AWWA WQTC60668

Sweetwater Authority (SWA) owns and operates the Robert A. Perdue Water TreatmentPlant (WTP), a 30 mgd conventional filtration plant located in San Diego County,California. This paper documents the results of SWA's pilot testing of chlorine dioxide(ClO₂), dissolved air flotation (DAF), and submerged microfiltration/ultrafiltration(MF/UF) membranes, begun in early 2004, as a reliable and cost-effective treatmentstrategy for meeting future disinfection byproduct (DBP) regulations.The Perdue WTP treats two source waters, local surface water from SweetwaterReservoir (SWR) (average total organic carbon (TOC) = 6.5 mg/L, bromide up to 0.5mg/L) and San Diego County Water Authority (CWA) aqueduct water (average TOC =2.5 mg/L, low bromide). SWA currently applies free chlorine and potassiumpermanganate (KMnO₄) to the raw SWR water and uses chloramines in the distributionsystem. However, excessive trihalomethanes (THMs) formation is a potential concern forcompliance with the Stage 2 Disinfection Byproducts Rule using the LocationalRunning Annual Average (LRAA) method. The current testing program was preceded bypilot testing of intermediate-ozone with enhanced coagulation (30 mg/L ferric chloride)and bench-scale testing of ClO₂ and ferric chloride doses up to 80 mg/L, results of whichare also highlighted in this paper.CWA was responsible for the first phase of DAF and MF/UF membrane testing at thePerdue WTP site, using the CWA Aqueduct water as the pilot feedwater. With DAF aspretreatment, both of the submerged membrane systems tested provided reliable waterquality at fluxes above 30 U.S. gallons per square foot per day (gfd) (51 liters per hourper square meter), with recoveries around 95%, for at least 30 days before the need formembrane clean-in-place (CIP).For the SWR water testing, the full-scale WTP influent is being treated with ClO₂ atdoses up to 1.5 mg/L, and chlorite is controlled by applying ferrous chloride (FeCl₂) at a3.3:1 ratio of ferrous ion to chlorite. The first two weeks of the SWR water testing usedDAF pretreated water as the feedwater to the membrane pilots while the following sixweeks used settled water from the full-scale plant as the membrane feedwater to comparethe effects of these two pretreatment options on membrane operation. Membrane fluxeswere set initially based on the results from the CWA water testing and optimized toprovide a minimum 30 day CIP interval. ClO₂ was evaluated as the plant primarydisinfectant with chloramines downstream of the membranes for distribution systemresidual. In addition to monitoring the performance of the DAF and membrane systems,simulated distribution system (SDS) testing was conducted on the membrane filtrate on aweekly basis to estimate disinfection byproduct (DBP) formation.The process combination of ClO₂, DAF, and submerged membranes represents apromising process combination for agencies seeking to meet the Stage 2 DBP Rule withsource waters with high bromide and highly reactive TOC. Includes 3 references, figures.

Product Details

Edition:

Vol. - No.

Published:

11/15/2004

Number of Pages:

13

File Size:

1 file , 2 MB