Removal of nitrogen and phosphorus from sediment and overlying water by double electrolytic-driven remediation and its effect on microbial community structure in sediment

To test the effect of electrolysis and microbial remediation technology in polluted river sediment, we explored the possibility of using electrolysis method to remove ammoniacal nitrogen–nitrogen (NH3–N), nitrate-nitrogen (NO3––N) and phosphate ions-phosphorous (PO43−–P). The electrolysis was carried out by double electrolysis reaction system with a pair of a titanium (Ti) mesh cathode, a Ti/Ti dioxide (TiO2)/Ruthenium (IV) oxide (RuO2) (RuO2–IrO2/Ti) mesh anode, and another pair of magnesium–aluminum (Mg–Al) alloy anode and a titanium mesh cathode placed within the sediment and overlying water. Results showed approximately 151.82 ± 21.69 mg total nitrogen (TN) in sediment was removed, which was five times than the non-electrolytic controls (30.21 ± 13.73 mg). Furthermore, NH3–N concentration in the sediment was substantially reduced (up to 2.9 times) compared to the non-electrolytic controls. Its efficiency lies in the electrolysis process, which may directly remove NH3–N through electrochemical oxidation and simultaneously produce oxygen which helps nitrifying bacteria to convert NH3–N into an NO3−–N by anode; moreover, electrolysis may directly remove NO3−–N in the overlying water through electrochemical reduction while simultaneously producing hydrogen electron donors for hydrogen autotrophic microorganisms, such as Hydrogenophohaga. This genus of hydrogen autotrophic denitrifying bacteria dominated the removal of NO3−–N by a cathode in electrolytic sediment. Electrolysis also reduced the PO43−–P through electro-coagulation since Mg2+ ions also produced a sacrificial Mg–Al alloy anode. This anode was used in conjunction with electro-deposition on a Ti mesh cathode to increase PO43−-P removal in the overlying water and sediment. This study verifies the benefits of electrolysis-driven bioremediation as a sustainable technology for the bioremediation of N and P polluted river sediment.