Optimization of Gravity Belt Thickener Performance – A Comprehensive Full-Scale Study

Gravity belt thickeners (GBT) have been widely applied to thicken secondary waste sludge and primary sludge at wastewater treatment facilities. However, because of varying sludge characteristics and applied polymer type, GBT performance can be different from one facility to another. In this paper, a comprehensive test was conducted on the newly installed GBT process at the City of Indianapolis' Belmont Wastewater Treatment Facility. Several process parameters, i.e. GBT feed rate, polymer dose rate, and belt speed, were examined systematically in the study. It was found that GBTs are able to achieve the highest cake with a dosage of about 50 kg/Dton (or 2.25 kg/Dton active polymer) regardless of sludge feed rates. Polymer dosage higher than 50 kg/Dton will result in polymer waste and/or even cake solids decrease. In addition, the study also shows that low belt speeds, 0.1 m/s to 0.17 m/s, contribute to producing a higher cake for the sludge feed rates lower than 1,701 L/min. However, a higher belt speed, up to 0.33 m/s, favors the high sludge feed rates over 1,890 L/min.