DISINFECTION BYPRODUCT PRECURSORS FROM WASTEWATER ORGANICS: FORMATION POTENTIAL AND INFLUENCE OF BIOLOGICAL TREATMENT PROCESSES
Open Access
- Author:
- Tang, Hao
- Graduate Program:
- Environmental Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 08, 2011
- Committee Members:
- John M. Regan, Committee Chair/Co-Chair
Yuefeng F. Xie, Committee Chair/Co-Chair
Brian A. Dempsey, Committee Member
Yen-Chih Chen, Committee Member - Keywords:
- wastewater
disinfection byproduct
disinfection byproduct formation potential
biological treatment process
swimming pool - Abstract:
- Wastewater organics are an important source of various disinfection byproduct (DBP) precursors in downstream potable water supplies. Because of the various biological treatment processes adopted at wastewater treatment plants (WWTPs), the effluents may have a wide range of qualities, especially in DBP precursors. To minimize the risks posed by DBP-related issues, it is necessary to investigate the essence of DBP precursors in wastewater and evaluate the influence of biological treatment processes. Because conventional practices for evaluating DBP precursors in drinking water cannot be used directly in wastewater due to the complexity of wastewater constituents, a DBP formation potential (FP) quantification method was developed and used for wastewater samples. Sample pretreatment was required to maintain the level of DBPFP and filtration coupled with acidification to pH less than 2 produced stable samples for DBPFP assessment and has advantages for long-term storage. The proposed method for quantification of DBPFP in wastewater is based on the standardized parameters in the chlorination conditions, which include 20 mg/L chlorine dose, pH 7, 25°C, and an incubation of 3 days in the dark. Proper dilution is a key to assure that free chlorine residual remains after incubation. It is recommended that the dilution ratio be determined based on the ammonia level. The proposed method was validated by varying chlorine doses and ammonia levels, and could be used to quantify DBPFP for a broad range of wastewater samples. A survey on DBPFP of treated effluents from various WWTPs was conducted to explore the influence of different biological treatment processes on DBP precursors. The WWTPs that achieved better organic matter removal and nitrification tended to result in low DBPFP in treated effluents. By focusing on a model WWTP that had two biological processes for the same primary effluent treatment, the survey found that haloacetic acid (HAA), trihalomethane (THM) and chloral hydrate (CH) precursors were in predominant concentrations in wastewater. The combination of trickling filter and modified Ludzack-Ettinger process was more efficient in dissolved organics and DBPFP removal than the activated sludge process. The FPs of haloacetonitriles and haloketones showed the highest removal efficiencies in both systems compared to the FPs of other predominant DBP species such as HAAs and THMs. In addition, WWTP changed the DBPFP speciation profile by lowering the HAAFP/THMFP ratio. The DBP yields and specific ultraviolet absorbance increased after secondary treatment, indicating that the remaining organic matters tend to be more humic. The study implied that oxic and anoxic conditions, soluble microbial products, nitrification, and solid retention time may impact DBPFPs. The study is a comprehensive survey on an assessment of DBP precursor removal efficiencies in a large-scale WWTP. Three continuously stirred tank reactors (CSTRs) and two sequencing batch reactors (SBRs) were designed to simulate different biological treatment processes in the laboratory. For the three CSTRs, HAAFP decreased as nitrification improved from a poor to a good level. THMFP, however, was not found to be clearly correlated with nitrification. For the two SBRs that were operated at the same SRTs and with complete nitrification, the oxic-anoxic SBR with better denitrification had decreased DBPFP. During an 8-h cycle of an SBR operation, the majority of DBP precursor removal was completed with the bulk removal of wastewater organics. The oxic reactions had a faster removal rate and greater removal efficiency than the anoxic reactions. Although the majority of wastewater organics were removed by biological treatment processes, the remaining organic matter had a higher potential to form DBPs upon chlorination. The study provides information on the effectiveness of wastewater treatment processes on a variety of wastewater parameters, organic matter, and precursors for DBPs. The information can be beneficially used by wastewater and water professionals to minimize the health risks posed by wastewater-derived DBPs. Materials of human origin (MHOs) are the main constituents of wastewater organics. This research monitored DBPs in an indoor swimming pool over a 1-year period following water change, explored DBPFP from MHOs, and developed a model to simulate DBPs in swimming pool water. As the time since the water change increased, the HAA concentrations increased up to 1650 µg/L while the THM concentrations fluctuated in a range between 40 and 181 µg/L over the 1-year period in the monitored pool. The difference between the concentrations of HAAs and THMs is attributed to three factors: (1) MHOs from pool users; (2) slow HAA reduction; and (3) long water retention. The model developed based on a mass balance and pseudo first-order kinetics achieved a good simulation of a real swimming pool system at long water age. The sensitivity analysis indicates that MHO loadings would impact DBPs in swimming pool water. The research reveals that MHOs contribute to DBP formation and are an important source of DBPs in swimming pools. As MHOs are continuously brought in by swimmers and pools are continuously exposed to disinfectants, pool water represents extreme cases of disinfection that differ from the disinfection of drinking water, and the net-accumulated HAAs could pose negative health risks to human beings. The study can help water professionals to better understand the contribution of MHOs to DBP precursors.