AWWA WQTC64163

A full-scale case study is presented where coagulation of water characterized by high totalorganic carbon (TOC) concentrations is optimized using measurements of zeta potential. Eachspring, snowmelt runoff water percolates through the forest floor of the Cache la Poudre River(Poudre River) watershed resulting in high TOC, low alkalinity water that must be treated by theCity of Fort Collins, Colorado, Water Treatment Facility (FCWTF). During the 2005 snowmeltrunoff period, the raw Poudre River TOC ranged up to 13 mg/L, with the TOC at or above 8mg/L for 23 days. The increased TOC is predominantly made up of humic substances thatcontrol the coagulant demand. Modification of the coagulation process to treat this water at theFCWTF consists of conditioning the raw water with a 30% lime slurry and carbon dioxide gasprior to alum addition in order to achieve a coagulated water pH within the range of 6.5 to 6.8.The rapidly changing water quality conditions that occur during the spring snowmelt runoffperiod require the operators to make rapid decisions about alum dose changes. During the 2005snowmelt runoff, the alum dose was adjusted to keep the zeta potential within the ¿¿¿¿ 3 mV rangeas the TOC rose to its peak and then descended back down towards its baseline value. A newgeneration of zeta potential instruments allows for frequent measurements of zeta potential thatare reliable and that are not user-dependent. The adjustment of the alum dose based on zetapotential resulted in the alum dose closely following the TOC, with the alum dose being adjustedby about 3.5 mg/L for each mg/L change in raw water TOC. While maintaining the postcoagulationtargets for pH and zeta potential, the full-scale process performance was evaluatedwith respect to the ability to meet the multiple goals of a combined filter effluent turbidity of lessthan 0.1 ntu, a TOC removal greater than 50%, and a residual aluminum less than 100 µg/L.The results of this full-scale case study showed that zeta potential measurements can besuccessfully used by plant operators as a key process control and optimization tool duringchallenging conditions of high TOC water, allowing them to meet their multiple plant effluentgoals. Includes 21 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2006

Number of Pages:

17

File Size:

1 file , 460 KB