Formation and Fate of Chlorination Byproducts in Desalination Systems
Year Released: 2009
Funding Partners: Bureau of Reclamation, California State Water Resources Control Board, Trojan UV
Total Investment: $83,000 (Cash: $80,000, In-Kind: $3000)
Principal Investigator: David L. Sedlak, University of California at Berkeley
Chlorination is a common practice in many modern desalination plants because it is cost-effective and reliable. Previous studies conducted at coastal power plants and a limited number of desalination plants indicate that chlorination produces byproducts that can pose risks for human health and aquatic ecosystems. Some low-molecular weight byproducts can pass through reverse osmosis membranes. Additionally, desalinated water often contains relatively high concentrations of bromide. Chlorination of blends containing desalinated water can produce brominated disinfection byproducts.
Goals and Objectives
The project assesses the occurrence of contaminants of concern in water produced by desalination systems when chlorine is used for seawater pre-treatment or for disinfection. The project also considers the potential impacts of these contaminants on human health in desalinated water and on aquatic organisms in waters that receive desalination concentrate.
The project includes a comprehensive review of chlorine disinfection byproducts in desalination systems; studies of their formation after chlorination of seawater from different locations; removal of chlorine disinfection byproducts in a pilot-scale seawater desalination system; and the formation of disinfection byproducts after chlorination of desalinated water, before and after blending with water from other sources. Tasks include:
- Chlorine DBPs: Trihalomethanes, haloacetic acids (HAA9), haloacetonitriles, and bromophenols.
- Organic precursors: dissolved organic carbon, UVA254
- Other water quality parameters including bromide concentrations, pH and conductivity
- Samples collected from 3 California Coast locations, Gulf of Mexico and Singapore.
- Chlorination conditions (normal dose, high dose and contact time) typically employed in pilot and full-scale plants.
Pilot Plant Chlorination
- Sample locations at the intake, reverse osmosis feed, retentate and permeate.
- Assessed formation, concentration and rejection of disinfection byproducts.
- 72-hour benchscale simulated distribution system study with chlorination and chloramination of blends of desalinated water with freshwater sources.
- Freshwater samples include local treated tap water and raw water from local reservoir and the Colorado River.
Findings and Conclusions
- The variability in the concentrations of disinfection byproducts (DBP) formed after seawater chlorination cannot be predicted from aggregate parameters such as dissolved organic carbon. Disinfection byproduct production exhibits considerable temporal and spatial variability. However, the concentrations produced do not normally exceed thresholds for effects on aquatic organisms.
- Some low molecular organics are not completely rejected by the desalination reverse osmosis membranes. The molecular weight and charge of the DBP affect the rejection of the disinfection byproducts. Under typical conditions, concentrations of disinfection byproducts in desalinated water are well below threshold for human health effects.
- The blending of desalinated water with freshwater affects the types and concentrations of disinfection byproducts formed during chlorination because desalinated water contains relatively high concentrations of bromide. While blending organic-rich surface water with desalinated water reduces the concentrations of disinfection byproduct precursors, the concentrations of certain disinfection byproducts formed can increase due to the high reactivity of HOBr.