EVALUATION OF A SEQUENTIAL FEEDING SCHEME FOR TEMPERATURE-PHASED ANAEROBIC DIGESTION (TPAD) SYSTEM TREATING MUNICIPAL SLUDGE

The stability and performance of a sequential batch Temperature-Phased Anaerobic Digestion (TPAD) scheme aimed at satisfying the 40 CFR Part 503 Class A time-temperature requirements (24 hours at 55 °C) were evaluated. The system, fed with a 40:60 mixture (dry weight basis) of primary sludge and waste activated sludge at 5.5% total solids, showed stable performance at system retention times as short as 12 days. The maximum volatile solids removal (VSR) of 49.6% was achieved at a system retention time of 16 days. The system did not show any effects of shock loading at the retention times studied and the system performance was comparable to a semi-continuously fed TPAD system. The sequential-batch TPAD system outperformed a “conventional” single stage mesophilic system operated at a longer retention time with respect to VSR. The methane recovery efficiency of the system ranged from 0.62 – 0.65 liter methane per gram of volatile solids destroyed, which was comparable to the single-stage mesophilic system.