Enhancement in mesophilic aerobic digestion of waste activated sludge by chemically assisted thermal pretreatment method

The effects of hybrid microwave (MW)-alkali pretreatment methods on the efficiency of mesophilic aerobic digestion were studied. The MW-alkali pretreatment (95 °C-pH 12) was observed to enhance the sludge solubilization synergistically from 0.5% (raw) to 52.5% (MW-NaOH) and 48.7% (MW-KOH), which are 20% greater than the additive value of MW only and alkali only (16%MW + 28.4%NaOH = 44.4% and 16%MW + 25.5KOH = 41.5). The higher VSS solubilization was observed for hybrid MW-NaOH (53.9%) and MW-KOH (47.4%) methods. The batch mesophilic (35 °C) aerobic digestion system led to 81.1% TCOD degradation and 72.4% VSS degradation at 20 days of retention time, with 35% higher TCOD and VSS reduction in comparison with the control system. The filterability of microwave-alkali pretreated sludge was improved remarkably after aerobic digestion. Moreover, the proposed method is capable of effectively sanitize the sewage sludge and produce Class A biosolids.