Abstract:
One of the greatest challenges facing the societies today is the increased emission of greenhouse gas from fossil fuel combustion, with consequent change in climatic conditions. Hence the need for cleaner and renewable energy source. This study was carried out to produce biomethane from fresh cassava wastewater in a liquid phase biodigester. Fresh cassava wastewater (FCWW) (1000 ml) was charged into 5 liter capacity fixed bed bioreactor and were subjected to anaerobic digestion for a period of 28 days at ambient temperature. The physicochemical parameters and the persistent organic compounds in the wastewater were determined before and after 28 days of biodigestion using standard methods. Isolation, characterization and determination of microbial population were carried-out at the end of biodigestion using plate count method. The main problem of biogas production from cassava waste effluents is the acid forming-bacteria that produces acids resulting in the decline in pH below 7 thus reducing the growth of methane forming bacteria in the biodigester. One of the methods to overcome this challenge as adopted in this work is the use of Ca(OH)2 to regulate pH by sequestrating CO2 which can be used in the production of economically important substances such as biocarbonic acid. After 28 days of biodigestion, the composition of flammable biogas were determined using a Bacharach combustible gas analyzer. The following composition of gases were obtained: CO2 = 12%, CO = 8%, NO = 3%, H2 = 3%, CH4 = 74% indicating that FCWW is a good substrate for biogas generation. The microbial isolation and characterization after 28 days of digestion indicated the presence of both Gram positive and Gram negative bacteria (Proteus, Vibrio, Bacillus, Staphylococcus, Escherichia and Salmonella) and a microbial population of 5.5× 108cfu. The fresh cassava wastewater had a pH of 5.70 which decreased to 3.01 after biodigestion. GC-MS analysis were conducted to determine the persistent organic compounds in the FCWW and the Sludge. The chromatogram for the FCWW showed 5 peaks with various organic compounds. The chromatograph for the Sludge showed 3 peaks and the presence of two organic compounds in each peak, indicating that anaerobic digestion is an effective means of bioremediation. The anaerobic digestion of cassava wastewater and other organic waste substrates in the production of biogas will contributes to proving the domestic energy need. This will also improve the quality of the environment by ridding the processing sites of pollution and reducing the emission of greenhouse gases.
