AWWA WQTC63962

The U.S. Environmental Protection Agency (USEPA) will require increased disinfection capability and lower disinfection byproductlevels when the proposed Long Term Enhanced Surface Treatment Rule (LT2ESWTR) ispromulgated. The future target pathogen will be Cryptosporidium sp., which is 16 times moreresistant to inactivation than the current target protozoan, Giardia sp. according to the USEPAproposed CT tables for ozone and chlorine dioxide. While disinfection requirements willincrease, it is more difficult for ozone plants with bromide source water to comply with thebromate maximum contaminant level (MCL) of 10 ppb. Even more daunting for ozonation is thepossibility of a lower bromate MCL at 5 ppb in the future.The literature review revealed three treatment options available for lowering bromates that include: chlorine dioxide pre-oxidation of ozone; ammonia addition; and, pH control. Thesetreatment methods were evaluated in an AWWARF study performed in Contra Costa, Californiain 2002. The highlights of the Contra Costa study demonstrated that: chlorine dioxide and pH6.0 substantially reduced the bromate formation; chlorine dioxide had similar coagulant dosesas ozone; chlorine dioxide did not adversely affect filter operation; modest energyreduction resulted; chlorite byproduct played a role in bromate reduction; and, ammoniaaddition was less effective than chlorine dioxide and pH adjustment.Because chlorine dioxide does not cause bromates and reduced bromate formation fromozonation by 75% in laboratory and plant studies at Contra Costa, California in 2002, the El PasoWater Utilities approved a laboratory and plant study at the 60 mgd Jonathan Rogers Water Plantin El Paso, Texas. Also, the literature review showed synergistic disinfection benefit ofcombining disinfectants in Cryptosporidium sp. inactivation while lowering disinfection byproductlevels. Since El Paso already had extensive experience with combining chlorinedioxide and chlorine treatment to lower TTHMs and increasing disinfection capability, it madesense to further evaluate the potential of combining ozone and chlorine dioxide for preventingbromates with the possibility of increased disinfection capability.Therefore, the El Paso Water Utilities management authorized installation of chlorine dioxidegeneration equipment supplied by Eka Chemicals at the Jonathan Rogers Water Plant in order toproceed with the laboratory and plant study during the March through September 2005 period.The bromate study objectives were to: determine the effect of ozone residual and contact timeon bromate formation; determine effect of chlorine dioxide on reducing bromates; and,determine the effect of ozone on chlorite and chlorate levels.There were three major assumptions made based on the literature review and previousexperiences in other studies. They were that: bromate formation is primarily due to the ozoneconcentration (residual) and contact time; peroxone treatment prevents additional bromateformation after the first cell treatment with ozone for disinfection credit; and, chlorine dioxideprevents bromate formation. Includes 5 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2006

Number of Pages:

19

File Size:

1 file , 720 KB