Treatment of a pesticide-containing wastewater using combined biological and solar-driven AOPs at pilot scale

Abstract

The present work focuses on treatment of a pesticide-containing wastewater resulting from phytopharmaceutical plastic containers washing, combining a preliminary biological pre-treatment step, using an immobilized biomass reactor (IBR), with further advanced oxidation processes (AOPs). Heterogeneous (TiO2/UV and TiO2/H2O2/UV, both with and without acidification) and homogeneous (UV, H2O2/UV, Fe2+/H2O2/UV and Fe2+/H2O2) systems were tested using a solar pilot plant with compound parabolic collectors (CPCs). The wastewater exhibited a moderate organic load (COD = 1662-1960 mg O-2 L-1; DOC = 513-696 mg C L-1), high biodegradability (BOD5 = 1350-1600 mg O-2 L-1) and nineteen pesticides were quantified in the range of 0.02-45 mg L-1, representing 14-19% of total DOC. Due to its high biodegradability, a biological treatment was performed prior to AOPs, leading to a COD. DOC and BOD5 reduction of 46-54%, 41-56% and 88-90% respectively, resulting in a recalcitrant wastewater with a residual pesticide content corresponding to 24-34% of DOC. The photo-Fenton reaction, performed with an initial iron concentration of 140 mg Fe2+ L-1, leading to an average dissolved iron concentration of 14 mg L-1 after FePO4 precipitation, proved to be the most efficient process, showing an initial reaction rate 8.4, 8.7 and 5.1 times higher than for H2O2/UV. TiO2/H2O2/UV-without and with acidification systems, respectively. The reaction required 167 mM of H2O2 and 21 kJ(UV) L-1 to achieve 86% mineralization and only 8 kJ(UV) L-1 to eliminate eighteen of the nineteen pesticides initially quantified to levels below the respective quantification limit. Despite the Fenton reaction revealed a slower mineralization profile, it can be quite efficient for significant pesticide abatement compared to the other AOPs employed.