Operation and Performance of a Farm-Scale Anaerobic Sequencing Batch Reactor Treating Dilute Swine Manure

Abstract

Abstract. A 400 m3 anaerobic sequencing batch reactor (ASBR) treating dilute (0.30% to 1.0% total solids) swine manure produced by a 120-sow farrow-to-finish farm was monitored for one calendar year. The digester was operated at full reactor volume (20-day hydraulic retention time, HRT) and at conditions considered optimal for biogas production (5-day HRT). Reactor temperature during 20-day HRT operation ranged between 22°C and 32°C, and solids retention time (SRT) averaged 51 days. During 5-day HRT operation, reactor temperature was 22°C to 24°C and SRT averaged 26 days. Organic matter removal efficiency, measured as the difference between daily mass of chemical oxygen demand (COD) entering the reactor and COD leaving with decanted liquids, was 73% during 20-day HRT operation and 57% during 5-day HRT operation. Methane yield was 0.55 m3 CH4 kg-1 volatile solids (VS) during 20-day HRT and 0.38 m3 CH4 kg-1 VS during 5-day operation. In general, organic matter removal was lower and methane yield was higher than results using similar manure in laboratory-scale reactors. Volumetric reactor efficiency (VRE) was 0.18 m3 CH4 m-3 reactor d-1 under both operating conditions. Flushed manure was diluted 30:70 with recycled aerobic lagoon effluent to provide sufficient volume to achieve 5-day HRT operation. The VRE of an ASBR treating flushed manure without lagoon effluent dilution at 5-day HRT was estimated to be greater than 0.70 m3 CH4 m-3 reactor d-1 based on microbial kinetic models.