Optimized Coagulation Assessment for a Highly Organic Surface Water Supply (PDF)

Jar‐test experiments were used to study optimized coagulation for removal of nonpurgeable dissolved organic carbon (NPDOC), color, and turbidity for highly organic surface water. The coagulants alum, polyaluminum chloride, ferric sulfate, and ferric chloride were capable of meeting the required Step 1 50% total organic carbon removal criteria. Disinfection byproduct precursor removal was a function of coagulant type, coagulant dose, and flocculation pH. Iron‐based coagulants were capable of 10% higher NPDOC removal than aluminum‐based coagulants. However, aluminum‐based coagulants generally provided higher color removal. Based on treatment performance, cost, and other factors, sulfate‐based coagulants—alum and ferric sulfate—were the overall coagulants of choice for this water. Additional testing with alum and ferric sulfate demonstrated the benefit of optimizing rapid and slow mix conditions, polymer selection, and solids addition for enhanced turbidity removal. The benefits of impounding raw river water in a surface water reservoir before treatment were also identified.