Influence of Retention Time on the Optimization of Biogas Production from Water Hyacinth and Cow Dung Blend

The aim of this study was to evaluate the influence of retention time on the production of biogas from a blend of cow dung and water hyacinth. The study was designed to include three production trials. These were the Cow dung Production Trial (CPT), Water Hyacinth Production Trial (WPT) and Cow dung-Water hyacinth Production Trial (CWPT). For the CPT, 0.5 kg of cow dung was dissolved in 7 litres of water to form slurry which was sieved before being introduced into the digester alone, while for the WPT, chopped water hyacinth was introduced into the digester alone and for the CWPT, cow dung slurry alongside chopped water hyacinth was introduced into the digester. The three production trials were performed at the temperature of 35ºC and pH of 6.8 and lasted for 40 days in ranges of 0-10, 11-20, 21-30 and 31-40. Results obtained from the study showed a uniform trend in the production of biogas for the three different production trials. Highest level of biogas production was recorded at day 11-21 thus, CPT (53.7 ml), WPT (35.67 ml) and CWBPT (89.37 ml). This was followed the values recorded on day 31-40 as follows; CPT (38.1 ml), WPT (22.1 ml) and CWBPT (60.02 ml). However, this was elevated compared to the values obtained for day 0-10. In conclusion, this study has established that biogas production from cow dung, water hyacinth as well as their combination is most efficiently achieved between 11th-21st day of production.