Dewaterability and degradability of municipal wastewater sludge by electrooxidation/electrocoagulation (EOx/EC) and ultrasound-assisted electrooxidation/electrocoagulation(US/EOx/EC) processes: Determination of operational conditions.

In this study, the potential use of electrooxidation-electrocoagulation and ultrasound-assisted electrooxidation-electrocoagulation processes with hybrid electrodes to improve the dewaterability and degradability of active sludge was investigated. Effects of electrode type, current density, electrode connection mode, air injection flow rate, and electrode distance on sludge dewaterability and degradability were determined through measuring specific resistance to filtration (SRF), filtration time (s), degree of degradation (DD, %) and sludge moisture content (Mc, %). To determine the effects of the ultrasound-assisted electrochemical process, experiments were conducted in a different reactor under optimum conditions of the electrochemical process, constant frequency (40 kHz), and varying ultrasound powers (60–240 W). The experiments results showed that for all electrode materials, at high values of current density, the dewaterability of the sludge decreased while the degradability of the sludge increased. Besides, both filtration times and degree of degradation decreased with increasing air injection flow rates. Under the optimum operational conditions (TiPbO 2 -Fe-SS-SS hybrid electrode type, 100 A/m² current density, MP-P connection mode, 1 L/min air injection flow rate, 1 cm electrode distance, and 20 min operation time), SRF value decreased from 50 × 10¹² m/kg to 2.02 × 10¹² m/kg, filtration times decreased from 132 s to 9 s, DD value was observed as 20.2% and Mc value was observed as 42.3%. Under the optimum operational conditions of electrooxidation-electrocoagulation process, sludge DD values in the ultrasound-assisted electrooxidation-electrocoagulation process increased, but SFR values decreased. The structural change in the sludge after each process was determined by SEM analysis. [Display omitted] • Effects of combined EOx-EC, US-EOx-EC and only US processes on sludge were studied. • EOx-EC process was an effective method to dewaterability of sludge and reduced 99% specific resistance to filtration. • US-EOx-EC process improved both dewaterability and degradability of sludge. • Only US process was more effective to degradability of sludge and enhanced 32.3% degree of degradation. • The optimum operation parameters for treatment processes were determined. [ABSTRACT FROM AUTHOR]