Optimization of Co-Fermentation Ratio of Water Hyacinth (Eichornia Crassipes) and Cow Dung Feedstock for Production of Biogas

Abstract

Water hyacinth (WH) Eichornia crassipes, is a water weed that thrives in polluted water bodies. It has wreaked havoc in Kenyan water bodies due to its negative environmental, social and economic impacts. Despite its great potential as a source of biogas, optimization of the quantity and quality of the gas produced remains a challenge as individuals adopt do-it-yourself approach without carefully addressing the key issues that govern production. The study sought to determine the best biogas yield using cow dung (CD) as a eo-fermentation feedstock. The following proportions ofCD:WH were studied: 1:0 (no hyacinth), 1:1, 1:2, 1:3 and 1:5. Analysis of the conductivity, Total Dissolved Solids (TDS), pH, temperature, gas yields and composition were done. The experiments were conducted in a 6m3 flexible bag batch digester using different CD: WH ratios. Results showed that various ratios did not show any specific trend in electrical conductivity, however average biogas yield (in m') for ratios 1:0, 1:1, 1:2, 1:3 and 1:5 were 3.32, 6.58, 5.18, 4.1and 3.56 respectively. A similar trend was observed in the total dissolved solids (TDS).,The initial pH was between 7.0 and 7.4 while the anaerobic digestion temperature during the study ranged between 23.8-33.6 °C for all the ratios tested. The maximum biogas production rate was highest at 30.7 "C, whereas the highest gas yield were realized with ratio 1:1 while ratio I' 1:5 had the lowest yield. When the biogas was scrubbed with 15% w/v NaOH there was an increase of methane content which ranged from, 52.7% - 58.4% before scrubbing to 71.2% - 74.2% after scrubbing. The ratio of 1:1 CD:WH produced the highest volume of gas hence best eo fermentation for the ratios tested. The study has demonstrated that the potential of water hyacinth- as a biogas substrate can be enhanced by eo-fermenting with cow dung and can be utilized as a sustainable renewable energy source.