Effect of sludge conditioning by microbial fuel cell on electro-dewatering performance

Abstract

Electro-dewatering (EDW) is an efficient and energy-saving technology for deep dewatering of sludge. It is significantly influenced by the physicochemical properties (e.g., conductivity, pH and zeta potential) of sludge, which can be altered by conditioning. In this study, sludge conditioning by microbial fuel cell (MFC) was innovatively coupled with EDW. In a single-chamber MFC filled with municipal sludge, a maximum power density of 436 mW/m3 was achieved after a 5-day operation. Substantial changes in the physicochemical properties of the sludge were observed. Compared with raw sludge, the sludge subjected to 7-day MFC conditioning had higher liquid-phase conductivity (425 μS/cm vs. 301 μS/cm), higher pH (6.8 vs. 6.3) and a more negative zeta potential (−16.0 mV vs. −12.8 mV). These changes facilitated EDW. Generally, longer MFC conditioning time led to higher electric current, higher filtrate flow rate and less final moisture content during a 12-min constant-voltage (25 V) EDW process. The final sludge moisture content after EDW was 64.0 % without conditioning and 54.8 % with 7-day MFC conditioning. Although sludge EDW with longer MFC conditioning time required more energy, the dewatering efficiency was noticeably higher, making the process more economically beneficial. Seven days of MFC conditioning is the recommended scheme in this study due to its low Ksi (1.6 kWh·h/kgDS2) and the potential to generate ~0.0336 USD/ton dry solids as green energy revenue. The study has newly developed an MFC-EDW coupled process that recovers bioresources through electricity generation while MFC conditions the sludge to facilitate EDW simultaneously.