Heterogeneous electro-Fenton treatment of coking wastewater using Fe/AC/Ni cathode: optimization of electrode and reactor organic loading.

A self-developed iron-loaded activated carbon-based nickel foam electrode (Fe/AC/Ni cathode) was used to construct electro-Fenton reaction system to treat coking wastewater. To meet the gap between laboratory beaker experiments and field trials for practical applications, we proposed and validated a method for obtaining organic loads, the essential parameters used in the design of electrochemical systems for wastewater treatment. The three influencing factors most relevant to organic loading, the effective surface area of cathode, chemical oxygen demand (COD) concentration of influent, and treatment time, were selected and investigated for their effects on the COD removal rate of coking wastewater by single-factor experiments and further optimized by response surface method. The appropriate electrode area load (La) and reactor volume load (Lv) were calculated by their corresponding intrinsic relationships with the three factors. The optimum application conditions were effective surface area of cathode 28.5 cm2, COD concentration of influent 1.76 kg·m-3, and treatment time 160.43 min. Under these conditions, the maximum COD removal rate was 98.51%. The La and Lv were 8.905 mgCOD·cm-2·h-1 and 0.634 kgCOD·m-3·h-1, respectively. The characterization experiment results showed that the Fe/AC/Ni cathode had a significant effect on the treatment of refractory organic contaminants in coking wastewater.

Preparation of Fe-loaded needle coke particle electrodes and utilisation in three-dimensional electro-Fenton oxidation of coking wastewater.

Novel iron-loaded needle coke spherical electrodes were fabricated for the first time using the sintering method. With DSA as the anode, nickel foam as the cathode and the spherical electrodes as the particle electrodes, a three-dimensional (3D) electro-Fenton system was constructed to treat coking wastewater. Using the chemical oxygen demand (COD) removal efficiency of coking wastewater as an indicator of electrode performance, the optimal conditions for particle electrode preparation were determined by single-factor experiments as consisting of a 4:1 catalyst-to-binder ratio, Fe2+ loading for the preparation of the particle electrodes of 2.5%, a particle size of 5.5 ± 0.5 mm, and a sintering temperature of 400 °C. Response surface methodology was applied to model and optimise the 3D electro-Fenton process for treating coking wastewater. Under the optimal conditions of an electrode spacing of 5 cm, applied voltage of 11.15 V, initial pH of 2.62, and particle electrode dosing of 12.23 g L-1, the removal rates of COD, NH3-N, NO3--N, total nitrogen, colour, and UV254 were 87.5%, 100%, 72.2%, 84.8%, 95%, and 72.4%, respectively. Spectral analysis revealed that the 3D electro-Fenton system strongly degraded coking wastewater, causing decomposition of large molecules of organic compounds and residuals primarily consisting of olefins and alkanes. Because the prepared particle electrodes exhibited stable physical and chemical structure, they have great potential for engineering applications due to their resistance to water flow erosion, stable catalytic reaction activity, and reusability.

Treatment of landfill leachate evaporation concentrate by a modified electro-Fenton method.

Landfill leachate evaporation concentrate (LLEC) is difficult to treat due to its complex pollutant composition, which involves large amount of organic matter and inorganic salts such as scaling ions. Because of its high conductivity and high chloride-ion content, this study employed the modified electro-Fenton method with a self-developed iron-loaded cathode to treat LLEC wastewater. The operating variables were optimized according to the response surface methodology where the chemical oxygen demand (COD) removal efficiency was considered as the response based on single-factor experiments. A second-order polynomial regression model was obtained, and an application experiment revealed that it could be applied to determine LLEC treatment conditions. The removal rates of COD and colour were 100% and 99.8%, respectively, under the optimal operating conditions of an initial pH of 6, electrode spacing of 1 cm and applied voltage of 9 V. Three-dimensional fluorescence spectroscopy demonstrated that the humic acid and fulvic acid pollutants were almost completely removed. Scanning electron microscopy and energy dispersive spectroscopy analysis showed that the iron catalyst was loaded in activated carbon pores and exhibited almost no consumption during the reaction, which effectively solved the problem of iron sludge precipitation caused by electro-Fenton oxidation technology. The atomic distribution in the crystal was also analyzed by X-ray diffraction. The specific energy consumption of electrochemical oxidation was 0.498 Wh·mg-1 COD. The results indicate that the modified electro-Fenton technique with the proposed novel cathode is an effective method for treating LLEC.

Study on anti-scaling of landfill leachate treated by evaporation method.

In the mechanical vapor recompression (MVR) treatment of landfill leachate, scaling in the evaporator and heat exchanger poses a serious problem. This study explored the reasons for such scaling and proposed acid or ion-exchange pre-treatments to reduce the alkalinity of the landfill leachate nanofiltration concentrate (LLNC) to prevent scaling. The feasibility of these two methods was evaluated and the technical and economic parameters for application were obtained via experiments. A large amount of HCO3- in the LLNC was the main cause of scaling. The acid addition experiment and field application demonstrated that this method could prevent fouling problems. The cost of acid addition was USD 0.18/t. LLNC pre-treatment by ion-exchange showed that a weakly acidic cation-exchange resin performed better than a strongly acidic cation-exchange resin did. The amount of solid residue under an alkalinity of 0 mg/L could be decreased by 92.9% compared with that of raw LLNC during evaporation. Both methods could alleviate scaling and enable the wide application of the MVR evaporation process in landfill leachate treatment.