Electricity Enhances Biological Fe(III) Reduction and Phosphorus Recovery from FeP Complex: Proof of Concept and Kinetic Analysis

In wastewater treatment plants (WWTPs), it remains a challenge to remobilize and recover phosphorus from the insoluble FeP complex which is produced via iron-enhanced primary precipitation (IEPP). This study demonstrated that an electricity-enhanced biological reducing (EEBR) process can efficiently reduce Fe(III) into Fe(II) and release phosphorus from the FeP complex in the post-IEPP sludge. With a fixed potential of 0.35 V, the electroactive biofilm was enriched in the EEBR system and participated in the electron transfer chain for Fe(III) reduction. In the EEBR system, the highest phosphorus release efficiency was 61.6% with a final dissolved total phosphorus of 89.4 mg/L, which was ∼10 times that in a traditional biological system. Kinetic analysis was also conducted in this study, and the Fe(III) reduction in the EEBR system was estimated as a 2/3-order reaction. The overall mechanism was hypothesized to be that the electrons from the electrode were quickly transferred into the FeP complex by the biofilm, which finally reduced Fe(III) and released phosphorus ions. The proposed EEBR process was proved to be efficient, energy-wise, and sustainable, representing promising feasibility for phosphorus recovery from the IEPP sludge in the WWTPs.