Anaerobic Co-digestion of Pig Manure and Spent Coffee Grounds for Enhanced Biogas Production

Abstract

The selection of appropriate co-substrates is very important to the feasibility of an anaerobic co-digestion process. A proper choice of co-substrate compositions leads to system balance and increased methane generation. Spent coffee grounds (SCG) are an unexploited material produced in large quantities which seems suitable for anaerobic digestion. During this study SCG were tested for biogas production in both batch and continuous reactors. Specifically, the biochemical methane potential of SCG was calculated in serum bottle test reactors at two different inoculum to substrate ratios (ISRs). In addition, co-digestion of SCG with liquid pig manure as co-substrate was monitored in a pilot scale continuously stirred tank reactor. Maximum methane production was similar at both ISRs, indicating no inhibition effects. Moreover, results from continuous experiments show that the methane production rate increased significantly after the addition of SCG to the digester. The reactor treating the liquid pig manure produced approximately 0.12 Lbiogas/Lreactor/d before the addition of SCG and 1.4 Lbiogas/Lreactor/d after the addition. The average removal of dissolved chemical oxygen demand increased from 20 to 40% after the addition of SCG. The concept of co-digestion could be a promising perspective for anaerobic digestion units as it increases methane production significantly.