Feasibility and performance of high-rate psychrophilic dry anaerobic digestion of high solids content dairy manure

Purposes The main purpose of the R&D was to develop anovel high-rate psychrophilic dry anaerobic digestion(PDAD) for processing a mixture of cow feces and wheatstraw(CFWS) in sequencing batch bioreactor (SBR) operatedat high organic loading rate (OLR). The main research questionwas to assess the feasibility of operating the PDAD-SBRat OLR of 9.0 and 10.0 g TCOD kg-1 inoculum day-1.Methods Two pairs of 40 L duplicate bioreactors located ina temperature-controlled room (20 C) were operated assequencing batch reactors (SBRs) and were fed CFWS (27 %total solids) at OLRs of 9.0 and 10.0 g TCOD kg-1inoculum day-1 during three successive treatment cycles of21 days each. The biogas production, biogas composition,volatile fatty acids, and volatile solids were monitored toassess the performance of the PDAD-SBRs.Results The PDAD process fed with cow feces and wheatstraw (TS of 27 %) at OLR 9.0 and 10.0 g TCOD kg-1inoculum day-1 (6.53 ± 0.06 and 7.27 ± 0.12 g VS kg-1inoculum day-1) resulted in average specific methane yields(SMYs) of 134.0 ± 7.7, 136.4 ± 4.9 NL CH4 kg-1 VS fed,respectively, with an average volatile solids removal of 35 %at the ends of treatment cycles (21 days).Conclusions This study reports for the first time successfuloperation of psychrophilic (20 C) dry anaerobic digestion(PDAD) of cow feces with wheat straw (CFWS) at 27 % totalsolids and OLR of 9.0 and 10.0 g TCOD kg-1 inoculumday-1 in relatively short treatment cycle length (21 days).