Recirculation of solid digestate to enhance energy efficiency of biogas plants: Strategies, conditions and impacts

This article aims at providing insight into the recirculation of (post-treated) solid digestate (SD) within digesters. Such a practice has been further identified as promising for anaerobically digesting recalcitrant feedstocks and improving energy efficiency continuously stirred tank reactor (CSTR) agricultural biogas plants. Firstly, implementation strategies potential impact SD direct on five CSTR plants were investigated. According to selected strategy, results indicated that plant methane production could rise by 0.6 6.3% or feedstock shortage 64 1431 tons/year be compensated. Secondly, relevance additional post-treatments these initial was evaluated. Thermo-chemical successfully increased biodegradability 30 46% although their costs not compensated production. Short-term aerobic failed in increasing (up 21% loss biomethane potential). Hence, full scale, quick excluding any post-treatment appears optimal condition apply. Finally, conditions full-scale theoretically studied. proved increase retention time 11 38% total content 6 20%. Thus, critical point its should capacity mixing system handle such an solids. The needs determined case-by-case basis. Consequently, first time, this provides framework where can relevant management practice. Overall, demonstrates how simple low-cost mean efficiency. It also highlights importance achieving efficient sector order reduce