The research of steady-state electrochemical kinetics of effective and selective conversion of total nitrogen to N2

Technological Parameters of Rotating Electrochemical and Electrobiological Disk Contactors Depending on the Effluent Quality Requirements

Soilless tomato cultivation wastewater, with typically low COD, high concentrations of phosphorus, and oxidized forms of nitrogen, may be effectively treated in a rotating electrochemical disk contactor (RECDC) and in a bioelectrochemical reactor (BER), such as a rotating electrobiological disk contactor (REBDC). The aim of this study was to determine the technological parameters of both reactors, i.e., electric current density (J) and hydraulic retention time (HRT), depending on the effluent quality requirements. The study was conducted with four one-stage RECDCs and with four one-stage REBDCs, at four hydraulic retention times, i.e., 4, 8, 12, and 24 h, and electric current densities of 0.63, 1.25, 2.50, 5.00, and 10.00 A/m2. It was demonstrated that soilless tomato cultivation wastewater could be effectively treated in electrochemical and electrobiological disk contactors, and then discharged to sewage system facilities. In a RECDC, the highest denitrification (53.4%) and dephosphatation (99.8%) performance was achieved at J = 10.0 A/m2 and HRT = 24 h. If the effluents are to be discharged to natural reservoirs, their effective treatment is only feasible in a REBDC. The bioelectrochemical disk contactor ensured over 90% dephosphatation effectiveness. At HRT = 24 h and all electric current densities studied, the concentrations of pollutants in the effluent met requirements set for industrial wastewater discharged into natural waters and the ground. By applying J = 2.5 A/m2 and HRT = 24 h in the REBDC, it was possible to achieve a phosphorus concentration below 3.0 mg P/L and concentrations of ammonia nitrogen and nitrites lower than the permissible levels for treated industrial wastewater introduced to waters and to the ground. Given the nitrate concentration (exceeding 30 mg N/L), an external carbon source is recommended to aid a treatment process that uses a technological system with a REBDC. Technological schemes were proposed for wastewater treatment plants (WWTPs) with a RECDC and a REBDC, for discharging treated wastewater to natural waters, the ground, and sewage systems.

Application of lead oxide electrodes in wastewater treatment: A review

Electrochemical oxidation (EO) based on hydroxyl radicals (·OH) generated on lead dioxide has become a typical advanced oxidation process (AOP). Titanium-based lead dioxide electrodes (PbO₂/Ti) play an increasingly important role in EO. To further improve the efficiency, the structure and properties of the lead dioxide active surface layer can be modified by doping transition metals, rare earth metals, nonmetals, etc. Here, we compare the common preparation methods of lead dioxide. The EO performance of lead dioxide in wastewater containing dyes, pesticides, drugs, landfill leachate, coal, petrochemicals, etc., is discussed along with their suitable operating conditions. Finally, the factors influencing the contaminant removal kinetics on lead dioxide are systematically analysed.

Electrochemical removal of nitrate from a Donnan dialysis waste stream

The objective of this work was to investigate electrochemical removal of nitrate from a high salinity waste stream generated by Donnan dialysis. Donnan dialysis for nitrate removal is a promising technique. It produces a distinctive composition of a high salinity waste stream of NaCl or Na₂SO₄ that requires a viable disposal method. The waste stream has the full anionic composition of contaminated groundwater, but the only cation is sodium. Experiments were conducted in a batch system setup. A copper cathode was chosen over brass, aluminum and graphite cathodes. A dimensionally stable anode (DSA), Ti/PbO₂, was selected over a Ti/Pt anode. Electrochemical denitrification of high salinity Donnan dialysis nitrate wastes was successfully achieved, with different behavior exhibited in high salinity NaCl solution than in high salinity Na₂SO₄ solution. NaCl inhibited nitrate removal at high salinities while Na₂SO₄ did not. The maximum removals after 4 h operation in the high salinity wastes were 69 and 87% for the NaCl and Na₂SO₄ solutions respectively.