AWWA ACE94197

Several bench scale studies were undertaken to evaluate the effectiveness of enhanced coagulation in controlling chlorination byproducts and to assess the impact of coagulation pH preadjustment on TOC removal and plant operations cost. The tests were conducted on a variety of surface water sources, including a blend of the Trinity River water and Lake Houston water, Texas, the Sacramento River, California, the Mississippi River in Minneapolis, Minnesota, the Big Sioux River, South Dakota, the Weiser River, Idaho and the Missouri River in Kansas City, Kansas. The TOC of the water sources ranged from 2.0 to 11.0 mg/l. The results of the studies showed that an iron based coagulant such as ferric chloride, was consistently more effective than alum in removing natural organic matter (NOM). Coagulation pH appeared to be a determining factor for maximum NOM removal, when ferric chloride was used as a primary coagulant. Typically, preadjustment of pH at a value of 6.0 plus or minus 0.2 increased NOM overall removal to as much as 65 percent, and reduced the coagulant dose by up to 60 percent. Enhanced coagulation led to higher overall operating costs; however, preadjustment of pH with sulfuric acid reduced costs by reducing coagulant dose as well as sludge production. In all cases, enhanced coagulation with pH adjustments achieved the percent TOC reductions outlined in the proposed D/DBP Rule as a function of the raw water initial TOC and alkalinity. In most cases, enhanced coagulation was also a viable technique to reduce DBP formation potential below the MCLs proposed in the D/DBP Rule.