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  • REVIEW ARTICLE
    Shuchang Wang, Binbin Shao, Junlian Qiao, Xiaohong Guan
    Frontiers of Environmental Science & Engineering, 2021, 15(5): 80. https://doi.org/10.1007/s11783-020-1373-3

    • 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.

  • RESEARCH ARTICLE
    Wei Mao, Lixun Zhang, Tianye Wang, Yichen Bai, Yuntao Guan
    Frontiers of Environmental Science & Engineering, 2021, 15(4): 52. https://doi.org/10.1007/s11783-020-1344-8

    • A novel Bi2WO6/CuS composite was fabricated by a facile solvothermal method.

    • This composite efficiently removed organic pollutants and Cr(VI) by photocatalysis.

    • The DOM could promoted synchronous removal of organic pollutants and Cr(VI).

    • This composite could be applied at a wide pH range in photocatalytic reactions.

    • Possible photocatalytic mechanisms of organic pollutants and Cr(VI) were proposed.

    A visible-light-driven Bi2WO6/CuS p-n heterojunction was fabricated using an easy solvothermal method. The Bi2WO6/CuS exhibited high photocatalytic activity in a mixed system containing rhodamine B (RhB), tetracycline hydrochloride (TCH), and Cr (VI) under natural conditions. Approximately 98.8% of the RhB (10 mg/L), 87.6% of the TCH (10 mg/L) and 95.1% of the Cr(VI) (15 mg/L) were simultaneously removed from a mixed solution within 105 min. The removal efficiencies of TCH and Cr(VI) increased by 12.9% and 20.4%, respectively, in the mixed solution, compared with the single solutions. This is mainly ascribed to the simultaneous consumption electrons and holes, which increases the amount of excited electrons/holes and enhances the separation efficiency of photogenerated electrons and holes. Bi2WO6/CuS can be applied over a wide pH range (2–6) with strong photocatalytic activity for RhB, TCH and Cr(VI). Coexisiting dissolved organic matter in the solution significantly promoted the removal of TCH (from 74.7% to 87.2%) and Cr(VI) (from 75.7% to 99.9%) because it accelerated the separation of electrons and holes by consuming holes as an electron acceptor. Removal mechanisms of RhB, TCH, and Cr(VI) were proposed, Bi2WO6/CuS was formed into a p-n heterojunction to efficiently separate and transfer photoelectrons and holes so as to drive photocatalytic reactions. Specifically, when reducing pollutants (e.g., TCH) and oxidizing pollutants (e.g., Cr(VI)) coexist in wastewater, the p-n heterojunction in Bi2WO6/CuS acts as a “bridge” to shorten the electron transport and thus simultaneously increase the removal efficiencies of both types of pollutants.

  • VIEWS & COMMENTS
    Qingyan Chen
    Frontiers of Environmental Science & Engineering, 2021, 15(3): 35. https://doi.org/10.1007/s11783-020-1328-8

    It is well recognized that Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) virus could be spread through touch and large droplets. However, we may have under-estimated the disease transmission by small droplets or aerosols that contain SARS-CoV-2 virus. Social distancing in public transport vehicles, such as airplanes, is not feasible. It is also not possible to wear masks in restaurant. This paper recommended wearing masks in airplanes and use partition screens in the middle of a table in a restaurant to reduce the infection caused by SARS-CoV-2 virus. Advanced ventilation systems, such as personalized ventilation and displacement ventilation, are strongly recommended for transport vehicles and buildings.

  • RESEARCH ARTICLE
    Huan He, Qinjin Yu, Chaochao Lai, Chen Zhang, Muhan Liu, Bin Huang, Hongping Pu, Xuejun Pan
    Frontiers of Environmental Science & Engineering, 2021, 15(2): 18. https://doi.org/10.1007/s11783-020-1310-5

    • An innovative bubble column tower BPE was designed to treat the black-odorous water.

    • PO43, S2 and turbidity were removed, and dissolved oxygen was enriched in the BPE.

    • An aluminum bipolar electrode gave the best oxygen enrichment and pollutant removal.

    • Changes of microorganisms confirmed the improvement in water quality achieved.

    The large amount of municipal wastewater discharged into urban rivers sometimes exceeds the rivers’ self-purification capacity leading to black-odorous polluted water. Electro-flocculation has emerged as a powerful remediation technology. Electro-flocculation in a bubble column tower with a bipolar electrode (BPE) was tested in an attempt to overcome the high resistance and weak gas-floatation observed with a monopolar electrode (MPE) in treating such water. The BPE reactor tested had a Ti/Ta2O5-IrO2 anode and a graphite cathode with an iron or aluminum bipolar electrode suspended between them. It was tested for its ability to reduce turbidity, phosphate and sulphion and to increase the concentration of dissolved oxygen. The inclusion of the bipolar electrode was found to distinctly improved the system’s conductivity. The system’s electro-flocculation and electrical floatation removed turbidity, phosphate and sulphion completely, and the dissolved oxygen level improved from 0.29 to 6.28 mg/L. An aluminum bipolar electrode performed better than an iron one. Changes in the structure of the microbial community confirmed a significant improvement in water quality.

  • RESEARCH ARTICLE
    Yang Li, Yixin Zhang, Guangshen Xia, Juhong Zhan, Gang Yu, Yujue Wang
    Frontiers of Environmental Science & Engineering, 2021, 15(1): 1. https://doi.org/10.1007/s11783-020-1293-2

    • Gas diffusion electrode (GDE) is a suitable setup for practical water treatment.

    • Electrochemical H2O2 production is an economically competitive technology.

    • High current efficiency of H2O2 production was obtained with GDE at 5–400 mA/cm2.

    • GDE maintained high stability for H2O2 production for ~1000 h.

    • Electro-generation of H2O2 enhances ibuprofen removal in an E-peroxone process.

    This study evaluated the feasibility of electrochemical hydrogen peroxide (H2O2) production with gas diffusion electrode (GDE) for decentralized water treatment. Carbon black-polytetrafluoroethylene GDEs were prepared and tested in a continuous flow electrochemical cell for H2O2 production from oxygen reduction. Results showed that because of the effective oxygen transfer in GDEs, the electrode maintained high apparent current efficiencies (ACEs,>80%) for H2O2 production over a wide current density range of 5–400 mA/cm2, and H2O2 production rates as high as ~202 mg/h/cm2 could be obtained. Long-term stability test showed that the GDE maintained high ACEs (>85%) and low energy consumption (<10 kWh/kg H2O2) for H2O2 production for 42 d (~1000 h). However, the ACEs then decreased to ~70% in the following 4 days because water flooding of GDE pores considerably impeded oxygen transport at the late stage of the trial. Based on an electrode lifetime of 46 days, the overall cost for H2O2 production was estimated to be ~0.88 $/kg H2O2, including an electricity cost of 0.61 $/kg and an electrode capital cost of 0.27 $/kg. With a 9 cm2 GDE and 40 mA/cm2 current density, ~2–4 mg/L of H2O2 could be produced on site for the electro-peroxone treatment of a 1.2 m3/d groundwater flow, which considerably enhanced ibuprofen abatement compared with ozonation alone (~43%–59% vs. 7%). These findings suggest that electrochemical H2O2 production with GDEs holds great promise for the development of compact treatment technologies for decentralized water treatment at a household and community level.

  • RESEARCH ARTICLE
    Kun Zhang, Jialuo Xu, Qing Huang, Lei Zhou, Qingyan Fu, Yusen Duan, Guangli Xiu
    Frontiers of Environmental Science & Engineering, 2020, 14(6): 92. https://doi.org/10.1007/s11783-020-1271-8

    • Air masses from Zhejiang Province is the major source of O3 in suburban Shanghai.

    • O3 formation was in VOC-sensitive regime in rural Shanghai.

    • O3 formation was most sensitive to propylene in rural Shanghai.

    A high level of ozone (O3) is frequently observed in the suburbs of Shanghai, the reason for this high level remains unclear. To obtain a detailed insight on the high level of O3 during summer in Shanghai, O3 and its precursors were measured at a suburban site in Shanghai from July 1, 2016 to July 31, 2016. Using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model and concentration weighted trajectories (CWT), we found that Zhejiang province was the main potential source of O3 in suburban Shanghai. When the sampling site was controlled by south-western winds exceeding 2 m/s, the O3-rich air masses from upwind regions (such as Zhejiang province) could be transported to the suburban Shanghai. The propylene-equivalent concentration (PEC) and ozone formation potential (OFP) were further calculated for each VOC species, and the results suggested that propylene, (m+p)-xylene, and toluene played dominant roles in O3 formation. The Ozone Isopleth Plotting Research (OZIPR) model was used to reveal the impact of O3 precursors on O3 formation, and 4 base-cases were selected to adjust the model simulation. An average disparity of 18.20% was achieved between the simulated and observed O3 concentrations. The O3 isopleth diagram illustrated that O3 formation in July 2016 was in VOC-sensitive regime, although the VOC/NOx ratio was greater than 20. By introducing sensitivity (S), a sensitivity analysis was performed for O3 formation. We found that O3 formation was sensitive to propylene, (m+p)-xylene, o-xylene and toluene. The results provide theoretical support for O3 pollution treatment in Shanghai.

  • REVIEW ARTICLE
    Jianzhi Huang, Huichun Zhang
    Frontiers of Environmental Science & Engineering, 2020, 14(5): 76. https://doi.org/10.1007/s11783-020-1255-8

    • Mechanisms of redox reactions of Fe- and Mn-oxides were discussed.

    • Oxidative reactions of Mn- and Fe-oxides in complex systems were reviewed.

    • Reductive reaction of Fe(II)/iron oxides in complex systems was examined.

    • Future research on examining the redox reactivity in complex systems was suggested.

    Conspectus Redox reactions of Fe- and Mn-oxides play important roles in the fate and transformation of many contaminants in natural environments. Due to experimental and analytical challenges associated with complex environments, there has been a limited understanding of the reaction kinetics and mechanisms in actual environmental systems, and most of the studies so far have only focused on simple model systems. To bridge the gap between simple model systems and complex environmental systems, it is necessary to increase the complexity of model systems and examine both the involved interaction mechanisms and how the interactions affected contaminant transformation. In this Account, we primarily focused on (1) the oxidative reactivity of Mn- and Fe-oxides and (2) the reductive reactivity of Fe(II)/iron oxides in complex model systems toward contaminant degradation. The effects of common metal ions such as Mn2+ , Ca2+, Ni2+, Cr3+ and Cu2+, ligands such as small anionic ligands and natural organic matter (NOM), and second metal oxides such as Al, Si and Ti oxides on the redox reactivity of the systems are briefly summarized.

  • REVIEW ARTICLE
    Xinjie Wang, Yang Li, Jian Zhao, Hong Yao, Siqi Chu, Zimu Song, Zongxian He, Wen Zhang
    Frontiers of Environmental Science & Engineering, 2020, 14(4): 56. https://doi.org/10.1007/s11783-020-1235-z

    • Magnetotactic bacteria (MTB) synthesize magnetic nanoparticle within magnetosomes.

    • The morphologic and phylogenetic diversity of MTB were summarized.

    • Isolation and mass cultivation of MTB deserve extensive research for applications.

    • MTB can remove heavy metals, radionuclides, and organic pollutants from wastewater.

    Magnetotactic bacteria (MTB) are a group of Gram-negative prokaryotes that respond to the geomagnetic field. This unique property is attributed to the intracellular magnetosomes, which contains membrane-bound nanocrystals of magnetic iron minerals. This review summarizes the most recent advances in MTB, magnetosomes, and their potential applications especially the environmental pollutant control or remediation. The morphologic and phylogenetic diversity of MTB were first introduced, followed by a critical review of isolation and cultivation methods. Past research has devoted to optimize the factors, such as oxygen, carbon source, nitrogen source, nutrient broth, iron source, and mineral elements for the growth of MTB. Besides the applications of MTB in modern biological and medical fields, little attention was made on the environmental applications of MTB for wastewater treatment, which has been summarized in this review. For example, applications of MTB as adsorbents have resulted in a novel magnetic separation technology for removal of heavy metals or organic pollutants in wastewater. In addition, we summarized the current advance on pathogen removal and detection of endocrine disruptor which can inspire new insights toward sustainable engineering and practices. Finally, the new perspectives and possible directions for future studies are recommended, such as isolation of MTB, genetic modification of MTB for mass production and new environmental applications. The ultimate objective of this review is to promote the applications of MTB and magnetosomes in the environmental fields.

  • RESEARCH ARTICLE
    Jun Yang, Jingyun Wang, Pengwei Qiao, Yuanming Zheng, Junxing Yang, Tongbin Chen, Mei Lei, Xiaoming Wan, Xiaoyong Zhou
    Frontiers of Environmental Science & Engineering, 2020, 14(3): 37. https://doi.org/10.1007/s11783-019-1216-2

    • A method was proposed to identify the main influence factors of soil heavy metals.

    • The influence degree of different environmental factors was ranked.

    • Parent material, soil type, land use and industrial activity were main factors.

    • Interactions between some factors obviously affected soil heavy metal distribution.

    Identifying the factors that influence the heavy metal contents of soil could reveal the sources of soil heavy metal pollution. In this study, a categorical regression was used to identify the factors that influence soil heavy metals. First, environmental factors were associated with soil heavy metal data, and then, the degree of influence of different factors on the soil heavy metal contents in Beijing was analyzed using a categorical regression. The results showed that the soil parent material, soil type, land use type, and industrial activity were the main influencing factors, which suggested that these four factors were important sources of soil heavy metals in Beijing. In addition, population density had a certain influence on the soil Pb and Zn contents. The distribution of soil As, Cd, Pb, and Zn was markedly influenced by interactions, such as traffic activity and land use type, industrial activity and population density. The spatial distribution of soil heavy metal hotspots corresponded well with the influencing factors, such as industrial activity, population density, and soil parent material. In this study, the main factors affecting soil heavy metals were identified, and the degree of their influence was ranked. A categorical regression represents a suitable method for identifying the factors that influence soil heavy metal contents and could be used to study the genetic process of regional soil heavy metal pollution.

  • RESEARCH ARTICLE
    Wenchao Jiang, Ping Tang, Zhen Liu, Huan He, Qian Sui, Shuguang Lyu
    Frontiers of Environmental Science & Engineering, 2020, 14(2): 18. https://doi.org/10.1007/s11783-019-1197-1

    • Complete CT degradation was achieved by employing HA to CP/Fe(II)/FA process.

    • Quantitative detection of Fe(II) regeneration and HO• production was investigated.

    • Benzoic acid outcompeted FA for the reaction with HO•.

    • CO2 was the dominant reductive radical for CT removal.

    • Effects of solution matrix on CT removal were conducted.

    Hydroxyl radicals (HO•) show low reactivity with perchlorinated hydrocarbons, such as carbon tetrachloride (CT), in conventional Fenton reactions, therefore, the generation of reductive radicals has attracted increasing attention. This study investigated the enhancement of CT degradation by the synergistic effects of hydroxylamine (HA) and formic acid (FA) (initial [CT] = 0.13 mmol/L) in a Fe(II) activated calcium peroxide (CP) Fenton process. CT degradation increased from 56.6% to 99.9% with the addition of 0.78 mmol/L HA to the CP/Fe(II)/FA/CT process in a molar ratio of 12/6/12/1. The results also showed that the presence of HA enhanced the regeneration of Fe(II) from Fe(III), and the production of HO• increased one-fold when employing benzoic acid as the HO• probe. Additionally, FA slightly improves the production of HO•. A study of the mechanism confirmed that the carbon dioxide radical (CO2), a strong reductant generated by the reaction between FA and HO•, was the dominant radical responsible for CT degradation. Almost complete CT dechlorination was achieved in the process. The presence of humic acid and chloride ion slightly decreased CT removal, while high doses of bicarbonate and high pH inhibited CT degradation. This study helps us to better understand the synergistic roles of FA and HA for HO• and CO2 generation and the removal of perchlorinated hydrocarbons in modified Fenton systems.