Ferrate treatment for inactivation of bacterial community in municipal secondary effluent

Comparison of the disinfection efficacy between ferrate(VI) and chlorine in secondary effluent

Disinfection is essential for the microbial safety of reclaimed water. Traditional chlorine disinfection leads to secondary problems such as disinfection by-products and chlorine-resistant bacteria. Ferrate (Fe(VI)) is a novel green disinfectant. However, research on the disinfection characteristics of Fe(VI) remains insufficient. This study compared the disinfection efficacy between Fe(VI) and chlorine in secondary effluent, including the inactivation efficiency of coliforms and heterotrophic bacteria and the control effect on typical chlorine-resistant bacteria. The results showed that Fe(VI) was more effective than chlorine in inactivating Escherichia coli and total coliforms at low doses, whereas chlorine was more effective than Fe(VI) in inactivating heterotrophic bacteria. A severe trailing phenomenon was observed in Fe(VI) disinfection. Based on bacterial community structure analysis, Fe(VI) was also found to be capable of controlling the relative abundance of some chlorine-resistant bacteria such as Sphingomonas, Bacillus, Mycobacterium and Legionella except for Pseudomonas. The results of this study could have implications in evaluating Fe(VI) disinfection ability and optimizing Fe(VI) dosing for disinfection.

Effectiveness of potassium ferrate (VI) as a green agent in the treatment and disinfection of carwash wastewater

Carwash wastewater treatment with potassium ferrate (VI) (K₂FeO₄) was optimized by response surface methodology. The optimum conditions for chemical oxygen demand removal were established a pH 3.5, 0.328 g/L dose of K₂FeO₄, and with a process duration of 48 min. At these conditions, chemical oxygen demand, total organic carbon, total nitrogen, and total phosphorus decreased by 70.3, 58.9, 73.3, 82.0%, respectively; and the putrid odor was reduced. Simultaneously, the total viable count, total coli count, most probable number of fecal enterococci, and the total proteolytic bacteria count decreased by 89.5, 93.1, 92.9, and 95.0 %, respectively. Comparatively, an application of 0.450 g/L FeCl₃·6H₂O corresponding to the iron content in 0.328 g/L of K₂FeO₄ resulted in a decrease of total viable count, total coli count, most probable number of fecal enterococci and the total proteolytic bacteria count only by 38.1, 31.2, 42.9, and 58.0%, respectively. Therefore, flocculation with polyacrylamide anionic flocculant combined with potassium ferrate (VI) oxidation is a more effective alternative to coagulation with FeCl₃ and the same flocculant. The use of potassium ferrate (VI) is a viable option for the treatment of carwash wastewater.

Ferrate self-decomposition in water is also a self-activation process: Role of Fe(V) species and enhancement with Fe(III) in methyl phenyl sulfoxide oxidation by excess ferrate

To reveal the role of ferrate self-decomposition and the fates of intermediate iron species [Fe(V)/Fe(IV) species] during ferrate oxidation, the reaction between ferrate and methyl phenyl sulfoxide (PMSO) at pH 7.0 was investigated as a model system in this study. Interestingly, the apparent second-order rate constants (k_app) between ferrate and PMSO was found to increase with ferrate dosage in the condition of excess ferrate in borate buffer. This ferrate dosage effect was diminished greatly in the condition of excess PMSO where ferrate self-decomposition was lessened largely, or counterbalanced by adding a strong complexing ligand (e.g. pyrophosphate) to sequester Fe(V) oxidation, demonstrating that the Fe(V) species derived from ferrate self-decomposition plays an important role in PMSO oxidation. A mechanistic kinetics model involving the ferrate self-decomposition and PMSO oxidation by Fe(VI), Fe(V) and Fe(IV) species was then developed and validated. The modeling results show that up to 99% of the PMSO oxidation was contributed by the ferrate self-decomposition resultant Fe(V) species in borate buffer, revealing that ferrate self-decomposition is also a self-activation process. The direct Fe(VI) oxidation of PMSO was impervious to presence of phosphate or Fe(III), while the Fe(V) oxidation pathway was strongly inhibited by phosphate complexation or enhanced with Fe(III). Similar ferrate dosage effect and its counterbalance by pyrophosphate as well as the Fe(III) enhancement were also observed in ferrate oxidation of micropollutants like carbamazepine, diclofenac and sulfamethoxazole, implying the general role of Fe(V) and promising Fe(III) enhancement during ferrate oxidation of micropollutants.

Effect of ferrate and monochloramine disinfection on the physiological and transcriptomic response of Escherichia coli at late stationary phase

Biological mechanisms of disinfection not only vary by disinfectant but also remain not well understood. We investigated the physiological and transcriptomic response of Escherichia coli at late stationary phase to ferrate and monochloramine in amended lake water. Although ferrate and monochloramine treatments similarly reduced culturable cell concentrations by 3-log₁₀, 64% and 11% of treated cells were viable following monochloramine and ferrate treatment, respectively. This observed induction of viable but non-culturable (VBNC) state following monochloramine treatment but not ferrate is attributed to slower monochloramine disinfection kinetics (by 2.8 times) compared to ferrate. Transcriptomic analysis of E. coli at 15 min of exposure revealed that 3 times as many genes related to translation and transcription were downregulated by monochloramine compared to ferrate, suggesting that monochloramine treatment may be inducing VBNC through reduced protein synthesis and metabolism. Downregulation of universal stress response genes (rpoS, uspA) was attributed to growth-related physiological stressors during late stationary phase which may have contributed to the elevated expression levels of general stress responses pre-disinfection and, subsequently, their significant downregulation post-disinfection. Both disinfectants upregulated oxidative stress response genes (trxC, grxA, soxS), although levels of upregulation were time sensitive. This work shows that bacterial inactivation responses to disinfectants is mediated by complex molecular and growth-related responses.

One-step Ferrate(VI) treatment as a core process for alternative drinking water treatment

Traditional water treatment plants adopt multiple treatments to sequentially treat raw water for producing potable water. Besides complex treatment design and operation, they typically require a large space to accommodate different reactors. Furthermore, emerging issues (e.g. poor removal of persistent micro-pollutants) challenge the conventional treatment train. In this study, bench-scale tests were performed with real surface waters to evaluate ferrate(VI) treatment as a key alternative process for traditional water treatment. Of note, most earlier investigations on ferrate(VI) for water treatment utilized ferrate(VI) merely for pre- or post-treatment or simply as a disinfecting agent. Fundamentally different from the previous efforts, this study aimed to assess whether one-step ferrate(VI) addition, coupled with sedimentation, provided a comprehensive treatment, better than or equivalent to conventional surface water treatment. Results show that ferrate(VI) could simultaneously and effectively remove turbidity, degrade natural organic matter (NOM), and inactivate bacterial indicators in one single dose. The treatment performance relied heavily on ferrate(VI) dose and pH. Generally, higher ferrate(VI) dose improved the treatment results, except that it might re-suspend particles at a high dose at an alkaline condition. Lower pH favored coagulation due to reduction of zeta potentials on particle surface and promotion of their aggregation and enhanced the degradation of NOM because of higher Fe(VI) reactivity toward reductive moieties. In contrast, higher pH benefited the disinfection efficiency due to better stability and greater exposure of ferrate(VI). This study demonstrates that ferrate(VI) treatment can serve as a core treatment process in alternative water treatment designs for addressing various challenges.

Chitosan Encapsulation of FerrateVI for Controlled Release to Water:Mechanistic Insights and Degradation of Organic Contaminant

Tetraoxy-anion of iron in +6 oxidation state (Fe^VIO₄²⁻, Fe^VI), commonly called ferrate, has shown tremendous potential as a green oxidative agent for decontaminating water and air. Encapsulation of solid potassium salt of ferrate (K₂FeO₄) circumvents the inherent drawbacks of the instability of ferrate under humid conditions. In the encapsulated strategy, controlled release without exposing the solid ferrate to the humid environment avoids self-decomposition of the oxidant by water in the air, and the ferrate is mostly used to decontaminate water efficiently. This study demonstrated the formulation of oxidative microcapsules with natural materials present in chitosan, whose release rate of the core material can be controlled by the type of intermediate hydrocarbon layer and the pH-dependent swelling of chitosan shell. The pH played a pivotal role in swelling chitosan shell and releasing the core oxidant. In a strong acidic solution, chitosan tended to swell quickly and release Fe^VI at a faster rate than under neutral conditions. Additionally, among the several long-chain hydrocarbon compounds, oleic acid exhibited the strongest “locking” effect when applied as the intermediate layer, giving rise to the slow release of Fe^VI. Coconut oil and mineral oil, in comparison, allowed Fe^VI to penetrate the layer within shorter lengths of time and showed comparable degrees of degradation of target contaminant, methylene orange, under ambient temperature and near-neutral conditions. These findings have practical ramifications for remediating environmental and industrial processes.

Influence of algal organic matter of Microcystis aeruginosa on ferrate decay and MS2 bacteriophage inactivation

Surface water contaminated with algae and with enteric viruses is a global problem. When surface water is used as a drinking water source, it is important to know the influence of algal organic matter on the disinfection of viruses. In this work, we studied the disinfection efficacy of ferrate and the influence of algal organic matter on the disinfection. We determined the MS2 inactivation kinetics by ferrate under three pH conditions (7, 8, and 8.7). The experimental results and pH-dependent calculation suggest that H₂FeO₄ and HFeO₄^- are 1935 and 8 times as effective as FeO₄^2- in MS2 inactivation. We also found that intracellular algal organic matter (IAOM) had a stronger effect on MS2 inactivation kinetics than extracellular algal organic matter (EAOM) suggesting that IAOM led to higher consumption of Fe(VI) compared to EAOM. At pH 8.7, while significant consumption of FeO₄^2- by as low as 8 mg C/L of EAOM and 2 mg C/L of IAOM was detected, MS2 inactivation was negatively influenced only when 13 mg C/L of IAOM present. This study showed that it is important to control pH and to determine the concentration of algal organic matter if ferrate is used for disinfection of surface water contaminated with algae.

A critical review of ferrate(VI)-based remediation of soil and groundwater

Over the past few decades, diverse chemicals and materials such as mono- and bimetallic nanoparticles, metal oxides, and zeolites have been used for soil and groundwater remediation. Ferrate (Fe^VIO₄^2-) has been widely employed due to its high-valent iron (VI) oxo compound with high oxidation/reduction potentials. Ferrate has received attention for wide environmental applications including water purification and sewage sludge treatment. Ferrate provides great potential for diverse environmental applications without any environmental problems. Therefore, this paper provides comprehensive information on the recent progress on the use of (Fe^VIO₄^2-) as a green material for use in sustainable treatment processes, especially for soil and water remediation. We reviewed diverse synthesis recipes for ferrates (Fe^VIO₄^2-) and their associated physicochemical properties as oxidants, coagulants, and disinfectants for the elimination of a diverse range of chemical and biological species from water/wastewater samples. A summary of the eco-sustainable performance of ferrate(VI) in water remediation is also provided and the future of ferrate(VI) is discussed in this review.

Degradability of chlorophenols using ferrate(VI) in contaminated groundwater

The production and use of chlorophenolic compounds in industry has led to the introduction of many xenobiotics, among them chlorophenols (CPs), into the environment. Five CPs are listed in the priority pollutant list of the U.S. EPA, with pentachlorophenol (PCP) even being proposed for listing under the Stockholm Convention as a persistent organic pollutant (POP). A green procedure for degrading such pollutants is greatly needed. The use of ferrate could be such a process. This paper studies the degradation of CPs (with an emphasis on PCP) in the presence of ferrate both in a spiked demineralized water system as well as in real contaminated groundwater. Results proved that ferrate was able to completely remove PCP from both water systems. Investigation of the effect of ferrate purity showed that even less pure and thus much cheaper ferrate was applicable. However, with decreasing ferrate purity, the degradability of CPs may be lower.

Impaired Performance of Pressure-Retarded Osmosis due to Irreversible Biofouling

Next-generation pressure-retarded osmosis (PRO) approaches aim to harness the energy potential of streams with high salinity differences, such as wastewater effluent and seawater desalination plant brine. In this study, we evaluated biofouling propensity in PRO. Bench-scale experiments were carried out for 24 h using a model wastewater effluent feed solution and simulated seawater desalination brine pressurized to 24 bar. For biofouling tests, wastewater effluent was inoculated with Pseudomonas aeruginosa and artificial seawater desalination plant brine draw solution was seeded with Pseudoalteromonas atlantica. Our results indicate that biological growth in the feed wastewater stream channel severely fouled both the membrane support layer and feed spacer, resulting in ∼50% water flux decline. We also observed an increase in the pumping pressure required to force water through the spacer-filled feed channel, with pressure drop increasing from 6.4±0.8 bar m(-1) to 15.1±2.6 bar m(-1) due to spacer blockage from the developing biofilm. Neither the water flux decline nor the increased pressure drop in the feed channel could be reversed using a pressure-aided osmotic backwash. In contrast, biofouling in the seawater brine draw channel was negligible. Overall, the reduced performance due to water flux decline and increased pumping energy requirements from spacer blockage highlight the serious challenges of using high fouling potential feed sources in PRO, such as secondary wastewater effluent. We conclude that PRO power generation using wastewater effluent and seawater desalination plant brine may become possible only with rigorous pretreatment or new spacer and membrane designs.

Inactivation of bacteriophage MS2 with potassium ferrate(VI)

Ferrate [Fe(VI); FeO(4)(2-)] is an emerging oxidizing agent capable of controlling chemical and microbial water contaminants. Here, inactivation of MS2 coliphage by Fe(VI) was examined. The inactivation kinetics observed in individual batch experiments was well described by a Chick-Watson model with first-order dependences on disinfectant and infective phage concentrations. The inactivation rate constant k(i) at a Fe(VI) dose of 1.23 mgFe/L (pH 7.0, 25 °C) was 2.27(±0.05) L/(mgFe × min), corresponding to 99.99% inactivation at a Ct of ~4 (mgFe × min)/L. Measured k(i) values were found to increase with increasing applied Fe(VI) dose (0.56-2.24 mgFe/L), increasing temperature (5-30 °C), and decreasing pH conditions (pH 6-11). The Fe(VI) dose effect suggested that an unidentified Fe byproduct also contributed to inactivation. Temperature dependence was characterized by an activation energy of 39(±6) kJ mol(-1), and k(i) increased >50-fold when pH decreased from 11 to 6. The pH effect was quantitatively described by parallel reactions with HFeO(4)(-) and FeO(4)(2-). Mass spectrometry and qRT-PCR analyses demonstrated that both capsid protein and genome damage increased with the extent of inactivation, suggesting that both may contribute to phage inactivation. Capsid protein damage, localized in the two regions containing oxidant-sensitive cysteine residues, and protein cleavage in one of the two regions may facilitate genome damage by increasing Fe(VI) access to the interior of the virion.