Combined electrocoagulation and UV-based sulfate radical oxidation processes for treatment of pulp and paper wastewater

Integrated processes have been proposed for high strength wastewaters such as pulp and paper wastewater. In this work, electrocoagulation (EC) followed by UV/oxidant system was studied for the removal of organic compounds from pulp and paper wastewater. EC process was optimized by Box–Behnken design. Under optimum conditions (natural pH, time = 33.7 min and current density = 5.55 mA/cm2), about 61% COD removal was achieved. The obtained effluent was remediated by UV/persulfate (PS) and UV/peroxymonosulfate (PMS). The results showed that UV/PS had the best performance in natural pH (pH of electrocoagulated effluent i.e. pH = 8.2) while UV/PMS required pH adjusting since pH = 4.0 provided the best efficiency. The scavenging effect was observed in overdosing oxidant in UV/PS while in UV/PMS, increase in PMS dosage increased the removal efficiency. The partial oxidation parameter showed that with increase of time, total oxidation was the predominant mechanism compared to partial oxidation. EC process was not effective in case of biodegradability improvement whereas EC along with UV/oxidant could significantly increase biodegradability (BOD5/COD ratio). In addition, the solar irradiation was tested as an alternative for UV source and the related results exhibited a negligible efficiency. Electrical energy consumption and current efficiency were also calculated.