In this study, a three-dimensional electrochemical oxidation system, with steel slags as particle electrodes, was applied to deal with landfill leachate. The characteristics of particle electrodes were investigated by scanning electron microscope (SEM), X-ray fluorescence spectroscopy (XRF) and X-ray diffraction (XRD) measurements. It was found that the steel slag exhibited rough and irregular surface and mainly consisted of SiO₂ (Quartz), which indicated the enhanced absorbed and electroconducted abilities. Subsequently, comparative degradation tests between two-dimensional (2D) and three-dimensional (3D) electrochemical oxidation systems were carried out and results indicated removal efficiencies of COD. Moreover, NH₄⁺-N from landfill leachate in 3D system was greatly improved compared with that of 2D system. Besides, operating conditions were also optimized to interelectrode distance of 1 cm, current density of 20 mA·cm⁻², initial pH value of 4.4 and steel slag concentration of 0.30 g·mL⁻¹, all of which were determined to guarantee excellent landfill leachate removal efficiency. In addition, a possible removal mechanism for this system was proposed. The introduction of steel slag particle electrodes in three-dimensional electrochemical oxidation system implied the concept for “using waste to treat waste”, providing a workable way in pollutant elimination.

Temperature is an important factor influencing the treatment effect of biological aerated filters (BAFs). In this study, BAFs incorporating biological manganese oxides (BMOs) were used to treat micro-polluted source water containing organic masses and ammonia, and the influence of temperature on the removal efficiency of the pollutants was investigated. The results showed that after the formation of biogenic manganese oxides (BMOs) in the filter layer, the removal efficiency of CODMn significantly improved. When the water temperature was approximately 24 °C, 16 °C, and 6~8 °C, the removal rates of COD_Mn, ammonia, and manganese were 60.64, 42.55, and 20.48; 98.40, 95.58, and 85.04; and 98.70, 97.63, and 96.38%, respectively. The influence of water temperature on the removal efficiency of the pollutants was hierarchically structured as follows: COD_Mn > ammonia > manganese. Analysis of the removal efficiencies of the pollutants along the filter layer showed that COD_Mn had been eliminated in every filtration layer, and ammonia and manganese were mainly removed in the 0~0.4 m and 0~0.8 m regions of the filter layer, respectively. With a decreasing water temperature, the concentrations of COD_Mn, ammonia, and manganese along the filter layer increased. The biological COD_Mn, manganese, and ammonia removal processes were all first-order kinetic reactions. With a decreasing water temperature, the kinetic constant k gradually decreased, and the reaction half-life (t_1/2) gradually increased.

In order to improve the removal efficiency of refractory organic matters in micro-polluted source water, biological manganese oxides (BMOs) were generated in situ in the biological aerated filter (BAF) (BAF 2^#), which could oxidize the refractory organic matters into biodegradable organic matters. COD_Mn and NH₄⁺-N in the effluent of BAF 2^# both stabilized on the 39th day, while COD_Mn and NH₄⁺-N in the effluent of the control BAF (BAF 1^#) stabilized on the 38th and 42nd days, respectively. In the steady phase, the removal rates of COD_Mn and NH₄⁺-N in BAF 1^# were 41.51% and 94.79%, respectively, while in BAF 2^#, they were 54.52% and 95.55%, respectively. BMOs generated in BAF 2^# evidently improved the efficiency of COD_Mn removal. With the increase in the influent Mn²⁺ in BAF 2^#, the rate of COD_Mn removal was gradually improved to 63.60%, while the efficiency of NH₄⁺-N removal was slightly improved, COD_Mn was evidently removed in each section of the filter layer, and ammonia was mainly removed in the 0~0.8 m layer of the filter. COD_Mn was evidently removed in each section of the filter layer, and NH₄⁺-N was mainly removed in the 0~0.8 m layers of the filter. Biological COD_Mn, Mn²⁺, and NH₄⁺-N removal all followed the first-order kinetic reaction. As the influent Mn²⁺ gradually increased from 0 to about 0.5, 1, and 2 mg/L, the efficiency of COD_Mn removal along the filter layer was significantly improved, but the efficiency of NH₄⁺-N removal was slightly improved. The kinetic constant k of biological COD_Mn removal significantly increased, while the kinetic constant k of biological Mn²⁺ and NH₄⁺-N removal gradually increased.

Nitrite produced during ammonia oxidation can inhibit the activity of microorganisms. To provide guidance for the optimization and design of a biofilter, a pilot-scale biofilter was established to investigate the influence of nitrite on organic matter and manganese removal and on the kinetics. The results demonstrated that COD_Mn, ammonia, and manganese in effluent were 2.77, 0.034, and 0.026 mg/L in the steady phase, respectively. Organic matter and manganese removal were affected by nitrite during the start-up process, as well as in the ammonia increasing process. When ammonia increased from about 0.5 to 1 and 2 mg/L, organic matter, and manganese removal were affected at 4 and 3 days and 6 and 5 days, respectively. When organic matter, ammonia, and manganese in the influent were 6.27, 2.07, and 1.19 mg/L, respectively, organic matter, ammonia, and manganese oxidation all followed a first-order kinetic rate. The k-value was 0.0268, 0.268, and 0.216 min⁻¹, and the half-life time was 24.236, 2.583, and 3.202 min, respectively. The influence of nitrite on the structure of microbial communities in the biofilter will be investigated in the future.

Sulfamethazine (SMT) contamination in aquatic environments and its propensity to induce antibiotic resistance pose critical risks to ecosystems and public health, necessitating effective remediation strategies. Here, we develop a MOF-derived copper core–shell activator, Cu-MOFs400@PSN, by coating a calcined Cu-MOF derivative (Cu-MOFs400) with a nitrogen/phosphorus/sulfur-doped shell and systematically evaluate its peroxymonosulfate (PMS) activation performance toward SMT degradation. Comprehensive characterization confirms successful N/P/S incorporation and the formation of a smooth spherical core–shell architecture that enhances chemical stability; the Cu-MOFs400@PSN/PMS system achieves complete SMT removal within 120 min and maintains 99.33% efficiency after five reuse cycles. Bicarbonate markedly promotes degradation, whereas chloride, nitrate, and phosphate exert negligible interference, indicating strong tolerance to common background ions. Radical-quenching tests identify singlet oxygen (¹O₂) and superoxide (•O₂⁻) as the dominant reactive species, with minor contributions from sulfate and hydroxyl radicals; the system facilitates complete SMT mineralization and reduces resistance-inducing intermediates. These results highlight Cu-MOFs400@PSN as a robust and reusable PMS activator for practical remediation of SMT-contaminated waters and mitigation of antibiotic-resistance risks.