Biogas production potential of different substrate combinations from Kaitui location, Kericho County, Kenya

Abstract

The over-dependence on fossil and wood fuels as primary energy source has led to multitudes of problems such as global climatic change, environmental degradation and various human health problems. Energy supplied from fossil fuels is not easily recycled and takes a long time to form, hence is exhaustible and not renewable. Renewable energy has remained one of the best alternatives for sustainable energy development. This study investigated the anaerobic digestion of biomass to convert energy stored in organic matter into useful biogas energy. The objectives were to study energy sources consumed per household, determine biogas production volumes from co-digestion of cow manure with goat manure, avocado pulp and bagasse and to derive wood fuel savings arising from adoption and use of biogas at the household level. The study was done within Kaitui location in Kericho County using interview schedule and empirical research method for data collection. Eight identical plastic bio-digesters of 15liters capacity were constructed and used to investigate the anaerobic digestion of the stated feedstocks. Cow dung was used as a control for the experiments and as an inoculum for other substrates. Feedstocks were collected and subjected to pre-anaerobic digestion treatments of pulverization, screening and mixing. The materials were blended at a ratio of 1:1 and mixed with water at a ratio of 1:2 then introduced to the bio-reactor as homogenized slurry after stirring. The data collected were tabulated then subjected to excel computer package for analysis. The high heat value of biogas was compared with the heat energy from other sources by performing experiments on quantity of heat. This helped in deriving the wood-fuel savings arising from the adoption of biogas technology at household level. The data collected revealed that firewood was mostly used (64.79%) while electricity was least used (2.81%). The other forms of fuel used by households in the study area were charcoal (16.9%) kerosene (7.05%) and liquefied petroleum gas (8.45%). Biogas energy had not been adopted (0%). The average energy use per household was 70MJ per week which is equivalent to 2m3 of biogas. Co-digestion of feedstocks yielded more biogas compared to single substrate digestions. Co-digestion of cow manure with avocado pulp gave the greatest volume coefficient of 3 with a standard deviation of 3.69 and 113% increase in biogas production volume. The study found out that co-digestion of cow manure with avocado pulp has the highest biogas potential and upon its adoption, tonnes of woodfuel would be conserved and reflected on the effective forest cover.