Enhanced coagulation: its effect on NOM removal and chemical costs

Coagulation pH appeared to be a determining factor for maximum NOM removal. Several bench‐scale studies were conducted to evaluate the effectiveness of enhanced coagulation for controlling chlorination by‐products and to assess the impace of coaqulation pH preadjustment on total organic carbon (TOC) removal and plant operating costs. Tests were conducted on a variety of surface water sources with TOC values ranging from 2 to 1 mg/L. An iron‐based coagulant, such as ferric chloride, was consisitently 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 ± 0.2 increased NOM overall removal to as much as 65 percent and reduced the coagulant dose by as much as 60 precent. Enhanced coagulation led to higher overall operating costs, but preadjustment of pH with sulfuric acid reduced costs, by lowering the coagulant dosage as well as sludge production.