CC BY-NC-ND
0CrossMark
Available online at www.sciencedirect.com
ScienceDirect
Procedía Environmental Sciences 35 (2016) 785 - 794
International Conference on Solid Waste Management, 5IconSWM 2015
Biogas Production from Surplus Plant Biomass Feedstock: Some Highlights of Indo-UK R&D Initiative
Dipam Patowarya, Helen Westb, Michèle Clarkec, D.C. Baruahd*
aResearch Scholar, Energy Conservation Laboratory, Department of Energy, Tezpur University, Napaam, Assam, India bAssociate Professor, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Leicestershire LE12 5RD, UK cProfessor, School of Geography, University of Nottingham, University Park, Nottingham NG7 2RD, UK dProfessor, Energy Conservation Laboratory, Dept. of Energy, Tezpur University, Napaam, Assam, India
Abstract
Reliable supply of feedstock is one of the major factors accountable for acceptance and hence success of biogas technology. Cow dung (CD) has been the traditional feedstock for production of biogas which is utilized for domestic cooking in rural areas. Search for alternative feedstock becomes inevitable with increasing interest in biogas technology and prospect to extend its application up to power generation. Here, feasibility of two locally available surplus biomass viz., (i) Ipomoea carnea (IC) and (ii) rice straw (RS) were investigated for biogas production. Identified biomass was separately mixed with cow dung (in ratios of 40:60 and 60:40) and fed to 0.25 m commercial biogas reactors and 20 L batch biogas reactors. The work focused on biogas production potential, methane content and calorific value of biogas from the commercial biogas reactors. Biogas yield from the four treatments of different mixing ratios were compared with control i.e., CD as only feedstock. Both Ipomoea carnea and rice straw yielded more gas compared to the control. However, IC co-digested with CD yielded more biogas than rice straw co-digested samples (IC:CD::60:40 with 0.209 Nm3/kg volatile solid (VS) added per day and IC:CD:: 40:60 with 0.205 Nm3/kg VS added per day whereas, RS:CD::60:40 with 0.192 Nm3/kg VS added per day and RS:CD::40:60 with 0.190 Nm3/kg VS added per day). In addition, the work also focused on determination of the methane content of IC and RS co-digested biogas samples which were also more than the control.
CrownCopyright ©2016PublishedbyElsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the organizing committee of 5IconSWM 2015
Keywords: Biogas, Biomass, Feedstock, Ipomoea carnea, Rice Straw;
* Corresponding author.
E-mail address: baruahd@tezu.ernet.in
1878-0296 Crown Copyright © 2016 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.Org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the organizing committee of 5IconSWM 2015
doi:10.1016/j.proenv.2016.07.094
1. Introduction
Sustainable supply of energy has been one of the major challenges that mankind will have to face in the near future. Therefore, it is necessary to develop sustainable energy supply systems that aim at fulfilling the energy demand. The use of renewable energy sources is becoming increasingly essential, in order to reduce emissions from fossil fuel sources that have impacts on global warming. As far as the projected global energy demand is concerned, the theoretical potential for renewable energy exceeds it by a large extent. In this context, the bigger challenge lies in capturing and utilizing a sizable share of this potential that can provide the desired energy demand in a cost-effective and environmentally sound manner [1]. Biomass, a renewable energy source can make a significant contribution in supplying the rapidly increasing energy demand in a sustainable way. As far as biomass is concerned, it is the oldest source of energy known to mankind. Even today, it is the largest source of renewable energy, accounting for almost 10% of world total primary energy supply [2]. One of the key technologies for the sustainable use of biomass as renewable energy source is biogas. It is a flexible renewable energy source obtained from the anaerobic digestion of manure, wastes, residues, energy crops, aquatic weeds [2-4].
It is not only advantageous over other forms of bioenergy production but also the most energy efficient and environmentally beneficial technology for bioenergy production [5]. Biogas is the primary energy obtained from anaerobic digestion (AD) whereas the digested slurry produced as a by-product can be considered as a secondary energy source, which is utilised in preparing briquettes for burning in stoves or as fertiliser for agricultural applications [6, 7]. Presently, there are many applications of biogas starting from cooking fuel to producing electricity and fuel vehicles. However, these applications contrast over a wide range within developed and the developing countries. One of the most challenging parts of building and operating an anaerobic digestion system is the feedstock that will go into it. Table 1 shows some explored biomass as favourable sources for biomethanation.
Table 1: Feedstock used in AD
Biomass References
Cow manure [8]
Municipal solid waste [9]
Kitchen waste [3]
Micro algae [10-11]
Mango leaves [12]
Coconut pith [13]
By far, biogas production has been quite dominant at household and community levels rather than large scale in India [14]. However in spite of using many organic substrates as mentioned in Table 1, there still remain various biomasses which are not adequately explored. In addition, these biomasses need to be technically feasible for biogas production. Besides the technical feasibility, a given feedstock should not have better competitive uses. Despite these, uncertainty with the feedstock availability is also an important factor.
Rice straw and Ipomoea carnea are two types of biomass found in abundance in rural areas of India [15-16]. The Ipomoea carnea plant is about four to sixteen feet tall and has heart shaped leaves and pink flowers. The plant is not regarded as a resource because it forms a tangled mass in water bodies causing water-logging problems [16]. The plant has also been reported as toxic [17] and in general, it is not eaten by animals. Prolific growth of this plant result in it covering huge patches of productive land [18]. At present, there is no commercial use for this plant that grows amply in the wetlands of India. Hence, it does not have any competitive use. It has been reported that on anaerobic digestion of Ipomoea fistulosa leaves and stem, biogas production was higher from leaves compared to its stems [19]. Considering the fact that the leafy portion of Ipomoea is quite suitable for biogas production, only the leaf portion was taken into account for the present study.
Rice is grown in abundance in various regions of rural India. It is India's largest cereal crop and in addition to 104 million tonnes of grain and husk, India produces 97,192 kilo tonnes of rice straw annually [20]. It is mostly used as cattle feed or bedding material in rural households. However, after harvesting rice, a large portion of straw left uncut which is often burnt in fields without any energy recovery. It has been estimated that 23% of rice straw (equivalent 22,289 kilo tonnes) is surplus waste and this is burnt prior to the cultivation of the next crop [20]. In this context, anaerobic digestion of surplus rice straw could be one probable source of power supply [3]. Rice straw has already been reported as a favourable feedstock for biomethanation [21].
This study reports the feasibility of (i) Ipomoea carnea and (ii) rice straw, co-digested with cow dung as possible feedstock combinations for biogas production. The benefits of co-digesting plant material or straw with animal manure were reported by [22, 23] and it was found that manure could provide buffering capacity and a wide range of nutrients. Lehtomaki [24] conducted a laboratory study investigating co-digestion of energy crops and crop residues with cow manure for methane production and reported an increase in overall methane production. In this study, samples of these two biomasses were separately mixed with cow dung (in ratios 40:60 and 60:40) and fed to experimental biogas reactors for monitoring the biogas production.
2. Materials and Methods
As mentioned earlier, the present study investigated the feasibility of utilization of Ipomoea carnea and rice straw as potential feedstock for anaerobic digestion processes in combination with cow dung. The methodologies concerning (a) feedstock characterization, (b) anaerobic digestion and assessment of biogas potential are described below.
2.1. Feedstock
Three locally available surplus biomass sources viz., cow dung, leaves of Ipomoea carnea and rice straw were considered for the present investigation. The heart shaped leaves of Ipomoea (Fig. 1a) were collected from the roadside near Tezpur University, Sonitpur as well as from wetlands on the banks of the river Jia Bharali situated in Sonitpur. The Ipomoea leaves were chopped prior to their use. Rice straw (Fig. 1b) collected from nearby fields as well as from the local farmers near the University campus was chopped prior to use. Cow dung which is the most used feedstock in anaerobic digestion systems was collected from a local farmer near the University campus. Total of five treatments were considered for experiments as given in Table 2.
Fig. 1. Ipomoea carnea leaves (a), rice straw (b)
Table 2: Different feedstock treatments used for biogas production
Sl. No. Treatments Nomenclature
1 60% Ipomoea carnea leaves + 40% Cow dung (total dry mass) MIC
2 40% Ipomoea carnea leaves + 60% Cow dung (total dry mass) mIC
3 60% rice straw + 40% Cow dung (total dry mass) MRC
4 40% rice straw + 60% Cow dung (total dry mass) mRC
5 Cow dung only CD
2.2. Feedstock characterisation
The volatile solids (VS), ash content (AC), and fixed carbon (FC) were determined by heating the selected biomass samples at different temperatures, ranging from 100°C to 950°C following ASTM E870-82 (2006) and results of the analysis are presented in Table 3.
Table 3: Characteristics of the feedstock fed into the biogas digesters
Treatments VS (%) AC (%) FC (%)
MRC 70.042 13.548 16.41
mRC 67.628 14.422 17.95
MIC 72.304 10.404 17.292
mIC 69.136 12.326 18.538
CD 66.5 16.2 17.33
2.3. Anaerobic digester loading for assessing biomethanation potential
One of the studies included the maximum biogas yield over a period of 30 days. The experiments were conducted in parallel anaerobic digesters with a working volume of 1.5L. The glass bottle reactors (Fig. 2.) were equipped with a gas collecting pipe as well as a slurry outlet from which the pH of the digestate was measured on a regular basis.
50g of dry matter was fed to each of the digesters. Reactors were inoculated with anaerobic digestate from a biogas digester of 1m3 that uses kitchen waste as its feed. It is situated in one of the hostels of the University campus. The reactors were operated at a temperature range of 25o-30o C. The gas was collected in inverted measuring cylinders by a downward water displacement method. The gas readings were recorded twice daily. The pH of the digestate was measured weekly by a digital pH meter (Systronics, pH meter 802).
Fig. 2. Glass bottle reactors
Besides the biogas yield from the 1.5L digesters, digesters of 0.25m3 were used for assessing the maximum biogas production from each specified treatment on a daily basis. The digesters were stirred regularly and the ambient temperature as well as the pH of the digestate coming out the digestate outlet pipe was monitored daily. An amount of 0.2kg dry mass was regularly fed into the digesters. The biogas produced was recorded every 12 hours. The 0.25m3 digester, called Shakti Surabhi, was developed by Vivekananda Kendra, Natural Resources Development Project (NARDEP), Kanyakumari, India for producing biogas from kitchen and vegetable waste. The plant is a result of research of almost a quarter century as well as field-work carried out by the engineers and extension workers of VK - NARDEP. It is an improvement over the general floating drum type biogas plant. The plants were equipped with an inlet pipe for waste feed, inverted floating gas holder, water jacket, gas delivery system and digestate outlet pipe (Figure 3).
Fig. 3. Shakti Surabhi biomethanation plant used as continuous digesters
2.4 Biogas characteristics
Biogas production and composition were measured daily every 12 hours. The biogas production was measured using a gas flow meter that recorded the gas flow in litres. The composition of the biogas was measured using a Biogas Analyzer (Ambetronics Engineers Private. Ltd., Model No: MS panel 830213). The calorific value of the biogas was also measured using a Junker's Gas Calorimeter.
The batch bottle reactors were well equipped with a gas collection system. The downward water displacement technique was used for daily storage of the gas produced. The monitoring of the gas production was performed twice daily and hence the readings were recorded in ml/day and converted to Nm3/day (normal cubic meter per day).
In the case of the continuously fed digesters, 0.2 kg of dry mass of the selected treatments was fed daily for a period of 20 days. The reactors were initially fed with CD to initiate the digestion process as directed by the maker of the reactors. After the biogas production from cow dung ceased, respective feedstock mixes were fed into the digesters. A flexible pipe was connected to the gas holder via a valve for carrying the gas so as to determine its composition as well as the daily gas production. The biogas produced daily was recorded by passing the gas pipe into a gas flow meter which recorded the gas flow in litres/minute. Biogas produced was monitored at 12-hour intervals for 30 days.
3. Results and discussion
3.1 Daily biogas yieldfrom batch bottle reactors
For a period of 30 days of digestion the biogas yields of all the treatments in 1.5 litre batch bottle reactors was measured and Fig. 4 shows the trend of biogas production from all five treatments mentioned earlier. During the
digestion period of 30 days, MIC produced the maximum biogas with 6.56 litres (0.0065Nm3) of biogas whereas mIC produced about 5.92 litres (0.0059Nm3) of biogas during this period followed by MRC with 5.84 litres (0.0058Nm3). mRC which consisted of a smaller proportion of rice straw compared to MRC produced about 5.5 litres (0.0055Nm3) of biogas during the digestion period followed by the control i.e. CD which produced 5.39 litres (0.0054Nm3).
123456789 1011121314151617181920212223242526272829303132 MIC mIC MRC — mRC CD Days
Fig. 4. Daily biogas yield from the five treatments in batch bottle reactors
Average daily biogas production from MIC was
about 205ml/day (0.205 X 10-3Nm3/day) followed by mIC, which produced biogas at an average of about 185ml/day (0.185 X 10-3 Nm3/day). MRC produced an average of about 182.5ml/day (0.182 X 10-3Nm3/day), whereas mRC produced an average of about 171.8ml/day (0.171 X 10-3 Nm3/day). The control i.e. CD produced the least biogas compared to the other reactors at an average of about 168.7ml/day (0.168 X 10-3Nm3/day). It
is expected that the higher volatile matter content in MIC resulted in the higher biogas production as it degraded over the digestion period.
3.2 Change in pH in batch bottle reactors
Figure 5 shows the change in pH during the digestion period of batch bottle reactors. It is taken into consideration that the pH is above 6.8 for the entire period of digestion. It has been reported that a pH value falling below 6.8 results in low biogas production [21]. However, it can be seen from the figure that MIC recorded a low biogas production of about 120ml at the beginning of the third week of the digestion period. The pH during this period was about 6.7. It can be clearly interpreted that the pH drop is the reason for the low biogas production and NaOH was added to the respective biomass mix to raise the pH so as to increase the biogas production. The pH of the rest of the treatments remained above the optimum value of 6.8. Hence, less change in the biogas production was observed in them.
7.9 V-- N. •
7.1 6.9 • /
4 a 12 16 30 24 28 32
Days -•-MIC —•— mIC —»—MRC —•— mRC -*-CD
Fig. 5. Change in pH of the five selected treatments used in batch bottle reactors
3.3 Daily biogas yield from continuously fed commercial reactors
An amount of 0.2kg dry mass was regularly fed into the 0.25m3 Shakti Surabhi digesters and biogas production measured every 12 hours. Fig. 6 shows the daily trend of the biogas production of all the treatments used. The daily biogas production of MIC recorded the highest among all the other treatments. It produced about 0.209 Nm3/ kg VS/ day of biogas followed by mIC, which produced about 0.205 Nm3/ kg VS/ day of biogas. MRC which had a large amount of rice straw yielded about 0.192Nm3/kg VS/day of biogas as compared to mRC which produced about 0.190Nm3/kg VS/day of biogas. The control i.e., CD produced the least among all the other treatments which is about 0.185 Nm3/kg VS/day of biogas. The biogas production in these reactors followed the same trend as in the batch bottle reactors. Straw has higher lignin content [25], making it more difficult to digest compared to Ipomoea. Moreover, higher volatile solids content in Ipomoea is also one of the reasons for the increased biogas production as compared to rice straws. The results are comparable to the values reported by [19, 21].
0.1S =
1 2 3 4 5 6 7 S 9 10 11 12 13 14 35 16 17 13 19 20
Mic ^^mic *-mrc -»-mRC —»—CD Days
Fig. 6. Daily biogas yield from the five treatments in continuously fed reactors
3.4 Change in pH in the continuously fed digesters
Figure 7 shows the change in pH during the 20 day monitoring period. The pH of the digestate coming out of the digestate outlet pipe was measured daily and made sure that the pH never fell below 6.8. However, during the observation period the pH of either of the treatments never fell below 6.8. Although, the pH of the digestate of mRC fell drastically from over 7.5 to 6.9 during the period, there was no corresponding change in the biogas yield comparable to that magnitude.
Fig. 7. pH change of the selected treatments in continuously fed digesters
3.5 Average methane yield in continuously fed digesters
The composition of the biogas produced was measured using a Biogas Analyzer which measures CH4 in %V/V. Fig. 8 shows the average methane yields of the selected treatments in the continuously fed digester. The average methane content of MIC was highest at about 67.8% and it yielded about 0.142 Nm3/kg VS/day of methane. The reactor mIC had a methane content of 67.66% and yielded about 0.139 Nm3/kg VS/day of methane followed by MRC. It had a methane content of 64.98% and yielded about 0.125 Nm3/ kg VS/day of methane during the monitoring period. The methane content of the mRC was about 63.8%and its methane yield was about 0.121Nm3/ kg VS/ day whereas the control i.e. CD attained the lowest methane concentration of all at 62.87% with a methane yield of about 0.116 Nm3/ kg VS/ day. Sharma [19] reported that Ipomoea leaves resulted in methane concentrations of about 71% and rice straw in 60% methane. The results obtained in this study are comparable to those in the literature. One of the reasons for the higher methane content of the Ipomoea treatments can be the high VS degradation as compared to the rice straw treatments as reported by Sharma [19].
MIC mIC MRC mRC CD
Treatments
Fig. 8. Average methane yield from the continuously fed digesters
3.6 Determination of calorific value of biogas produced from continuously fed digesters
The calorific value (CV) of the biogas was determined using a Junker's Gas calorimeter. Fig. 9 clearly shows that the calorific value for both MIC and mIC are quite similar with about 25.60 MJ/m3 and 25.57MJ/m3 of biogas produced respectively. It can be interpreted that as their methane contents did not vary by much, the CV would be similar. However the CV of MIC was more than that for mIC towards the later days of the observation period. MRC, mRC and CD attained an average of 24.56MJ.m3, 24.15MJ/m3 and 23.82MJ/m3 respectively.
Fig. 9. Calorific value of the treatments used in continuously fed digesters
4. Conclusions
The appropriate conversion of surplus biomass to biogas can lead to a solution to the domestic energy crisis. Based on the experimental results, MIC and MRC can be considered as the suitable ratios of biomass mixes for biogas production. Moreover, the methane content of the selected biomass mixes was also higher than the other treatments considered in the current the experimental analysis.
Acknowledgements
The authors would like to acknowledge the financial assistance from the Engineering and Physical Sciences Research Council (EPSRC), UK for this study. In addition, special thanks to Mr. Moonmoon Hiloidhari and Ms. Sampriti Kataki for their help throughout the study.
References
1) Cowling, E. B. (1975). Physical and chemical constraints in the hydrolysis of cellulose and lignocellulosic materials. In Biotechnology and Bioengineering Symposium (No. 5, p. 163).
2) de Pérez, O. C. A. (2012). Experimental poisoning of goats by Ipomoea carnea subsp. fistulosa in Argentina: A clinic and pathological correlation. Pesq. Vet. Bras, 32(1), 37-42.
3) Dueblein, D. & Steinhauser, A. (2008). Biogas from waste and renewable resources. KGaA: Wiley-VCH Verlag GmbH and Co.
4) Fehrenbach, H., Giegrich, J., Reinhardt, G., Sayer, U., Gretz, M., Lanje, K., & Schmitz, J. (2008). KriterieneinernachhaltigenBioenergienutzungimglobalenMaßstab. UBA-Forschungsbericht, 206, 41-112.
5) Gadde, B., Menke, C., & Wassmann, R. (2009). Rice straw as a renewable energy source in India, Thailand, and the Philippines: overall potential and limitations for energy contribution and greenhouse gas mitigation. Biomass and Bioenergy, 33(11), 1532-1546.
6) Gunaseelan, V. N. (1997). Anaerobic digestion of biomass for methane production: a review. Biomass and Bioenergy, 13(1), 83-114.
7) Hashimoto, A. G. (1983). Conversion of straw-manure mixtures to methane at mesophilic and thermophilic temperatures. Biotechnology and Bioengineering, 25(1), 185-200.
8) Hills, D. J. & Roberts, D. W. (1981). Anaerobic digestion of dairy manure and field crop residues. Agricultural Wastes, 3(3), 179-189.
9) IEA 2010a. Energy Technologies Perspectives: Scenarios and Strategies to 2050. International Energy Agency, Paris, France. 710 pp.
10) IPCC, 2011: Summary for Policymakers. In: IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation.
11) Kataki, S., Hiloidhari, M., & Baruah, D. C. (2012). An Investigation on Ipomoea (Ipomoea carnea) concerning its availability and bioenergy generation potential in Assam. International Journal of Innovative Research and Development, 1(7), 118-127.
12) Kratzeisen, M., Starcevic, N., Martinov, M., Maurer, C. & Müller, J. (2010). Applicability of biogas digestate as solid fuel. Fuel, 89(9), 2544-2548.
13) Lehtomäki, A., Huttunen, S., &Rintala, J. A. (2007). Laboratory investigations on co-digestion of energy crops and crop residues with cow manure for methane production: effect of crop to manure ratio. Resources, Conservation and Recycling, 51(3), 591-609.
14) Mata-Alvarez, J., Cecchi, F., Pavan, P., & Llabres, P. (1990). The performances of digesters treating the organic fraction of municipal solid wastes differently sorted. Biological Wastes, 33(3), 181-199.
15) Radhika, L. G., Seshadri, S. K., & Mohandas, P. N. (1983). A study of biogas generation from coconut pith. Journal of Chemical Technology and Biotechnology, 33(3), 189-194.,
16) Rehl, T., & Müller, J. (2011). Life cycle assessment of biogas digestate processing technologies. Resources, Conservation and Recycling, 56(1), 92-104.
17) Renewable Energy: Biogas, India Landscape 2012, Published by Athena Infonomics India Pvt. Ltd. Accessed from http://www.athenainfonomics.in /assets/ Renewable%20Energy%20-%20Biogas .pdf
18) Sharma, S. K., Mishra, I. M., Sharma, M. P., & Saini, J. S. (1988). Effect of particle size on biogas generation from biomass residues.
Biomass, 17(4), 251-263.
19) Shyam, M., & Sharma, P. K. (1994). Solid-state anaerobic digestion of cattle dung and agro-residues in small-capacity field digesters. Bioresource Technology, 48(3), 203-207.
20) Shyam, M., & Sharma, P. K. (1994). Solid-state anaerobic digestion of cattle dung and agro-residues in small-capacity field digesters. Bioresource Technology, 48(3), 203-207.
21) Sialve, B., Bernet, N., & Bernard, O. (2009). Anaerobic digestion of microalgae as a necessary step to make microalgal biodiesel sustainable. Biotechnology Advances, 27(4), 409-416.
22) Somayaji, D., & Khanna, S. (1994). Biomethanation of rice and wheat straw. World journal of Microbiology & Biotechnology, 10(5), 521523.
23) Sudhakar, K., Ananthakrishnan, R., & Goyal, A. (2013). Biogas Production from a mixture of Water Hyacinth, Water Chestnut and Cow Dung.
24) Yen, H. W., & Brune, D. E. (2007). Anaerobic co-digestion of algal sludge and waste paper to produce methane. Bioresource Technology, 98(1), 130-134.
