Measuring Sludge Network Strength Using Rheology and Relation to Dewaterability, Filtration, and Thickening—Laboratory and Full-Scale Experiments

Researchers Ormeci and Abu-Orf used rheology; a fundamental character of sludge, to arrive at a standard protocol for measuring network strength in terms of energy required to break up the structure of a certain volume of sludge. A mathematical derivation showed that the area under the rheograms indicated energy dissipation within the sludge system, which was related to the network strength. The research described in this paper investigates the use of this protocol for measuring sludge network strength at different polymer doses and relates the results to filtration, thickening, and dewatering. Laboratory tests used anaerobically digested sludge and both capillary suction time and filtration tests to indicate dewaterability and filtration. Network strength measurements used a torque rheometer. At full scale, dose response testing was used to correlate the measured network strength of the conditioned sludge to both centrifugation and gravity belt thickening performance as indicated by solids output. Both laboratory and full-scale testing showed that the network strength could be used to identify the optimum polymer conditioning to achieve good water removal from the sludge. The network strength increased with increasing the polymer dose, however, within the optimum dose range, a "drop" in the network strength occurred. This paper also discusses how to use the sludge network strength information to achieve the desired dryness from a dewatering device, and ultimately automate conditioning and dewatering processes.