Effect of Co-Digestion on Anaerobic Digestion of Pig Slurry with Maize Cob at Mesophilic Temperature

Abstract

The 21st century faces the problem of growing energy consumption and diminishing supplies of fossil fuels, which has led to researches on the use of renewable energy sources and, consequently, the development of new technological processes of energy production. Pig slurry and maize stalk constitute nuisance to our environment and should be got rid of. Co-digestion has been found by researchers to improve the product of anaerobic digestion.  This work determined the effect of co-digestion on anaerobic digestion of pig slurry with maize cob. Pig slurry and maize cobs were co-digested at ratios 3:1, 1:1 and 1:3 using the percentage volatile solid of each substrate. The experiment was carried out in a laboratory scale batch experiment. The digester was fed with pig slurry-maize cob mixtures calculated for the selected ratios based on the volatile solid (VS) concentration of the selected substrates. Co-digestion of pig slurry with maize cobs at ratios 3:1, 1:1 and 3:1 at mesophilic temperature (37^oC) gave biogas yields of 0.323, 0.392 and 0.486m³/kgoDM respectively while the methane yields were 0.240, 0.305 and 0.358 m³CH₄/kgoDM respectively. From the fresh mass of the substrate, biogas yields of 0.035, 0.057 and 0.109 m³/kgFM were obtained for pig slurry-maize cob ratios of 3:1, 1:1 and 1:3 respectively while the methane yields from the fresh mass for the same ratios were 0.026, 0.044 and 0.080 CH₄/kgFM respectively. Co-digestion of pig slurry with maize cob was found to have methane concentrations of 74.30, 77.90 and 73.68% at pig slurry/maize cob combinations of 3:1, 1:1 and 1:3 respectively. The study revealed that co-digesting pig slurry with maize cob at ratio 1:3 is optimum for biogas production (yields).

Keywords: Co-digestion, pig slurry, maize cob, batch experiment, mesophilic temperature