Psychrophilic dry anaerobic digestion of dairy cow feces: Long-term operation

[Display omitted] •Psychrophilic dry anaerobic digestion (PDAD) of cow feces (CF) is feasible.•PDAD of CF is as efficient as mesophilic and thermophilic AD at TCL 21days.•CF (13–16% TS at OLR 5.0gTCODfedkg−1inoculumd−1) yielded 222±27NLCH4kg−1VSfed. This paper reports experimental results which demonstrate psychrophilic dry anaerobic digestion of cow feces during long-term operation in sequence batch reactor. Cow feces (13–16% total solids) has been anaerobically digested in 12 successive cycles (252days) at 21days treatment cycle length (TCL) and temperature of 20°C using psychrotrophic anaerobic mixed culture. An average specific methane yield (SMY) of 184.9±24.0, 189.9±27.3, and 222±27.7 NLCH4kg−1 of VSfed has been achieved at an organic loading rate of 3.0, 4.0, and 5.0gTCODkg−1inoculumd−1 and TCL of 21days, respectively. The corresponding substrate to inoculum ratio (SIR) was 0.39±0.06, 0.48±.02, 0.53±0.05, respectively. Average methane production rate of 10±1.4 NLCH4kg−1VSfedd−1 has been obtained. The low concentration of volatile fatty acids indicated that hydrolysis was the reaction limiting step.