Efficient electrochemical generation of ferrate(VI) by iron coil anode imposed with square alternating current and treatment of antibiotics

Removal of microorganic pollutants in aquatic environment: The utilization of Fe(VI)

Microorganic pollutants (MOPs) in aquatic environment with low levels but high toxicity are harmful to ecosystem and human health. Fe(VI) has a dual-functional role in oxidation and coagulation, and can effectively remove MOPs, heavy metal, phosphate, particulates and colloids. Moreover, Fe(VI) can combine with traditional coagulants, or use as a pretreatment for membrane treatment because of its characters to generate nanoparticles by degradation in water. Based on the relevant toxicity experiments, Fe(VI) had been proved to be safe for the efficient treatment of MOPs. For better utilization of Fe(VI), its oxidation and coagulation mechanisms are summarized, and the knowledge about the control parameters, utilization methods, and toxicity effect for Fe(VI) application are reviewed in this paper. pH, different valences of iron, environmental substances, and other parameters are summarized in this study to clarify the important factors in the treatment of MOPs with Fe(VI). In the future study, aiming at cost reduction in Fe(VI) preparation, transportation and storage, enhancement of oxidation in the intermediate state, and better understanding the mechanism between interface and Fe(VI) oxidation will help promote the application of Fe(VI) in the removal of MOPs. This study offers guidelines for the application and development of Fe(VI) for the treatment of MOPs in aquatic environment.

Unveiling the mechanism of imidacloprid removal by ferrate(VI): Kinetics, role of oxidation and adsorption, reaction pathway and toxicity assessment

Imidacloprid (IMI), an emerging pollutant, has high toxicity to non-target organisms. This paper presents the kinetics of IMI removal by ferrate(VI) at different pH (6.0-9.0), molar ratios ([ferrate(VI)]:[IMI]) and added Fe(III) ions. The apparent second-order rate constant (k_app) decreased with increase in pH from pH 6.0 to 9.0 (i.e., (1.2 ± 0.1) × 10² M^-1 s^-1 to (8.3 ± 0.3) M^-1 s^-1). The species-specific rate constants were obtained as k (HFeO₄^-) = 1.3 × 10² M^-1 s^-1 and k (FeO₄^2-) = 6.9 M^-1 s^-1. The decreases in the concentration of HFeO₄^- with increase in pH caused the observed pH dependence in k_app. At pH 7.0, the removal of IMI increased with the molar ratio from 1.0 to 10.0 with complete removal at the highest ratio. The variation in pH from 6.0 to 9.0 had no obvious effect on removal of IMI. Experiments indicate that IMI removal is mainly by ferrate(VI) oxidation and to a lesser extent by Fe(III) adsorption. Mineralization of IMI was also observed (20-26%). The addition of Fe(III) ions to ferrate(VI)-IMI at pH 7.0 and 8.0 resulted in enhanced removal of IMI, but the presence of Ca²⁺, SO₄^2-, HCO₃^-, and humic acid (HA) has negative effects. The presence of coexisting substances in river water slightly decreased IMI removal by ferrate(VI) by less than 10%. Identification of products and frontier electron density (FED) calculations demonstrated involvement of opening of the five-membered heterocyclic moiety of IMI by ferrate(VI). Toxicity assessment with NIH 3T3 fibroblasts and ECOSAR analysis indicated lower toxicity of oxidized products than parent IMI.

Using potassium ferrate control hazardous disinfection by-products during chlorination

The generation of hazardous disinfection by-product is one of the major problems in drinking water chlorination. This study aims to investigate the potential of potassium ferrate (K₂FeO₄) on by-product control. Filtered raw water from a water treatment plant in Jinan was used to evaluate the effects of K₂FeO₄ dose, pH, ammonia nitrogen, and Br^- concentration on trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP). The results present that 3 mg/L K₂FeO₄ effectively reduced ultraviolet absorbance at 254 nm (UV₂₅₄) by 45%, but removed little dissolved organic carbon (DOC) by 12% at pH 7.40, since K₂FeO₄ tends to attack the electron-rich part of organic matter molecules but with restricted mineralization ability. Fluorescence excitation-emission matrix (EEM) analyses indicate the effective removal of fulvic acid and humic acid. Increasing K₂FeO₄ dose reduced THMFP but increased HAAFP, due to their precursors reacting with K₂FeO₄ in different pathway, while the rising pH or Br^- concentration increased THMFP but decreased HAAFP. Both THMFP and HAAFP decrease with increasing ammonia nitrogen concentrations. Additionally, it was found that under alkaline conditions, trihalomethanes (THMs) were dominated by haloacetic acids (HAAs).

Enhanced primary treatment during wet weather flow using ferrate as a coagulant, coagulant aid and disinfectant

This study evaluated the dual-function of ferrate as a coagulant and disinfectant for chemically-enhanced primary treatment during wet weather flow (WWF). For the first time, ferrate was thoroughly examined as a coagulant aid with aluminum sulfate (alum) to minimize the organic and inorganic contents along with microbial level during WWF. Ferrate as a coagulant was evaluated based on a two-level factorial design. At an optimized condition, a ferrate dose of 0.5 mg/L Fe with a cationic polymer (1.25 mg/L) removed 83% of turbidity, 87% of total suspended solids (TSS), 70% of chemical oxygen demand (COD), and 23% of ortho-phosphate (OP). Linear models were developed and used to adequately predict the removals. Ferrate as a coagulant aid added with alum showed better removal of TSS while no improvement was observed in the removals of turbidity and COD. The disinfection capacity of ferrate was evaluated at different dosing points when it was used as a coagulant, coagulant aid and as post dosed as a disinfectant. In particular, ferrate dose of 8 mg/L Fe removed only 2 logs of E. coli when it was used as a coagulant compared to more than 3-log removal of E. coli when ferrate was used as a coagulant aid and as a disinfectant. At optimal ferrate dose of 10 mg/L Fe as a coagulant aid with 6 mg/L Al achieved the target levels of turbidity (<8 NTU), TSS (<25 mg/L), and ferrate-induced iron particles (<0.6 mg/L) along with 5-log removal of E. coli within 31 min. This study suggested that using ferrate as a coagulant aid/disinfectant might be considered an effective approach for treating the wastewater during WWF.