Reusing treated wastewater might provide a promising solution for the crisis of water scarcity under changing environments. Disinfection byproducts (DBPs) are formed when disinfectants reacting with waterborne dissolved organic matters (DOM). DBPs are considered as probable human and animal carcinogen in multiple risk assessments. Their presences in waters dependent on the quality and concentration of source water, disinfectant type, precursors, and water treatment strategies. Previous studies have focused on formation of DBPs in drinking water; however, very limited studies investigate the formation and occurrence of DBPs in constructed wetlands receiving effluents from wastewater treatment plants (WWTP).
This study aims to investigate how the habitat structures of wetland influence DOM quality (the DBP precursors) and thus the presence of DBPs in the marsh, mangrove flat and WWTP effluent inflow of the wetland. Materials and methods include sampling from various sites, spectroscopic analysis of DOM, and chemical analysis of DBPs following EPA Method 551.1.Results show that wetland structures significantly shaped DOM characteristics. Optical properties of DOM (SUVA254, fluorescence index, humification index) indicated that DOM in the mangrove flats were dominated by aromatic, terrestrial-derived DOM compared to the WWTP effluent inflow and marsh zone. Haloacetic acids (HAA) is the major DBPs observed in the wetland water; however, their concentration was roughly 20–50% comparing to these in chlorinated tap water. HAA concentration was positively correlated with the terrestrial DOMs (tDOM); however, negatively correlated with salinity and total dissolved solids. Trihalomethanes (THM) levels were just 1–10% of tap water concentrations and were an order of magnitude lower than HAA concentrations at all sampling sites. We suggest that tDOM origin from mangroves accompanied with higher salinity might contribute to the formation of HAAs. Contrary, higher salinity may suppress DBP yields, likely due to differential chlorine demand or bromide incorporation.
Understanding of how the wetland habitat structures shape the DOM properties and thus DBP formation provides inform for wetland construction and management to mitigate DBP exposure risks when reusing the treated wastewater. This study supports the development of safer wastewater reuse practices and improved water quality management in constructed wetland-systems.