AWWA WQTC62467

Increased attention is being focused on solving taste and odor (T&O) problems facingmunicipal drinking water suppliers. For some municipalities, conventional solutions suchas powdered and granular activated carbon (PAC and GAC) have proven to beinadequate due to limited treatment efficacy. In addition, the application of ozonetechnology can be cost prohibitive and incapable of meeting Cryptosporidium treatmentrequirements and limits on bromate formation as set forth in the Long Term 2 EnhancedSurface Water Treatment Rule (LT2ESWTR) and the Disinfectant/DisinfectionByproducts Rule. Ultraviolet (UV) technologies, however, are currently experiencing rapid growth inmunicipal drinking water disinfection applications. For many utilities UV is the bestoption to comply with the treatment requirements of the LT2ESWTR. This is primarilybased on UV's ability to inactivate many microorganisms, especially Cryptosporidium,without forming harmful disinfection byproducts. In addition, there is a growingawareness of UV-based advanced oxidation processes for treating micropollutants inwater. Recent studies (Jobb et al, 1995; Linden et al, 2002; Romain et al, 2003) haveidentified UV-oxidation as an efficient means to treat T&O-causing compounds indrinking water.A T&O event typically lasts a few months while the disinfection requirement is year-round.To address this scenario, a new solution is proposed in which a single UV systemis operated in dual disinfection/oxidation modes. In disinfection mode, only a fraction ofthe total UV lamps and/or reactors installed would be operated thereby keeping theoperating costs at a minimum while simultaneously meeting disinfection requirements.During a T&O event, the UV system is operated in contaminant control mode. In thismode, additional UV lamps/reactors are energized and hydrogen peroxide is dosed intothe water upstream of the UV system. The combination of UV and hydrogen peroxidegenerates hydroxyl radicals that oxidize T&O-causing compounds as well as variousother contaminants potentially present in the water.A large-scale field study was performed in 2003 demonstrating the effectiveness of theUV/H2O2 process for treatment of geosmin and MIB contamination. MIB and geosminwere spiked into the plant's filter discharge line at about 200 ng/L (ppt) prior to treatmentby TrojanUVSwift™ ECT reactors utilizing medium-pressure lamps. Hydrogen peroxidewas also added to the reactor influent at concentrations varying from zero to 11 ppm.This system treated flows up to 6 MGD. The results of the pilot study clearlydemonstrated that the UV-oxidation treatment process is an effective and efficient processfor the treatment of MIB and geosmin in drinking water to levels below the odor thresholdvalues and, in fact, below the analytical detection limits. Several sample sets were analyzedfor disinfection byproducts including haloacetic acids (HAAs), trihalomethanes (THMs)and bromate and the results indicated that the UV/H2O2 process reduced THM and HAAlevels by an average of 25% and 12% respectively with no bromate formation. Thesesamples were also analyzed for assimilable organic carbon (AOC) levels before and aftertreatment and the results indicate that no statistically significant increases were observed. Includes 3 references, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2005

Number of Pages:

4

File Size:

1 file , 190 KB