Powdered Activated Carbon feed study on a 1.5 MGD conventional surface water treatment plant for Big Creek Utility District

Powdered Activated Carbon (PAC) is utilized by Big Creek Utility District (BCUD) to aid in the reduction of Total Organic Carbons (TOCs) at the Utility's Water Treatment Plant. BCUD's source is an approximate 75 acre lake with an approximate 1,500 acre drainage area in the upper reaches of Ranger Creek in the Cumberland River Basin, located near the Coalmont community of Grundy County, Tennessee. This study used a comparative analysis of historical and monitored data over a varied PAC feed range of 1-2 mg/L up to 25 mg/L at the flash mix within the treatment system along with trended comparisons of PAC dosage with other treatment chemicals. Raw and finished water characteristics were analyzed to determine effectiveness in the reduction of TOCs. BCUD has consistently low raw TOCs generally between 1.5-3 mg/L and low alkalinity. The pH remains fairly consistent in the 6.2-6.5 range unless heavy rain events upset the source. Hardness is generally due to manganese, and permanganate is fed as a preoxidant to combat the manganese.;A reduction of TOC's decreases available Natural Organic Material (NOM) which are considered precursors that may react with disinfectants used in the water treatment process and reduce potential Disinfection Byproducts (DBPs). The Stage 1 and Stage 2 Disinfectants and Disinfection Byproducts Rule(s) set maximum contaminant levels (MCLs) for Trihalomethanes (THMs) at 0.080 mg/L and Haloacetic acids (HAA5s) at 0.060 mg/L.;The findings of this study identify a minimum PAC feed dosage of 11-12 mg/L in order to consistently meet the 35% TOC reduction with the BCUD existing system. Trends within the analyzed data clearly show a correlation to TOC reductions to an increased PAC feed dosage. Analysis of the THM data provided trended correlations between reduced TOCs and THMs, with seasonal anomalies noted in warmer seasons. The analysis of the HAA5s data yield no discernable correlation to reduced TOCs. BCUD will continue to strive to control costs, improve service, while maintaining safe drinking water to the Utility's customers.