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Abstract
A key task in alcohol distilleries is the effective treatment of biomethanated spent wash after biogas recovery. This colored washwater exhibits low biodegradability index (BI < 0.2), high chemical oxygen demand (30,000 < COD < 40,000 mg/L), and recalcitrance to aerobic treatment. In this work, pretreatment of biomethanated distillery wastewater by Fenton oxidation was proposed for improved biogas recovery. The effects of temperature, solution pH, and H2O2 dosage on the efficacy of the oxidation process were studied. Using ferrous sulfate catalyst (36 mg/L) for diluted wastewater (BOD5 = 81; COD = 400 mg/L), 54% reduction in COD was achieved within 1 h in acidic medium (pH = 3) at ambient temperature (T = 30 °C). Post-oxidation, the BI value improved (0.33). After subsequent adsorption over activated carbon (loading 5%) for 1 h, COD reduction (70%), and BI value (0.43) improved further. Upon anaerobic treatment with 1% acclimatized biomass, 1 Nm3 of biogas (47% CH4) was additionally formed per m3 of treated wastewater; without pretreatment, this value was 0.9 Nm3 (just 11% CH4). Lastly, aerobic treatment was performed and the results were encouraging: BI = 0.51 and COD reduction = 94%. Many oxidation products were identified and first-order kinetic plots were made to describe COD conversion kinetics. In this way, useful insight on a plausible technique for valorization of biomethanated washwater was provided.