Improving anaerobic digestion sludge properties via heterogeneous activation of peroxydisulfate by CuMgAl-layered double hydroxide

Abstract

Improving anaerobic digestion sludge (ADS) properties by conditioning technology is necessary for subsequent treatment and disposal. In this study, CuMgAl-layered double hydroxide (CuMgAl-LDH) was prepared by co-precipitation method and applied to activate peroxydisulfate (PDS) for ADS conditioning. Experimental results indicated that under the optimal treatment condition (0.15 g LDH/g TS and 0.2 g PDS/g TS addition), the water content of sludge cake and the time to filter decreased from initial 90.83 % to 82.91 % and 75 min to 39.5 min, respectively, and ortho-P as well as non-biodegradable organics contents in the AD liquor (ADL) also decreased remarkably, which was beneficial for ADS dewatering and subsequent ADL backflow treatment. CuMgAl-LDH activating PDS could produce abundant reactive oxygen species (ROS), resulting in microbial cell disruption, bound water release, sludge particle size decrease and non-biodegradable organics degradation. Mechanisms investigation based on the X-ray photoelectron spectroscopy, electron paramagnetic resonance and ROS quenching experiments results indicated that Cu(I)/Cu(II) redox cycle was responsible for PDS activation, and SO4−· made primary contribution to sludge flocs and cells disruption. This research provided preliminary guideline to design copper-based LDH/PDS system for ADS conditioning in wastewater treatment plants.