Comparative study of electrochemical hybrid systems for the treatment of real wastewaters from agri-food activities

Agri-food wastewaters are characterized by high contents of hardly biodegradable organics and large amounts of inorganics especially nitrogen and phosphorus. The present work investigates the efficiency of two electrochemical treatment processes, namely electrochemical oxidation/reduction (EOR), electrocoagulation (EC) and their combination for the treatment of two types of effluents collected from poultry slaughterhouse (SHWW) and dairy (DWW) industries. The optimization of these treatment systems in terms of pollutant performance removal and energy cost were carried out. The EOR treatment was assessed on a bipolar cell with Boron-Doped Diamond (BDD) supported on silicon electrodes. While, the EC treatment was performed on a reactor containing mild steel electrodes with parallel configuration. The simultaneous removal efficiencies of the organic matter in term of the chemical oxygen demand (COD), nitrates, ammonium/ammonia and phosphates, as well as the electric energy consumption (EEC), were evaluated for the different electrochemical scenarios. Results indicated that the EOR treatment shows the highest removal efficiencies of COD, nitrates and ammonia from the two studied wastewaters. While, the phosphates were removed only by the EC process. On the other hand, the EC process shows a relatively low cost in term of EEC (0.01 kWh/g COD⁻¹), which is about 13 times lower than the one consumed during the EOR process. The combination of the two processes leads to the improvement of the removal rate of all coexistent pollutants when the EC technology was used as a pre-treatment step. While, this coupling mode has the highest EEC. However, when the EOR process was used before the EC one, the removal rates of COD and nitrates were globally similar to the EOR process alone with a relatively low EEC.