Dry anaerobic digestion of high solids content dairy manure at high organic loading rates in psychrophilic sequence batch reactor

Cow manure with bedding is renewable organic biomass available around the year on dairy farms. Developing efficient and cost-effective psychrophilic dry anaerobic digestion (PDAD) processes could contribute to solving farm-related environmental, energy, and manure management problems in cold-climate regions. This study was to increase the organic loading rate (OLR), fed to a novel psychrophilic (20 °C) dry anaerobic digestion of 27 % total solid dairy manure (cow feces and wheat straw) in sequence batch reactor (PDAD-SBR), by 133 to 160 %. The PDAD-SBR process operated at treatment cycle length of 21 days and OLR of 7.0 and 8.0 g total chemical oxygen demand (TCOD) kg−1 inoculum day−1 (5.2 ± 0.1 and 5.8 ± 0.0 g volatile solids (VS) kg−1 inoculum day−1) for four successive cycles (84 days) produced average specific methane yields (SMYs) of 147.1 ± 17.2 and 143.2 ± 11.7 normalized liters (NL) CH4 kg−1 VS fed, respectively. PDAD of cow feces and wheat straw is possible with VS-based inoculum-to-substrate ratio of 1.45 at OLR of 8.0 g TCOD kg−1 inoculum day−1. Hydrolysis was the limiting step reaction. The VS removal averaged around 57.4 ± 0.5 and 60.5 ± 5.7 % at OLR 7.0 and 8.0 g TCOD kg−1 inoculum day−1, respectively.