WERF: USING RHEOLOGY FOR MEASURING COMPARATIVE RESIDUALS NETWORK STRENGTH AND ITS RELATION TO DEWATERABILITY

The ability to measure floc strength is important in wastewater residuals and biosolids treatment and processing applications. Previous research has focused on measuring sludge floc strength indirectly through measuring other parameters such as floc size, floc density, and dewaterability of residuals. Direct measurements of floc strength as reported in the literature are not applicable to residuals, especially if conditioned prior to dewatering. In this research we will refer to raw or conditioned residuals suspension as “network” and thus measurements will indicate the network strength, which is important in dewaterability applications.This paper summarizes some of the results from a sixteen-months WERF Emerging Technology project that started January 2002. The research used rheology to arrive at a standard protocol to measure residuals network's strength in terms of energy dissipated in a given volume of a suspension. Another objective of this research is to correlate the network strength to the conditioning and dewaterability and study the factors affecting the network strength. Highlights form this project include:A mathematical model for determining biosolids floc or “network” strength using both torque and concentric rheometers has been developed;The reproducibility of the rheological measurements at the lab scale level was established;The correlation between the network strength and optimum polymer dose at the lab-scale level, where a “dip” in the network strength indicates the optimum polymer dose, was established;The “dip” in the network strength from full-scale centrifugation and gravity belt thickening of two different biosolids and residuals was also established; andThe major factors affecting the network strength (e.g., mixing conditions, rotational speed, polymer type) were studied.This paper addresses both the mathematical model for determining the network strength using rotational rheometers and the preliminary results showing the correlation between the network strength and the optimum polymer dose at the laboratory scale level only.