Evaluating criteria for enhanced coagulation compliance

Abstract

Jar testing of 31 natural waters suggests many utilities may need the proposed alternative performance criterion to comply with enhanced coagulation specified in the proposed D/DBP Rule. Jar tests were performed on 31 natural waters from a variety of sources across the United States. These tests indicate that the majority of utilities supplying samples will have difficulty meeting the Step 1 total organic carbon (TOC) removal requirements in the Disinfectants/Disinfection By‐products Rule. Utilities may need the proposed point of diminishing returns alternative performance criterion to achieve compliance with the enhanced coagulation requirement. Water sources with high TOC and low alkalinity were most likely to meet the proposed Step 1 TOC requirements. Those with low TOC were most likely to need the alternative performance criterion.

Enhanced coagulation using a magnetic ion exchange resin

“…The specific ultraviolet absorbance (SUVA) of each water was calculated as UV254/DOC Â 100, in units of L/mg-m. The SUVA of a water is believed to reflect its amenability to DOC removal by coagulation [7,9]. A sample of water was also taken for subsequent chlorination and analysis of its THMFP and HAAFP (see below).…”

“…This phenomenon was not seen for the MIEX-treated water. White et al [7] found a linear correlation between the critical alum dose required to initiate turbidity and TOC removal and the raw water TOC concentration. Indeed, as TOC concentration for all of the waters examined decreased following MIEX treatment, so did the amount of alum required to coagulate turbidity.…”

“…The purpose of the TOC removal requirements prior to disinfection, in addition to the specific MCLs set for THMs and HAAs, is to reduce the public's exposure to potentially harmful DBPs that have not yet been identified. Coagulation with alum or ferric salts is known to be effective for the removal of organic DBP precursors [3,5,6,7].…”

“…It has been well established [7,[8][9][10][11] that, for most natural waters, the concentration of DOC tends to control the coagulant dosage required for effective turbidity (particle) removal. Hence, application of the MIEX resin prior to coagulation is expected to remove a substantial portion of this DOC (NOM), thereby lowering the coagulant demand of the water for subsequent coagulation of particulate material.…”

Control of disinfection by products formation potential by enhanced coagulation

“…In recent years, process optimization with respect to NOM removal has gained a lot of attention. The main motivation for this is primarily concerns regarding unpleasant color, taste and odor, increased coagulant and disinfectant demands, known and unknown DBPs, re-growth in water distribution systems, and availability of hydrophobic organic and inorganic micropollutants associated with NOM (Black et al, 1996;White et al, 1997 andGao et al, 2005). The yellow/orange color alone makes these waters unacceptable for drinking purposes, but the most concern with this has been the formation of halogenated by-products.…”