RESEARCH CONCEPT PAPER:

EFFECT OF ENZYME PREDIGESTION AND SELECTED METHANOGENS ON METHANE PRODUCTION IN CELLULOLISIC-BASED FEEDSTOCK EXPERIMENTAL DIGESTERS.

Abstract:

Biogas production from waste has been proposed as an excellent complement to fossil fuel, especially for heating. However, inefficient hydrolysis of polymeric organics in the feedstock and competition, inhibition or low methogenesis potential of the microbial mix in the biodigester results in low biogas production relative to the quantity of feedstock. It is the hypothesis of this research that biogas production efficiency can be improved by enhancing feedstock breakdown and using selected, more efficient methanogens. The main objective of this study is to determine the effect of enzyme predigestion and methanogen selection on methane production in experimental biodigesters with lignocelluloses rich feedstock. The feed stocks will comprise bagasse and cow dung collected from various locations in Kenya. The raw material will be dried to standard moisture levels and specific quantities will be used in the tests. Aqueous solution of cellulolytic enzyme mix will be added to the samples and incubated at 35 ℃ - 45 ℃ for twelve hours. Biogas production will be carried out in 3.5 L laboratory sized digesters, using commercial methanogen cultures from the Japan Collection of Microorganisms RIKEN Bio Resource Centre and the German collection of microorganisms and cell cultures, with controls containing un-sterilized feedstock or sterilized feedstock without inoculation with the special methanogen collection. The methane will be measure by a gas meter and the composition of the biogas will be determined by gas chromatography. Data will be subjected to appropriate statistical analyses.

Background:

Biogas is an inexpensive source of energy for heating and many similar applications. Many biogas plant use ligno cellulose rich raw materials, such as solid manure, grass, maize Stover or Sudan grass as the feedstock. Complex biodigester feedstock is difficult to breakdown to primary substrate for methanogenesis (Vorgelegt 2012). In order to increase the availability of this feed stock and therefore to enhance the efficiency of biogas production it may be necessary to pre-treat the substrate (EU-Agro-Biogas project 2008).

Conversion of cellulosic material to methane (CH4) is a complex multistep process which involves a large number of microorganisms. Basically, it involves converting cellulose and other polymers in the biomass to carboxylic acids and then to methane (Vorgelegt 2012). Consequently, more than one group of microorganisms, some of which could compete or inhibit each other, occur in the biodigester (Hong et al 2007, Ike, et al 2010).

The quantity of methane produced from standard biodigester systems is small compared to the amount of organic substrates fed into the systems (Wang 2010). The causes of this low efficiency appear to include polymer hydrolysis, the mix of prevalent microbial groups in the digesters and prevailing physical conditions, including temperature and flow rates (Karanashes 2005). Under any given set of conditions, interactions between these microbial groups determine overall rate of methane formation and stability of the process (Vorgelegt 2012).

There is however limited study on the mix of microbes for optimum biogas synthesis, and the effect of enzyme predigestion and selected methanogens on methane production in cellulolisic-based feedstock experimental digesters.

Project Description:

Objectives

I. To determine the effect of enzyme enrichment on breakdown of cellulose-rich feedstock.

II.To determine the effect of a combination of selected methanogens on methane production.

Methodology

Schott glass reactors with a working capacity of 3.5L will be used. The temperature will be maintained at 30 ℃ - 45℃ , by the warm water jacket surrounding the reactor. The suspension mixing will be done by a magnetic stirrer. Effluent will be withdrawn and substrate feed into the reactor by opening the top cover after seven days of digestion. Biogas produced by the reactor will be passed through a gas meter; the gas will then be passed through a water seal, which will function as a barrier to avoid air back wash flow from the gas meter. The gas meter will be equipped with a built-in pulse generator which will be connected to a desktop computer and biogas flow rates (daily flow rates) will be measured with Rigamo V1.15 software and then collected in a gas pack collector (Nayono 2009).S.p.s.s. software will be used to analyze the data by two way ANOVA and tukeys test for post Hok comparison with a significant level of <0.05.

Feed stock enzyme predigestion.

3800 milliliters of the substrate feedstock from the stored feed stock batches will be poured into a table top laboratory blender, and the optimum volume of enzyme, will be added to the contents in the blender, the blenders contents will then be mixed for five minutes. The homogenate will then be poured into the digester and Batch anaerobic digestion tests will be conducted according to German Standard Procedure VDI 4630 (VDI 2006); 3 liters vessels will be filled with 2.5 liters inoculum and 100 grams feedstock material. The mixture will be balanced to the ODM Feedstock to ODM Inoculum ratio which will be equal to 0.5 (Suarez et al 2009).The reactors will be incubated and maintained at 35 °C.

The methanogenic discrimination/selection process.

For discriminative growth of methanogens the genus methanosarcinia will be targeted as the main genus of interest. All the nine species will be obtained from RIKEN Bio Resource Centre.800 millilitres broth of the purchased methanogen cultures will be prepared following the standards set by the German collection of microorganisms(cultivation of methanogens) these will be used as digesters feedstock inoculum material .

Expected results.

The volumetric readings of the enzyme pretreated feedstock are expected to be more than those of the untreated feedstock.

The discriminative/selective growth of methanogenic groups in the digesters is expected to give better performance. The methanogenic consortium with the optimum biogas yields will be determined.

Conclusion.

The methanogenic consortium with the optimum biogas yields will be recommended for more research to explore the possibilities of biodegradation of a diverse mix of organic substrate, with the aim of finding a solution for the improvement of anaerobic biodigesters in biogas generation.

Budget.

Work plan.

The work plan for the project which will be adopted is as shown below. The research will run for a total of seven months from the date of funds awarding.

Activity / 1st Month / 2nd month / 3rd month / 4th month / 5th month / 6th month / 7th moth
Proposal adjustment
Buying Equipment
Sample Collection
Sample Preparation
Data collection and experimentation
Data Analysis
Thesis Writing

REFERENCE

Attar, Y., Mhetre, S.T., Shawale, M.D., 1998. Biogas production enhancement by cellulytic strains of Actinomycetes.Biogas Forum I (72), 11–15.

Chen, Yud-len, Varel, V. H. and Hashimoto, A. G. (1980) Ind. Eng. Chem. Prod. Res. Dev., 19, 471.

Dimitar Karanashes, Daniel J. rat stone, Irene Angelidaki: Influence of Environmental condition on Methanogenic composition in Anaerobic Biogas Reaction: Applied and Environmental Microbiology January 2005 pg. 331 – 338 Vol 71 No1

Elizabeth J.P Jones et al. Stimulation of Methane Generation from nonproductive coal by addition of nutrients or a microbial consortium. Applied and environmental microbiology November. 2011 P 70 – 13 – 70122 vol 76: No: 21

EU-Agro-Biogas project, initiative to improve the yield of agricultural biogas plants, report on the improvement of digester level (enzymes, microorganisms, raw glycerin, celloloids) 2008.