Fate of emerging organic contaminants in Chinese wastewater treatment plants

There has been increasing concern about the widespread occurrence of emerging organic contaminants (EOCs) in the aquatic environment which could pose potential risks to humans and ecosystems. Wastewater treatment plants (WWTPs) are significant sources and major routes of EOCs entering the environment. There is therefore a need to study the fate of EOCs in WWTPs to improve the risk assessment for these EOCs. In this thesis, the passive sampling technique of diffusive gradients in thin-films (DGT) for in situ measurement of selected EOCs in water was developed in the laboratory and validated under the real world condition-a WWTP. This sampler was then employed to study the occurrence and removal efficiencies of EOCs in Chinese WWTPs, as China represents a significant and growing market for many of these chemicals. A novel DGT technique was developed for in situ measurement of EOCs in water, with hydrophilic-lipophilic-balanced (HLB) resin as the binding agent and agarose gel as the diffusion layer. The performance of DGT sampler (indicated by ratio of DGT-measured concentrations (CDGT) to the directly-measured concentration (Cb), the ratio of CDGT/Cb ranged from 0.9 to 1.1 indicating the excellent performance of DGT) in different pH, ionic strength and dissolved organic matter contents was tested with 11 chemicals and found to be relatively independent of pH (3.5-9.5), ionic strength (0.001-0.1 M) and dissolved organic matter (0-20 mg L-1). Time and diffusion layer thickness dependence experiments confirmed the principle of DGT for accumulated chemicals consistent with theoretical predictions. The performance comparison of three types of resins (HLB, XAD18 and Strata-XL-A) was undertaken. Resin properties and the interactions of functional groups between the resin and chemicals controlling the uptake of EOCs for DGT sampler were evaluated by comparing the uptake capacities and the kinetics of the test chemicals among three resins. The study in the laboratory, which is similar to above section for three types of DGT devices with HLB, XAD18 and Strata-XL-A resins as the binding gels, confirmed the potential application of DGT principle for in situ measurement of EOCs in water. This DGT sampler was then compared with active sampling approaches, auto-sampling and grab-sampling in a WWTP. This study showed that the DGT sampler can continuously uptake the majority of detected EOCs in wastewater for 7-18 days. The time-weighted average concentrations measured by DGT were found to be comparable with the results delivered from the auto-samplers, showing similar concentrations and patterns. The effect of diffusive boundary layer was estimated, and was found to be relatively limited and much less compared with other passive samplers, demonstrating the advantage of DGT sampler. The field validation confirmed applicability of DGT sampler for studying the fate of EOCs in the wastewater. Before application of the DGT sampler into a large scale of fate study in Chinese WWTP, a sensitive analytical method was developed for simultaneous determination of target EOCs in surface water and wastewater. This method was optimised from solid-phase extraction (SPE) procedures to liquid chromatography-mass spectrometer (LC-MS) analysis, and was demonstrated to provide reliable data for the samples with complex matrix and low enough detection limits for EOCs in the water. This analytical method could perform similarly or even better to some related studies for detection of the EOCs in wastewater. DGT devices with HLB resin gels were then applied to 10 WWTPs in China for studying the occurrence and removal of EOCs. All target EOCs could be found in the raw influent and majority of them (18 of 20) could still be detected in the final effluent. Removal efficiency of the EOCs varied, showing the performance of different treatment technology/processes on the EOCs removal in wastewater. The primary and secondary treatment units contributed to the most removal of the EOCs. This demonstrated that DGT sampler can be an effective and simple tool to study in fate of EOCs in wastewater. This research programme has shown that DGT sampler is an effective tool for studying the fate of wide range of emerging organic chemicals in the aquatic environment and assessing their risk/ toxicity of EOCs to the human and ecosystem