The effects of co-substrate and thermal pretreatment on anaerobic digestion performance

The influence of anaerobic co-digestion of leachate and sludge with organic fraction of municipal solid waste (OFMSW) under mesophilic condition in three batch digesters of 5 L capacity has been studied. OFMSW was mixed with leachate and sludge at three different ratios. Experimental results illustrated that the digester with a ratio of 2000/2500 (leachate (mL) or sludge/OFMSW (mL)) had significantly higher performance. Furthermore, this study compared the performance of anaerobic digestion of different substrates with three different mixing ratios with and without thermal pretreatment at low temperature (65°C) in terms of biogas production, chemical oxygen demand (COD) elimination as well as hydraulic retention time. In addition, to predict the biogas yield and evaluate the kinetic parameters, the modified Gompertz model was applied. Based on the results, the maximum biogas yield from adding different leachate and sludge ratios to OFMSW was recorded to be 0.45 and 0.38 m³kg^-1 COD which was higher about 7% in comparison with co-digestion original OFMSW without thermal pretreatment. In addition, thermal pretreatment accelerated the hydrolysis step. Moreover, the total COD elimination was relatively stable in the range of 52-60% at all types of substrate mixtures. Also, the modified Gompertz model demonstrated a good fit to the experimental results.

AD: anaerobic digester; BOD: biochemical oxygen demand; COD: chemical oxygen demand; FAAS: flame atomic absorption spectroscopy; HS: high solids; HRT: hydraulic retention time; LS: low solids; MS: medium solids; OFMSW: organic fraction of municipal solid waste; TCD: thermal conductivity detector; TS: total solid; TSS: total suspended solids.