Effect of substrate volume in a digester on biogas production from animal excreta

Abstract

Three animal excreta (cow dung, poultry excreta and swine dung) were digested in four substrate volumes (50, 60, 70 and 80% of the digester volume) in a 3 × 4 factorial design. Substrate temperature, pH and biogas yield were monitored during the 63-day study. The results showed that excreta type affected (p ≤0.05) pH and biogas yield with poultry excreta producing the highest yield (11.8 cm3 kg-1 VS fed day-1). Although the biogas yields from the different substrate volumes were not significantly (p> 0.05) different, 50% appeared not only to have produced the highest yield (7.89 cm3 kg-1 VS fed day-1) but maintained a constant higher yield during digestion. The study therefore concluded that cow dung, poultry excreta or swine dung slurry loaded between 50-80% of a digester volume would produce apparently the same biogas yield.