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The US Environmental Protection Agency (USEPA) has recently (December 1998)promulgated the Stage 1 Disinfectants/Disinfection Byproducts (D/DBP) Rule. Wheneffective (in 2001 for large systems), this rule, will require utilities tocomply with maximum contaminant levels (MCLs) for trihalomethanes (THMs),haloacetic acids (HAAs), bromate and chlorite. In order to reduce exposure toother DBPs, this rule will also require utilities to achieve specified removal ofnatural organic matter (NOM) as measured by total organic carbon (TOC). Allsurface water utilities with conventional treatment systems (includingsedimentation) are required to implement this treatment technique termed enhancedcoagulation. Enhanced coagulation can be achieved by increasing the coagulantdose, lowering the pH of coagulation or a combination of the two. Increasing thecoagulant dose typically results in the formation of greater quantities of flocswhich incorporate NOM and remove them through settling and filtration. On theother hand, lowering the pH of coagulation results in better chargeneutralization which increases the rate of incorporation of NOM into thesettleable and filterable flocs. Although both of these techniques may adequatelyremove NOM to satisfy the enhanced coagulation requirement, the latter methodwill generate smaller quantities of sludge and is preferable for some utilities.Utilities which practice enhanced coagulation by lowering the pH of coagulation,typically uses a mineral acid (e.g., sulfuric acid) for pH reduction. Analternative to the mineral acid for pH adjustment is the use of carbon dioxide.Carbon dioxide is commonly used in softening plants to perform recarbonationafter the softening process. It has recently been used as a means for pHreduction for enhanced coagulation at the City of Chandler, Arizona. This paperpresents various design and operational considerations for a carbon dioxidesystem for enhanced coagulation purposes. Includes tables, figures.

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Edition: Vol. - No. Published: 01/01/1999 Number of Pages: 9File Size: 1 file , 760 KB