Anaerobic digestion of liquid dairy manure pretreated by the microwave-enhanced advanced oxidation process.

The microwave-enhanced advanced oxidation process (MW-AOP) was utilized for the treatment of liquid dairy manure, prior to anaerobic digestion (AD). A significant amount of soluble chemical oxygen demand (SCOD) was formed in the treated solution, but there was no or little increase in volatile fatty acid (VFA). In this study, up-flow anaerobic sludge blanket (UASB) reactors were used in both the conventional AD system and as the methane phase reactor in a two-phase anaerobic digestion (TPAD) system. Both AD systems were capable of operating at very short hydraulic retention times (HRTs) to as low as about 3 days, and very high methane production rates were achieved. However, much higher methane production was obtained in the TPAD system. The phase separation of the acidogenesis and the methanogenesis in the TPAD system not only increased methane production but also maintained reactor stability throughout the experimental period. Thus, the combination of MW-AOP treatment and TPAD appears to be an effective means of energy recovery from dairy manure.