Mechanisms of simultaneous hydrogen production and estrogenic activity removal from secondary effluent though solar photocatalysis

Abstract

The mechanisms of simultaneous photocatalytic hydrogen production and estrogenic activity (EA) removal from secondary effluent were investigated by evaluating the effects of initial dissolved oxygen (DO), organic matter, and inorganic ions on the process. The photocatalytic process was enhanced and can be divided into two phases according to the availability of DO. In aerobic phase, the humic/fulvic-like compounds in hydrophilic substances fraction were preferentially decomposed by aerobic photo-formed reactive oxygen species (i.e. O2−, h+, and OH) with generation of electron donors (i.e. formaldehyde, acetaldehyde, acetate, and formate). Approximately 41% of dissolved organic carbon and 90% of EA were reduced in the aerobic phase. In the following anoxic phase, the hydrogen production was significantly improved (apparent photonic efficiency 3.04 × 10−3) by the generated electron donors and accompanied with completely EA removal by the anoxic photo-formed OH. Hydrogen production was enhanced with the presence of low concentrations of HPO42− (below 0.1 mmol/L) and HCO3− (below 0.2 mmol/L) through accelerating electrons accumulation while it was inhibited at high concentrations since the formed ion-radicals could not decompose humic/fulvic-like compounds. EA removal was inhibited by HPO42− and HCO3− through scavenging h+/$OH. The presence of NO3− (below 1 mmol/L) only resulted in minor impacts since NO3− was almost unreactive toward electronor OH in neutral conditions.