Effect of current density on groundwater arsenite removal performance using air cathode electrocoagulation

Naturally occurring arsenic enrichment in groundwater poses a huge threat to human health.Air cathode electrocoagulation(ACEC)has recently been proposed to enhance As(Ⅲ)oxidation and lower energy consumption.In this study,ACEC,EC/O_(2) and EC/N_(2) were evaluated with different current densities from 1 to 8 mA/cm^(2) to investigate the effect on As(Ⅲ)removal in different redox environments.Current density had no appreciable effect on arsenic removal efficiency given the same charge in ACEC because the concentration ratio of Fe/H2O_(2) under different current densities remained stable.However,in EC/O_(2) and EC/N_(2),As(Ⅲ)removal was inhibited at higher current densities(4–8 mA/cm^(2)),likely because more Fe(Ⅱ)competed with As(Ⅲ)for the oxidant,leading to less effective oxidation of As(Ⅲ).In all EC systems,the$OH units generated per power consumption reached the highest value at the lowest current density.Compared with other EC systems,the ACEC system showed lower energy consumption at all current densities due to the low energy consumption of the electrode reaction and more free radical generation.A lower current density saved more energy at the expense of time,showing the trade-off relationship between energy consumption and removal time.The operation costs for As(Ⅲ)removal under optimal conditions were calculated as 0.028$/m^(3) for ACEC,0.030$/m^(3) for EC/O_(2),and 0.085$/m^(3) for EC/N_(2)

Removal of refractory organics and heavy metals in landfill leachate concentrate by peroxi-coagulation process

Landfill leachate is a complex effluent and it is difficult to deal with. Electrochemical methods have been considered as a promising alternative technology for treatment of landfill leachate with refractory organic contaminants and heavy metals. Peroxi-coagulation(PC)process with iron anode and modified graphite felt cathode was developed for efficient landfill leachate concentrate treatment. Compared to electro-Fenton(EF) and electrocoagulation(EC) processes, the PC process was more cost-effective due to the combined action of·OH oxidation and iron hydroxides coagulation. A maximal TOC removal of 77.2% ± 1.4% was obtained after 360 min at initial p H = 5.0 and current density of 10 m A/cm^(2). After the PC process, concentrations of all seven heavy metals in the final effluents were below the allowable emission limits given by the present regulatory standards. The method preference for heavy metal removal was PC > EC > EF. Based on the three-dimensional fluorescence spectroscopy coupled with regional integration analysis during the PC treatment, the florescence peaks of both humic acids and fulvic acids disappeared after treatment for 360min. Decreasing trends were observed in the fluorescent regional standard volumes for aromatic protein Ⅰ(31.4%), aromatic protein Ⅱ(63.7%), fulvic acid-like(69.5%), soluble microbial by-product-like(75%) and humic acid-like regions(76.3%). The results indicate that comparing to the EF and EC process, the PC process provide a promising and more cost-effective alternative for the treatment of landfill leachate concentrate.