### Oct 2021, Volume 15 Issue 5

Cover illustration

• Front Cover Story (see: Shuchang Wang, Binbin Shao, Junlian Qiao, Xiaohong Guan, 2021, 15(5): 80)
The past two decades have witnessed the rapid development and wide application of Fe(VI) in the field of water de-contamination because of its environmentally benign character. Fe(VI) has been mainly applied as a highly efficient oxidant/disinfectant for the selective elimination of contaminan [Detail] ...

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Chunyan Wang, Jiangshan Wang, Yi Liu, Lei Zhang, Yong Sun, Jiuhui Qu

• A survey on individual’s perception of SARS-CoV-2 transmission was conducted.

• Waterborne transmission risks are far less perceived by individuals.

• Precautions of preventing wastewater mediated transmission are implemented.

• The precautions for wastewater transmission are less favored by the public.

• Education level differs the most regarding to waterborne transmission perception.

SARS-CoV-2 has been detected in various environmental media. Community and individual-engaged precautions are recommended to stop or slow environmentally-mediated transmission. To better understand the individual’s awareness of and precaution to environmental dissemination of SARS-CoV-2, an online survey was conducted in Beijing during March 14–25, 2020. It is found that the waterborne (especially wastewater mediated) spreading routes are far less perceived by urban communities. The precautions for wastewater transmission are less favored by the public than airborne and solid waste mediated spreading routes. Such risk communication asymmetry in waterborne transmission will be further enlarged in places with fragile water system. Furthermore, education level is the most significant attribution (Sig.<0.05) that causes the difference of awareness and precautions of the waterborne transmission among the respondents, according to the variance analysis results. Our survey results emphasize the urgent need for evidence-based, multifactorial precautions for current and future outbreaks of COVID-19.

• RESEARCH ARTICLE
Seyyed Salar Meshkat, Ebrahim Ghasemy, Alimorad Rashidi, Omid Tavakoli, Mehdi Esrafili

• Synthesis of NS-CNTS is used in a high desulfurization performance.

• Synthesizing NS-CNT is considered as a novel adsorbent from low-cost precursors.

• A high sulfur removal capacity for NS-CNT is attained compared with recent works.

Herein, nitrogen and sulfur co-doped carbon nanotubes (NS-CNT) adsorbents were synthesized via the chemical vapor deposition technique at 1000°C by employing the camphor, urea and sulfur trioxide pyridine. In this study, desulfurization of two types of mercaptans (dibenzothiophene (DBT) and tertiary butyl mercaptan (TBM) as nonlinear and linear forms of mercaptan) was studied. In this regard, a maximum capacity of NS-CNT was obtained as 106.9 and 79.4 mg/g and also the removal efficiencies of 98.6% and 88.3% were achieved after 4 h at 298K and 0.9 g of NS-CNT for DBT and TBM, respectively. Characterization of the NS-CNTs was carried out through exploiting scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and elemental analysis (CHN). The isotherm equilibrium data could be ascribed to the Freundlich nonlinear regression form and the kinetic data was fitted by nonlinear form of the pseudo second order model. The negative values of ΔS0, ΔH0 and ΔG0 specify that the adsorption of both types of mercaptans was a natural exothermic process with a reduced entropy. Maintenance of more than 96% of the adsorption capacity even after nine cycles suggest the NS-CNT as a superior adsorbent for mercaptans removal in the industry. Density functional theory (DFT) calculations were also performed to peruse the effects of S/N co-doping and carbon monovacancy defects in CNTs toward the adsorption of DBT and TBM.

• RESEARCH ARTICLE
Guowen Hu, Zeqi Zhang, Xuan Zhang, Tianrong Li

• Size and shape-dependent MnFe2O4 NPs were prepared via a facile method.

• Ligand-exchange chemistry was used to prepare the hydrophilic MnFe2O4 NPs.

• The catalytic properties of MnFe2O4 NPs toward dye degradation were fully studied.

• The catalytic activities of MnFe2O4 NPs followed Michaelis–Menten behavior.

• All the MnFe2O4 NPs exhibit selective degradation to different dyes.

The magnetic nanoparticles that are easy to recycle have tremendous potential as a suitable catalyst for environmental toxic dye pollutant degradation. Rationally engineering shapes and tailoring the size of nanocatalysts are regarded as an effective manner for enhancing performances. Herein, we successfully synthesized three kinds of MnFe2O4 NPs with distinctive sizes and shapes as catalysts for reductive degradation of methylene blue, rhodamine 6G, rhodamine B, and methylene orange. It was found that the catalytic activities were dependent on the size and shape of the MnFe2O4 NPs and highly related to the surface-to-volume ratio and atom arrangements. Besides, all these nanocatalysts exhibit selectivity to different organic dyes, which is beneficial for their practical application in dye pollutant treatment. Furthermore, the MnFe2O4 NPs could be readily recovered by a magnet and reused more than ten times without appreciable loss of activity. The size and shape effects of MnFe2O4 nanoparticles demonstrated in this work not only accelerate further understanding the nature of nanocatalysts but also contribute to the precise design of nanoparticles catalyst for pollutant degradation.

• RESEARCH ARTICLE
Guolong Zeng, Yiyang Liu, Xiaoguo Ma, Yinming Fan

• Magnetic multi-template molecularly imprinted polymer composite was synthesized.

• MIP composite was used as the adsorbent for removal of tetracyclines from water.

• MIP composite showed excellent adsorption selectivity toward tetracyclines.

• MIP composite possessed good reusability.

Antibiotic contamination of the water environment has attracted much attention from researchers because of their potential hazards to humans and ecosystems. In this study, a multi-template molecularly imprinted polymer (MIP) modified mesoporous silica coated magnetic graphene oxide (MGO@MS@MIP) was prepared by the surface imprinting method via a sol-gel process and was used for the selective, efficient and simultaneous removal of tetracyclines (TCs), including doxycycline (DC), tetracycline (TC), chlorotetracycline (CTC) and oxytetracycline (OTC) from water. The synthesized MIP composite was characterized by Fourier transform infrared spectroscopy, transmission electron microscope and thermogravimetric analysis. The adsorption properties of MGO@MS@MIP for these TCs were characterized through adsorption kinetics, isotherms and selectivity tests. The MIP composite revealed larger adsorption quantities, excellent selectivity and rapid kinetics for these four tetracyclines. The adsorption process was spontaneous and endothermic and followed the Freundlich isotherm model and the pseudo-second-order kinetic model. The MGO@MS@MIP could specifically recognize DC, TC, CTC and OTC in the presence of some chemical analogs. In addition, the sorption capacity of the MIP composite did not decrease significantly after repeated application for at least five cycles. Thus, the prepared magnetic MIP composite has great potential to contribute to the effective separation and removal of tetracyclines from water.

• RESEARCH ARTICLE
Majid Mustafa, Huijiao Wang, Richard H. Lindberg, Jerker Fick, Yujue Wang, Mats Tysklind

• Effect of converting ozonation to E-peroxone was studied on pharmaceutical removal.

• A QSAR model was developed for selected 89 pharmaceuticals of special concern.

• Both processes abated the pharmaceuticals of moderate and high $kO3$ quickly.

• E-peroxone process accelerated the elimination of pharmaceuticals with low $k O3$.

• Developed QSAR model reliably predicted $kO3$ of 418 out of 491 pharmaceuticals.

The abatements of 89 pharmaceuticals in secondary effluent by ozonation and the electro-peroxone (E-peroxone) process were investigated. Based on the results, a quantitative structure-activity relationship (QSAR) model was developed to explore relationship between chemical structure of pharmaceuticals and their oxidation rates by ozone. The orthogonal projection to latent structure (OPLS) method was used to identify relevant chemical descriptors of the pharmaceuticals, from large number of descriptors, for model development. The resulting QSAR model, based on 44 molecular descriptors related to the ozone reactivity of the pharmaceuticals, showed high goodness of fit (R2 = 0.963) and predictive power (Q2 = 0.84). After validation, the model was used to predict second-order rate constants of 491 pharmaceuticals of special concern ($kO3$) including the 89 studied experimentally. The predicted $k O3$ values and experimentally determined pseudo-first order rate constants of the pharmaceuticals’ abatement during ozonation (kOZ) and the E-peroxone process (kEP) were then used to assess effects of switching from ozonation to the E-peroxone process on removal of these pharmaceuticals. The results indicate that the E-peroxone process could accelerate the abatement of pharmaceuticals with relatively low ozone reactivity ($kO3$<~102 M-1·s1) than ozonation (3–10 min versus 5–20 min). The validated QSAR model predicted 66 pharmaceuticals to be highly O3-resistant. The developed QSAR model may be used to estimate the ozone reactivity of pharmaceuticals of diverse chemistry and thus predict their fate in ozone-based processes.

• RESEARCH ARTICLE
Ziyue Yin, Qing Lin, Shaohui Xu

• The long-period groundwater evolution was identified by hydrochemical signatures.

• The dominant processes in the groundwater evolution were verified.

• Groundwater quality in the coastal areas was susceptible to deterioration due to SI.

• Groundwater contamination arose from fertilizer, livestock manure & domestic sewage.

The evolution of hydrochemical compositions influenced by long-period interactions between groundwater and the geo-environment is a fundamental issue for exploring groundwater quality and vulnerability. This study systematically investigated the hydrochemical processes and anthropogenic interference occurring in the river basin by bivariate plots, Gibbs diagrams, saturation index, and the major ions ratios. Apparent changes in groundwater hydrochemistry have been observed in the study area, illustrating the origins of major ions are affected by various internal and external factors. Results highlighted that TDS varied from freshwater to brackish water, ranging between 187.90 and 2294.81 mg/L. Ca2+ and HCO3 are the dominant ions in the studied samples. The results gained by Gibbs diagrams, bivariate plots, saturation index, and the major ions ratios demonstrated that minerals dissolution/precipitation, cation exchange, and human inputs play crucial roles in the unconfined aquifers. Moreover, the overuse of nitrogen fertilizer, livestock manure, and industrial/domestic sewage led to nitrate and nitrite contamination and brought significant challenges to the surrounding hydrogeo-environment. The present study could make an unambiguous identification of natural processes and anthropogenic interventions influencing groundwater hydrochemistry’s long-period evolution and create a preliminary strategy for groundwater resources management.

• RESEARCH ARTICLE
Yuan Meng, Weiyi Liu, Heidelore Fiedler, Jinlan Zhang, Xinrui Wei, Xiaohui Liu, Meng Peng, Tingting Zhang

• PPCPs had the highest removal efficiency in A2O combined with MBR process (86.8%).

• ARGs and OPFRs were challenging to remove (6.50% and 31.0%, respectively).

• Octocrylene and tris(2-ethylhexyl) phosphate posed high risks to aquatic organisms.

• Meta-analysis was used to compare the ECs removal in wastewater treatment.

• Membrane treatment technology is the most promising treatment for ECs removal.

Reclaimed water has been widely applied in irrigation and industrial production. Revealing the behavior of emerging contaminants in the production process of reclaimed water is the first prerequisite for developing relevant water quality standards. This study investigated 43 emerging contaminants, including 22 pharmaceuticals and personal care products (PPCPs), 11 organophosphorus flame retardants (OPFRs), and 10 antibiotic resistance genes (ARGs) in 3 reclaimed wastewater treatment plants (RWTPs) in Beijing. The composition profiles and removal efficiencies of these contaminants in RWTPs were determined. The results indicated that the distribution characteristics of the different types of contaminants in the three RWTPs were similar. Caffeine, sul2 and tris(1-chloro-2-propyl) phosphate were the dominant substances in the wastewater, and their highest concentrations were 27104 ng/L, 1.4 × 107 copies/mL and 262 ng/L, respectively. Ofloxacin and sul2 were observed to be the dominant substances in the sludge, and their highest concentrations were 5419 ng/g and 3.7 × 108 copies/g, respectively. Anaerobic/anoxic/oxic system combined with the membrane bioreactor process achieved a relatively high aqueous removal of PPCPs (87%). ARGs and OPFRs were challenging to remove, with average removal rates of 6.5% and 31%, respectively. Quantitative meta-analysis indicated that tertiary treatment processes performed better in emerging contaminant removal than secondary processes. Diethyltoluamide exhibited the highest mass load discharge, with 33.5 mg/d per 1000 inhabitants. Octocrylene and tris(2-ethylhexyl) phosphate posed high risks (risk quotient>1.0) to aquatic organisms. This study provides essential evidence to screen high priority pollutants and develop corresponding standard in RWTPs.

• RESEARCH ARTICLE
Kangying Guo, Baoyu Gao, Jie Wang, Jingwen Pan, Qinyan Yue, Xing Xu

•PSBF performed better than PAC and PAM in CODCr removals.

•PSBF was more insensitive to changing pH than PAC and PAM.

•PAC could remove humic acid-like pollutants and dye particles.

•PSBF was efficient in removing tryptophan-like pollutants from PPDW.

•A secondary coagulation-flocculation process (PAC→PSBF) is proposed here.

In our previous studies, several papermaking sludge-based flocculants (PSBFs) were synthesized from wood pulp papermaking sludge. The structure-activity relationships of the PSBFs have been investigated in simulated dye wastewater treatment, but their efficiencies in practical printing and dyeing wastewater (PPDW) treatment are unknown. Herein, an PSBF was prepared, and its performance is discussed in comparison to polyaluminium chloride (PAC) and polyacrylamide (PAM) in PPDW treatment. The PSBF was used in three ways: as an independent flocculant, as a PAC aid, or used to treat the effluent of the PAC system. The results indicated that adding PSBF alone produced similar color and chemical oxygen demand (CODCr) removals as the PAC system alone, but PSBF performed better than PAC when the pH of PPDW was higher than 7.0. Adding PSBF as a PAC aid improved the color, CODCr and turbidity removals, but the elimination efficiencies were slightly lower than those of the PAC+ PAM system. However, when PSBF was used as a flocculant to treat the effluent of the PAC system (PAC→PSBF), the effluent qualities were enhanced. Compared with the PAC system, the color and CODCr removals of PAC→PSBF system increased by 16.21% and 13.26%, respectively. The excitation and emission matrix fluorescence results indicated that PSBF removed tryptophan-like pollutants more efficiently than PAC. Considering the pH requirements of the subsequent bioreactor treatment in practice, the PAC→PSBF system were also investigated at the PPDW pH level of 7.0. Its maximum removal efficiencies of color, CODCr and turbidity were 90.17%, 32.60% and 82.50%, respectively.

• RESEARCH ARTICLE
Hao Wang, Defang Ma, Weiye Shi, Zhiyu Yang, Yun Cai, Baoyu Gao

•HAAs was dominant among the DBPs of interest.

•Rising time, dose, temperature and pH raised TCM and HAAs but reduced HANs and HKs.

•Low time, dose and temperature and non-neutrality pH reduced toxic risks of DBPs.

•The presence of EPS decelerated the production of DBPs.

•EPS, particularly polysaccharides were highly resistant to chlorine.

Periodic chemical cleaning with sodium hypochlorite (NaClO) is essential to restore the membrane permeability in a membrane bioreactor (MBR). However, the chlorination of membrane foulants results in the formation of disinfection by-products (DBPs), which will cause the deterioration of the MBR effluent and increase the antibiotic resistance in bacteria in the MBR tank. In this study, the formation of 14 DBPs during chemical cleaning of fouled MBR membrane modules was investigated. Together with the effects of biofilm extracellular polymeric substances (EPS), influences of reaction time, NaClO dosage, initial pH, and cleaning temperature on the DBP formation were investigated. Haloacetic acids (HAAs) and trichloromethane (TCM), composed over 90% of the DBPs, were increasingly accumulated as the NaClO cleaning time extended. By increasing the chlorine dosage, temperature, and pH, the yield of TCM and dichloroacetic acid (DCAA) was increased by up to a factor of 1‒14, whereas the yields of haloacetonitriles (HANs) and haloketones (HKs) were decreased. Either decreasing in the chlorine dosage and cleaning temperature or adjusting the pH of cleaning reagents toward acidic or alkaline could effectively reduce the toxic risks caused by DBPs. After the EPS extraction pretreatment, the formation of DBPs was accelerated in the first 12 h due to the damage of biofilm structure. Confocal laser scanning microscopy (CLSM) images showed that EPS, particularly polysaccharides, were highly resistant to chlorine and might be able to protect the cells exposed to chlorination.

• RESEARCH ARTICLE
Chengjie Xue, Juan Wu, Kuang Wang, Yunqiang Yi, Zhanqiang Fang, Wen Cheng, Jianzhang Fang

• Biochar enhanced the mobility and stability of zero-valent iron nanoparticles.

• Particle performance was best when the BC:nZVI mass ratio was 1:1.

• Bagasse-BC@nZVI removed 66.8% of BDE209.

The addition of nano zero-valent iron (nZVI) is a promising technology for the in situ remediation of soil. Unfortunately, the mobility and, consequently, the reactivity of nZVI particles in contaminated areas decrease due to their rapid aggregation. In this study, we determined how nZVI particles can be stabilized using different types of biochar (BC) as a support (BC@nZVI). In addition, we investigated the transport behavior of the synthesized BC@nZVI particles in a column filled with porous media and their effectiveness in the removal of BDE209 (decabromodiphenyl ether) from soil. The characterization results of N2 Brunauer–Emmett–Teller (BET) surface area analyses, scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) indicated that nZVI was successfully loaded into the BC. The sedimentation test results and the experimental breakthrough curves indicated that all of the BC@nZVI composites manifested better stability and mobility than did the bare-nZVI particles, and the transport capacity of the particles increased with increasing flow velocity and porous medium size. Furthermore, the maximum concentrations of the column effluent for bagasse–BC@nZVI (B–BC@nZVI) were 19%, 37% and 48% higher than those for rice straw–BC@nZVI (R–BC@nZVI), wood chips–BC@nZVI (W–BC@nZVI) and corn stalks–BC@nZVI (C–BC@nZVI), respectively. A similar order was found for the removal and debromination efficiency of decabromodiphenyl ether (BDE209) by the aforementioned particles. Overall, the attachment of nZVI particles to BC significantly increased the reactivity, stability and mobility of B–BC@nZVI yielded, and nZVI the best performance.

• RESEARCH ARTICLE
Yi Qian, Weichuan Qiao, Yunhao Zhang

• OBS inhibited the growth of P. stutzeri and destroyed its structure.

• OBS was toxic to the aerobic denitrification process of P. stutzeri.

• OBS induced the production of ROS in P. stutzeri.

• OBS affected the expression of key genes involved in denitrification and SOD.

The toxicities of sodium perfluorononyloxy-benzenesulfonate (OBS) to animals and plants are similar to those of perfluorooctane sulfonate. However, the mechanism of its toxicity to aerobic denitrifying bacteria is still unclear. In the present study, the ecotoxicity of OBS on an aerobic denitrifying strain, Pseudomonas stutzeri, was evaluated. The results showed that a dosage of OBS clearly affected the growth and aerobic denitrification of P. stutzeri. When compared with an unamended control, the degradation efficiency of the total nitrogen decreased by 30.13% during exposure to 200 mg/L of OBS, and the complete degradation time of nitrate-nitrogen was delayed by 4 h. The lactate dehydrogenase and superoxide dismutase produced by the bacteria increased with the concentration of OBS, and reactive oxygen species were also detected by confocal laser scanning microscope imaging. Transmission electron microscope imaging revealed chromosome deformation of the cells and damage to cell content; moreover, outer membrane vesicles were secreted from the bacteria, which was the important detoxification mechanism of P. stutzeri to OBS. Expression of the genes involved in aerobic nitrification and oxidative stress were also changed under OBS stress, which further confirmed the toxicity of OBS to P. stutzeri. This study reveals the environmental exposure risk of OBS from the perspective of microorganisms.

• ERRATUM
• RESEARCH ARTICLE
Zhifei Ma, Huali Cao, Fengchun Lv, Yu Yang, Chen Chen, Tianxue Yang, Haixin Zheng, Daishe Wu

• The MCNZVI is prepared as an interesting material for PS activation.

• Graphitized carbon shells facilitate electron transfer from Fe0.

• The MCNZVI exhibits excellent performance to degrade RB5 by 1O2.

• The MCNZVI has high stability and reusability in the oxidation system.

High-efficiency and cost-effective catalysts with available strategies for persulfate (PS) activation are critical for the complete mineralization of organic contaminants in the environmental remediation and protection ﬁelds. A nanoscale zero-valent iron-embedded modified mesoporous carbon (MCNZVI) with a core-shell structure is synthesized using the hydrothermal synthesis method and high-temperature pyrolysis. The results showed that nZVI could be impregnated within mesoporous carbon frameworks with a comparatively high graphitization degree, rich nitrogen doping content, and a large surface area and pore volume. This material was used as a persulfate activator for the oxidation removal of Reactive Black 5 (RB5). The effects of the material dosage, PS concentration, pH, and some inorganic anions (i.e., Cl, SO42) on RB5 degradation were then investigated. The highest degradation efficiency (97.3%) of RB5 was achieved via PS (20 mmol/L) activation by the MCNZVI (0.5 g/L). The pseudo-ﬁrst-order kinetics (k = 2.11 × 102 min1) in the MCNZVI/PS (0.5 g/L, 20 mmol/L) was greater than 100 times than that in the MCNZVI and PS. The reactive oxygen species (ROS), including 1O2, SO4·, HO·, and ·O2, were generated by PS activation with the MCNZVI. Singlet oxygen was demonstrated to be the primary ROS responsible for the RB5 degradation. The MCNZVI could be reused and regenerated for recycling. This work provides new insights into PS activation to remove organic contamination.

• REVIEW ARTICLE
Violeta Makareviciene, Egle Sendzikiene, Ieva Gaide

• Microalgae oil application for biodiesel synthesis is discussed.

• Catalytic effectiveness of ferment preparations and chemical catalyst is disputed.

• Application of heterogeneous catalysts for biodiesel synthesis is reviewed.

• Possibilities of catalyst regeneration is shown.

Recently, there is a growing interest in the use of microalga in various fields. Microalgae have properties such as rapid reproduction and high biomass accumulation, and under certain conditions, some are able to accumulate a large amount of oil. However, microalgae oil often contains more free fatty acids than the vegetable oil and is therefore unsuitable for biodiesel synthesis using alkaline catalysts. For this reason, some authors suggest the application of heterogeneous catalysis. A particular interest in the use of immobilized enzymes has developed. Other solid substances can also be used as heterogeneous catalysts are usually metal oxides, carbonates or zeolites. The use of these catalysts results in simpler biodiesel synthesis, especially purification processes, a cleaner end product and a less polluted environment. The molar ratio of alcohol to oil is lower during enzymatic transesterification, and more than 90% ester yield is obtained using a molar ratio of alcohol to oil of 3:1 to 4.5:1. The alcohols do not have a negative effect on the effectiveness of chemical catalysts, so it is possible to use alcohols in molar ratio from 4:1 to 12:1. The optimal temperature of enzymatic process is 30℃‒50℃. An ester yield of more than 95% was obtained in 12‒48 h. Using chemical catalysts, greater than a 95% yield of esters was obtained at higher temperatures in a shorter time. Material costs of enzymatic catalysis can be reduced by reusing the catalysts directly or after regeneration.

• RESEARCH ARTICLE
Yuanyuan Luo, Yangyang Zhang, Mengfan Lang, Xuetao Guo, Tianjiao Xia, Tiecheng Wang, Hanzhong Jia, Lingyan Zhu

• The source of DOM in surface water and sediment is inconsistent.

• The DOC content changes differently in surface water and sediment.

• The content of DOC in the surface water is lower than that in the sediment.

• The DOM in the surface water had higher photodegradation potentials than sediment.

Dissolved organic matter (DOM) in rivers is a critical regulator of the cycling and toxicity of pollutants and the behavior of DOM is a key indicator for the health of the environment. We investigated the sources and characteristics of DOM in surface water and sediment samples of the Wei River, China. Dissolved organic carbon (DOC) concentration and ultraviolet absorbance at 254 nm (UV254) increased in the surface water and were decreased in the sediment downstream, indicating that the source of DOM in the water differed from the sediment. Parallel factor (PARAFAC) analysis of the excitation-emission matrices (EEM) revealed the presence of terrestrial humus-like, microbial humus-like and tryptophan-like proteins in the surface water, whereas the sediment contained UVA humic-like, UVC humic-like and fulvic-like in the sediment. The DOM in the surface water and sediment were mainly derived from microbial metabolic activity and the surrounding soil. Surface water DOM displayed greater photodegradation potential than sediment DOM. PARAFAC analysis indicated that the terrestrial humic-like substance in the water and the fulvic-like component in the sediment decomposed more rapidly. These data describe the characteristics of DOM in the Wei River and are crucial to understanding the fluctuations in environmental patterns.

• RESEARCH ARTICLE
Shan Xue, Shaobin Sun, Weihua Qing, Taobo Huang, Wen Liu, Changqing Liu, Hong Yao, Wen Zhang

• 1,4-Dioxane was degraded via the photo-Fenton reactive membrane filtration.

• Degradation efficiency and AQY were both enhanced in photocatalytic membrane.

• There is a tradeoff between photocatalytic degradation and membrane permeation flux.

• Degradation pathways of 1,4-Dioxane is revealed by DFT analysis.

The present study evaluated a photo-Fenton reactive membrane that achieved enhanced 1,4-Dioxane removal performance. As a common organic solvent and stabilizer, 1,4-Dioxane is widely used in a variety of industrial products and poses negative environmental and health impacts. The membrane was prepared by covalently coating photocatalyst of goethite (α-FeOOH) on a ceramic porous membrane as we reported previously. The effects of UV irradiation, H2O2 and catalyst on the removal efficiency of 1,4-Dioxane in batch reactors were first evaluated for optimized reaction conditions, followed by a systematical investigation of 1,4-Dioxane removal in the photo-Fenton membrane filtration mode. Under optimized conditions, the 1,4-Dioxane removal rate reached up to 16% with combination of 2 mmol/L H2O2 and UV365 irradiation (2000 µW/cm2) when the feed water was filtered by the photo-Fenton reactive membrane at a hydraulic retention time of 6 min. The removal efficiency and apparent quantum yield (AQY) were both enhanced in the filtration compared to the batch mode of the same photo-Fenton reaction. Moreover, the proposed degradation pathways were analyzed by density functional theory (DFT) calculations, which provided a new insight into the degradation mechanisms of 1,4-Dioxane in photo-Fenton reactions on the functionalized ceramic membrane.

• RESEARCH ARTICLE
Qinxue Wen, Shuo Yang, Zhiqiang Chen

• Thermophilic AD was more effective in eliminating resistance genes than mesophilic.

• ARGs variations in AD were mainly affected by succession of microbial community.

• Methane production was significant associated to ARGs reduction.

The role of norfloxacin (NOR) and sulfamethoxazole (SMX) in mesophilic and thermophilic anaerobic digestion (AD) of pig manure, with respect to methane production and variations in the microbial community and resistance genes, including antibiotic resistance genes (ARGs), class I integrase (intI1), and heavy metal resistance genes (MRGs), was investigated. The results indicated that NOR exerted little influence on the microbial community, whereas SMX negatively affected the acetoclastic methanogens. The abundance of two sulfonamide resistance genes (sul1 and sul2), three quinolone resistance genes (qnrS, parC, and aac(6’)-Ib-cr), and intI1 decreased by 2‒3 orders of magnitude at the end of thermophilic AD. In contrast, mesophilic AD was generally ineffective in reducing the abundance of resistance genes. According to the results of redundancy analysis, the abundance of ARGs was affected primarily by microbial community dynamics (68.5%), rather than the selective pressure due to antibiotic addition (13.3%). Horizontal gene transfer (HGT) through intI1 contributed to 26.4% of the ARG variation. The archaeal community also influenced the changes in the resistance genes, and ARG reduction was significantly correlated with enhanced methane production. Thermophilic AD presented a higher methane production potential and greater reduction in resistance gene abundance.

• RESEARCH ARTICLE
Mengqing Ge, Tao Lin, Kemei Zhou, Hong Chen, Hang Xu, Hui Tao, Wei Chen

• N-Cl-DCAM, an emerging N-DBP in drinking water was investigated.

• A new BAC has a better removal efficiency for N-Cl-DCAM precursors than an old BAC.

• N-Cl-DCAM precursors are more of low molecular weight and non-polar.

• Adsorption of GAC plays a major role in removal of N-Cl-DCAM precursors by an O3-BAC.

N-chloro-2,2-dichloroacetamide (N-Cl-DCAM) is an emerging nitrogenous disinfection by-product (N-DBP) which can occur in drinking water. In this study, an analytical method based on liquid chromatography with tandem mass spectrometry (LC-MS/MS) was developed to validate the concentration of N-Cl-DCAM, which was found to be 1.5 mg/L in the effluent of a waterworks receiving raw water from Taihu Lake, China. The changes of N-Cl-DCAM formation potential (N-Cl-DCAMFP) in the drinking water treatment process and the removal efficiency of its precursors in each unit were evaluated. Non-polar organics accounted for the majority of N-Cl-DCAM precursors, accounting for 70% of the N-Cl-DCAM FP. The effect of conventional water treatment processes on the removal of N-Cl-DCAM precursors was found to be unsatisfactory due to their poor performance in the removal of low molecular weight (MW) or non-polar organics. In the ozonation integrated with biological activated carbon (O3-BAC) process, the ozonation had little influence on the decrease of N-Cl-DCAM FP. The removal efficiency of precursors by a new BAC filter, in which the granular activated carbon (GAC) had only been used for four months was higher than that achieved by an old BAC filter in which the GAC had been used for two years. The different removal efficiencies of precursors were mainly due to the different adsorption capacities of GAC for individual precursors. Low MW or non-polar organics were predominantly removed by GAC, rather than biodegradation by microorganisms attached to GAC particles.

• RESEARCH ARTICLE
Qiuzhun Chen, Xiang Zhang, Bing Li, Shengli Niu, Gaiju Zhao, Dong Wang, Yue Peng, Junhua Li, Chunmei Lu, John Crittenden

• Activated carbon was proposed to be an efficient accelerant for molded red mud catalyst.

• The surface acidity and reducibility were highly improved, as well as the pore structure.

• The enrichment of the surface Fe2+ and the adsorbed oxygen account for the improvement.

Our previous study proved that the acid-pretreatment process could efficiently activate red mud (RM) for the selective catalytic reduction (SCR) of NOx. However, in terms of the molding process, which is the key step determining whether it can be applied in large-scale industrial, the surface acidity and reducibility of catalyst always decreased dramatically, and part of surface area and pore structure were lost. In this study, we prepared monolithic honeycomb red mud (MHRM) catalysts with activated carbon (AC) as an accelerant and investigated the effect of AC on the MHRM. The results showed that the MHRM with 3 wt.% of AC (MHRM-AC3) exhibited the best SCR performance, and kept more than 80% NOx conversion in the range of 325°C–400°C. Compared with the MHRM, MHRM-AC1, and HMRM-AC5, the MHRM-AC3 has more mesoporous and macroporous structures, which can provide more adsorption active sites. The AC significantly improved NH3 adsorption and surface reducibility, which was mainly due to the increase of the surface acid sites (especially the Brönsted acid sites), the concentration of Fe(II), and the surface adsorbed oxygen. The presence of more Fe(II) enriched the surface oxygen vacancies, as well as the surface adsorbed oxygen, due to the charge imbalance and unsaturated chemical bond. And surface adsorbed oxygen exhibited more active than lattice oxygen owing to its higher mobility, which was conducive to NOx reduction in the SCR reaction.

• RESEARCH ARTICLE
Ruijie Li, Mengmeng Zhou, Shilong He, Tingting Pan, Jing Liu, Jiabao Zhu

• UASB reactor can work efficiently with high COD/SO42- ratios when SDBS exists.

• Outcome of the competition between SRB and MPA was affected by SDBS.

• Presence of SDBS makes methanogens with H2/CO2 as a substrate dominant.

• Microbial diversity decreases in the presence of SDBS.

In this study, the effects of organic sulfur on anaerobic biological processes were investigated by operating two up-flow anaerobic sludge blanket (UASB) reactors with sodium dodecylbenzene sulfonate (SDBS) as a representative of organic sulfur. The results indicated that the specific methanogenic activity (SMA) and chemical oxygen demand (COD) removal efficiency of R2 (with SDBS added) were higher than those of R1 (without SDBS) when the COD/SO42 ratio was above 5.0. However, when the COD/SO42 ratio was lower than 5.0, the sulfate reduction efficiency of R2 was higher than that of R1. These results and the observed SDBS transformation efficiency in anaerobic reactors indicate that low concentrations of SDBS accelerate methane production and the continuous accumulation of SDBS does not weaken the reduction of sulfate. Similarly, the calculated electron flux for a COD/SO42 ratio of 1.0 indicates that the utilization intensity of electrons by sulfate-reducing bacteria (SRB) in R2 was 36.48% higher than that of SRB in R1 and exceeded that of methane-producing archaea (MPA) under identical working conditions. Moreover, the addition of SDBS in R2 made sulfidogenesis the dominant reaction at low COD/SO42, and Methanobacterium and Methanobrevibacter with H2/CO2 as the substrate and Desulfomicrobium were the dominant MPA and SRB, respectively. However, methanogenesis was still the dominant reaction in R1, and Methanosaeta with acetic acid as the substrate and Desulfovibrio were the dominant MPA and SRB, respectively.

• RESEARCH ARTICLE
Byungjin Lee, Eun Seo Jo, Dong-Wha Park, Jinsub Choi

• Submerged arc plasma was introduced in terms of wastewater treatment.

• Ozone oxidation was coupled with submerged arc plasma system.

• Ozone was converted into O and O2 by submerged arc plasma.

• Decomposition rate was accelerated by submerged arc plasma.

• Introduction of ozone led to significant increase in mineralization.

Submerged arc plasma technology was assessed for the removal of phenols from wastewater. The OH radicals generated from the boundary between the plasma and waste solution were considered as a significant factor on the degradation reaction. In this study, the effects of highly energetic electrons released from the submerged arc plasma were mainly studied. The highly energetic electrons directly broke the strong chemical bond and locally increased the reaction temperatures in solution. The effects of the submerged-arc plasma on the decomposition of phenol are discussed in terms of the input energy and initial concentration. The single use of submerged arc plasma easily decomposed the phenol but did not increase the mineralization efficiency. Therefore, the submerged arc plasma, coupled with the ozone injection, was investigated. The submerged arc plasma combined with ozone injection had a synergic effect, which led to significant improvements in mineralization with only a small increase in input energy. The decomposition mechanism of phenol by the submerged arc plasma with the ozone was analyzed.

• RESEARCH ARTICLE
Liu Cao, Lu Yang, Clifford S. Swanson, Shuai Li, Qiang He

• Exposure to indoor microbiomes is a public health concern in educational facilities.

• Indoor microbiomes were characterized in two multifunctional university buildings.

• Human occupancy had significant impact on the composition of indoor microbiomes.

• The skin microbiota of occupants represented important sources of indoor microbiomes.

Educational facilities serve as community hubs and consequently hotspots for exposure to pathogenic microorganisms. Therefore, it is of critical importance to understand processes shaping the indoor microbiomes in educational facilities to protect public health by reducing potential exposure risks of students and the broader community. In this study, the indoor surface bacterial microbiomes were characterized in two multifunctional university buildings with contrasting levels of human occupancy, of which one was recently constructed with minimal human occupancy while the other had been in full operation for six years. Higher levels of human occupancy in the older building were shown to result in greater microbial abundance in the indoor environment and greater proportion of the indoor surface bacterial microbiomes contributed from human-associated microbiota, particularly the skin microbiota. It was further revealed that human-associated microbiota had greater influence on the indoor surface bacterial microbiomes in areas of high occupancy than areas of low occupancy. Consistent with minimal impact from human occupancy in a new construction, the indoor microbiomes in the new building exhibited significantly lower influence from human-associated microbiota than in the older building, with microbial taxa originating from soil and plants representing the dominant constituents of the indoor surface bacterial microbiomes. In contrast, microbial taxa in the older building with extensive human occupancy were represented by constituents of the human microbiota, likely from occupants. These findings provide insights into processes shaping the indoor microbiomes which will aid the development of effective strategies to control microbial exposure risks of occupants in educational facilities.

• RESEARCH ARTICLE
Yueqi Jiang, Jia Xing, Shuxiao Wang, Xing Chang, Shuchang Liu, Aijun Shi, Baoxian Liu, Shovan Kumar Sahu

• PM2.5-related deaths were estimated to be 227 thousand in BTH & surrounding regions.

• Local emissions contribute more to PM2.5-related deaths than PM2.5 concentration.

• Local controls are underestimated if only considering its impacts on concentrations.

• Rural residents suffer larger impacts of regional transport than urban residents.

• Reducing regional transport benefits in mitigating environmental inequality.

The source-receptor matrix of PM2.5 concentration from local and regional sources in the Beijing-Tianjin-Hebei (BTH) and surrounding provinces has been created in previous studies. However, because the spatial distribution of concentration does not necessarily match with that of the population, such concentration-based source-receptor matrix may not fully reflect the importance of pollutant control effectiveness in reducing the PM2.5-related health impacts. To demonstrate that, we study the source-receptor matrix of the PM2.5-related deaths instead, with inclusion of the spatial correlations between the concentrations and the population. The advanced source apportionment numerical model combined with the integrated exposure–response functions is used for BTH and surrounding regions in 2017. We observed that the relative contribution to PM2.5-related deaths of local emissions was 0.75% to 20.77% larger than that of PM2.5 concentrations. Such results address the importance of local emissions control for reducing health impacts of PM2.5 particularly for local residents. Contribution of regional transport to PM2.5-related deaths in rural area was 22% larger than that in urban area due to the spatial pattern of regional transport which was more related to the rural population. This resulted in an environmental inequality in the sense that people staying in rural area with access to less educational resources are subjected to higher impacts from regional transport as compared with their more resourceful and knowledgeable urban compatriots. An unexpected benefit from the multi-regional joint controls is suggested for its effectiveness in reducing the regional transport of PM2.5 pollution thus mitigating the associated environmental inequality.

• RESEARCH ARTICLE
Tianyi Li, Chengwu Zhang, Jingyi Zhang, Song Yan, Chuanyu Qin

• Nano CaO2 is evaluated as a remediation agent for 2,4-DCP contaminated groundwater.

• 2,4-DCP degradation mechanism by different Fe2+ concentration was proposed.

• 2,4-DCP was not degraded in the system for solution pH>10.

• The 2,4-DCP degradation area is inconsistent with the nano CaO2 distribution area.

This study evaluates the applicability of nano-sized calcium peroxide (CaO2) as a source of H2O2 to remediate 2,4-dichlorophenol (2,4-DCP) contaminated groundwater via the advanced oxidation process (AOP). First, the effect and mechanism of 2,4-DCP degradation by CaO2 at different Fe concentrations were studied (Fenton reaction). We found that at high Fe concentrations, 2,4-DCP almost completely degrades via primarily the oxidation of •OH within 5 h. At low Fe concentrations, the degradation rate of 2,4-DCP decreased rapidly. The main mechanism was the combined action of •OH and O2•−. Without Fe, the 2,4-DCP degradation reached 13.6% in 213 h, primarily via the heterogeneous reaction on the surface of CaO2. Besides, 2,4-DCP degradation was significantly affected by solution pH. When the solution pH was>10, the degradation was almost completely inhibited. Thus, we adopted a two-dimensional water tank experiment to study the remediation efficiency CaO2 on the water sample. We noticed that the degradation took place mainly in regions of pH<10 (i.e., CaO2 distribution area), both upstream and downstream of the tank. After 28 days of treatment, the average 2,4-DCP degradation level was ≈36.5%. Given the inadequacy of the results, we recommend that groundwater remediation using nano CaO2: (1) a buffer solution should be added to retard the rapid increase in pH, and (2) the nano CaO2 should be injected copiously in batches to reduce CaO2 deposition.

• RESEARCH ARTICLE
Kehui Liu, Jie Xu, Chenglong Dai, Chunming Li, Yi Li, Jiangming Ma, Fangming Yu

• The OA supply significantly increased the water-extractable Mn in all soils.

• All OA supply levels promoted plant growth in unexplored soil.

• Low OA supply level promoted plant growth in explored and tailing soils.

• OA amendment increased the Mn concentrations and total Mn in P. pubescens.

P. pubescens experienced less Mn stress in unexplored soil than in the other two soils.

The current study evaluated the effects of oxalic acid (OA) application on the growth and Mn phytoremediation efficiency of Polygonum pubescens Blume cultivated in three different manganese (Mn)-contaminated soils sampled from an unexplored area (US), an explored area (ES) and a tailing area (TS) of the Ertang Mn mine, South China. The supplied levels of OA were 0 (control), 1 (low level), 3 (medium level), and 9 (high level) mmol/kg, referred to as CK, OA1, OA3 and OA9, respectively. The results revealed that the average water-extractable Mn concentrations US, ES and TS amended with OA increased by 214.13, 363.77 and 266.85%, respectively. All OA supply levels increased plant growth and Mn concentrations in US. The low OA supply level increased plant growth in ES and TS; however, contrasting results were found for the medium and high OA supply levels. Plant Mn concentrations and total Mn increased in ES and TS in response to all OA supply levels. Total Mn in the aerial parts increased by 81.18, 44.17 and 83.17% in US, ES and TS, respectively; the corresponding percentages for the whole plants were 81.53, 108.98 and 77.91%, respectively. The rate of ·O2 production and malondialdehyde (MDA) concentrations increased in response to OA amendment, especially the medium and high OA supply levels in ES and TS. In general, antioxidant enzymes might play a vital role in alleviating Mn stress in plants cultivated in US, while non-enzymatic antioxidants might be the main factor for plants cultivated in ES and TS.

• RESEARCH ARTICLE
Xinzheng Li, Zhiming Li, Zhihui Xing, Zhimin Song, Bei Ye, Zhengming Wang, Qianyuan Wu

• UV-LED with shorter wavelength was beneficial for photocatalytic degradation.

• SRNOM dramatically inhibit the degradation.

• Degradation mainly undergoes oxidation, hydrolysis and chain growth reactions.

In this work, LED-based photocatalysis using mixed rutile and anatase phase TiO2 (P25) as the photocatalyst could effectively remove 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT) and methylisothiazolone (MIT) simultaneously, with removal efficiencies above 80% within 20 min. The photocatalytic degradation of both CMIT and MIT could be modeled using a pseudo-first-order rate equation. The photocatalytic degradation rates of CMIT and MIT under LED280 illumination were higher than under LED310 or LED360 illumination. At concentrations below 100 mg/L, the degradation rate of CMIT and MIT under LED illumination significantly increased with increasing catalyst dosage. Additionally, the effects of the chloride ion concentration, alkalinity and dissolved organic matter on the photocatalytic degradation reaction were also investigated. The ·OH free radicals were determined to play the primary role in the photocatalytic degradation reaction, with a degradation contribution of >95%. The photocatalytic degradation of CMIT and MIT mainly occurred via oxidation, hydrolysis, and chain growth reactions. Finally, the possible photocatalytic degradation pathways of CMIT and MIT over LED/P25 are proposed.

• REVIEW ARTICLE
Mengzhi Ji, Zichen Liu, Kaili Sun, Zhongfang Li, Xiangyu Fan, Qiang Li

•Phages can be better indicators of enteric viruses than fecal indicator bacteria.

•Multiple phages should be added to the microbial source tracking toolbox.

•Engineered phage or phage cocktail can effectively target resistant bacteria.

•In phage use, phage-mediated horizontal gene transfer cannot be ignored.

•More schemes are needed to prevent phage concentration from decreasing.

Wastewater is a breeding ground for many pathogens, which may pose a threat to human health through various water transmission pathways. Therefore, a simple and effective method is urgently required to monitor and treat wastewater. As bacterial viruses, bacteriophages (phages) are the most widely distributed and abundant organisms in the biosphere. Owing to their capacity to specifically infect bacterial hosts, they have recently been used as novel tools in water pollution control. The purpose of this review is to summarize and evaluate the roles of phages in monitoring pathogens, tracking pollution sources, treating pathogenic bacteria, infecting bloom-forming cyanobacteria, and controlling bulking sludge and biofilm pollution in wastewater treatment systems. We also discuss the limitations of phage usage in water pollution control, including phage-mediated horizontal gene transfer, the evolution of bacterial resistance, and phage concentration decrease. This review provides an integrated outlook on the use of phages in water pollution control.

• RESEARCH ARTICLE
Junlian Qiao, Yang Liu, Hongyi Yang, Xiaohong Guan, Yuankui Sun

• Sulfidation significantly enhanced As(V) immobilization in soil by zerovalent iron.

• S-ZVI promoted the conversion of exchangeable As to less mobile Fe-Mn bound As.

• Column test further confirmed the feasibility of sulfidated ZVI on As retention.

• S-ZVI amendment and magnetic separation markedly reduced TCLP leachability of As.

In this study, the influences of sulfidation on zero-valent iron (ZVI) performance toward As(V) immobilization in soil were systemically investigated. It was found that, compared to unamended ZVI, sulfidated ZVI (S-ZVI) is more favorable to immobilize As(V) in soil and promote the conversion of water soluble As to less mobile Fe-Mn bound As. Specifically, under the optimal S/Fe molar ratio of 0.05, almost all of the leached As could be sequestrated by>0.5 wt.% S-ZVI within 3 h. Although the presence of HA could decrease the desorption of As from soil, HA inhibited the reactivity of S-ZVI to a greater extent. Column experiments further proved the feasibility of applying S-ZVI on soil As(V) immobilization. More importantly, to achieve a good As retention performance, S-ZVI should be fully mixed with soil or located on the downstream side of As migration. The test simulating the flooding conditions in rice culture revealed there was also a good long-term stability of soil As(V) after S-ZVI remediation, where only 0.7% of As was desorbed after 30 days of incubation. Magnetic separation was employed to separate the immobilized As(V) from soil after S-ZVI amendment, where the separation efficiency was found to be dependent of the iron dosage, liquid to soil ratio, and reaction time. Toxicity characteristic leaching procedure (TCLP) tests revealed that the leachability of As from soil was significantly reduced after the S-ZVI amendment and magnetic separation treatment. All these findings provided some insights into the remediation of As(V)-polluted soil by ZVI.

• RESEARCH ARTICLE
Aifang Gao, Junyi Wang, Jianfei Luo, Aiguo Li, Kaiyu Chen, Pengfei Wang, Yiyi Wang, Jingyi Li, Jianlin Hu, Hongliang Zhang

•Annual mean PM2.5 in Shijiazhuang were 87, 95, and 82 µg/m3 in 2015–2017.

•Health risk of cardiovascular system was higher than respiratory system.

•Premature mortality attributed to PM2.5 was 5088 people in 2017.

•ΔMort and YLL reduced by 84.2% and 84.6% when PM2.5 reduced to 10 µg/m3.

•Health risks due to PM2.5 were severe in Shijiazhuang in 2015–2017.

Shijiazhuang is one of the cities in the North China Plain. In recent decades, this city has experienced high levels of fine particulate matter (PM2.5), which have potentially significant effects on human health. In this study, the health effects of PM2.5 exposure in Shijiazhuang were estimated by applying an integrated exposure-response model. Premature mortality, years of life lost (YLL), and the mortality benefits linked to reduced levels of PM2.5 were quantified for the period 2015–2017. In 2015, 2016, and 2017, cerebrovascular diseases caused the highest premature mortality (2432, 2449, and 2483, respectively), followed by ischemic heart diseases (1391, 1479, and 1493, respectively), lung cancer (639,660, and 639, respectively), and chronic obstructive pulmonary diseases (533, 519, and 473, respectively). Notably, the total number of premature deaths caused by PM2.5 exposure in Shijiazhuang in 2015, 2016, and 2017 were 4994, 5107, and 5088, respectively. Moreover, the YLL in the same years were 47001, 47880 and 47381, respectively. Interestingly, the YLL per 1000 females was lower than that per 1000 males. Finally, we noted that premature mortality and YLL decreased by 84.2% and 84.6% when the PM2.5 levels diminished to 10 µg/m3. Overall, the results of this study improve our understanding of how high PM2.5 concentrations affect human health and suggest the application of more stringent measures in Shijiazhuang to alleviate the associated health risks.

• RESEARCH ARTICLE
Zeshen Tian, Bo Wang, Yuyang Li, Bo Shen, Fengjuan Li, Xianghua Wen

• AOA’s ammonia oxidizing capacity was enhanced under moderate magnetic field.

• AOA possessed a certain magnetotaxis under uneven magnetic field.

• Enhanced ammonia oxidizing capacity was lost once magnetic field was removed.

Ammonia-oxidizing archaeon (AOA) could play important roles for nitrogen removal in the bioreactors under conditions such as low pH and low dissolved oxygen. Therefore, enhancing ammonia oxidation capability of AOA has great significance for water and wastewater treatment, especially under conditions like low dissolved oxygen concentration. Utilizing a novel AOA strain SAT1, which was enriched from a wastewater treatment plant by our group, the effect of magnetic field on AOA’s ammonia oxidation capability, its magnetotaxis and heredity were investigated in this study. Compared with control experiment, AOA’s maximum nitrite-N formation rate during the cultivation increased by 56.8% (0.65 mgN/(L·d)) with 20 mT magnetic field. Also, it was testified that AOA possessed a certain magnetotaxis. However, results manifested that the enhancement of AOA’s ammonia oxidation capability was not heritable, that is, lost once the magnetic field was removed. Additionally, the possible mechanism of improving AOA’s ammonia oxidation capability by magnetic field was owing to the promotion of AOA single cells’ growth and fission, rather than the enhancement of their ammonia oxidation rates. The results shed light on the application of AOA and methods to enhance AOA’s ammonia oxidation capability, especially in wastewater treatment processes under certain conditions.

• REVIEW ARTICLE
Shuchang Wang, Binbin Shao, Junlian Qiao, Xiaohong Guan

• The properties of Fe(VI) were summarized.

• Both the superiorities and the limitations of Fe(VI) technologies were discussed.

• Methods to improve contaminants oxidation/disinfection by Fe(VI) were introduced.

• Future research needs for the development of Fe(VI) technologies were proposed.

The past two decades have witnessed the rapid development and wide application of Fe(VI) in the field of water de-contamination because of its environmentally benign character. Fe(VI) has been mainly applied as a highly efficient oxidant/disinfectant for the selective elimination of contaminants. The in situ generated iron(III) (hydr)oxides with the function of adsorption/coagulation can further increase the removal of contaminants by Fe(VI) in some cases. Because of the limitations of Fe(VI) per se, various modified methods have been developed to improve the performance of Fe(VI) oxidation technology. Based on the published literature, this paper summarized the current views on the intrinsic properties of Fe(VI) with the emphasis on the self-decay mechanism of Fe(VI). The applications of Fe(VI) as a sole oxidant for decomposing organic contaminants rich in electron-donating moieties, as a bi-functional reagent (both oxidant and coagulant) for eliminating some special contaminants, and as a disinfectant for inactivating microorganisms were systematically summarized. Moreover, the difficulties in synthesizing and preserving Fe(VI), which limits the large-scale application of Fe(VI), and the potential formation of toxic byproducts during Fe(VI) application were presented. This paper also systematically reviewed the important nodes in developing methods to improve the performance of Fe(VI) as oxidant or disinfectant in the past two decades, and proposed the future research needs for the development of Fe(VI) technologies.