Abstract
AbstractPhase separation of sludge digestion was investigated using a suspended growth system for the acid phase and a fixed‐film system for the methane phase. A thermophilic temperature of 50°C was used in the methane reactor, while a mesophilic temperature of 37°C was maintained in the acid reactor. During the acid‐phase stage, the volatile acid concentration and the reduction of volatile solids averaged approximately 2200 mg dm−3 as acetic acid and 13% (w/v), respectively, under a hydraulic retention time of 2 days. These parameters were not significantly affected by the applied solids concentration. Reduction of the retention time in the acid reactor from 2 days to 1 day decreased the methane content (18% versus 28%) and the volatile solids destruction (8% versus 13%), but produced the same amount of volatile acids. The total gas production for 10 days overall retention time was slightly higher than that for conventional single‐phase sludge digestion. The significant cost saving in reactor volume and enhanced methane production may offset the increased energy consumption required for maintaining a thermophilic temperature during the methane phase.
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