Evaluating the removal of emerging contaminants from the eThekwini Municipality REMIX Water Treatment Plant

Abstract

The eThekwini Municipalities Department of Water and Sanitation (EWS) has initiated feasibility studies to determine whether it is financially and environmentally viable to implement direct potable water reuse (DPR) projects, and one of them is the REMIX Water Treatment Plant (RWTP) which is located within the Port of Durban and abstracts wastewater and sea water for treatment and potential future re-use. However, a review of the extant literature has highlighted that wastewater and seawater are primary sources and "sinks" for various contaminants of emerging concern (CEC). Emerging contaminants (ECs) can be endocrine-disrupting chemicals or cancercausing agents in humans and animals if they are constantly present in drinking water. This study evaluated the efficiency of the RWTP for the removal of different classes of pharmaceutical compounds by measuring the feed water and effluent of each treatment unit along the RWTP. The Quantitative structure-activity relationship (QSAR) model and OPBT criteria were used to screen these compounds for persistence, bioaccumulation, and toxicity (PBT) behaviour in the water matrix. This was done to produce a priority list that allowed effective monitoring of each treatment unit for observed PBT compounds that should not be present in reclaimed water intended for human consumption. The QSAR is a suitable alternative to the costly and labourintensive in vivo screening experiments in the water matrix. It works in tandem with the new animal rights regulations, is safer than laboratory experiments, and also saves time. The study found that 4 out of 20 compounds were identified as potential PBT compounds by consensus agreement in both methodologies. The goal of this study was to assess the removal of ECs prioritised using the QSARINS model and OPBT criteria by carrying out a human risk analysis for reclaimed water proposed for drinking purposes within the City of Durban. This informed decision-makers, plant managers, and operators on what to constantly monitor or add to the treatment plant for the safe production of drinking water. Excellent removal rates of ECs were observed in the membrane biological reactor (MBR) and the reverse osmosis systems (ROs). The removal rates in MBR and ROs ranged from 38% to 100% and 96%, respectively. Excellent removal rates for heavy metals and nutrients across the treatment technology were also achieved in the final product water. The calculated risk/hazard quotients (RQ) for all ECs and heavy metals were also conducted in the reclaimed REMIX water. An RQ/HQ > 1 meant a high risk of ECs or heavy metals, and <1 meant the risk was negligible. Except for some anomalies caused by ion suppression or matrix effects during the analysis, the majority of the ECs in the reclaimed water RQ were found to be less than 1. Identification of chemical, biological, and physical hazards using HACCP system principles led to the identification of critical control points for the technology. Five critical control points were examined, and techniques for successful RWTP monitoring were proposed based on the study findings.