Sludge degradation and microbial community structures analysis in a microbial electrolysis cell-coupled up flow anaerobic blanket reactor with an ultrasound treatment system

Abstract

This study proposed a sludge degradation system comprised of: (i) an ultrasound treatment (UT) system to disintegrate sludge; (ii) an up flow anaerobic sludge blanket (UASB) reactor to degrade the disintegrated sludge; and (iii) a microbial electrolysis cell (MEC) in replacement of a three-phase UASB separator to deeply degrade the disintegrated sludge. The influence of the ultrasound power, the temperature, and the voltage on the sludge degradation process was discussed. The experimental results showed that the UT unit effectively promoted sludge disintegration, thereby leading to deterioration of the quality of the reactor effluent. The temperature and the voltage parameters were found to be key for the anaerobic degradation (AD) process within this system. The volatile suspended solid concentration in the effluent was maintained at 320–380 mg L⁻¹ (ca. 0.08 times the raw sludge concentration), thereby validating the utilization of MEC as a three-phase separation unit. The total chemical oxygen demand removal was maintained at 61.3% during 5 days of AD upon intermittent exposure of the sludge to the UT unit, thereby showing that the system can effectively degrade solid organic matter. The bacterial community structure of the raw sludge significantly changed, with the high biodiversity of this system increasing the ecological stability. This system can degrade sludge with high efficiency and could be used in further engineering applications.