Integrated anaerobic-aerobic treatment followed by electro-fenton oxidation for COD reduction in pine resin processing wastewater

ABSTRACT

Pine resin processing industry generates valuable materials but also produces wastewater with high organic loads (chemical oxygen demand [COD] ≈ 5,000 mg/L) and structurally complex organic compounds, making conventional treatments challenging. This study aimed to evaluate the electrochemical method as a complement to biological wastewater processing, using an electrocatalytic reactor equipped with a metal-oxide electrode (Ti/RuIrO2). Variables investigated in this study included cathode material, processing time, pH, and ferrous sulphate dose. Biological degradation was conducted in a 5-liter scale-up flow anaerobic reactor integrated with a 2.5-liter aerobic unit at a flow rate of 2.3 L/d. The anaerobic unit was inoculated with activated microorganisms at a 30% (w/v) microorganism-to-wastewater ratio, sourced from a Wastewater Technology Laboratory; the aerobic unit received 23.23 mg/L mixed liquor suspended solids from a textile-industry wastewater treatment plant. COD removal reached 42% in the anaerobic process and 68% in the aerobic process. Electrochemical treatment using a Ti/RuIrO2 cylindrical electrode–carbon plate pair achieved 77% COD removal after 3 h at pH 3 with 4 g/L coarse salt and 0.03 g/L FeSO4. In conclusion, integrating electrochemical and biological treatments reduced effluent COD to meet the local discharge standard.