Abstract:
Optimisation of biogas production from a given substrate and digester is an issue that needs to be addressed during the development of anaerobic digestion. To maximise the biogas production rate, the operating parameters that influence anaerobic digestion must be controlled and monitored. The research was carried out using a 0.15 m3 laboratory digester. The study was aimed at evaluating the effect of different cow dung and maize silage mix ratios of 1:1; 1:3 and 3:1 which were compared to pure substrates at a constant temperature of 20℃, temperature (20°C, 25°C and 30°C with 3:1 feedstock mix ratio) and the stirring of 100 rpm for minutes was varied at different intervals of 1 hour, 2 hours, 6 hours and 12 hours with no stirring as a control. The Temperature of the digester was controlled and monitored by Programmable Temperature Controller (Multispan UTC 421). SIEMENS LOGO PLC and ATV12HU15M2 Drive automatically controlled the 100 rpm and the stirring intervals. The mix ratios, temperatures and stirring intervals showed a significant effect on biogas production (P≤0.05) with mix ratios 3:1 and 1:1 improved biogas production by 31.24% and 15.52% respectively compared to cow dung. The temperatures of 25℃ and 30℃ increased biogas by 26.99% and 47.35% and the methane increase by 3.92% and 11.76% respectively compared to the psychrophilic temperature of 20℃. The stirring intervals of 6 hours and 12 hours increased biogas by 3.11% and 1.48%, and the methane increase by 8.77% and 1.75%, respectively. The 2 hours and 1 hour reduced biogas by 26.5% and 39.35%, and methane decreased by 3.52% and 15.79%, respectively compared to control (implying that the frequent stirring is not good for biogas). The study thus, recommends a mix ratio of 3:1, the optimal temperature of 30℃, and a stirring interval of 6 hours at 3 minutes stirring for a 0.15 m3 laboratory temperature controlled fixed-dome anaerobic digester of cow dung and maize silage as a substrate when fed as a batch reactor.
