Abstract
Ferric sludge pollution and unsustainable utilization of Fe(II) reagent were tough nuts to crack for homogeneous Fenton treatment. Previous Fe(II) regeneration methods are still limited by high reagent consumption or low regeneration rate. In this work, granular sludge was introduced into the biocathode of microbial electrolysis cell (MEC), to improve Fe(II)-regeneration rate from actual ferric sludge at near neutral pH. Wastewater constituents in the bioanode of dual-chamber MEC were used as the reducing power to regenerate Fe(II). In the flow-through biocathode, 175 ± 16 mg/L of dissolved Fe(II) was efficiently regenerated from actual ferric sludge. The regeneration rate of dissolved Fe(II) was 7.2 times higher than that of the previously reported biocathode. Besides, the actual and synthetic ferric sludge had a similar Fe(II) regeneration performance. Interestingly, recalcitrant organics and 20 mg/L NO3–N in ferric sludge were removed by 96% and 100% during Fe(II) regeneration. The biomass in the granular sludge biocathode was 12 times that of the control biocathode, in which Clostridium sensu stricto dominated. These findings provide insights and theoretical support for developing a viable biotechnology platform, to close the gap for the efficient and sustainable iron cycle.
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