Thermo-Biological Modification of the Return Sludge Line to Reduce Excess Sludge in an Activated Sludge Process

This study investigates the application of a thermo-biological approach in the return sludge line of an activated sludge system to reduce excess sludge production and improve overall treatment performance. The effects of increasing the return sludge temperature on pollutant removal efficiency and sludge characteristics were evaluated under real operational conditions. This experimental-analytical study investigated the impact of thermal conditioning of return sludge on pollutant removal efficiency and excess sludge reduction in a full-scale activated sludge wastewater treatment system. Return sludge was heated to ۴۰ °C, ۵۰ °C, and ۶۰ °C, and the system's performance was monitored over ۶۰ days by measuring parameters such as Chemical Oxygen Demand (COD), Total Suspended Solids (TSS), Mixed Liquor Suspended Solids (MLSS), and Sludge Volume Index (SVI). All measurements adhered to APHA standards, and data were analyzed using Analysis of Variance (ANOVA) and descriptive statistics to determine the significance of the observed effects. Experimental results demonstrated that elevating the return sludge temperature to ۴۰°C significantly improved the removal efficiencies of TSS and COD, while also reducing the sludge yield coefficient and enhancing sludge settleability, as indicated by the SVI. Over a ۱۸۰-day operation period, excess sludge volume and weight were reduced by ۴۷.۰۵% and ۳۶.۰۷%, respectively, at ۴۰ °C. These reductions increased to ۵۶.۹۳% and ۶۲.۳۰% at ۵۰ °C, and to ۵۹.۹۲% and ۷۵.۴۱% at ۶۰ °C. However, effluent quality declined at temperatures above ۴۰°C, highlighting the trade-off between sludge reduction and treatment performance. The optimal operating condition was determined to be a return sludge temperature of ۴۰°C, with a cell retention time of ۲۵ days and a hydraulic retention time of ۲۰ hours, offering the best balance between sludge reduction and effluent quality.

کلیدواژه ها:

Activated sludge ، Anoxic holding tank ، Effluent quality ، Excess sludge reduction ، Return sludge treatment ، Thermal conditioning