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 (TiO 2 /UV and TiO 2 /H 2 O 2 /UV, both with and without acidification) and homogeneous (UV, H 2 O 2 /UV, Fe 2+ /H 2 O 2 /UV and Fe 2+ /H 2 O 2 ) 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 (BOD 5  = 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 BOD 5 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 Fe 2+  L −1 , leading to an average dissolved iron concentration of 14 mg L −1 after FePO 4 precipitation, proved to be the most efficient process, showing an initial reaction rate 8.4, 8.7 and 5.1 times higher than for H 2 O 2 /UV, TiO 2 /H 2 O 2 /UV-without and with acidification systems, respectively. The reaction required 167 mM of H 2 O 2 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.