Photocatalytic oxidation of six endocrine disruptor chemicals in wastewater using ZnO at pilot plant scale under natural sunlight

Abstract

Endocrine disruptors (EDs) are xenobiotics that interfere with the synthesis, secretion, transport, binding, action, and elimination of the natural hormones. In this paper, the photodegradation of six EDs in municipal wastewater treatment plant effluents at pilot plant scale is reported. The EDs were bisphenol A, bisphenol B, diamyl phthalate, butyl benzylphthalate, methyl p-hydroxybenzoate, and ethyl 4-hydroxybenzoate. ZnO as photocatalyst in tandem with Na₂S₂O₈ as electron acceptor under natural sunlight were used. The process was previously optimized under laboratory conditions through a photoreactor under artificial UVA irradiation studying the role of some key operating parameters (catalyst loading, effect of electron acceptor, and pH). Results carried out at pilot plant scale show that addition of ZnO in tandem with Na₂S₂O₈ strongly enhances degradation rates compared with photolytic test. At the end of the irradiation time (240 min), the remaining amounts of EDs ranged from 24% (butyl benzylphthalate) to 0% (< LOQ bisphenol B). The degradation rates were in the order: bisphenols > parabens > phthalates. After the photoperiod, 83% of the initial dissolved organic carbon was removed and toxicity decreased to acceptable values (11% inhibition to Vibrio fisheri). The photodegradation process was found to follow pseudo-first-order kinetic model with DT₅₀ ranging from 5 min (bisphenol B) to 102 min (butyl benzylphthalate). Thereby, photocatalytic oxidation using ZnO is an area of environmental interest for the treatment of polluted water, particularly relevant for Mediterranean countries, where solar irradiation is highly available.