Phosphorus Removal Using Cu-Fe/SAC Particle Reactor

[Objective] High phosphorus loads caused by rainfall runoff are a major source of phosphorus exceedances in rivers, lakes, and reservoirs. While many researchers have studied phosphorus removal using three-dimensional electrode electrocoagulation, such studies are limited to simulated or domestic wastewater and suffer from long processing times. This study proposes a phosphorus removal technology using a Cu-Fe/sodium silicate-alginate carbon microsphere (Cu-Fe/SAC) particle reactor. Taking combined sewer runoff from the Huandi River as the research object, the study explains the phosphorus removal mechanism of the particle reactor through optimization of operational parameters and validation experiments, providing a new approach for rapid phosphorus removal from high-impact rainwater-sewage mixtures. [Methods] The Cu-Fe/SAC material was characterized using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and X-ray Diffraction (XRD) for morphology, while pore size distribution was determined by Discrete Fourier Transform (DFT). The experimental setup of the particle reactor was innovatively equipped with key components such as micro-nano aeration membranes and a pulse power supply. Using simulated wastewater, the study investigated phosphorus removal efficiency under different current densities, Cu-Fe/SAC filling amounts, and micro-nano aeration intensities. It also compared the phosphorus removal performance of different reactors under optimal conditions and validated the performance of the particle reactor on actual rain-sewage mixtures under optimal conditions. [Results] Characterization and pore distribution results indicated that Cu-Fe/SAC has a high specific surface area and moderate average pore size, with copper and iron uniformly loaded onto the SAC carbon microspheres as an alloy. Phosphorus removal experiments with simulated wastewater showed that the optimal conditions for the particle reactor were: current density of 5 mA/cm2, Cu-Fe/SAC filling amount of 12 g/L,and aeration intensity of 120 mL/min. Under these optimal conditions, after the same reaction time, the phosphorus removal efficiencies of three electrochemical devices ranked as: Cu-Fe/SAC particle reactor > three-dimensional electrode electrocoagulation (with SAC particle electrodes) > two-dimensional electrode electrocoagulation. Furthermore, validation experiments with actual rain-sewage mixtures showed that under optimal conditions and 30 minutes of reaction, the reactor achieved a total phosphorus (TP) removal rate of 90.6%. [Conclusions] The Cu-Fe/SAC microspheres developed in this study demonstrate excellent surface morphology, pore structure, and electrical conductivity, which enhance the efficiency of pollutant contact-adsorption and electron transfer. Using Cu-Fe/SAC as particle electrodes, the particle reactor achieves optimal phosphorus removal conditions, and under these optimal conditions, after 30 minutes of treatment, the total phosphorus (TP) removal rate in rain-sewage is verified, and the treated water meets the Class III water quality standard for surface water (GB 3838—2002). The phosphorus removal mechanism involves: under an alternating electric field, polarized particle electrodes first enrich and immobilize low-concentration phosphate ions via electro-adsorption, forming particulate phosphorus; then, during electro-desorption, the phosphates are released into the solution at high concentrations and, assisted by micro-nano aeration, rapidly react with precipitated high-concentration metal ions (Fe2+, Fe3+, and Cu2+), forming phosphate precipitates and thus achieving high-efficiency phosphorus removal.