Fuel 95 (2012) 495–498
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Fuel
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Study on biogas production by anaerobic digestion of garden-waste
Priyanka Gupta a,⇑, Raj Shekhar Singh a, Ashish Sachan b, Ambarish S. Vidyarthi b, Asha Gupta a
a Central Institute of Mining & Fuel Research (CSIR), Dhanbad, Jharkhand 826 015, Indiab Department of Biotechnology, Birla Institute of Technology, Mesra, Ranchi, Jharkhand, India
a r t i c l e i n f o
Article history:Received 17 August 2011Received in revised form 31 October 2011Accepted 2 November 2011Available online 15 November 2011
Keywords:Anaerobic digestionInoculumMediumMicro-organismBio-gasification
0016-2361/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.fuel.2011.11.006
⇑ Corresponding author. Tel.: +91 970 9158133/326E-mail address: [email protected] (P. Gup
a b s t r a c t
As petroleum and good quality coal reserves in India are depleting, hence alternative renewable source ofenergy is the demand of the time. At the same time management of huge quantities of garbage producedin India is also a serious problem. Therefore, anaerobic digestion of garden-waste was tried using someindigenous natural sources to find potential microbes for the gasification of garden-waste. For this studyfour natural sources i.e. cow-dung, paddy field soil, mine water and termites were used. From the study itis inferred that microbes present in paddy field soil when enriched on garden-waste gave best results outof four natural sources.
� 2011 Elsevier Ltd. All rights reserved.
1. Introduction
Population and pollution are interrelated, due to increasingpopulation there is increase in waste generation. In many develop-ing countries the most serious environmental and health problemsare related with inadequate solid waste management. The waste,mainly organic waste, dumped in open places, causes heavy envi-ronmental pollution to soil, groundwater and surface waters [1,2].
The extraction of biogas out of solid waste is considered as an is-sue that has only come up in the recent past. Sandec, the Departmentof Water and Sanitation in Developing Countries at the Swiss FederalInstitute for Aquatic Science and Technology (Eawag), conducted aresearch on biomethanation of biodegradable solid waste for lowand middle income countries.
Citizens can be relieved from the nuisance of organic waste byscientific treatment through a cost-effective, quick, and non-polluting method or by recycling. Biological conversion of solidwastes containing higher percentage of organic matter by anaero-bic treatment is the best possible option. This process results in therecovery of useful energy in the form of biogas, thus reducing fossilfuel and green house gas sources [3].
Mixed microbial populations endowed with characteristic andspecific metabolic capabilities occur widely in niches of naturalhabitats. Their coexistence is sustained by metabolic interactions
ll rights reserved.
2396433.ta).
that allow the flow of carbon, energy and other intermediatestoward their mutual benefit. Methanogenic archeae, a diversegroup of obligate anaerobes, occurring in most anaerobic habitats,form the terminal electron sink during anaerobic digestion of or-ganic matter to methane. Methanogens derive the energy forgrowth only by methanogenesis and are the only organisms knownto produce methane as a catabolic end product [4].
Methane fermentation is a complex process, which can be dividedup into four phases: hydrolysis, acidogenesis, acetogenesis/dehy-drogenation, and methanation. Hydrolytic bacteria bring about ini-tial degradation of complex biopolymers such as cellulose,hemicellulose, proteins and lipids into dicarboxylic acids, volatilefatty acids (VFAs), ammonia, carbon dioxide, and hydrogen. Metha-nogenic bacteria which play a key role in the terminal step of anaer-obic digestion use only a few compounds like acetate, methanol,methylamine, hydrogen and carbon dioxide. VFA and dicarboxylicacids are thus needed to be converted as much as possible to acetate,hydrogen and carbon dioxide for maximum production of methane.This is brought about by hydrogen producing acetogenic bacteriawhich grow only in syntrophic association with hydrogen scaveng-ers such as sulphate reducing or methanogenic bacteria [5].
The present study explores garden-waste as substrate for anaer-obic digestion. Cow dung, paddy field soil, mine water, and ter-mites were used as inocula.
Typically, the garden refuse stream consists of a wide range ofmaterial including leaves, grass-clippings, perennial and annualplant’s material, tree and shrub branches and other woody waste,etc.
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2. Materials and methods
2.1. Collection of sample for substrate
Garden-waste was collected from the botanical garden ofCIMFR, Dhanbad, India. Collected material was dried in the sunfor 1 week, and stored in airtight container.
2.2. Proximate analysis of the garden waste sample
After mixing properly, a part of the sun-dried samples wasground to fine size for the proximate analysis. Proximate analysiswas done as per Indian Standard 1350 (Part I) – 1984 and reaf-firmed in 2001 [6]. All analyses were done in triplicate samples.
Moisture: Moisture content was determined by drying 10 gsample in a pre weighed dish at 108 ± 2 �C in an electric oven(Micro-thermal, Kolkata, India) for 1 h, cooled the dish in a des-iccator, and weighed, repeated the process till constant weight.Volatile Matter: Volatile matter was determined by heating 1 gsample in a pre weighed silica VM crucible covered with lid at900� ± 10 �C for a period of 7 min in the muffle furnace.Ash: One gram sample was heated in pre weighed silica cruciblewithout covering with lid (i.e. in presence of air) at 815 �C for1 h and repeated the process till constant weight.Fixed Carbon: Fixed carbon was determined by calculation[100 – (Moisture + volatilematter + ash)].
2.3. Collection of natural sources of microbes for inoculum
Four materials collected to use as source of microbes for thebio-gasification of the garden-waste, care was taken to maintainanaerobic conditions:
(i) Fresh cow dung sample was collected in a poly bag andzipped immediately.
(ii) Paddy field soil was collected from the water logged paddyfield in a bottle during paddy season.
(iii) Mine water sample was collected from the undergroundsump at the depth of more than 1 m from a gassy-mine nearJharia, Dhanbad (Jeetpur coalmine, ISCO, SAIL India).
(iv) Termites were collected from a tree of botanical garden[CIMFR, Dhanbad, India] just before the inoculation. Ten ter-mites were crushed by glass grinder and ground materialtaken into 5 ml medium for inoculation.
2.4. Medium
Barker’s enrichment medium mineral salts [7] of the followingcomposition were used for all the experiments.
g/l in tap water
Ammonium chloride
1.00 Di-potassium hydrogen phosphateanhydrous
0.31Magnesium chloride 6H2O
0.10 pH adjusted 7.02.5. Experimental setup
The experiments were conducted in specially designed glassapparatus that contained one reaction vessel and one reservoirfor the collection of gas by water displacement method. 100 ml
autoclaved Barker’s medium was taken into the reaction vessel,0.325 g of Na2S, 3 ml of 5% solution of Na2CO3, 0.0001 g resazurine,and 10 g UV sterile garden-waste of mesh size below 10 mm werealso added to the reaction vessel and inoculated with 5 ml of inoc-ulum. The reaction vessel was immediately evacuated to removeair and re-filled with inert gas (helium) to establish anaerobic con-ditions. The collection vessel (reservoir) was completely filled withwater. Both the vessels were connected together with black pres-sure tubing. Reaction vessel was also connected with mercurymanometer.
2.6. Measurements
Pressure developed due to production of gas was measuredusing mercury manometer everyday and amount of water equiva-lent to the pressure in the vessel drown out of the reservoirthrough stopper at the bottom of the vessel and volume of waterdrained out was measured by a measuring cylinder.
Gas collected in the reservoir periodically analyzed for methaneand carbon dioxide contents by Haldane Gas Analysis Apparatus(Meghna, India). The ratio of methane to carbon dioxide deter-mined was in the range of 55:45–52:48.
2.7. Experiments with different source of bacteria
Four experiments (triplicate of each) using different sources ofmicrobes i.e. cow dung, paddy field soil, mine-water, and termiteswere carried out using garden-waste as substrate for about2 months [8]. Enrichment of each culture was done by sub-culturingmethodology where garden waste was used as specific energysource.
3. Results and discussion
3.1. Proximate analysis
In the garden-waste sample, moisture content was 10.07%. Majorcontents were of volatile matter (66.01%) and fixed carbon (16.14%).Ash content was only 7.78. Volatile matter and fixed carbon togethermakes garden-waste as potential waste for the bio-gasification.
3.2. Comparative results with different source of bacteria
Cow dung inoculum experiments were conducted for a couple ofmonths but no methane was produced. This shows that microbespresent in cow dung were not capable of using garden-waste sub-strate for methane production. With paddy field inoculum maxi-mum methane (mean value of triplicates 3.94 cc) production wasfound on 28th day and then declined. It may be due to the coexis-tence of methylotrophs in the paddy field soil [9,10]. Mine waterinoculum gave consistent methane production. Microbes presentin mine water were able to grow on garden-waste but only 8.9 ccmethane gas was produced in 56 days. Microbes present in termitegut produced 10.88 cc methane gas in 42 days and then declined to5.35 cc in 56 days may be due to some methane consumingcontaminants.
Comparative results of methane production using different nat-ural sources of inoculum on garden-waste are depicted in Fig. 1. Ontaking direct natural sources as inocula, maximum methane pro-duction was found with termite but within few days, the methanegot declined. Cow dung inoculum did not work on garden-waste,and with paddy field soil inoculum, production of methane wasvery low. Mine water inoculum gave consistent increasing pattern.
Fig. 1. Methane production from garden-waste using natural sources as inoculum.
Fig. 2. Methane produced from garden-waste using paddy field soil as inoculum.
Fig. 3. Methane produced from garden-waste using mine water as inoculum.
P. Gupta et al. / Fuel 95 (2012) 495–498 497
3.3. Enrichments of paddy field soil inoculum
The culture grown from paddy field soil on garden-waste wasused as inoculum for first enrichment. There was a little improve-ment in methane production compared to initial set of experi-ments. Maximum mean value of methane (19.74 cc) wasdetermined on 49th day.
Similarly in 2nd enrichment experiments the methane produc-tion was higher than the first enrichment. Maximum methane(107.90 cc) was determined on 49th day.
In the similar manner, third enrichment experiments were setup. Maximum mean value of methane (73.91 cc) was determinedon 35th day. Methane detected in 3rd enrichment was less thanthat of second enrichment. Therefore, further enrichments werenot done.
The results of methane produced by paddy field soil inoculumand its subsequent enrichments are depicted in Fig. 2.
3.4. Enrichments of mine-water inoculum
The culture grown from mine-water inoculum on garden-wastewas used as inoculum for first enrichment.
First enrichment of mine water inoculum on garden-waste pro-duced only 12.38 cc methane in 2 months.
Second enrichment of mine water inoculum produced maxi-mum methane in 42 days (about 30 cc methane) and then slightlydeclined in next 2 weeks.
Third enrichment of mine water inoculum produced only14 cc ofmethane in 28 days and thereafter it declined to 4.66 cc in 2 months.
No further enrichment was done after 3rd enrichment due todeclined activity of the culture.
The results of methane produced by mine-water inoculum andits subsequent enrichments on garden-waste are depicted in Fig. 3.
3.5. Enrichments of termite gut inoculum
The culture grown from termite gut inoculum on garden-wastewas used as inoculum for first enrichment.
First enrichment of termite inoculum produced 39.98 cc ofmethane in 49 days.
Second enrichment of termite inoculum produced 45.32 cc ofmethane in 42 days. The methane was declined thereafter.
Third enrichment of termite gut microbes produced methane inthe same patter as in 2nd enrichment.
As there was no enhancement in methane production in 3rdenrichment, hence further enrichment was not done.
The results of methane produced by termite gut inoculum andits subsequent enrichments on garden-waste are depicted in Fig. 4.
Fig. 4. Methane produced from garden-waste using termites as inoculum.
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4. Conclusion
� Paddy-field soil proved to be superior to cow-dung, mine water,or termite guts as a source of microbial inoculums to initiatereactors for the conversion of garden waste to methane.� Recommended ratio of paddy-field soil to garden waste 1:100.� Repeated sub-culturing (2 or 3) is needed to achieve the fastest
rates of methane formation. The addition of paddy-field soil isonly needed during the startup of the reactor, but not for subse-quent sub-culturing events.� Sub-culturing should be performed every 40 days to maintain
maximum rates of methane formation.� Residual solids from anaerobic digestion can be used as garden
mulch.
� Future work is needed to demonstrate that paddy-field soilfrom different locations can be used reliably as an inoculumfor the anaerobic digestion of garden waste.
Acknowledgements
Director, Central Institute of Mining & Fuel Research is greatlyacknowledged for providing funds & facilities. Authors are alsograteful to the mine authorities of Jeetpur coalmine, ISCO, SAIL In-dia for the help in collecting mine sump water.
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