Reactivity of Island Drainage Water DOC Towards Disinfection Byproduct Formation Following Coagulation.

The Sacramento-San Joaquin Delta provides drinking water to roughly 25 million people in California. Delta islands are used for agricultural purposes and water is pumped off drains on these islands to maintain agricultural production. This drain water typically contains elevated levels of dissolved organic carbon (DOC), which is a concern for drinking water because DOC reacts upon chlorination to form carcinogenic disinfection by-products (DBPs). Coagulation of organic matter with polyvalent metal cations (Al3+ and Fe3+) is an economical and effective treatment process for the removal of DOC, forming organic flocs through two major processes: charge neutralization and adsorption. A CALFED/Department of Water Resources funded project was initiated to investigate the feasibility of using coagulation to remove DOC from island drainage water prior to release into Delta channels, in conjunction with the use of constructed wetlands to reverse subsidence. We have begun to investigate the seasonal reactivity of DOC, in terms of DBP formation after coagulation at various doses for further research in constructed wetlands to reduce DOC and DBP precursor exports from Delta islands. Coagulation at optimal doses removed up to 85 percent of the total DOC. The composition of remaining DOC following varied coagulant doses was also examined using non-ionic macroporous resins (XAD-4/DAX-8). Our data suggest that coagulation removes the hydrophobic portion of DOC and the main components responsible for the formation of several DBPs including THMs and HAAs. Trihalomethane formation potential incrementally decreased with decreasing DOC concentrations as coagulant dose increased. In contrast, haloacetic acid precursor concentrations did not begin decreasing until after the intermediate dose of coagulant had been reached corresponding to roughly 67 percent of the total DOC removal.