Pilot scale investigation of an advanced photo-electro-chemical oxidation process for treatment of effluents from pesticides manufacturing plants

This paper reports on the effectiveness of an innovative hybrid advanced oxidation process-scheme aiming to degrade recalcitrant organic compounds in industrial effluents. Following targeted experimental work, a pilot unit was developed/built combining two advanced oxidation processes, based on in-situ production of powerful hydroxyl radicals (HO); i.e., electrochemical anodic oxidation (AO) employing boron-doped diamond (BDD) electrodes and photochemical oxidation via H2O2 photolysis under UV-C irradiation (H2O2/UV-C). The pilot-unit was operated, in batch mode for six months in a pesticides manufacturing plant, treating colored effluents characterized by high, recalcitrant organic load (typically ~3300 mg/L COD, ~1000 mg/L TOC). The effect was examined of key process parameters, including current density, UV-C dose, H2O2 concentration, recirculation flow rate and processing time, on system performance, mainly regarding organic-matter mineralization and discoloration rate. For the aforementioned effluent organic load, applying a near-optimal set of process-parameter values (i.e. 40 mA/cm2 current density, 0.65 W/L UV-C dose, ‘on-line’ dosing of approx. 1140 mgL-1h-1 H2O2 and 8.4 L/min recirculation flow rate), TOC and color removal reached 71% and 93%, respectively. The effectiveness of the combined AO/H2O2/UV-C process, mainly due to high utilization of injected H2O2 (approx. 80-90%), is judged as remarkable, considering that complete degradation (>99%) was observed of the 53 out of the total 54 organic compounds identified in the wastewater. Furthermore, the treated effluents by the hybrid AO/H2O2/UV-C process meet the standards (i.e. COD<1000 mg/L and TSS<350 mg/L) for safe disposal to local/regional biological effluent-treatment plant. Therefore, the demonstrated technology is an attractive, sustainable alternative to the currently employed special treatment, which involves chemical coagulation/granular activated carbon adsorption and necessitates costly extra-treatment of the resulting secondary wastes. Steps are currently in progress towards implementation at large scale, of the hybrid AO/H2O2/UV-C technology, for treatment of similar heavily polluted industrial effluents.