In-situ power generation and nutrients recovery from waste activated sludge – Long-term performance and system optimization

This study reports an integrated sludge treatment and resource recovery system that consisted of a sludge pre-treatment reactor and a microbial fuel cell (MFC) aiming for simultaneous energy and nutrients recovery. Nearly one year performance of the system in terms of power generation, nutrients removal efficiency, key dissolved organic matters (DOMs) transformation and microbial community change were investigated and reported. Volatile fatty acids (VFAs) and other soluble organic matters was produced from fermentation of waste activated sludge under thermophilic alkaline condition. Fermented liquor (FL) was used as feed for MFC, which produced maximum voltage of 0.477 V and power density of 8.07 W m⁻³. Humic-like substances (HSs) were removed by 48.27% within a 5 days cycle. The analysis on DOMs transformation revealed both high and low molecular weight protein and polysaccharides, and HSs were converted and contributed to power generation. Some unknown compounds in FL could enhance the power generation by 5.5 times more compared to pure VFA as feed. 90.59% of ammonium was removed with majority concentrated in the cathode. Phosphorus was removed and stored in the biomass in the form of polyphosphate (poly-P). Microbial community analysis indicated that Exoelectrogenic was the dominant community while Aquamicrobium, Nitrosomonas, Achromobacter and Rhodocyclaceae were also enriched in the anode. This work demonstrates that the integrated system can successfully remove and recover nutrients and generate power simultaneously with long-term stable performance.