AWWA ACE95199

The real reason for enhanced coagulation is to provide an optimum environment for coagulation so that the removal of total organic carbon (TOC) is maximized. This "enhanced" terminology is being expanded to include the optimization of Cryptosporidium as well. The compounds expressed as (TOC) are a wide array of naturally occurring organic matter (NOM) and synthetic organic chemicals (SOC) that will vary from site to site. Thus the protocol for the optimal removal will likewise vary. Coagulation is a critical step in minimizing the DBP (Disinfection Byproducts) formation. Not all compounds that can show up as TOC and are DBP precursors can be removed by activated carbon. Likewise a certain stubborn fraction will not "remove" through normal coagulation (charge neutralization and precipitate enmeshment) practices. The goal is choosing which coagulant and coagulation program will maximize the precursor removal and reduce the dependence on alternate disinfection or adsorption technology. This paper describes a study involving over thirty six municipalities and their incumbent coagulation programs versus opportunities for improvement. These water treatment systems are located on all types of water quality with wide ranges of TOC, color, turbidity, and alkalinity. An effort was made to encompass small and large plants, as well as a variety of treatment configurations. Chemical programs were considered. The majority of the subjects used alum and many of those used cationic polymers as coagulation adjuncts. Three plants used only cationic polymers (poly DADMAC). The rest of the subject utilities used either ferric chloride, ferric sulfate, polyaluminum hydroxychlorides (PACl) or polyaluminum chlorosulfates (PACS). The results revealed that corrosion considerations, pH adjustment expense, heavy metals in sludge and coagulant induced color play an important part in consideration of which coagulant is better for these specific cases. Often the optimum dosage window for iron based coagulants was much narrower for best TOC removal versus optimum turbidity removal. There was little indication of this affect in aluminum based coagulants although coagulant induced color is typically not a problem in aluminum based or polymeric coagulants.

Product Details

Published:

01/01/1995

ISBN(s):

0898678315

Number of Pages:

12

File Size:

1 file , 360 KB