Dual Polymer Conditioning of Water Treatment Residuals

Conditioning of either wastewater biosolids or water treatment residuals conventionally utilizes a single polymer to improve subsequent dewatering. The sequential addition of two polymers has been reported to enhance biosolids dewaterability, but comparable benefits have not been demonstrated for water treatment residuals. This paper evaluated the use of cationic and nonionic polymers, singly and in combination (dual), to investigate whether dual polymer conditioning of residuals offers any advantages, and to determine whether the results could be accommodated by current mechanistic understandings. For this purpose, lab-scale tests used capillary suction time (CST), supernatant viscosity, zeta potential, streaming current, turbidity, floc size, and rheometric analyses. Comparisons of CST and viscosity results for single and dual polymer additions indicated that dual polymer use gave moderately improved dewaterability, possibly due to the increased mixing utilized for dual polymer addition. Using a cationic polymer produced a less turbid supernatant. Zeta potential and streaming current were not good indicators of conditioning efficacy when a nonionic polymer was used. Rheometric analyses were only meaningful in one selected method for treatment of the data: the area under the rheogram up to a shear rate of 30?inverse?s. Overall, implementation of dual polymer use does not appear warranted.