Fenton-based technologies as efficient advanced oxidation processes for microcystin-LR degradation

Comparative genomic analysis and functional investigations for MCs catabolism mechanisms and evolutionary dynamics of MCs-degrading bacteria in ecology

Microcystins (MCs) significantly threaten the ecosystem and public health. Biodegradation has emerged as a promising technology for removing MCs. Many MCs-degrading bacteria have been identified, including an indigenous bacterium Sphingopyxis sp. YF1 that could degrade MC-LR and Adda completely. Herein, we gained insight into the MCs biodegradation mechanisms and evolutionary dynamics of MCs-degrading bacteria, and revealed the toxic risks of the MCs degradation products. The biochemical characteristics and genetic repertoires of strain YF1 were explored. A comparative genomic analysis was performed on strain YF1 and six other MCs-degrading bacteria to investigate their functions. The degradation products were investigated, and the toxicity of the intermediates was analyzed through rigorous theoretical calculation. Strain YF1 might be a novel species that exhibited versatile substrate utilization capabilities. Many common genes and metabolic pathways were identified, shedding light on shared functions and catabolism in the MCs-degrading bacteria. The crucial genes involved in MCs catabolism mechanisms, including mlr and paa gene clusters, were identified successfully. These functional genes might experience horizontal gene transfer events, suggesting the evolutionary dynamics of these MCs-degrading bacteria in ecology. Moreover, the degradation products for MCs and Adda were summarized, and we found most of the intermediates exhibited lower toxicity to different organisms than the parent compound. These findings systematically revealed the MCs catabolism mechanisms and evolutionary dynamics of MCs-degrading bacteria. Consequently, this research contributed to the advancement of green biodegradation technology in aquatic ecology, which might protect human health from MCs.

Degradation performance and mechanism of microcystins in aquaculture water using low-temperature plasma technology

The eutrophication of aquaculture water bodies seriously restricts the healthy development of the aquaculture industry. Among them, microcystins are particularly harmful. Therefore, the development of technologies for degrading microcystins is of great significance for maintaining the healthy development of the aquaculture industry. The feasibility and mechanism of removing microcystins-LR by dielectric barrier discharge (DBD) plasma were studied. DBD discharge power of 49.6 W and a treatment time of 40 min were selected as the more suitable DBD parameters, resulting in microcystin-LR removal efficiency of 90.4%. Meanwhile, the effects of initial microcystin-LR concentration, initial pH value, turbidity, anions on the degradation effect of microcystin-LR were investigated. The removal efficiency of microcystin-LR decreased with the increase of initial microcystin-LR concentration and turbidity. The degradation efficiency of microcystin-LR at pH 4.5 and 6.5 is significantly higher than that at pH 8.5 and 3.5. HCO3- can inhibit the removal efficiency of microcystin-LR. Furthermore, five intermediates products (m/z = 1029.5, 835.3, 829.3, 815.4, 642.1) were identified in this study, and the toxicity analysis of these degradation intermediates indicated that DBD treatment can reduce the toxicity of microcystin-LR. e－aq, •OH, H2O2, and O3 have been shown to play a major role in the degradation of microcystin-LR, and the contribution ranking of these active species is e－aq > •OH > H2O2 > O3. The application of DBD plasma technology in microcystin-LR removal and detoxification has certain development potential.

Non-negligible inhibition effect of microcystin-LR biodegradation products target to protein phosphatase 2A

Though biodegradation is an important regulation pathway for microcystins (MCs) pollution, more consideration needs to be given to the potential risk associated with related biodegradation products (MC-BDPs). In this work, typical MCLR-BDPs were prepared and their toxicity was evaluated by protein phosphatases (PPs) inhibition assay. Results showed the initial ring opening of MCLR played a crucial role in detoxification. However, partial MCLR-BDPs still retained the critical structures and thus exhibited certain toxicity (2.8-43.5% of MCLR). With the aid of molecular simulation, the mechanism for the potential toxicity of BDPs targeting PP2A was elucidated. The initial ring opening made the loss of hydrogen bond Leu2←Arg89, and pi-H bond Adda5-His191, which was responsible for the significant reduction in the toxicity of MCLR-BDP. However, the key hydrogen bonds MeAsp3←Arg89, Glu6←Arg89, Adda5←Asn117, Adda5←His118, Arg4→Pro213, Arg4←Arg214, Ala1←Arg268, and Mdha7←Arg268, metal bond Glu6-Mn12+, and ionic bonds Glu6-Arg89, and Glu6-Mn22+ were preserved in varying degrees. Above preserved interactions maintained the interactions between PP2A and Mn2+ ions (reducing the exposure of Mn2+ ions). Above preserved interactions also hindered the combination of phosphate groups to Arg214 residual and thus exhibited potential toxicity.

Effect and mechanism of norfloxacin removal by Eucalyptus leaf extract enhanced the ZVI/H2O2 process

The conventional ZVI/H2O2 technology suffers from poor reagent utilization, excess iron sludge generation, and strong low pH dependence. Therefore, eucalyptus leaf extract (ELE) was introduced to improve ZVI/H2O2 technology, and the efficacy and mechanism of ELE promoting ZVI/H2O2 technology were deeply explored. The results showed that the norfloxacin (NOR) removal and kobs of the ZVI/H2O2/ELE process were enhanced by 35.64 % and 3.27 times, respectively, compared to the ZVI/H2O2 process. In the ZVI/H2O2 process, the production of three reactive oxygen species (ROS: 1O2，·O2-，·OH) was effectively promoted by ELE so that the reaction efficacy was significantly enhanced. Moreover, the attack and degradation of pollutants by ROS was the main way to remove pollutants. With the introduction of ELE, the reactive sites on the catalyst appearance were increased to some extent, and the Fe(III)/Fe(II) cycle was improved. The analysis showed that ELE is rich in titratable acids and the ZVI/H2O2 technology is promoted mainly by lowering the pH of the process. In addition, the chelation of ELE and the reduction in pH by the ELE synergistically enhanced the ZVI/H2O2 technology, which significantly improved the reagent utilization (4.70 times for ZVI and 3.03 times for H2O2), broadened the pH range of the technology (6-9) and was able to effectively reduce the iron sludge contamination (30.33 %) of the process. Therefore, the study offers an important value to study eucalyptus leaves in micron-scale ZVI-Fenton technology.

Feasibility and mechanism of removing Microcystis aeruginosa and degrading microcystin-LR by dielectric barrier discharge plasma

Harmful cyanobacterial bloom is one of the serious environmental problems worldwide. Microcystis aeruginosa is a representative harmful alga in cyanobacteria bloom. It is of great significance to develop new technologies for the removal of Microcystis aeruginosa and microcystins. The feasibility and mechanism of removing microcystis aeruginosa and degrading microcystins by dielectric barrier discharge (DBD) plasma were studied. The suitable DBD parameters obtained in this study are DBD (41.5 W, 40 min) and DBD (41.5 W, 50 min), resulting in algae removal efficiency of 77.4% and 80.4%, respectively; scanning electron microscope and LIVE-DEATH analysis demonstrate that DBD treatment can disrupt cell structure and lead to cell death; analysis of elemental composition and chemical state indicated that there are traces of oxidation of organic nitrogen and organic carbon in microcystis aeruginosa; further intracellular ROS concentration and antioxidant enzyme activity analysis confirm that DBD damage microcystis aeruginosa through oxidation. Meanwhile, DBD can effectively degrade the microcystin-LR released after cell lysis, the extracellular microcystin-LR concentration in the DBD (41.5 W) group decreased by 88.7% at 60 min compared to the highest concentration at 20 min; further toxicity analysis of degradation intermediates indicated that DBD can reduce the toxicity of microcystin-LR. The contribution of active substances to the inactivation of microcystis aeruginosa is eaq- > •OH > H2O2 > O3 > 1O2 > •O2- > ONOO-, while on the degradation of microcystin-LR is eaq- > •OH > H2O2 > O3 > •O2- > 1O2 > ONOO-. The application of DBD plasma technology in microcystis aeruginosa algae removal and detoxification has certain prospects for promotion and application.

Sustainable bioremediation technologies for algal toxins and their ecological significance

The emergence of algal toxins in water ecosystems poses a significant ecological and human health concern. These toxins, produced by various algal species, can lead to harmful algal blooms, and have far-reaching consequences on biodiversity, food chains, and water quality. This review explores the types and sources of algal toxins, their ecological impacts, and the associated human health risks. Additionally, the review delves into the potential of bioremediation strategies to mitigate the effects of algal toxins. It discusses the role of microorganisms, enzymes, and algal-bacterial interactions in toxin removal, along with engineering approaches such as advanced oxidation processes and adsorbent utilization. Microbes and enzymes have been studied for their environmentally friendly and biocompatible properties, which make them useful for controlling or removing harmful algae and their toxins. The challenges and limitations of bioremediation are examined, along with case studies highlighting successful toxin control efforts. Finally, the review outlines future prospects, emerging technologies, and the need for continued research to effectively address the complex issue of algal toxins and their ecological significance.

Feasibility and mechanism of recycling carbon resources from waste cyanobacteria and reducing microcystin toxicity by dielectric barrier discharge plasma

Recycling carbon resources from discarded cyanobacteria is a worthwhile research topic. This study focuses on the use of dielectric barrier discharge (DBD) plasma technology as a pretreatment for anaerobic fermentation of cyanobacteria. The DBD group (58.5 W, 45 min) accumulated the most short chain fatty acids (SCFAs) along with acetate, which were 3.0 and 3.3 times higher than the control. The DBD oxidation system can effectively collapse cyanobacteria extracellular polymer substances and cellular structure, improve the biodegradability of dissolved organic matter, enrich microorganisms produced by hydrolysis and SCFAs, reduce the abundance of SCFAs consumers, thereby promoting the accumulation of SCFAs and accelerating the fermentation process. The microcystin-LR removal rate of 39.8% was obtained in DBD group (58.5 W, 45 min) on day 6 of anaerobic fermentation. The toxicity analysis using the ECOSAR program showed that compared to microcystin-LR, the toxicity of degradation intermediates was reduced. The contribution order of functional active substances to cyanobacteria cracking was obtained as eaq- > •OH > 1O2 > •O2- > ONOO-, while the contribution order to microcystin-LR degradation was eaq- > •OH > •O2- > 1O2 > ONOO-. DBD has the potential to be a revolutionary pretreatment method for cyanobacteria anaerobic fermentation.

Bibliometric analysis and literature review of ultrasound-assisted degradation of organic pollutants

Ultrasound as a clean, efficient, and cheap technique gains special attention in wastewater treatment. Ultrasound alone or coupled with hybrid processes have been widely studied for the treatment of pollutants in wastewater. Thus, it is essential to conduct a review about the research development and trends on this emerging technique. This work presents a bibliometric analysis of the topic associated with multiple tools such as Bibliometrix package, CiteSpace, and VOSviewer. The literature sources from 2000 to 2021 were collected from Web of Science database, and the data of 1781 documents were selected for bibliometric analysis in respect to publication trends, subject categories, journals, authors, institutions, as well as countries. Detailed analysis of keywords in respect to co-occurrence network, keyword clusters, and citation bursts was conducted to reveal the research hotspot and future directions. The development of the topic can be divided into three stages, and the rapid development begins from 2014. The leading subject category is Chemistry Multidisciplinary, followed by Environmental Sciences, Engineering Chemical, Engineering Environmental, Chemistry Physical, and Acoustics, and there exists difference in the publications of different categories. Ultrasonics Sonochemistry is the most productive journal (14.75 %). China is the leading country (30.26 %), followed by Iran (15.67 %) and India (12.35 %). The top 3 authors are Parag Gogate, Oualid Hamdaoui, and Masoud Salavati-Niasari. There exists close cooperation between countries and researchers. Analysis of highly cited papers and keywords gives a better understanding of the topic. Ultrasound can be employed to assist various processes such as Fenton-like process, electrochemical process, and photocatalysis for degradation of emerging organic pollutants for wastewater treatment. Research topics in this field evolve from typical studies on ultrasonic assisted degradation to latest studies on hybrid processes including photocatalysis for pollutants degradation. Additionally, ultrasound-assisted synthesis of nanocomposite photocatalysts receives increasing attention. The potential research directions include sonochemistry in pollutant removal, hydrodynamic cavitation, ultrasound-assisted Fenton or persulfate processes, electrochemical oxidation, and photocatalytic process.

Self-Immolative Polythiophene for Sunlight Inactivation of Harmful Cyanobacteria

Harmful cyanobacterial blooms and the released microcystins (MCs) caused serious environmental and public health concerns to drinking water safety. Photo-oxidation is an appealing treatment option and alternative to conventional flocculation and microbial antagonists, but the performances of current photosensitizers (either inorganic or organic) are unsatisfactory. Here, a polythiophene photosensitizer (PT10) with both high yield of reactive oxygen species (ROS) production (mainly ¹O₂, Φ_Δ = 0.51, > 8 h continuous generation) and moderate photostability was used as a powerful algaecide to inhibit Microcystis aeruginosa. Due to the positive charge of PT10, the algal cells were quickly flocculated, followed by efficient inactivation in 4 h under white light irradiation (96.7%, 10 mW/cm²). Meanwhile, PT10 was self-immolated in about 6 h. Upon biosafety evaluation with adult zebrafish, the low toxicity of PT10 and the degradation products of PT10 and algae (early logarithmic growth stage) were confirmed. In addition, microcystin-LR (MC-LR), a toxic microcystin that will be released during the destruction of the algal cells, was also degraded. Therefore, PT10-based photoinactivation of M. aeruginosa featured both high performance and low secondary pollution. In real-world aquatic systems, PT10 was confirmed to be capable of sunlight-assisted inactivation of M. aeruginosa and prevent algal blooms, thus making it appealing for environmental remediation.

Degradation of refractory organic matter in MBR effluent from treating landfill leachate by the UV-nZVI-H2O2 system

In this study, nano zero-valent iron (nZVI) was used as the Fe²⁺ source in the Fenton reaction, and a UV-nZVI-H₂O₂ system was constructed to efficiently degrade and mineralize refractory organic matter in landfill leachate. The results showed that under the optimal conditions (initial pH = 3, UV = 14 W, nZVI = 0.5 g/L, and [H₂O₂] = 30 mM), the removal efficiencies of total organic carbon, absorbance at 254 nm, and color number were 61.38%, 83.89%, and 85.79%, respectively. Control experiments show that the UV-nZVI-H₂O₂ system has the highest removal rate and mineralization rate of refractory organic matter. The excellent performance of the UV-nZVI-H₂O₂ system is related to a higher H₂O₂ utilization rate. The H₂O₂ residue in the UV-nZVI-H₂O₂ system was the lowest, and the effective utilization rate of H₂O₂ was as high as 98.80%. Alcohol quenching experiments and hydroxyl radical quantitative experiments showed that the dominant reactive oxygen species in the UV-nZVI-H₂O₂ system was HO^• and the yield of HO^• was as high as 2007.80 μM, which was much higher than that in other systems. The results of spectra analysis showed that the low molecular weight, high fluorescence frequency organic matter, and relatively stable aromatic organic matter were significantly degraded after treatment with the UV-nZVI-H₂O₂ system and the aromatic degree, humification degree, molecular weight, and molecular polymerization degree of refractory organic matter were also significantly decreased. The mechanism of the UV-nZVI-H₂O₂ reaction includes homogeneous and heterogeneous Fenton reactions and adsorption and precipitation of organic matter by iron-based colloids. This study can provide theoretical and technical support for the advanced treatment of refractory organic matter in landfill leachate.

Degradation of Organic Methyl Orange (MO) Dye Using a Photocatalyzed Non-Ferrous Fenton Reaction

Removal of recalcitrant organic pollutants by degradation or mineralization from industrial waste streams is continuously being explored to find viable options to apply on the commercial scale. Herein, we propose a titanium nanotube array (based on a non-ferrous Fenton system) for the successful degradation of a model contaminant azo dye, methyl orange, under simulated solar illumination. Titanium nanotube arrays were synthesized by anodizing a titanium film in an electrolyte medium containing water and ethylene glycol. Characterization by SEM, XRD, and profilometry confirmed uniformly distributed tubular arrays with 100 nm width and 400 nm length. The non-ferrous Fenton performance of the titanium nanotube array in a minimal concentration of H₂O₂ showed remarkable degradation kinetics, with a 99.7% reduction in methyl orange dye concentration after a 60 min reaction time when illuminated with simulated solar light (100 mW cm^-2, AM 1.5G). The pseudo-first-order rate constant was 0.407 µmol^-1 min^-1, adhering to the Langmuir-Hinshelwood model. Reaction product analyses by TOC and LC/MS/MS confirmed that the methyl orange was partially fragmented, while the rest was mineralized. The facile withdrawal and regeneration observed in the film-based titanium nanotube array photocatalyst highlight its potential to treat real industrial wastewater streams with a <5% performance drop over 20 reaction cycles.

Effect of three commercial algaecides on cyanobacteria and microcystin-LR: implications for drinking water treatment using activated carbon

Toxic cyanobacterial blooms in aquatic ecosystems are associated to both public health and environmental concerns worldwide. Depending on the treatment technologies used, the removal capacity of cyanotoxins by drinking water treatment plants (DWTPs) is not sufficient to reach safe levels in drinking water. Likewise, controlling these blooms with algaecide may impair the efficiency of DWTPs due to the possible lysis of cyanobacterial cells and consequent release of cyanotoxins. We investigated the effects of three commercial algaecides (cationic polymer, copper sulfate, and hydrogen peroxide) on the growth parameters of the cyanobacterium Microcystis aeruginosa and the release of microcystin-LR (MC-LR). The potential interference of each algaecide on the MC-LR removal by adsorption on activated carbon (AC) was also tested through adsorption isotherms and kinetics experiments. Most algaecides significantly decreased the cell density and biovolume of M. aeruginosa, as well as increased the release of MC-LR. Interestingly, the presence of the algaecides in binary mixtures with MC-LR affected the adsorption of the cyanotoxin. Relevant adsorption parameters (e.g., maximum adsorption capacity, adsorption intensity, and affinity between MC-LR and AC) were altered when the algaecides were present, especially in the case of the cationic polymer. Also, the algaecides influenced the kinetics (e.g., by shifting the initial adsorption and the desorption constant), which may directly affect the design and operation of DWTPs. Our study indicated that algaecides can significantly impact the fate and the removal of MC-LR in DWTPs when the adsorption process is employed, with important implications for the management and performance of such facilities.

Contribution of photocatalytic and Fenton-based processes in nanotwin structured anodic TiO2 nanotube layers modified by Ce and V

In the present work, nanotwin structured TiO₂ nanotube (TNT) layers are prepared by the electrochemical anodization technique to form the anatase phase and by surface modification via spin-coating of Ce and V precursors to form Ce-TNT and V-TNT, respectively. The surface and cross-sectional images by SEM revealed that the nanotubes have an average diameter of ∼130 nm and a length of ∼14 μm. In addition, the TEM images revealed the nanotwin structures of the nanotubes, especially the anatase (001) and (112) twin surfaces, that increase the transport of photogenerated charges. The photoinduced degradation of caffeine (CAF) by TNT, Ce-TNT, and V-TNT led to a degradation extent of 16%, 26% and 33%, respectively, whereas it increased to 26%, 38%, and 46% in the presence of H₂O₂, owing to the involvement of Fenton-based processes (in addition to photocatalysis). The effect of the Fenton-based processes accounts for about 10% of the total degradation extent of CAF. Finally, the mechanism of the photoinduced degradation of CAF was investigated. The main oxidative species were the hydroxyl radicals, and the better efficiency of V-TNT over Ce-TNT and TNT was ascribed to its negative surface, thus improving the interactions with CAF.

The detoxification activities and mechanisms of microcystinase towards MC-LR

Microcystins (MCs) are the most common and toxic cyanotoxins that are hazardous to human health and ecosystems. Microcystinase is the enzyme in charge of the initial step in the biodegradation of MCs. The characterization, application conditions, and detoxification mechanisms of microcystinase from an indigenous bacterium Sphingopyxis sp. YF1 towards MC-LR were investigated in the current study. The microcystinase gene of strain YF1 was most similar to Sphingomonas sp. USTB-05 and contained a CAAX-family conversed abortive Infection (ABI) domain. The microcystinase was successful obtained and purified by overexpression in Escherichia coli. The highest degradation rate of MC-LR was 1.0 μg/mL/min under the optimal condition of 30 ℃, pH 7, 20 μg/mL MC-LR, and 400 μg/mL microcystinase. The MC-degrading product was identified as linearized MC-LR, which possessed a much lower inhibitory activity against protein phosphatase 2A than MC-LR. Microcystinase interacted with MC-LR via amino acid residues involved in through the formation of conventional Hydrogen Bond, Pi-Pi T-shapes, Van der Waals force, and so on. The optimal MC-degrading condition of pure microcystinase and its detoxification mechanisms against MC-LR were revealed. The toxicity of purified linearized MC-LR was explored for the first time. These findings suggest that pure microcystinase may efficiently detoxify MCs and it is promising in the bioremediation of MC-polluted environments.

Preparation of a Heterogeneous Catalyst CuO-Fe2O3/CTS-ATP and Degradation of Methylene Blue and Ciprofloxacin

A heterogeneous particle catalyst (CuO-Fe2O3/CTS-ATP) was synthesized via injection molding and ultrasonic immersion method, which is fast and effective. The particle catalyst applied attapulgite (ATP) wrapped by chitosan (CTS) as support, which was loaded dual metal oxides CuO and Fe2O3 as active components. After a series of characterizations of catalysts, it was found that CuO and Fe2O3 were successfully and evenly loaded on the surface of the CTS-ATP support. The catalyst was used to degrade methylene blue (MB) and ciprofloxacin (CIP), and the experimental results showed that the degradation ratios of MB and CIP can reach 99.29% and 86.2%, respectively, in the optimal conditions. The degradation mechanism of as-prepared catalyst was analyzed according to its synthesis process and ∙OH production, and the double-cycle catalytic mechanism was proposed. The intermediate products of MB and CIP degradation were also identified by HPLC-MS, and the possible degradation pathways were put forward.

Degradation of the mixed organic solvents of tributyl phosphate and n-dodecane by heterogeneous Fenton-like oxidation using nanoscale zero-valent iron as the catalyst

The treatment and disposal of spent radioactive organic solvents, i.e., tributyl phosphate (TBP) and diluent (such as kerosene, n-dodecane, etc.), produced in the reprocessing of spent fuel in the closed cycle are crucial for the sustainable development of the nuclear industry. In this study, the synthesized nanoscale zero-valent iron (nZVI) was used as the heterogeneous Fenton-like catalyst to promote the generation of hydroxyl radicals (•OH) by reacting with H₂O₂ to degrade the mixed organic solvents of TBP and n-dodecane. nZVI was characterized by scanning electron microscopy (SEM), nitrogen adsorption/desorption isotherms, and X-ray photoelectron spectroscopy (XPS) to investigate the micro-morphology, nano-particle size, and surface valence state. The change of Fe²⁺/Fe³⁺ concentration ratio during the reaction was measured to clarify the performance of nZVI. The effects of temperature, catalyst dosage, H₂O₂ dosage, and acidifier concentration on the degradation of TBP and n-dodecane were studied, and the results were complemented by the COD of the aqueous solution and the volume reduction rate of the organic phase. The mixed organic solvents of TBP and n-dodecane containing Co²⁺ were used to simulate the spent radioactive organic solvents and to study the distribution of nuclides after the reaction. The results showed that most of the radioactivity was in the residual solution, and the condensate contained almost no radioactivity. The degradation of TBP and n-dodecane was carried out separately, which showed that n-dodecane was more difficult to degrade. Density functional theory (DFT) calculations were applied to determine the adsorption energy of organic solvents and nZVI. According to the Fourier transform infrared spectra (FTIR) and their corresponding DFT calculations, liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) of the sample after the reaction, the possible intermediates were analyzed, and the degradation mechanism was speculated.

Multiple pathways for the anaerobic biodegradation of microcystin-LR in the enriched microbial communities from Lake Taihu

Anaerobic biodegradation is a non-negligible elimination approach for microcystin (MC) pollution and exhibits important bioremediation potential for environmental problems. However, the specific anaerobic MC-degrading mechanism remains unclear and few functional bacteria have been found. In this study, three microbial communities of sludges from different locations in Lake Taihu were collected and further enriched by microcystin-LR (MC-LR) under anaerobic conditions. MC-LR (1 mg/L) could be completely degraded by these enriched microbial communities under anaerobic conditions, but their degradation rates were significantly different. In addition, two different ring-opening sites of MC-LR in Ala-Leu and Arg-Adda were observed, and three new anaerobic degradation products were first identified, including two hexapeptides (MeAsp-Arg-Adda-Glu-Mdha-Ala and Adda-Glu-Mdha-Ala-Leu-MeAsp) and one end-product pentapeptide (Glu-Mdha-Ala-Leu-MeAsp). Based on the chemical structures and temporal trends of all detected degradation products, two novel anaerobic biodegradation pathways of MC-LR were proposed. Moreover, the MC-degrading genes mlrABC were not detected among all microbial communities, which suggested that some new MC-degrading mechanisms might exist under anaerobic conditions. Finally, through the comparison of microbial community structure, Gemmatimonas and Smithella were deduced as possible anaerobic MC-degrading bacteria. These findings strongly indicate that anaerobic biodegradation is an important method of self-repair in the natural environment and provides a potential removal strategy for MC pollution.

Removal of microcystins from water and primary treatment technologies - A comprehensive understanding based on bibliometric and content analysis, 1991-2020

Microcystins are a group of heptapeptide hepatotoxins produced by a variety of algae and are frequently detected in aquatic ecosystems, posing a global threat to ecological stability and human health. However, it is difficult to eliminate them completely and innocuously from water by conventional water treatment processes. This study comprehensively evaluated a total of 821 original articles retrieved from the Web of Science (1991-2020) about the removal of microcystins using bibliometric and content analysis to provide a qualitative and quantitative research landscape and a global view of research hotspots and future research directions. Furthermore, the primary and promising treatment technologies for microcystin pollution were also summarized and discussed. The results indicated an urgent practical demand to remediate microcystin pollution according to the increasing number of publications since 2005. China had the highest number of publications, whereas the United States was the core country in the international collaboration network. The Chinese Academy of Sciences and University of Cincinnati showed their leading positions considering article amounts and academic cooperation. Dionysiou DD contributed the most articles, and Carmichael WW had the highest number of co-citations. Three treatment technologies, including biodegradation, chemical oxidation and adsorption, were the major strategies to remediate the pollution of microcystins in water. In addition, the toxicity of toxins/their metabolites, degradation kinetics, and elimination mechanism were also important research contents. Bacterial degradation, photocatalytic degradation, and multiple-technologies approach have been identified with great potential and should be given more attention in future studies. This work summarizes the current research status on microcystin management, provides a valuable reference for researchers to identify potential opportunities for collaboration in related fields, and guides future research directions to inter-disciplinary and multi-perspective approaches.

Austenitic Stainless Steel as a Catalyst Material for Photo-Fenton Degradation of Organic Dyes

In this paper, a typical austenitic stainless steel was used as a catalyst in the visible photo-Fenton degradation process of two model dyes, methylene blue and methylorange, in the presence of hydrogen peroxide and potassium persulfate as free radical-generating species. The concentration intervals for both peroxide and persulfate were in the range of 333–1667 μg/L. Very high photodecoloration efficiencies have been achieved using peroxide (>93%), while moderate ones have been achieved using persulfate (>75%) at a pH value of 6.5. For methylene blue, the maximum mineralization yield of 74.5% was achieved using 1665 μg/L of hydrogen peroxide, while methylorange was better mineralized using 999 μg/L of persulfate. The photodegradation of the dye occurred in two distinct steps, which were successfully modeled by the Langmuir–Hinshelwood pseudo-first-order kinetic model. Reaction rate constants k between 0.1 and 4.05 h−1 were observed, comparable to those presented in the reference literature at lower pH values and higher concentrations of total iron from the aqueous media.

Polythiophene for Near Full pH Photo-antimicrobial

Microbial infections are currently one of the world’s major public health cares, the evolution of which has resulted in the development of multiple tolerances (not just the drug or antibiotic...

A Critical Review on Removal of Gaseous Pollutants Using Sulfate Radical-based Advanced Oxidation Technologies

Excessive emissions of gaseous pollutants such as SO₂, NO_x, heavy metals (Hg, As, etc.), H₂S, VOCs, etc. have triggered a series of environmental pollution incidents. Sulfate radical (SO₄•^-)-based advanced oxidation technologies (AOTs) are one of the most promising gaseous pollutants removal technologies because they can not only produce active free radicals with strong oxidation ability to simultaneously degrade most of gaseous pollutants, but also their reaction processes are environmentally friendly. However, so far, the special review focusing on gaseous pollutants removal using SO₄•^--based AOTs is not reported. This review reports the latest advances in removal of gaseous pollutants (e.g., SO₂, NO_x, Hg, As, H₂S, and VOCs) using SO₄•^--based AOTs. The performance, mechanism, active species identification and advantages/disadvantages of these removal technologies using SO₄•^--based AOTs are reviewed. The existing challenges and further research suggestions are also commented. Results show that SO₄•^--based AOTs possess good development potential in gaseous pollutant control field due to simple reagent transportation and storage, low product post-treatment requirements and strong degradation ability of refractory pollutants. Each SO₄•^--based AOT possesses its own advantages and disadvantages in terms of removal performance, cost, reliability, and product post-treatment. Low free radical yield, poor removal capacity, unclear removal mechanism/contribution of active species, unreliable technology and high cost are still the main problems in this field. The combined use of multiactivation technologies is one of the promising strategies to overcome these defects since it may make up for the shortcomings of independent technology. In order to improve free radical yield and pollutant removal capacity, enhancement of mass transfer and optimization design of reactor are critical issues. Comprehensive consideration of catalytic materials, removal chemistry, mass transfer and reactor is the promising route to solve these problems. In order to clarify removal mechanism, it is essential to select suitable free radical sacrificial agents, probes and spin trapping agents, which possess high selectivity for target specie, high solubility in water, and little effect on activity of catalyst itself and mass transfer/diffusion parameters. In order to further reduce investment and operating costs, it is necessary to carry out the related studies on simultaneous removal of more gaseous pollutants.

Sucrose-derived N-doped carbon xerogels as efficient peroxydisulfate activators for non-radical degradation of organic pollutants

Metal-free activation of peroxydisulfate (PDS) for degrading organic pollutants in water has received increasing attention because it can prevent secondary pollution. However, most of the catalysts that are efficient are derived from non-renewable fossil resources, are very expensive and have complex preparation processes. Also, the emerging non-radical mechanism is still unclear. Herein, 3D sucrose-derived N-doped carbon xerogels (NCXs) were synthesized by a simple and sustainable hydrothermal process and then employed as novel metal-free PDS activators to degrade organic pollutants. The structure, composition and performance of NCXs were regulated by changing the carbonization temperature. The sample carbonized at 900 °C (NCX900) exhibited the best catalytic performance, completely removing bisphenol A in 60 min. Quenching experiments and linear sweep voltammograms demonstrated that PDS was activated mainly through an electron-transfer non-radical mechanism. It was found that graphitic N played a critical role in activating PDS. With this non-radical mechanism, the NCX900/PDS system could adapt well to the wide pH range (3-11) and high Cl^- concentration; it selectively oxidized organic pollutants with low ionization potentials. This work provides a sustainable approach to the low-cost and efficient metal-free catalysts for wastewater treatment.