Anaerobic Digestion Of Pennisetum Gianteum Lin And Other Organic Compounds For Biogas Production

Biogas is a colorless gas produced when organic material is broken down by microorganisms in an oxygen free environment,so called anaerobic digestion.The production of biogas through anaerobic digestion of organic materials provides a renewable energy that can be used to replace some of the fossil fuels,and minimize the emissions of greenhouse gases.The Pennisetum gianteum lin is one of the most important grass species for biogas production.Pennisetum gianteum lin as an energy plant is used as a renewable energy source for biogas production;it can also be used as the culture substrate for cultivation of edible and medicinal fungi.Pennietum gianteum lin has a fast growth rate,high competitiveness,can adapt easily to different soil types and climatic conditions.The aims and objectives of the Study is to understand the microbiological processes of anaerobic digestion and degradation of the organic materials by the microbes during fermentation process in biogas reactors for the efficient production of biogas or methane gas,and to determine the sequence of four biological processes in the fermentation digester,and also to find the relevancy between material degradation and microbial community variation during anaerobic digestion process.In this study,Pennisetum gianteum lin was utilized as the main biomass related energy plant to generate biogas.The other organic substrate materials used include residues of different mushroom species such as Agrocybe cylindraceae,Tremella fuciformis and Pleurotus eryngii,sugarcane straw and wheat-seed-shells.The main purpose of this experiment was to compare the daily biogas yield of Pennisetum gianteum lin and other different organic materials during anaerobic digestion process in the laboratory,at mesophilic constant temperature of 37℃.The methane gas concentration for most of the substrates increased with fermentation period and reached the maximum concentration level after 15 days.The biogas digesters began the digestion process within the pH range of(6.0 to7.4).The maximum biogas yield increased to 250 ml by wheat seed shells,but it however,showed a rapid drop in biogas yield after 2 days.On the other hand,Pennisetum gianteum lin has shown a steady drop in biogas yield with time as compared to other substrate materials used and as such made its total biogas yield the highest.Pennisetum gianteum lin gave more yields in terms of the cumulative biogas production.This was the biogas yield from the start until the end of the fermentation period with anaerobic digestion period of 23 days.The mixing of substrate materials can enhance biogas and methane gas production.Moreover,it is advisable to select the right substrate material if it is going to be used as a co-substrate material.The purpose of this experiment was to analyze the substrate initial and final nutrients content including volatile fatty acids(VFA),total organic carbon,total sugar,cellulose,hemi-cellulose,lignin and total nitrogen.This was to help understand and be able to determine the biodegradation of the organic material(Pennisetum gianteum lin)by the microbes for the entire fermentation period.The total solid residues degradation increased steadily after 6 days of the anaerobic digestion,after which a slight change increase was noticed with fermentation period after 18 days.The volatile fatty acids concentration was high at the initial stages of the fermentation process at 4.4g/l,but it started to decrease steadily after 8 days.It however,decreased quickly with fermentation period after 9 days to 15 days,with now a degradation rate of 1.2g/l after which it became slightly constant until it reached the end of the anaerobic digestion process.The soluble sugar content from the substrate material decreased very quickly in the first 3 to 6 days of the fermentation process from 16.2%soluble sugar content to 6.2%and then to 4%respectively.In this case,the protein content from the substrate material decreased very quickly in the first 3 to 6 days of the fermentation process from 8%protein content to 1.8%and then lastly to 0.5%after 6 days.The cellulose content increased slightly after 3 days of fermentation from 25%to 34%,the cellulose content became constant until the end of the fermentation period.The hemicellulose content remained the same at 34%for the entire period of the anaerobic digestion,like in the case of cellulose.The composition of biogas-producing microbial communities commonly is determined via construction of 16S-rDNA clone libraries and subsequent sequencing of 16S-rDNA amplicons.The bacteria contain Clostridium,Fusobacterium,Bacteroids,Butyrivibrio,Selenomonas,and Streptococcus.The highest abundance of the archaeal sequences belongs to the genus Methanoculleus,Methanobacterium,and Methanosaeta.