A start-up of psychrophilic anaerobic sequence batch reactor digesting a 35 % total solids feed of dairy manure and wheat straw

Zero liquid discharge is currently an objective in livestock manure management to minimize water pollution. This paper reports the start-up phase of a novel psychrophilic (20 degrees C) dry anaerobic digestion of dairy manure with bedding fed at 35 % total solids and an organic loading rate of 3.0 g total chemical oxygen demand kg(-1) inoculum day(-1) in anaerobic sequence batch reactors. The specific methane (CH4) yield ranged from 165.4 +/- 9.8 to 213.9 +/- 13.6 NL CH4 kg(-1) volatile solids (VS) with an overall average of 188 +/- 17 NL CH4 kg(-1) VS during 11 successive start-up cycles (231 days) and a maximum CH4 production rate of 10.2 +/- 0.6 NL CH4 kg(-1) VS day(-1). The inoculum-to-substrate (VS-based) ratio ranged from 4.06 to 4.47. Although methanogenesis proceeded fairly well the hydrolysis seemed to be the rate limiting step. It is possible start up psychrophilic dry anaerobic digestion of cow feces and wheat straw at feed TS of 35 % within 7-10 successive cycles (147-210 days).