Study on removal of phosphorus and COD in wastewater by sinusoidal AC Fenton oxidation-coagulation.

In order to treat domestic wastewater containing phosphorus and chemical oxygen demand (COD), the new technology of Sinusoidal Alternating Current (AC) Fenton Oxidation-Coagulation (SACFOC) was used to improve the removal efficiency (Re) and reduce energy consumption (EEC). The morphology, elemental composition, crystal structure and functional groups of the sludge were characterised by Scanning Electron Microscope (SEM), Energy-dispersive X-ray Spectroscopy (EDS), X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The results show that total phosphorus removal efficiency {Re(TP)} and removal efficiency of organic matter {Re(COD)} can reach 97.56% and 87.77%, respectively, but EEC is only 0.09 kWh·m-3 under the optimum conditions of pH0 = 3, current density (j) = 0.5 A·m-2, c0(TP) = 18 mg·dm-3, c0(COD) = 300 mg·dm-3, c0(H2O2) = 0.06 mol·dm-3, t = 45 min. As compared with direct current (DC) Fenton Oxidation-Coagulation (DCFOC), the COD removal efficiency of SACFOC treatment was improved by 37%, but the energy consumption was reduced by 45%. The degradation process of total phosphorus and COD by SACFOC abides by the quasi-first-order kinetic model. The process of SACFOC includes double effects of electrocoagulation of iron sol by electrolysis and degrade COD by oxidation of formed hydroxyl radicals (·OH) in wastewater, which improves removal efficiency of total phosphorus and COD in wastewater. Our research findings will provide technical guidance and a theoretical basis for the simultaneous treatment of wastewater containing phosphorus and COD applying SACFOC process.

Removal of phosphorus in wastewater by sinusoidal alternating current coagulation: performance and mechanism.

The effects of initial total phosphorus (TP) concentration, current density, conductivity and initial pH value on the removal rate of TP and energy consumption, as well as the behaviour and mechanism of phosphorus removal, were investigated by sinusoidal alternating current coagulation (SACC). The flocs produced by SACC were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy FTIR and X-ray photo electron spectroscopy. The thermodynamic and kinetic behaviours of phosphorus removal by iron sol adsorption were also studied in detail. In a self-made SACC reactor equipped with five sets of parallel iron electrodes spacing 10 mm, the removal rate of TP reached 90.9% for a pH 7.0 wastewater with 5 mg dm-3 TP (κ = 800 µS cm-1) after being treated for 60 min by applying 2.12 mA cm-2 sinusoidal alternating current. Compared with direct current coagulation (DCC), SACC exhibits a higher removal efficiency of phosphorus due to the stronger adsorption of the produced flocs. It was found that the adsorption in the SACC process follows pseudo-second-order kinetic with the involvement of the intra-particle model. The adsorption of iron sol to phosphorus was an endothermic and spontaneous process, and its adsorption behaviour can be characterized with Langmuir and Redlich-Peterson isothermal adsorption models. SACC may be employed for the treatment of more complex wastewater combined with biological and/or electrochemical techniques.