Fenton oxidation and adsorption pretreatment for superior biogas recovery from biomethanated spent wash

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.

Keywords:

• Activated carbon
• Biogas
• Biomethanation
• Fenton oxidation
• Spent wash

Additional information

Funding

G. M. Bhoite is grateful to the Rajiv Gandhi Science and Technology Commission (RGSTC), Government of Maharashtra, India, for financial support (RGSTC/File 2013/DPP-111/CR-26, dated 14 Feb-2014).