Biodegradation and biotransformation of wastewater organics as precursors of disinfection byproducts in water

Laboratory experiments were carried out to investigate wastewater organics as the precursors of disinfection byproducts (DBPs) in drinking water supply. The focus was on the change in wastewater DBP precursors during biological degradation under simulated natural conditions. The wastewater and its treated secondary effluent were characterized for DBP formation potential (DBPFP) and DBP speciation profile, including trihalomethanes, haloacetic acids, chloral hydrate, and nitrogen-containing DBPs. Several model organic compounds, including humic acid, tannic acid, glucose, starch, glycine, and bovine serum albumin (BSA), were used to represent the different types of organic pollutants in wastewater discharge. The results show that the DBPFP of wastewater decreased after biodegradation, but the remaining organic matter had a greater DBPFP yield with chlorine. Different model organics displayed different changes in DBPFP during biodegradation. The DBPFP remained largely unchanged for the glycine solution, decreased greatly for the tannic acid and BSA solutions, and increased nearly 3-fold for the glucose and starch solutions after 10 d of biodegradation. Meanwhile, the DBPFP yield increased from 3 for glycine to 51 μg DBP mg−1 C for its degradation residue, and from 1 for glucose and starch to 87 and 38 μg DBP mg−1 C for their organic residues, respectively. Although biodegradation may effectively remove some DBP precursors, biotransformation during the process produces new DBP precursors in the form of soluble microbial products (SMPs). The experimental results reveal that SMPs may be an important source of wastewater-derived DBP precursors in natural waters.