Formation and Fate of Chlorination Byproducts in Desalination Systems
Year Released: 2009
Funding Partners: Bureau of Reclamation, California State Water Resources Control Board, Trojan Technologies
Total Investment: $102,945.30 (Cash: $99,976.82, In-Kind: $2,968.48)
Principal Investigator: David L. Sedlak, University of California at Berkeley
Recent improvements in membrane technology have decreased the costs and technical challenges associated with reverse osmosis (RO) systems. As a result, the worldwide capacity of seawater desalination systems approximately doubled between 1994 and 2004 and additional capacity is being planned in populated coastal areas in California, Spain, and Australia. The high quality of water produced by RO systems has been touted as an advantage of desalination plants relative to other water sources, such as wastewater effluent. Despite the widespread success of existing desalination plants and the excellent performance of RO membranes in removing salts and chemical contaminants, the large investments in desalination being contemplated by utilities around the world necessitate a careful examination of the potential occurrence of chemicals that pose human health or ecological risks in water produced by desalination systems.
Goals and Objectives
The project assesses the occurrence of contaminants of concern in water produced by desalination systems. 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.
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.