Replacement of Alum and PolyDADMAC with Natural Polymers—Turbidity Removal and Residuals Reduction Impacts

Natural polymers (derived from corn and tapioca starch) were evaluated as replacements for treatment with alum plus polyDADMAC at a midwestern US water treatment facility. Factors evaluated included settled water turbidity, residuals production, and thickening and dewatering characteristics of resulting clarifier residuals. The facility studied did not practice enhanced coagulation; therefore, removal of total organic carbon was not a project goal and was not evaluated. Settled water turbidity in bench‐scale testing with natural polymers was similar to or lower than with alum plus polyDADMAC. Residuals with natural polymer without alum were easier to thicken and dewater than residuals produced from alum plus polyDADMAC. Potential benefits of replacing alum plus polyDADMAC with natural polymers could include less metal content in residuals, residuals reduction, improved thickening and dewatering characteristics of residuals, and increased biodegradability of residuals (biodegradable cornstarch or tapioca starch replacing nonbiodegradable alum plus polyDADMAC), rendering the residuals suitable for disposal, discharge, or reuse applications not currently possible using alum plus polyDADMAC.