Electrochemical generation of high strength magnetite nanoparticles (MNP) for sulfide and phosphate removal in domestic wastewater

The impact of various hydraulic retention time and increasing target MNP-Fe concentration on the efficiency of MNP electrochemical generation, process stability, power requirements, and product characteristics were investigated. The results revealed that it is possible to electrochemically generate MNP up to 58.9 ± 0.6 g L −1 MNP-Fe at high Coulombic efficiencies of 97.0 ± 1.7% to 99.0 ± 0.4% at stable electrochemical cell performance and low power requirements (≤ 2.5 ± 0.1 V). Consequently, practical application of the electrochemically generated MNP was demonstrated for removal of sulfide and phosphate from domestic wastewater. MNP were found to effectively decrease sulfide concentration (by 7.2 ± 0.1 mg L −1 S) at a removal capacity of 0.30 g S/g MNP Fe. Very low sulfide concentration of 0.1 ± 0.0 mg L −1 S was achieved at a removal capacity of 0.17 g S/g MNP Fe. Preferential removal of sulfide was observed in the presence of both sulfide and phosphate. In the absence of sulfide, phosphate concentration decreased (by 13.6 ± 0.1 mg L −1 P) at a removal capacity of 190 mg P/g MNP Fe. Very low phosphate concentration of 0.05 ± 0.0 mg L −1 P was achieved at a removal capacity of 120 mg P/g MNP Fe. Finally, the in-sewer dosed sulfide loaded MNP was aerobically regenerated and beneficially reused for phosphate removal (by 21.1 ± 0.6 mg L −1 P) in downstream activated sludge tanks at a removal capacity of 170 mg P/g MNP-Fe.