Anaerobic Digestion; Biodiesel; Jatropha Curcas; Jatropha Oil Cake; Methane Percent; Volatile Solids Reduction
Introduction Recent years more attention is being directed towards other unconventional sources of energy namely biogas, briquetting, wind energy etc. One hundred years ago anaerobic fermentation was envisaged for not only as a simple waste disposal technique but also for harvesting of energy/fuel in the form of methane. But as fossil fuel was available easily and at cheaper rate, nobody worried about the energy requirement. But as the population growth and industrial growth competing with each other, gradual decrease in the fuel availability was felt. At this juncture, biogas and briquetting as an alternative fuel source were thought of. Based on this problem biogas technology was initiated in many developing countries. India is such a country where biogas technology got a boost and biogas plants were advocated at rural levels due to easy availability of cattle dung as the biomass substrate. Moreover in India more than 70% of the total population inhabits rural areas and has the world’s largest population of livestock. Along with biogas production, many modifications in configuration of biogas plants were also tried but recently attempts are being made to increase the total gas production and also increase the methane content with unusual waste biomass as amendments. Few easily available biomasses like mustard oil cake and waste soya sludge as an amendment in biogas have been reported [1 & 2]. Studies were also made on fresh water hyacinth and dry water hyacinth powder as an additive with cattle dung [3]. Enhancement of biogas production by addition of poultry droppings has indicated sufficient increase in the gas production without ammonia toxicity which is encountered in case of only poultry dropping based biogas plants [4]. Parthenium weed is also a good source of biomass with potential to energy production but due to its allergy causing potential and health hazard it did not receive much public favour [5]. Powdered leaves of some plants and legumes have been found to enhance biogas production between 18% and 40% [6 & 7]. Recently more attempts are being made to produce biodiesel as an alternative source of ecofriendly energy using International Journal of Energy Science, Vol. 5 No. 1‐September 2015 17 2218‐6026 15/01 017‐06, © 2015 DEStech Publications, Inc. doi: 10.12783/ijes.2015.0501.03
18 SANJAY L. PAL, ATUL P. VANERKAR, SHANTA SATYANARAYAN
biomass of plant origin. One such biomass is Jatropha curcas. But during biodiesel production from 100 kgs of Jatropha seed only 30 kgs of oil is extracted while 70 kgs of de‐oiled cake is generated as a byproduct [8]. This cake has been tried as a fertilizer and the results were quite encouraging [9]. Some workers have quoted this cake used as a substrate for biogas production [10] and wherein it is reported that Jatropha cake were admixed with buffalo dung gave more gas production with methane content of 71.74%. Jatropha defatted oil cake as an alternative substrate feed for biogas plant was reported [11] but what amount of Jatropha amended with cattle dung and what was volatile solid destructions etc. have not been reported anywhere. Laboratory studies on 1 litre capacity digesters with Jatropha oil cake by anaerobic fermentation has been carried out. But a long residence time of 60 days have been needed to convert the digestible fraction completely [12]. It is reported in literature that 1:4 ratio of water and jatropha cake is suitable as a best combination to obtain a biogas production of 220‐250 litres/kg of oil cake [13 & 14]. Experiments were carried out using contact process, UASB and anaerobic filter for the biogas production using jatropha press cake as the substrate. Report further says that UASB and contact processes are not suitable for using these substrates [15]. Jatropha oil cake has been identified as an amendment with cattle dung to enhance biogas production. This idea was envisaged to take advantage of the high volatile solids content of jatropha cake. Jatropha cake is produced every year and it needs fruitful disposal. One such option is to use it as a substrate in the cattle dung based biogas plants and also harvest energy in the form of methane. Considering the above studies, amendment in the cattle dung feed with Jatropha curcas oil cake after oil extraction has been studied in detail and reported in the present study. Selection of Amendment Jatropha oil cake has been tried for land application and also for biogas production along with cattle dung to see its feasibility for enhancing biogas production. So it was envisaged to take the advantage of the high volatile solids content of jatropha cake. This cake is toxic in nature as it contains few toxic materials like curcin, toxalbumin and phorebolic acids which makes it unsuitable as an animal feed [16], but it can be applied on land as a manure. A physico‐chemical characteristic of jatropha oil cake is presented in table 1. This cake has its own limitations as cattle feed. TABLE 1 PHYSICO‐CHEMICAL CHARACTERISTICS OF JATROPHA OIL MEAL
Sr. No.
Parameter
Values
1
pH
5.64 – 6.0
2
Conductivity (μsm/cm2)
2560
3
Acidity as CaCO3 (mg/l)
2300
4
Total Hardness as CaCO3 (mg/l)
1040
5
Calcium Hardness as CaCO3 (mg/l)
600
6
Magnesium Hardness as CaCO3 (mg/l)
440
7
Chloride as Cl (mg/l)
265‐286
8
Total solid (%)
91.09
9
Volatile solid(%)
75.97
10
Volatile solid of total solid(%)
83.40
11
Moisture (%)
8.9
12
Ash (%)
13.2‐15.17
13
Total Nitrogen (%)
3.85‐5.60
14
Total Phosphate (%)
1.4‐2.09
15
Potassium (%)
1.2‐1.66
16
Sodium (%)
1.0‐1.4
17
Protein (%)
35
Acceleration of Biogas Production in Cattle Dung Digestion through Jatropha Curcas Oil Cake as an Additive 19
Materials and Methods A total of 5‐10 liters capacity digesters were fabricated using 10 liters capacity aspirator bottles for use in the experiments. One digester was used as control with only cattle dung while other four digesters were used for amendment of jatropha curcas studies. Working volumes of digesters were maintained at 6 liters. Arrangements were provided to feed and withdrawal of the slurry and for the collection of daily gas production. Experiments were carried out at ambient temperature (35°C) with a detention time of 30 days. Organic loading was maintained between 2.11 and 2.3 KgVs/m3d. Cattle dung and jatropha de‐oiled cake meal needed for the experiments were procured from local cattle shed and from a village cottage industry run by a NGO respectively. Jatropha curcas slurry was prepared daily for feeding. While cattle dung was collected once in a week and prepared slurry was stored in a cold room having a temperature of 4°C. Cattle dung was diluted with water in 1:1 ratio to obtain solid concentration in the range of 8.6 to 8.8% approximately. Oven dried jatropha oil cake was weighed as per requirement and mixed with water to have a solid concentration of 8.6% slurry. Characteristics of a raw feed cattle dung and jatropha slurry is depicted in table 2. During the start of the experiment all the digesters were filled with well digested seed slurry from a working biogas plant for energizing the digesters. The characteristic of the seed slurry is shown in table 3. TABLE 2 CHARACTERISTICS OF RAW FEED CATTLE DUNG AND JATROPHA CAKE
Sr. No.
Parameters
Cattle dung
Jatropha cake
1
pH
6.90‐6.7
5.64
2
Alkalinity/Acidity (mg/l) as CaCO3
6200‐6320
2120‐2230
3
Volatile acid (mg/l) as CH3COOH
514‐860
490‐626
4
Total Ammonia nitrogen as NH3‐N (mg/l)
115‐220
226‐244
5
Total solid (%)
8.5‐8.8
8.6‐8.8
6
Total volatile solid (%)
6.32‐6.82
7.14‐7.36
7
Volatile solids of total solid (%)
74.35‐77.50
83.02‐83.63
8
Total nitrogen (%)
1.30‐1.54
3.96‐4.3
9
Total phosphate (%)
0.22‐0.28
1.62‐2.06
TABLE 3 CHARACTERISTICS OF SEED SLURRY
Sr. No.
Parameter
Values
1
pH
6.8
2
Alkalinity as CaCO3 (mg/l)
1280
3
Volatile acid as CH3COOH (mg/l)
410
4
Total ammonia nitrogen (mg/l)
84
5
Total solid (%)
5.26‐5.8
Regular cattle dung slurry feeding was initiated, and once the digesters were well stabilized as was observed from constant gas production, regular feeding of jatropha cake meal was started. Experimental digesters (four numbers) were fed with 10%, 15%, 20% and 25% jatropha amendment along with cattle dung slurry and one digester was fed with only cattle dung slurry as a control. After two turnovers regular sample collection was carried out. Every five days sample was composited and subjected to routine physico‐chemical parameters of importance in anaerobic fermentation. Parameters viz. pH, alkalinity, volatile solids, total ammonia‐nitrogen, total solids, total volatile solids, total nitrogen, total phosphates were analyzed as per the standard method [17]. Percent volatile solids destruction was calculated as per the literature [18]. The physico‐chemical characteristics of digested slurry/effluent are presented in table 4. Capillary suction time (CST) was estimated using CST apparatus.
20 SANJAY L. PAL, ATUL P. VANERKAR, SHANTA SATYANARAYAN
TABLE 4 PHYSICO‐CHEMICAL CHARACTERISTICS OF EFFLUENT FROM CONTROL AND EXPERIMENTAL DIGESTERS RECEIVING COW DUNG AND JATROPHA CAKE (DE‐OILED)
Jatropha de‐oiled cake
Sr. No.
Parameters
Cattle dung control
10%
15%
20%
25%
1
pH
7.0‐7.7
7.32‐7.46
7.33‐7.48
7.35‐7.50
7.41‐7.52
2
Alkalinity/Acidity as CaCO3 (mg/l)
4240‐4670
2160‐2238
2320‐2410
2460‐2500
2532‐2584
3
Volatile acid as CH3COOH (mg/l)
526‐548
394‐412
502‐540
562‐574
634‐652
4
Total Ammonia as nitrogen as NH3‐N (mg/l)
130‐192
176‐184
264‐286
280‐298
310‐336
5
Total Solids (%)
6.72‐7.0
6.9‐7.0
6.92‐7.0
6.88‐7.10
6.90‐7.20
6
Volatile solids (%)
4.72‐4.86
4.6‐4.63
4.60‐4.62
4.52‐4.61
4.40‐4.60
7
Total Nitrogen (%)
1.3‐1.46
2.09‐2.12
2.15‐2.28
2.57‐3.01
3.46‐3.82
8
Total Phosphate (%)
0.24‐0.36
0.85‐0.92
0.97‐1.02
1.10‐1.18
1.15‐1.32
9
CST (Capillary Suction Time) in seconds
326‐338
330‐342
348‐350
360‐370
376‐380
10
Vs reduction (%)
20.72‐23.75
26.22‐28.62
30.40‐32.28
34.4‐35.2
35.8‐36.4
11
Gas production (ml/day)
2780‐2860
3000‐3300
3400‐3660
3700‐3820
3950‐4280
12
m gas/kg Vs added
0.218‐0.226
0.229‐0.238
0.242‐0.257
0.264‐0.288
0.299‐0.340
13
Average gas volume (ml/day)
2817
3230
3530
3800
4160
3
Result and Discussions: Jatropha cake or Jatropha meal as it is commonly known is acidic in nature with a pH in the range of 5.50‐5.64 with an acidity of 2300 mg/l. It drastically, did not affect the cattle dung digester on its addition even at the maximum addition of 25% with cattle dung as shown in table 4. From table 2 it can be seen that the total solids content in cattle dung and Jatropha meal slurry were maintained in the same ranges. Nitrogen content in the Jatropha meal is much higher than the cattle dung. When addition of Jatropha meal increased, gradual increase in volatile acids and total ammonia nitrogen concentration in the treated effluent, also was noted but was well within the safe limit. At no instance the volatile acid to alkalinity ratio showed any increase beyond 0.3, indicating good buffering. pH of the digested slurry was in the range of 7.0 and 7.52. This indicates good buffering and balance of the reactor. pH of the reactor seemed very congenial for the methane bacteria to carry out their activity of methane production (table 4). As the amendment addition increased from 10% to maximum of 25%, the alkalinity showed, gradual increase but it was well within safe limit. This gradual increase showed that the performance of the digester was well balanced and efficient. Total nitrogen and phosphate content also showed a steady increase as the Jatropha oil meal addition increased. Nitrogen and phosphate content of control digester were in the range of 1.3‐1.46% and 0.24‐0.36% respectively. This range marginally increased when 10% amendment was carried out. But as the Jatropha addition increased to 15%, 20% and 25%, there was significant increase in the nitrogen and phosphate content resulting in good manurial quality of the digested slurry. Nitrogen and phosphate content varied in the range between 2.09‐2.12% and 0.85‐0.92% at 10% amendment, 2.15‐ 2.28% and 0.97‐1.02% at 15%, 2.8%‐3.01% and 1.100‐1.186% at 20% and 3.46‐3.82% and 1.15‐1.32% at 25% respectively (table 4). Percent volatile solids destruction improved tremendously with 12.65‐15.08% increase in 25% Jatropha addition with cattle dung. From the results it is very clear that the total nitrogen, total phosphate and volatile solids destruction are increasing with increase in addition of Jatropha meal to cattle dung. De‐water ability of the digested slurry showed marginal increase in the capillary suction time indicating that the Jatropha meal addition did not deteriorate the sludge quality in terms of capillary suction time. CST varied between 326 seconds and 380 seconds indicating good and balanced digestion without any adverse effect due to Jatropha meal addition. Daily gas production showed an increased trend with Jatropha but it, did not commensurate with the organic matter addition. In general the gas production was observed to be in the range of 0.218‐0.226, 0.229‐0.238, 0.242‐0.257, 0.264‐0.288 and 0.299‐0.340 m3/kgVs added with respect to only cattle dung,
Acceleration of Biogas Production in Cattle Dung Digestion through Jatropha Curcas Oil Cake as an Additive 21
10%, 15%, 20% and 25% Jatropha respectively. In general the increase in gas produced was observed as Jatropha amendment was added at 10%, 15%, 20% and 25% respectively (table 5). It is clear from the studies that as the quantity of Jatropha cake meal increased, gas production also increased but it did not commensurate with the corresponding organic matter addition. TABLE 5 COMPARATIVE GAS PRODUCTION IN DIFFERENT DIGESTERS RECEIVING DIFFERENT JATROPHA CAKE AMENDMENT (GAS PRODUCTION IN ML/DAY)
Sr. No.
Cow dung
Amount of Jatropha oil cake (JC)
Control
10%
15%
20%
25%
1
2780
3220
3550
3740
3960
2
2790
3060
3580
3860
3960
3
2800
3060
3560
3820
4000
4
2890
3200
3500
3700
4120
5
2820
3180
3540
3790
4280
6
2880
3260
3560
3800
4200
7
2740
3240
3590
3820
3990
8
2890
3300
3500
3790
4240
9
2880
3290
3520
3780
4260
10
2800
3280
3540
3790
4280
11
2750
3300
3480
3800
4190
12
2800
3270
3460
3800
4180
13
2820
3290
3500
3810
4180
14
2750
3280
3480
3820
4260
15
2800
3300
3540
3790
4280
16
2740*
3060*
3460*
3700*
3960*
17
2890**
3300**
3590**
3860**
4280**
18
2815***
3230***
3530***
3800***
4160***
All the readings are average of six days. (Min*, Max**, and Avg*** values )
Weekly gas analysis was also carried out and the result is shown in table 6. Percent Methane showed a significant increase as the amendment quantity increased. TABLE 6 COMPOSITION OF GAS WITH VARIOUS COMBINATIONS OF JATROPHA OIL CAKE AND CATTLE DUNG FEED
Sr. No.
Digester
CO2
CH4
1
Cattle dung (Control)
44.4%
55.6%
2
Cattle dung +10% JC
40.8%
59.2%
3
Cattle dung +15% JC
37.0%
63.0%
4
Cattle dung +20% JC
34.4%
65.6%
5
Cattle dung +25% JC
32.2%
67.8%
Conclusion Studies indicated that it is possible to enhance biogas production in cattle dung based digesters using feed stock amendment of Jatropha oil meal. Jatropha has been found to be one of the most suitable substrates that enhance gas production, many times in cattle dung based digesters but availability of Jatropha all around the year must be ensured. Moreover, Jatropha oil cake contains high percent volatile solids of 83.06% to 85.0%, making it very useful for biogas production. It is proved that efficiency of nitrogen content in cattle dung can overcome comfortably with nitrogen rich Jatropha oil cake meal addition. Studies showed that 20% amendment of Jatropha oil cake seems optimum with respect to gas production and volatile solids reduction.
22 SANJAY L. PAL, ATUL P. VANERKAR, SHANTA SATYANARAYAN
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