Optimization of the process of decreasing the filtration resistance of sewage sludge by thermal pretreatment: a case study for the Lviv WWTP

Abstract

The article presents the results of an experimental study of the effect of high-temperature thermal pretreatment on the specific resistance to filtration (SRF) of the sewage sludge (SS) from the Lviv wastewater treatment plant (WWTP), which is a combination of primary sludge and excess-activated sludge collected in primary sedimentation tanks. The kinetics of SRF reduction over time at temperatures of 140 − 150 °С are described by simple exponents, while at temperatures of 160 − 170 °С, they are described by modified two-parameter exponents. The study analyzed the dimensionless optimization function, which is the product of the final relative SRF of the sludge and the dimensionless time of thermal pretreatment. An optimal dimensionless thermal pretreatment time of 4.1 tr.0/2 was determined, and an empirical exponential equation for the time of SRF reduction by twice tr.0/2 was derived. Based on the analysis, it was found that the highest efficiency in reducing the SRF of Lviv WWTP SS occurs at a temperature of 170 °C and an optimal duration of thermal pretreatment of 55 min. HIGHLIGHTS Thermal pretreatment is an effective method for decreasing specific resistance to filtration (SRF) of sewage sludge (SS).; Two-parameter exponents are used as trendlines for SRF reduction during thermal pretreatment.; An optimization function is proposed for the thermal pretreatment of SS.; Optimal parameters for the thermal pretreatment of SS from the Lviv wastewater treatment plant are determined.;

Keywords

• dewaterability
• optimization parameter
• sewage sludge
• specific filtration resistance
• thermal pretreatment