Abstract
This study investigated the impact of effluent organic matter (EfOM) from wastewater effluent on the properties of organic matter in receiving water and the efficiency of its removal using photocatalysis. The organic matter is characterized using fluorescence excitation-emission matrices coupled with parallel factor analysis (EEM-PARAFAC), UV-Vis spectroscopy, and dissolved organic carbon (DOC) measurements. The experiments are conducted with water samples that were collected from upstream waters (used as a source of dissolved organic matter (DOM)), wastewater effluent (a source of EfOM), and waters downstream of a wastewater treatment plant, and with upstream water and wastewater effluent being mixed at different ratios in the lab (DOM/EfOM). EEM-PARAFAC analysis identifies three components: a humic-like component (C1), a tyrosine-like component (C2), and a terrestrial-like humic component (C3). When compared to DOM, EfOM has a higher specific ultraviolet absorbance at 254 nm (SUVA254), a higher fluorescence index (FI), and more abundant humic-like components. As the EfOM contribution increased, an increase in both humic-like components and a simultaneous decrease in the protein-like components are observed. The photocatalytic degradation of the organic matter using simulated solar irradiation with ZnO as a catalyst is examined. The removal efficiency of photocatalysis is calculated using the DOC, UV absorbance at 254 nm (UV254), and the maximum fluorescence intensity (Fmax) of the PARAFAC components. After 120 min of irradiation, the removal efficiency of photocatalysis differs between the DOM, EfOM, and EfOM-impacted samples due to the change in the properties of the organic matter in the source water. The photocatalytic degradation of organic matter follows pseudo-first-order kinetics, with the DOC and UV254 exhibiting a lower removal efficiency with the increasing contribution of EfOM, which indicated that EfOM has a potentially negative impact on the performance of drinking water treatment. The removal of PARAFAC components follows the order C3 > C1 > C2, indicating that humic-like components are preferentially removed when compared to protein-like components under sunlight irradiation.
Highlights
In the face of continuing climate change, population growth, rapid urbanization, and water scarcity, wastewater reclamation and reuse have become important strategies in the conservation of water supplies
The incomplete mineralization of effluent organic matter (EfOM) represented the refractory properties of the EfOM and its products [12,13], while the catalyst dosage and reaction time may have been insufficient. These results show that the presence of EfOM in drinking water sources may have a negative impact on the performance of drinking water treatment, due to differences in the properties of EfOM and dissolved organic matter (DOM), especially in terms of dissolved organic carbon (DOC) and UV absorbance at 254 nm (UV254) removal
This study investigated the impact of EfOM on receiving waters in terms of the properties of the organic matter and its removal efficiency by sunlight-driven photocatalysis
Summary
In the face of continuing climate change, population growth, rapid urbanization, and water scarcity, wastewater reclamation and reuse have become important strategies in the conservation of water supplies. When treated wastewater is discharged into receiving waters, the indirect potable reuse of wastewater occurs, and it serves as a source of drinking water. Treated wastewater adds a significant amount of effluent organic matter (EfOM) into the receiving waters. EfOM includes natural dissolved organic matter (DOM), soluble microbial products, synthetic organic compounds, endocrine-disrupting compounds, flame retardants, pesticides, artificial sweeteners, and disinfection. The characteristics and composition of EfOM are strongly dependent on the source of the wastewater and the operating conditions of the wastewater treatment facility. The complex composition and chemical properties of EfOM negatively affect the quality of receiving waters and the efficiency of reclamation treatment processes [2,3,4]. To the best of our knowledge, there have been few studies [3,6,7,8] focused on the characteristics, fate, transport, and impact of EfOM in receiving waters
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