Evaluation of potassium ferrate as an alternative disinfectant on cyanobacteria inactivation and associated toxin fate in various waters

Advances and challenges in the technologies for cyanobacterial cells removal in drinking water treatment

Harmful cyanobacteria in reservoirs pose a serious threat to drinking water safety due to the intracellular metabolites, such as toxins and unpleasant tastes & odours. Effective removal of harmful cyanobacteria with little to no cell damage is very important to ensure the safety of drinking water. This review first introduced development history of cyanobacterial removal technologies in drinking water treatment. Then, impacts of oxidation, coagulation and pre-oxidation enhanced coagulation processes on cyanobacterial removal and integrity of the cells were comprehensively evaluated and discussed. Oxidation can remove cyanobacteria, but high doses of oxidants can result in significant cell lysis and release of intracellular metabolites, especially when using chlorine or ozone. Although there is practically no cell damage during coagulation, the removal efficiency is low in many cases. Pre-oxidation may improve cyanobacterial removal by the subsequent solid-liquid separation processes, and moderate pre-oxidation with little to no cell lysis is very important. Mechanisms of interface interaction between pre-oxidants and cyanobacteria should be defined in future to ensure moderate pre-oxidation of algal cells. Fate of cyanobacterial cells in sludge is also reviewed because more and more waterworks return sludge supernatant to the inlet of plant. Damage to cyanobacterial cells in sludge depends mainly upon coagulant type and dosage, algal species, and cyanobacteria-containing sludge should be treated before cell lysis. Efficient techniques for harmless disposal of cyanobacteria-containing sludge should be developed in future. This paper will help to better understand the cyanobacterial removal processes and provide improved perspectives for future research in this field.

The synergistic effect of periodate/ferrate (VI) system on disinfection of antibiotic resistant bacteria and removal of antibiotic resistant genes: The dominance of Fe (IV)/Fe (V)

The proliferation of antibiotic resistant genes (ARGs) and antibiotic resistant bacteria (ARB) caused by antibiotic abuse has raised concerns about the global infectious-disease crisis. This study employed periodate (PI)/ferrate (VI) (Fe (VI)) system to disinfect Gram-negative ARB (Escherichia coli DH5α) and Gram-positive bacteria (Bacillus subtilis ATCC6633). The PI/Fe (VI) system could inactivate 1 × 108 CFU/mL of Gram-negative ARB and Gram-positive bacteria by 4.0 and 2.8 log in 30 min. Neutral and acidic pH, increase of PI dosage and Fe (VI) dosage had positive impacts on the inactivation efficiency of ARB, while alkaline solution and the coexistence of 10 mM Cl-, NO3-, SO42- and 20 mg/L humic acid had slightly negative impacts. The reactive species generated by PI/Fe (VI) system could disrupt the integrity of cell membrane and wall, leading to oxidative stress and lipid peroxidation. Intracellular hereditary substance, including DNA and ARGs (tetA), would leak into the external environment through damaged cells and be degraded. The electron spin resonance analysis and quenching experiments indicated that Fe (IV)/Fe (V) played a leading role in disinfection. Meanwhile, PI/Fe (VI) system also had an efficient removal effect on sulfadiazine, which was expected to inhibit the ARGs transmission from the source.

Research and application of active species based on high-valent iron for the degradation of pollutants: A critical review

Fe(VI), as a new green treatment agent, has two indispensable processes in water treatment: coagulation and oxidation. Fe(VI) has a strong oxidation ability. The intermediate iron species (Fe(V) and Fe(IV)) and reactive radical species (H2O2, •OH, and O2•-) produced by decomposition and reduction reaction have strong oxidation ability, in addition, the hydrolyzed product formed in situ with core (γ-Fe2O3)-shell (γ-FeOOH) structure also has good coagulation effect. Because Fe(VI) is easy to decompose and challenging to preserve, it limits the application and sometimes significantly reduces the subsequent processing effect. How to make Fe(VI) more efficient use is a hot spot in current research. This article summarizes the distribution of active substances during the hydrolysis of Fe(VI), distinguish the differences mechanisms in the similar regulation methods, reviews the current preparation methods of Fe(VI), and finally reviews the applications of Fe(VI) in the field of environmental remediation.

Reinvestigation on the Mechanism for Algae Inactivation by the Ultraviolet/Peracetic Acid Process: Role of Reactive Species and Performance in Natural Water

This study provided an in-depth understanding of enhanced algae inactivation by combining ultraviolet and peracetic acid (UV/PAA) and selecting Microcystis aeruginosa as the target algae species. The electron paramagnetic resonance (EPR) tests and scavenging experiments provided direct evidence on the formed reactive species (RSs) and indicated the dominant role of RSs including singlet oxygen (1O2) and hydroxyl (HO•) and organic (RO•) radicals in algae inactivation. Based on the algae inactivation kinetic model and the determined steady-state concentration of RSs, the contribution of RSs was quantitatively assessed with the second-order rate constants for the inactivation of algae by HO•, RO•, and 1O2 of 2.67 × 109, 3.44 × 1010, and 1.72 × 109 M-1 s-1, respectively. Afterward, the coexisting bi/carbonate, acting as a shuttle, that promotes the transformation from HO• to RO• was evidenced to account for the better performance of the UV/PAA system in algae inactivation under the natural water background. Subsequently, along with the evaluation of the UV/PAA preoxidation to modify coagulation-sedimentation, the possible application of the UV/PAA process for algae removal was advanced.

Ferrate(VI) mediated degradation of the potent cyanotoxin, cylindrospermopsin: Kinetics, products, and toxicity

The presence of cylindrospermopsin (CYN), a potent cyanotoxin, in drinking water sources poses a tremendous risk to humans and the environment. Detailed kinetic studies herein demonstrate ferrate(VI) (Fe^VIO₄^2-, Fe(VI)) mediated oxidation of CYN and the model compound 6-hydroxymethyl uracil (6-HOMU) lead to their effective degradation under neutral and alkaline solution pH. A transformation product analysis indicated oxidation of the uracil ring, which has functionality critical to the toxicity of CYN. The oxidative cleavage of the C5=C6 double bond resulted in fragmentation of the uracil ring. Amide hydrolysis is a contributing pathway leading to the fragmentation of the uracil ring. Under extended treatment, hydrolysis, and extensive oxidation lead to complete destruction of the uracil ring skeleton, resulting in the generation of a variety of products including nontoxic cylindrospermopsic acid. The ELISA biological activity of the CYN product mixtures produced during Fe(VI) treatment parallels the concentration of CYN. These results suggest the products do not possess ELISA biological activity at the concentrations produced during treatment. The Fe(VI) mediated degradation was also effective in the presence of humic acid and unaffected by the presence of common inorganic ions under our experimental conditions. The Fe(VI) remediation of CYN and uracil based toxins appears a promising drinking water treatment process.

Modifications to microplastics by potassium ferrate(VI): impacts on sorption and sinking capability in water treatment

Pre-treatment (oxidation) may induce potential modifications to microplastics (MPs), further affecting their behaviors and removal efficiency in drinking water treatment plants. Herein, potassium ferrate(VI) oxidation was tested as a pre-treatment for MPs with four polymer types and three sizes each. Surface oxidation occurred with morphology destruction and oxidized bond generation, which were prosperous under low acid conditions (pH 3). As pH increased, the generation and attachment of nascent state ferric oxides (Fe_xO_x) gradually became dominant, making MP-Fe_xO_x complexes. These Fe_xO_x were identified as Fe(III) compounds, including Fe₂O₃ and FeOOH, firmly attaching to the MP surface. Using ciprofloxacin as the targeted organic contaminant, the presence of Fe_xO_x enhanced MP sorption dramatically, e.g., the kinetic constant K_f of ciprofloxacin raised from 0.206 (6.5 μm polystyrene) to 1.062 L g^-1 (polystyrene-Fe_xO_x) after oxidation at pH 6. The sinking performance of MPs was enhanced, especially for small MPs (< 10 μm), which could be attributed to the increasing density and hydrophilicity. For instance, the sinking ratio of 6.5 μm polystyrene increased by 70% after pH 6 oxidation. In general, ferrate pre-oxidation possesses multiple enhanced removals of MPs and organic contaminants through adsorption and sinking, reducing the potential risk of MPs.

FT-ICR/MS deciphers formation of unknown macromolecular disinfection byproducts from algal organic matters after plasma oxidation

Algal organic matter (AOM) is a potential precursor of disinfection byproducts (DBPs) in water treatment. It is a major challenge to identify macromolecular DBPs due to the diversity of AOM. In this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS) was applied to diagnose the AOM diversity after algae removal by plasma oxidation and to recognize the macromolecular DBPs in subsequent chlorination. Significant removal of AOM released by M. aeruginosa, C. raciborskii, and A. spiroies was achieved by plasma oxidation, accompanied by decrease in the proportion of CHNO formulas and increase in CHO formulas. Without plasma treatment, chlorination generated approximately 2486 macromolecular carbonaceous DBPs (C-DBPs) and 1984 nitrogenous DBPs (N-DBPs), with C₁₁H_nO_mCl_x and C₁₈H_nN_mO_zCl_x as the most abundant DBPs. The numbers of C-DBPs and N-DBPs decreased by 63.3% and 62.9%, respectively, if plasma treatment was applied prior to chlorination. Network computational analysis revealed that Cl substitution was the main formation pathway of AOM-derived DBP formation rather than HOCl addition. The precursors of macromolecular DBPs contained a characteristic atomic number of C and O (7 ≤ C ≤ 18; 3 ≤ O ≤ 11). This study firstly disclosed the relationship between AOM diversity and novel macromolecular DBPs during algae-laden water treatment.

Oxidative degradation of sulfamethoxazole from secondary treated effluent by ferrate(VI): kinetics, by-products, degradation pathway and toxicity assessment

Sulfamethoxazole (SMX) is a typical antibiotic in the world, which is frequently detected in the aquatic environment. The current study was aimed to investigate the SMX degradation in secondary treated wastewater using potassium Ferrate [Fe(VI)]. The effects of various experimental conditions, EDTA and phosphate as chelating agents, and toxicity assessment were also considered. Secondary treated effluent was spiked with predefined SMX concentrations, and after desired reaction time with Fe(VI), residual SMX was measured using HPLC. Results indicated that SMX degradation by Fe(VI) was favored under acidic condition, where 90% of SMX degradation was achieved after 120 min. Fe(VI) and SMX reaction obeyed first-order kinetic; meantime, the SMX degradation rate under pH 3 was 7.6 times higher than pH 7. The presence of phosphate (Na₂HPO₄) and EDTA declined SMX degradation, while Fe (III) effect was contradictory. In addition to promising demolition, 10% TOC removal was achieved. Eighteen major intermediates were identified using LC-MS/MS and the degradation pathways were suggested. Transformation products (TPs) were formed due to hydroxylation, bond cleavage, transformation after bond cleavage, and oxidation reactions. The ECOSAR analysis showed that some of the SMX oxidation products were toxic to aquatic organisms (fish, daphnia and green algae).

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40201-021-00769-9.

Reinvestigation of the oxidation of organic contaminants by Fe(VI): Kinetics and effects of water matrix constituents

Since previous studies mostly ignored the contributions of Fe(IV) and Fe(V) during the determination of reaction rate constants of ferrate (Fe(VI)) with trace organic contaminants (TrOCs), the intrinsic oxidation ability of Fe(VI) was overestimated. For the first time, this study systemically evaluated the reactivity of Fe(VI) towards four kinds of TrOCs by blocking Fe(IV)/Fe(V) over the TrOCs degradation, and evaluated the effects of coexisting water matrix constituents. Results revealed that Fe(VI) exhibited superior reactivity towards phenolic compounds. Different from other tested TrOCs, phenolic compounds were mainly degraded by Fe(VI) rather than Fe(IV)/Fe(V). Taking bisphenol A (BPA) as the target TrOC, we found that the coexisting constituents can not only affect the reactivity of different ferrate species (i.e., Fe(IV), Fe(V), and Fe(VI)), but also alter the concentrations of ferrates. HPO₄^2- inhibited the reaction between Fe(VI) and H₂O₂, while Ca²⁺, Mg²⁺, and NH₄⁺ promoted the generation of Fe(IV)/Fe(V) from Fe(VI). Besides, humic acid could increase the contribution of Fe(IV)/Fe(V) to the oxidation of BPA. These findings were validated in real water samples. Taken together, this study provides a new perspective regarding the intrinsic oxidation reactivity of Fe(VI), thereby urging reconsideration of the proper strategies for utilization of high-valent Fe species in practices.

Inactivation of Microcystis Aeruginosa by peracetic acid combined with ultraviolet: Performance and characteristics

The inactivation of algae by a combined process of peracetic acid and ultraviolet irradiation (UV/PAA) was systematically investigated by choosing Microcystis aeruginosa as the reference algal species. Both hydroxyl (HO^•) and organic radicals (RO^•) contributed to the cell integrity loss and RO^• played the dominant roles. The algae inactivation kinetics can be well fitted by the typical Hom model, showing that the inactivation kinetic curves followed a type of shoulder and exponential reduction. The initial shoulder might be induced by the protection from the cell wall. Although the results from the cell morphology, UV-vis spectra and fluorescence excitation-emission matrices analysis suggested the cell lysis and the release of algal organic matter (AOM) in the UV/PAA process, the AOM could be subsequently degraded. Humic acid (1 - 5 mg/L) inhibited the algal cell inactivation, and the presence of chloride (0.5 - 2 mM) had little effect on the cell viability reduction. However, the addition of bicarbonate (1 - 5 mM) promoted cell integrity loss. The UV/PAA process displayed better performance under the natural water background, demonstrating the extensive potential for the practical application of this approach. This study suggests that the UV/PAA process is an effective strategy for algae inactivation.

Nanotechnology for Targeted Detection and Removal of Bacteria: Opportunities and Challenges

The emergence of nanotechnology has created unprecedented hopes for addressing several unmet industrial and clinical issues, including the growing threat so-termed "antibiotic resistance" in medicine. Over the last decade, nanotechnologies have demonstrated promising applications in the identification, discrimination, and removal of a wide range of pathogens. Here, recent insights into the field of bacterial nanotechnology are examined that can substantially improve the fundamental understanding of nanoparticle and bacteria interactions. A wide range of developed nanotechnology-based approaches for bacterial detection and removal together with biofilm eradication are summarized. The challenging effects of nanotechnologies on beneficial bacteria in the human body and environment and the mechanisms of bacterial resistance to nanotherapeutics are also reviewed.

Removal of cyanobacteria and cyanotoxins by ferrate from polluted lake water

Freshwater cyanobacterial blooms are becoming increasingly problematic microbiological pollutants, especially for the water resource and surface natural lakes. Cyanobacterial blooms, which produce toxins and microcystins, negatively affect the quality of water, animal, and human health, and they have also negative impact on recreational activities. The effect of electrochemically prepared potassium ferrate (green oxidation agent) on the water polluted by cyanobacteria and cyanotoxins was studied. The two most frequently occurring cyanobacterial genus Microcystis and Anabaena and the most toxic and abundant microcystin MC-LR were successfully inactivated and treated by ferrate. Potassium ferrates were applied at different conditions, such as varied hydrodynamics flow of samples, pH, and Fe(VI) concentrations. High detected elimination efficiency was consequently tested on the real water matrix from microbiological polluted natural lake Šaštín-Gazárka in Slovakia. The ferrate application leads to the better chemical, biological, microbiological, and ecotoxicological outcomes.

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.

Using sodium percarbonate to suppress vertically distributed filamentous cyanobacteria while maintaining the stability of microeukaryotic communities in drinking water reservoirs

The increasing frequency and intensity of blooms of toxin- and taste & odour-producing filamentous cyanobacteria in water sources is a growing global issue. Compared to the common spherical Microcystis genus, the removal of filamentous cyanobacteria is more difficult in drinking water treatment plants; hence, abatement and control of the occurrence and proliferation of harmful filamentous cyanobacteria within drinking water sources is important for water supply. In this study, the solid sodium percarbonate (SPC), Na₂CO₃·1.5H₂O₂, was used as an algaecide to eliminate the cyanobacteria distributed throughout the water column in the surface and bottom layer of a reservoir serving as a drinking water source. Results showed that although the oxidation capacity of SPC was higher in the surface water due to the higher light intensity than in the bottom water, 3.0 mg/L SPC can still suppress the harmful cyanobacteria in the bottom water after 36 h because the carbonate ion generated by SPC decomposition can act as an activator of H₂O₂ to generate many reactive oxygen species - including superoxide radicals, carbonate radical anions, and hydroxyl radicals - even in the light-limited environment. The obtained inactivation rates for the main cyanobacteria in this reservoir followed the order: Pseudanabaena limnetica > Raphidiopsis curvata > Cylindrospermopsis raciborskii. 3.0 mg/L SPC has a slight impact on microeukaryotic communities according to the 18S rRNA gene sequencing, while 6.0 mg/L SPC changed the composition of eukaryotic phytoplankton and zooplankton clearly. Eukaryotic co-occurrence networks showed that although the network of eukaryotic plankton in treated surface water was more compact and clustered, stability of microeukaryotes in the treated surface water was lower than for the treated bottom water, owing to the higher oxidation capacity of SPC in the surface water. The results above not only have important implications for full-scale control of harmful cyanobacteria in drinking water sources, especially filamentous cyanobacteria with vertical distributions, but also help to ensure the health and stability of the whole aquatic ecosystem.

Physicochemical implications of cyanobacteria oxidation with Fe(VI)

Increases in harmful algal blooms has negatively impacted many surface-sourced drinking water utilities. To control these blooms, many water utilities implement pre-oxidation with ozone, chlorine, or permanganate; however, pre-oxidation of algae has both positive and negative water quality outcomes. This study investigated ferrate (Fe(VI)) as an alternative oxidant by measuring its effect on cell lysing, surface characteristics, and coagulation in waters containing the cyanobacteria Microcystis aeruginosa. Bench scale studies were conducted to examine the complex combination of processes in a Fe(VI)-algae system. These processes were characterized by fluorescence index, surface charge, collision frequency modeling, particle counts and sphericity, total nitrogen, and ferrate decomposition measurements. Results showed that Fe(VI) lysed algal cells, but further oxidation of released organic matter is possible. The presence of algae did not significantly impact the rate of Fe(VI) decomposition. Fe(VI) pre-oxidation may also be capable of decreasing the formation of nitrogenated disinfection byproducts through subsequent oxidation of released nitrogen rich organic matter. Streaming current and zeta potential results indicate destabilization of the resulting algae and iron suspension was incomplete under most conditions. Particle collision frequency modeling indicates fluid shear to be an important aggregation mechanism of the resulting suspension. Overall, Fe(VI) is a viable alternative to other strong oxidants for water utilities struggling with harmful algal blooms, but the final fate of the resulting organic matter must be further studied.

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.

Interspecific competition between Microcystis aeruginosa and Pseudanadaena and their production of T&O compounds

Microcystis aeruginosa and Pseudanabaena are two common cyanobacterial species/genus and they can occur coincidently in many eutrophic lakes globally. These two cyanobacteria could produce Taste & Odor (T&O) compounds, and their production of T&O compounds might be changed when they are present coincidently. The amounts of T&O compounds and their producers may influence the effectiveness of water treatment processes. Therefore, the mutual interactions between Microcystis aeruginosa (FACHB-905, M) and Pseudanabaena sp. (FACHB-1277, P) on T&O compounds in co-cultures were evaluated in this study. Different initial cell concentrations of M and P, with ratios of M:P = 1:1, M:P = 1:2 and M:P = 2:1 were applied in the co-cultures. The growth of M was enhanced under all of the cyanobacterial cell ratios. The growth of P was enhanced under the ratio of M:P = 1:1, while it was inhibited under the ratios of M:P = 1:2 and M: P = 2:1. In addition, the growth of the two cyanobacteria and their production of β-cyclocitral and 2-methylisoborneol (2-MIB) in the filtrate of P were higher than those in the filtrate of M, which may be attributed to their associated secondary metabolites. The cell integrity and photosynthetic capacity of the two studied cyanobacteria are greatly affected by exposure to β-cyclocitral and 2-MIB. The results showed that β-cyclocitral and 2-MIB had the allelopathic effects on the two cyanobacteria species which might influence the composition of co-existing cyanobacteria and their production of T&O compounds.

Influences of the micropollutant erythromycin on cyanobacteria treatment with potassium permanganate

Cyanobacteria blooms and micropollutants (e.g., antibiotics) in source waters are two increasing environmental issues worldwide. This study hypothesized that the coexisting antibiotics may possibly alter the efficiency of water treatment processes through affecting the physiological and biochemical characteristics of cyanobacterial cells. A toxic strain of Microcystis aeruginosa was exposed to the common antibiotic erythromycin (ERY) at environmentally relevant concentrations; then, samples were collected on days 1, 4 and 6 to assess the efficiency of potassium permanganate (KMnO₄) in cyanobacteria oxidation. The percentage of intact cells remained constant after treatment with 2 mg L^-1 KMnO₄ in M. aeruginosa samples dosed with 0-5.0 μg L^-1 ERY. Although 6 mg L^-1 KMnO₄ could damage cyanobacterial cells, its ability was considerably reduced as the concentrations of ERY increased. KMnO₄ oxidation degraded the intracellular microcystins (MCs) in all of the cyanobacterial samples, even the samples with intact cells, possibly resulting from the stimulation of intracellular reactive oxygen species (ROS). The highest amounts of total MCs remained after oxidation with 2 and 6 mg L^-1 KMnO₄ in 0.2 μg L^-1 ERY-treated cyanobacterial samples, which may be due to large amounts of MC production. The 5.0 μg L^-1 ERY inhibited the growth of cyanobacterial cells and downregulated the expression of the MC synthesis gene (mcyB), which resulted in the lowest amounts of total MCs. However, it led to the highest concentration (4.6 μg L^-1) of extracellular MCs after treatment with 2 mg L^-1 KMnO₄ for 300 min. Generally, this study indicates that the effectiveness of KMnO₄ oxidation in cyanobacteria treatment decreased when the concentration of ERY increased. Hence, the possible risks caused by the coexistence of cyanobacteria and antibiotics, such as reduced efficiency of water treatment processes in cyanobacteria inactivation and degradation of the dissolved MCs, need to be taken into account.

Enhanced hydrogen production from food waste dark fermentation by potassium ferrate pretreatment

Hydrogen generation from food waste anaerobic dark fermentation is identified as a promising strategy for resource recovery. In this work, an innovative strategy of using potassium ferrate (PF), a strong oxidant, to promote anaerobic dark fermentation of food waste to produce hydrogen has been reported. The experimental results revealed that PF enhanced the hydrogen production from food waste, the maximal hydrogen yield was 173.5 mL/g, and the optimal PF dosage was 0.4 g/g total suspended solids. PF shortened the lag phase for hydrogen generation from 120 to 96 h. Mechanisms investigation revealed that PF accelerated the disintegration of organic compounds and increased the soluble organic matter in the liquid phase. The strong oxidation of PF inhibited the processes of hydrolysis, acidification, acetogenesis, homoacetogenesis, and methanogenesis by using synthetic wastewater in the fermentation process. The inhibition of PF on these processes was further verified by the enzyme activity analysis. Economic analysis indicated that 0.1 g/g PF was the optimal dosage. PF treatment is a promising strategy to enhance the production of hydrogen from food waste dark fermentation.

Nanoplastics Promote Microcystin Synthesis and Release from Cyanobacterial Microcystis aeruginosa

Although the fate of nanoplastics (<100 nm) in freshwater systems is increasingly well studied, much less is known about its potential threats to cyanobacterial blooms, the ultimate phenomenon of eutrophication occurrence worldwide. Previous studies have evaluated the consequences of nanoplastics increasing the membrane permeability of microbes, however, there is no direct evidence for interactions between nanoplastics and microcystin; intracellular hepatotoxins are produced by some genera of cyanobacteria. Here, we show that the amino-modified polystyrene nanoplastics (PS-NH₂) promote microcystin synthesis and release from Microcystis aeruginosa, a dominant species causing cyanobacterial blooms, even without the change of coloration. We demonstrate that PS-NH₂ inhibits photosystem II efficiency, reduces organic substance synthesis, and induces oxidative stress, enhancing the synthesis of microcystin. Furthermore, PS-NH₂ promotes the extracellular release of microcystin from M. aeruginosa via transporter protein upregulation and impaired cell membrane integrity. Our findings propose that the presence of nanoplastics in freshwater ecosystems might enhance the threat of eutrophication to aquatic ecology and human health.

Rapid and strong biocidal effect of ferrate on sulfidogenic and methanogenic sewer biofilms

For the control of sulfide and methane in sewers, it is favorable to reduce their production rather than to remove them after generation. In this study, we revealed rapid and strong biocidal effect of ferrate (Fe(VI)) on sulfidogenic and methanogenic sewer biofilms, leading to control of sulfide and methane production in sewer. The inactivation of the microorganisms in sewer biofilms by Fe(VI) could be accomplished within 15 min for a single dosing event and the biocidal effect could be enhanced by applying pulse dosing strategy. The microbiological analysis showed that the key functional genes involved in sulfide and methane production, i.e. dsrA and mcrA, in the viable cells after Fe(VI) dosing were decreased substantially by 84.2% and 86.6%, respectively. Significant drops were also observed in the relative abundances of viable sulfide reducing bacteria (SRB) and methanogenic archaea (MA). The direct dosing of Fe(VI) into a sewer reactor led to instant and complete suppression of sulfidogenic and methanogenic activities, and the recovery of the activities resembled the regrowth of residual SRB and MA. The results of this study suggested the feasibility for developing an efficient and cost-effective sulfide and methane control strategy using Fe(VI).

Impact of copper sulphate, potassium permanganate, and hydrogen peroxide on Pseudanabaena galeata cell integrity, release and degradation of 2-methylisoborneol

Frequent off-flavor events caused by geosmin and 2-methylisoborneol have caused concern among consumers about the quality of potable water. Pseudanabaena galeata, a filamentous cyanobacterium, is a known producer of 2-methylisoborneol in lakes and reservoirs. The use of algicides to control cyanobacteria must consider the potential release of contaminants into the water. This is the first study to systematically investigate the effectiveness of copper sulphate (CuSO₄), potassium permanganate (KMnO₄), and hydrogen peroxide (H₂O₂) on the cell viability and integrity of Pseudanabaena galeata. Following algicide or oxidant treatment, the release and degradation of 2-methylisoborneol was also examined. It is evident that all of these chemicals can decrease Pseudanabaena galeata viability and damage cell membranes and the filamentous Pseudanabaena galeata was more susceptible to treatment by these three algicides than unicellular colonial Microcystis aeruginosa. Of the three compounds used, KMnO₄ showed the stronger ability to compromise cell integrity and 5.0 mg/L KMnO₄ could induce 91 ± 1.5% lysis of Pseudanabaena galeata within 2 h. It was found that H₂O₂ had the potential to degrade 2-methylisoborneol with 16.0 ± 0.4% degraded by 20.0 mg/L H₂O₂ within 8 h. In contrast, 2-methylisoborneol could not be degraded by CuSO₄ (dosage: ≤ 1.5 mg/L; reaction time: ≤ 8 h) and KMnO₄ (dosage: ≤ 5.0 mg/L; reaction time: ≤ 3 h) basically. Results showed that the oxidation capacity of H₂O₂ against Pseudanabaena galeata was enhanced under sunlight. The results will help drinking water utilities to better understand the risk of Pseudanabaena galeata lysis and 2-methylisoborneol release during raw water treatment.

Study on the Degradation of Sodium Diethyldithiocarbamate (DDTC) in Artificially Prepared Beneficiation Wastewater with Sodium Hypochlorite

The degradation of DDTC in beneficiation wastewater has become an increasingly concerned issue due to the serious effects on the environment. In this study, the degradation characteristics of DDTC in artificially prepared beneficiation wastewater were investigated by adding sodium hypochlorite as an oxidant, and the influences of different degradation conditions on removal efficiency of DDTC were analyzed systematically. The results indicated that the degradation rate of DDTC without sodium hypochlorite added can reach 88.4% in a stewing time of 6 h. When the dosage of sodium hypochlorite was 400 mg·L−1, the degradation rate of DDTC can reach 91.28% for 1 min reaction time under the natural condition of pH value 5.98 and reaction temperature 25°C. The DDTC in the wastewater was firstly degraded into carbon disulfide and diethylamine, and then carbon disulfide was further degraded into CO2, S, or SO42−, while diethylamine was degraded into N2 and CO2. The research results can provide a technical basis for the treatment of beneficiation wastewater containing DDTC.

Microcystin-LR Enrichment from Freshwater by a Recombinant Plant-derived Antibody Using Sol-Gel-Glass Immunoextraction

Eutrophication of water bodies can promote cyanobacterial (blue-green algae) blooms, which has become a source of increasing concern for both recreational and drinking water use. Many bacterial species can produce toxins that pose threats to wildlife, domestic animals and humans. Microcystin-leucine-arginine (MC-LR) is the most frequent and most toxic microcystin congener. For the first time, lab-scale investigations were performed to test the application of a recombinant plant-derived anti-MC-LR antibody immobilized on an immunoaffinity support material to selectively extract the toxin from spiked freshwater samples. As a comparison, its hybridoma-derived counterpart (murine monoclonal antibody) was evaluated. The antibody-doped material was prepared via an optimized sol-gel process; its stability and binding efficiency of MC-LR in spiked freshwater samples were thoroughly tested using the ELISA and orthogonal LC-MS methods. For removal, two column-based procedures with sequential or continuous cyclic sample addition and a suspension mode (moving adsorbent) were tested. Noteworthy the results obtained with a crude antibody fraction were fully compatible with the highly purified preparation. This study paves the way for further investigation being focused on novel applications of plant-derived anti-MC-LR antibodies in bioremediation to selectively deplete the toxin from freshwater: a green and promising technology without secondary pollution.

Pharmaceuticals and pesticides in secondary effluent wastewater: Identification and enhanced removal by acid-activated ferrate(VI)

The emergence of resistance to antibacterial drugs and pesticides in water is unprecedented. This may have adverse consequences to human health and ecological systems. This paper first sought the identification of a wide range of pharmaceuticals and pesticides in two secondary effluent wastewaters (SEW) of different quality characteristics, followed by their removal by ferrate(VI) (Fe(VI), FeO₄^2-). Screening for 22 pharmaceuticals and 32 pesticides, revealed that 11 pharmaceuticals and 3 pesticides in SEW of plant A, and 14 pharmaceuticals and 5 pesticides in SEW of plant B were present at concentrations higher than the liquid chromatography mass spectrometry method quantitation limit. The concentrations of pharmaceuticals and pesticides ranged from 0.15 ng/L-413.03 ng/L. Investigation of the removal of these pharmaceuticals and pesticides by Fe(VI) showed that some had recalcitrant activity towards their oxidation. Acid-activated Fe(VI) resulted in enhanced oxidation (12.6%-56.2% degradation efficiency) of 6 and 7 pharmaceuticals in SEW of plant A and plant B, respectively, at a shorter time than Fe(VI) without activation (i.e. 3-5 min versus 15-30 min). The degradation of 1 and 3 pesticides in SEW of plant A and plant B respectively, has also been enhanced by activating Fe(VI) (13.8%-86.2% degradation efficiency). Results on testing of organic matter characterization of treated SEW with and without acid-activated Fe(VI) treatment are also presented. Acid-activated Fe(VI) treatment has potential in enhancing the removal of micropollutants in real wastewater.

Highly effective oxidation of roxarsone by ferrate and simultaneous arsenic removal with in situ formed ferric nanoparticles

Roxarsone (ROX) is used in breeding industry to prevent infection by parasites, stimulate livestock growth and improve pigmentation of livestock meat. After being released into environment, ROX could be bio-degraded with the formation of carcinogenic inorganic arsenic (As) species. Here, ferrate oxidation of ROX was reported, in which we studied total-As removal, determined reaction kinetics, identified oxidation products, and proposed a reaction mechanism. It was found that the apparent second-order rate constant (k_app) of ferrate with ROX was 305 M^-1s^-1 at pH 7.0, 25 °C, and over 95% of total As was removed within 10 min when ferrate/ROX molar ratio was 20:1. Species-specific rate constants analysis showed that HFeO₄^- was the dominant species reacting with ROX. Ferrate initially attacked AsC bond of ROX and resulted in the formation of arsenate and 2-nitrohydroquinone. The arsenate was simultaneously removed by ferric nanoparticles formed in the reduction of ferrate, while 2-nitrohydroquinone was further oxidized into nitro-1,4-benzoquinone. These results suggest that ferrate treatment can be an effective method for the control of ROX in water treatment.

Rapid oxidation of iodide and hypoiodous acid with ferrate and no formation of iodoform and monoiodoacetic acid in the ferrate/I-/HA system

Toxic and odorous iodinated disinfection byproducts (I-DBPs) could form in the chemical oxidation of iodine-containing water. A critical step for controlling the hazardous I-DBPs is to convert the iodine species into stable and harmless iodate (IO₃^-) while inhibiting the accumulation of highly reactive hypoiodous acid (HOI). Herein, the oxidation of I^- and HOI with ferrate was investigated, and the formation profile of HOI was determined based on 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) coloring method through a stopped-flow spectrophotometer. The second-order rate constants (k_app) of ferrate with HOI decreased from 1.6 × 10⁵ M^-1s^-1 to 8.3 × 10² M^-1s^-1 as the solution pH varied from 5.3 to 10.3, which were 7.5, 7.2 and 13.8 times higher than that of ferrate with I^- at pH 6.0, 7.0 and 8.0, respectively. Compared with other oxidants such as ozone, hypochlorous acid, chloramine and potassium permanganate, ferrate would swiftly oxidize HOI formed in the I^- oxidation process. For the ferrate oxidation of I-containing water, HOI was swiftly oxidized to IO₃^- from pH 5.0 to 9.0. Phosphate buffer promoted the oxidation of I^- while inhibited the oxidation of HOI with ferrate. When 5 mgC/L of humic acids (HA) existed in the solution, no formation of iodoform and monoiodoacetic acid (MIAA) was observed in the oxidation of iodide (20 μM) with ferrate (from 10 μM to 80 μM). These results suggested that ferrate oxidation could be an effective method for the control of I-DBPs in iodine-containing water treatment.

Mitigation of algal organic matter released from Chaetoceros affinis and Hymenomonas by in situ generated ferrate

This study demonstrates the application of in situ ferrate (Fe(VI)) for the efficient removal of dissolved algal organic matter (AOM) from seawater. Sodium hypochlorite (NaOCl) and ferric (Fe(III)) were used to produce in situ Fe(VI) by wet chemical oxidation. First, the removal efficiencies of two model AOM compounds, humic acid (HA) and sodium alginate (SA), were evaluated in the presence of sodium chloride with an initial influent dissolved organic carbon (DOC) concentration of 5.0 mg C L^-1 at different pH levels to establish the optimal doses for in situ Fe(VI) generation. The concentration of Fe(VI) was determined by the 2,2-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) ultraviolet-visible spectrophotometry method. In the case of HA, 72% DOC removal was recorded when applied with 1.5 mg L^-1 of Fe(III) and 1.5 mg L^-1 of NaOCl (in situ Fe(VI) concentration of 1.46 mg L^-1) while 42% DOC removal was observed for SA. Subsequently, the removal of AOM extracted from two bloom-forming algal species, Chaetoceros affinis (CA) and Hymenomonas (Hym), cultivated in seawater from the Red Sea, were tested with in situ generated Fe(VI) at the established optimum condition. In situ Fe(VI) recorded superior performance in removing AOM extracted from CA and Hym, showing 83% and 92% DOC removal when the influent DOC concentrations were 2.48 and 2.63 mg L^-1, respectively. A detailed AOM characterization was conducted using liquid chromatography-organic carbon detection.

Separation of acrylonitrile-butadiene-styrene and polystyrene waste plastics after surface modification using potassium ferrate by froth flotation

This work develops a simple and practical process for separation of acrylonitrile-butadienestyrene (ABS) and polystyrene (PS) waste plastics by froth flotation after surface modification using potassium ferrate. ABS plastics containing brominated flame retardants (BFRs) can release hazardous emissions during the process of disposal. Moreover, ABS and PS are typical styrene plastics with similar properties, posing severe restrictions on their separation for recycling. Thus, potassium ferrate modification was investigated and found to decrease selectively the floatability of ABS, providing available process for separation of ABS and PS. Contact angle measurements, FT-IR, XPS and SEM characterization analysis confirmed that potassium ferrate modification can induce the desired changes in the surface properties of ABS. With consideration to separation of ABS and PS, the optimum conditions are potassium ferrate concentration 0.15 M/L, modification time 15 min, temperature 60 °C, stirring rate 200 rpm, frother concentration 14.50 mg/L and flotation time 2 min. Under optimum conditions, separation of ABS and PS with different mixing ratios was accomplished with a recovery and purity of 98.60% and 98.62% respectively. Moreover, reusing of potassium ferrate solution is feasible, further eliminating emissions and cost of this process. Consequently, surface modification using potassium ferrate can be applied for facilitating flotation separation of ABS and PS waste plastics.