In the recent decade, a wide range of emerging contaminants (ECs) has been regularly detected in the wastewater treatment plants (WWTPs) effluent, surface water and even groundwater. Among all these ECs, organic micropollutants (OMPs) are receiving increasing attention due to their characteristics of low concentration, difficulty in degradation and their harmful effects on humans and the environment. Nineteen OMPs have been included on the contaminant watch list of the European Union Water Framework Directive since 2015 and efficient and reliable methods to eliminate them are researched worldwide. Therefore, in this study, five of these 19 OMPs (benzotriazole (BTA), carbamazepine (CBZ), diclofenac (DIC), ketoprofen (KET) and caffeine (CAF)) were selected as target OMPs. And the research objective is to fabricate a ternary composite photoanode and to investigate its photoelectrocatalytic degradation performance for all five target OMPs.

BiVO₄/(TiO₂/graphene oxide (GO))_mix ternary composite thin films were successfully deposited on fluorine-doped tin oxide (FTO) glass substrates using ultrasonic spray paralysis (USP) method to form a ternary heterojunction structure and to improve the photoelectrocatalytic performance for degradation of the five target OMPs. The morphology, crystal phase, surface chemical composition, optical and electrochemical properties of this ternary composite photoanode were analyzed by scanning electronic microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, incident photon-to-electron conversion efficiency (IPCE), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS), respectively. The results of these analyses showed that TiO₂ P25 nanoparticles and GO sheets were distributed uniformly on the brain-shaped BiVO₄ structure which indicated that the ternary heterojunction structure was formed successfully. From the UV-vis analysis, it could be estimated that the band gap energy for BiVO₄/(TiO₂/GO)_mix ternary composite photoanodes is 2.43 eV. Further, the LSV and EIS analysis showed that the photocurrent of the ternary composite photoanodes is lower than pure BiVO₄ photoanodes.
The degradation experiments were divided into five stages. The optimal photoanode type was first determined in the pre-experiment stage using methylene blue (MB) as indicator organic pollutant and then the effect of initial concentrations of target OMPs and initial pH on the degradation efficiency were studied in stage II and III, respectively. The highest removal efficiency of the five target OMPs was obtained with initial OMPs concentration at 10 μg·L^-1 and initial pH range of 3.5-4.0. The degradation experiments were triplicated under this optimal condition in stage IV. It was noticed from the results that the degradation efficiency of different OMPs after 3 hours of reaction time varied from 31.1 % to 99.5 %. To further confirm that there is competition between the five target OMPs during the photoelectrocatalytic degradation process, experiments were carried out in which individual OMPs were degraded independently. The reusability and stability of the photoanodes were evaluated in stage V. Trapping experiments using scavengers were also included in this stage, which showed that superoxide anions was the most active species during the degradation process. ... Read more

Over the last decade, a wide range of organic micropollutants (OMP) has been regularly detected in surface water, groundwater and wastewater treatment plant (WWTP) effluent. These OMPs consist mainly of synthetic organic compounds (SOC) such as pharmaceuticals and pesticides. Although their concentrations in water bodies are usually low, they can cause potential risks to disturbance and affect human as well as environmental health, which has attracted the attention of governments and institutions to search for reliable and simple methods with low cost to remove them. Powdered activated carbon (PAC) adsorption is considered to be an efficient, convenient and cheap method to remove OMPs with low concentrations. However, the adsorption capacity of PAC is not fully used due to a short contact time in the traditional adsorption treatment of dosing PAC into water directly. Therefore, some processes such as the Actiflo Carb or PAC membrane reactors, recirculate PAC in order to increase the contact time. Predicting the performance of older, recirculated PAC is difficult. The objective of this project was to simulate performance of aged PAC using a simple lab-scale experiment. Three different water matrices (tap water, WWTP effluent and diluted WWTP effluent) were used to make the OMPs solutions with 18 selected OMPs of 10 ug/L. PAC was added into the OMPs solutions to make two concentrations of PAC suspension (0.5 g/L and 0.25 g/L). Samples were collected at fixed time intervals. The breakthrough behavior of selected OMPs for aged PAC was then investigated and determined by analyzing the OMPs concentration, UV254 and DOC of samples. The setup was successfully used to record breakthrough curves of 5 different OMPs (Gabapentin, Sulfadimethoxine, Sulfamethoxazole, Metformin and Clofibric acid) and UV254 in 3 different water matrices. Gabapentin was the least adsorbable in tap water and the breakthrough occurred after 10 hours, while in WWTP effluent, Sulfadimethoxine was the least adsorbable OMP with the complete breakthrough time of 14 hours. Propranolol was the most adsorbable compound in both tap water and WWTP effluent. The breakthrough of UV254 was observed later in tap water and WWTP effluent, about 24 hours and 22 hours, respectively. However, parameter DOC can not be used to predicate the breakthrough of OMPs accurately. Model fitting based on the experimental adsorption data was also included. ... Read more