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  • REVIEW ARTICLE
    Yunping Han, Lin Li, Ying Wang, Jiawei Ma, Pengyu Li, Chao Han, Junxin Liu
    Frontiers of Environmental Science & Engineering, 2021, 15(3): 38. https://doi.org/10.1007/s11783-020-1330-1

    • Bioaerosols are produced in the process of wastewater biological treatment.

    • The concentration of bioaerosol indoor is higher than outdoor.

    • Bioaerosols contain large amounts of potentially pathogenic biomass and chemicals.

    • Inhalation is the main route of exposure of bioaerosol.

    • Both the workers and the surrounding residents will be affected by the bioaerosol.

    Bioaerosols are defined as airborne particles (0.05–100 mm in size) of biological origin. They are considered potentially harmful to human health as they can contain pathogens such as bacteria, fungi, and viruses. This review summarizes the most recent research on the health risks of bioaerosols emitted from wastewater treatment plants (WWTPs) in order to improve the control of such bioaerosols. The concentration and size distribution of WWTP bioaerosols; their major emission sources, composition, and health risks; and considerations for future research are discussed. The major themes and findings in the literature are as follows: the major emission sources of WWTP bioaerosols include screen rooms, sludge-dewatering rooms, and aeration tanks; the bioaerosol concentrations in screen and sludge-dewatering rooms are higher than those outdoors. WWTP bioaerosols contain a variety of potentially pathogenic bacteria, fungi, antibiotic resistance genes, viruses, endotoxins, and toxic metal(loid)s. These potentially pathogenic substances spread with the bioaerosols, thereby posing health risks to workers and residents in and around the WWTP. Inhalation has been identified as the main exposure route, and children are at a higher risk of this than adults. Future studies should identify emerging contaminants, establish health risk assessments, and develop prevention and control systems.

  • REVIEW ARTICLE
    Dongjie Shang, Jianfei Peng, Song Guo, Zhijun Wu, Min Hu
    Frontiers of Environmental Science & Engineering, 2021, 15(2): 34. https://doi.org/10.1007/s11783-020-1326-x

    • Characteristics and interannual variation of aerosol pollution are illustrated.

    • Mechanisms of secondary aerosol formation in winter haze of North China are reviewed.

    • Directions in future studies of secondary aerosol formation are provided.

    Severe haze pollution occurs frequently in the winter over the Beijing-Tianjin-Hebei (BTH) region (China), exerting profound impacts on air quality, visibility, and human health. The Chinese Government has taken strict mitigation actions since 2013 and has achieved a significant reduction in the annual mean PM2.5 concentration over this region. However, the level of secondary aerosols during heavy haze episodes showed little decrease during this period. During heavy haze episodes, the concentrations of secondary aerosol components, including sulfate, nitrate and secondary organics, in aerosol particles increase sharply, acting as the main contributors to aerosol pollution. To achieve effective control of particle pollution in the BTH region, the precise and complete secondary aerosol formation mechanisms have been investigated, and advances have been made about the mechanisms of gas phase reaction, nucleation and heterogeneous reactions in forming secondary aerosols. This paper reviews the research progress in aerosol chemistry during haze pollution episodes in the BTH region, lays out the challenges in haze formation studies, and provides implications and directions for future research.

  • 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.

  • REVIEW ARTICLE
    Wenwen Xie, Yanpeng Li, Wenyan Bai, Junli Hou, Tianfeng Ma, Xuelin Zeng, Liyuan Zhang, Taicheng An
    Frontiers of Environmental Science & Engineering, 2021, 15(3): 44. https://doi.org/10.1007/s11783-020-1336-8

    • Emission of microbe from local environments is a main source of bioaerosols.

    • Regional transport is another important source of the bioaerosols.

    • There are many factors affecting the diffusion and transport of bioaerosols.

    • Source identification method uncovers the contribution of sources of bioaerosols.

    Recent pandemic outbreak of the corona-virus disease 2019 (COVID-19) has raised widespread concerns about the importance of the bioaerosols. They are atmospheric aerosol particles of biological origins, mainly including bacteria, fungi, viruses, pollen, and cell debris. Bioaerosols can exert a substantial impact on ecosystems, climate change, air quality, and public health. Here, we review several relevant topics on bioaerosols, including sampling and detection techniques, characterization, effects on health and air quality, and control methods. However, very few studies have focused on the source apportionment and transport of bioaerosols. The knowledge of the sources and transport pathways of bioaerosols is essential for a comprehensive understanding of the role microorganisms play in the atmosphere and control the spread of epidemic diseases associated with them. Therefore, this review comprehensively summarizes the up to date progress on the source characteristics, source identification, and diffusion and transport process of bioaerosols. We intercompare three types of diffusion and transport models, with a special emphasis on a widely used mathematical model. This review also highlights the main factors affecting the source emission and transport process, such as biogeographic regions, land-use types, and environmental factors. Finally, this review outlines future perspectives on bioaerosols.

  • REVIEW ARTICLE
    Yang Yang
    Frontiers of Environmental Science & Engineering, 2020, 14(5): 85. https://doi.org/10.1007/s11783-020-1264-7

    • Byproduct formation mechanisms during electrochemical oxidation water treatment.

    • Control byproduct formation by quenchers.

    • Process optimization to suppress byproduct formation.

    Electrochemical oxidation (EO) is a promising technique for decentralized wastewater treatment, owing to its modular design, high efficiency, and ease of automation and transportation. The catalytic destruction of recalcitrant, non-biodegradable pollutants (per- and poly-fluoroalkyl substances (PFAS), pharmaceuticals, and personal care products (PPCPs), pesticides, etc.) is an appropriate niche for EO. EO can be more effective than homogeneous advanced oxidation processes for the degradation of recalcitrant chemicals inert to radical-mediated oxidation, because the potential of the anode can be made much higher than that of hydroxyl radicals (EOH = 2.7 V vs. NHE), forcing the direct transfer of electrons from pollutants to electrodes. Unfortunately, at such high anodic potential, chloride ions, which are ubiquitous in natural water systems, will be readily oxidized to chlorine and perchlorate. Perchlorate is a to-be-regulated byproduct, and chlorine can react with matrix organics to produce organic halogen compounds. In the past ten years, novel electrode materials and processes have been developed. However, spotlights were rarely focused on the control of byproduct formation during EO processes in a real-world context. When we use EO techniques to eliminate target contaminants with concentrations at μg/L-levels, byproducts at mg/L-levels might be produced. Is it a good trade-off? Is it possible to inhibit byproduct formation without compromising the performance of EO? In this mini-review, we will summarize the recent advances and provide perspectives to address the above questions.

  • 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.

  • 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.

  • 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.

  • REVIEW ARTICLE
    Jianfeng Zhou, Ting Wang, Cecilia Yu, Xing Xie
    Frontiers of Environmental Science & Engineering, 2020, 14(5): 78. https://doi.org/10.1007/s11783-020-1253-x

    • Nanowire-assisted LEEFT is applied for water disinfection with low voltages.

    • LEEFT inactivates bacteria by disrupting cell membrane through electroporation.

    • Multiple electrodes and device configurations have been developed for LEEFT.

    • The LEEFT is low-cost, highly efficient, and produces no DBPs.

    • The LEEFT can potentially be applicable for water disinfection at all scales.

    Water disinfection is a critical step in water and wastewater treatment. The most widely used chlorination suffers from the formation of carcinogenic disinfection by-products (DBPs) while alternative methods (e.g., UV, O3, and membrane filtration) are limited by microbial regrowth, no residual disinfectant, and high operation cost. Here, a nanowire-enabled disinfection method, locally enhanced electric field treatment (LEEFT), is introduced with advantages of no chemical addition, no DBP formation, low energy consumption, and efficient microbial inactivation. Attributed to the lightning rod effect, the electric field near the tip area of the nanowires on the electrode is significantly enhanced to inactivate microbes, even though a small external voltage (usually<5 V) is applied. In this review, after emphasizing the significance of water disinfection, the theory of the LEEFT is explained. Subsequently, the recent development of the LEEFT technology on electrode materials and device configurations are summarized. The disinfection performance is analyzed, with respect to the operating parameters, universality against different microorganisms, electrode durability, and energy consumption. The studies on the inactivation mechanisms during the LEEFT are also reviewed. Lastly, the challenges and future research of LEEFT disinfection are discussed.

  • RESEARCH ARTICLE
    Xuesong Liu, Jianmin Wang
    Frontiers of Environmental Science & Engineering, 2020, 14(6): 97. https://doi.org/10.1007/s11783-020-1276-3

    • Micro-plastics (MPs) significantly increase Pb toxicity.

    • Algae reduce the combined toxicity of MP and Pb.

    • The toxicity increase comes from high soluble Pb and MP-Pb uptake.

    • The toxicity reduction might come from energy related pathway.

    Microplastics (MPs) have been recognized as a new class of emerging contaminants in recent years. They not only directly impact aquatic organisms, but also indirectly impact these organisms by interacting with background toxins in the environment. Moreover, under realistic environmental conditions, algae, a natural food for aquatic organisms, may alter the toxicity pattern related to MPs. In this research, we first examined the toxicity of MPs alone, and their effect on the toxicity of lead (Pb) on Ceriodaphnia dubia (C. dubia), a model aquatic organism for toxicity survey. Then, we investigated the effect of algae on the combined toxicity of MPs and Pb. We observed that, MPs significantly increased Pb toxicity, which was related to the increase in soluble Pb concentration and the intake of Pb-loaded MPs, both of which increased the accumulation of Pb in C. dubia. The presence of algae mitigated the combined toxicity of MPs and Pb, although algae alone increased Pb accumulation. Therefore, the toxicity mitigation through algae uptake came from mechanisms other than Pb accumulation, which will need further investigation.

  • 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
    Jinjin Fu, Quan Zhang, Baocheng Huang, Niansi Fan, Rencun Jin
    Frontiers of Environmental Science & Engineering, 2021, 15(1): 17. https://doi.org/10.1007/s11783-020-1309-y

    • Anammox is promising for nitrogen removal from antibiotic-containing wastewater.

    • Most antibiotics could inhibit the anammox performance and activity.

    • Antibiotic pressure promoted the increase in antibiotic resistance genes (ARGs).

    • Antibiotic-resistance mechanisms of anammox bacteria are speculated.

    Antibiotic is widely present in the effluent from livestock husbandry and the pharmaceutical industry. Antibiotics in wastewater usually have high biological toxicity and even promote the occurrence and transmission of antibiotic resistant bacteria and antibiotic resistance genes. Moreover, most antibiotic-containing wastewater contains high concentration of ammonia nitrogen. Improper treatment will lead to high risk to the surrounding environment and even human health. The anaerobic ammonium oxidation (anammox) with great economic benefit and good treatment effect is a promising process to remove nitrogen from antibiotic-containing wastewater. However, antibiotic inhibition has been observed in anammox applications. Therefore, a comprehensive overview of the single and combined effects of various antibiotics on the anammox system is conducted in this review with a focus on nitrogen removal performance, sludge properties, microbial community, antibiotic resistance genes and anammox-involved functional genes. Additionally, the influencing mechanism of antibiotics on anammox consortia is summarized. Remaining problems and future research needs are also proposed based on the presented summary. This review provides a better understanding of the influences of antibiotics on anammox and offers a direction to remove nitrogen from antibiotic-containing wastewater by the anammox process.

  • RESEARCH ARTICLE
    Shengjie Qiu, Jinjin Liu, Liang Zhang, Qiong Zhang, Yongzhen Peng
    Frontiers of Environmental Science & Engineering, 2021, 15(2): 26. https://doi.org/10.1007/s11783-020-1318-x

    • Sludge fermentation liquid addition resulted in a high NAR of 97.4%.

    • Extra NH4+-N from SFL was removed by anammox in anoxic phase.

    • Nitrogen removal efficiency of 92.51% was achieved in municipal wastewater.

    • The novel system could efficiently treat low COD/N municipal wastewater.

    Biological nitrogen removal of wastewater with low COD/N ratio could be enhanced by the addition of wasted sludge fermentation liquid (SFL), but the performance is usually limited by the introducing ammonium. In this study, the process of using SFL was successfully improved by involving anammox process. Real municipal wastewater with a low C/N ratio of 2.8–3.4 was treated in a sequencing batch reactor (SBR). The SBR was operated under anaerobic-aerobic-anoxic (AOA) mode and excess SFL was added into the anoxic phase. Stable short-cut nitrification was achieved after 46d and then anammox sludge was inoculated. In the stable period, effluent total inorganic nitrogen (TIN) was less than 4.3 mg/L with removal efficiency of 92.3%. Further analysis suggests that anammox bacteria, mainly affiliated with Candidatus_Kuenenia, successfully reduced the external ammonia from the SFL and contributed approximately 28%–43% to TIN removal. Overall, this study suggests anammox could be combined with SFL addition, resulting in a stable enhanced nitrogen biological removal.

  • RESEARCH ARTICLE
    Hanzhong Jia, Yafang Shi, Xiaofeng Nie, Song Zhao, Tiecheng Wang, Virender K. Sharma
    Frontiers of Environmental Science & Engineering, 2020, 14(4): 73. https://doi.org/10.1007/s11783-020-1252-y

    • Regulation of redox conditions promotes the generation of free radicals on HM.

    • HM-PFRs can be fractionated into active and inactive types depending on stability.

    • The newly produced PFRs readily release electrons to oxygen and generate ROS.

    • PFR-induced ROS mediate the transformation of organic contaminants adsorbed on HM.

    The role of humic substance-associated persistent free radicals (PFRs) in the fate of organic contaminants under various redox conditions remains unknown. This study examined the characterization of original metal-free peat humin (HM), and HM treated with varying concentrations of H2O2 and L-ascorbic acid (VC) (assigned as H2O2-HM and VC-HM). The concentration of PFRs in HM increased with the addition of VC/H2O2 at concentrations less than 0.08 M. The evolution of PFRs in HM under different environmental conditions (e.g., oxic/anoxic and humidity) was investigated. Two types of PFRs were detected in HM: a relatively stable radical existed in the original sample, and the other type, which was generated by redox treatments, was relatively unstable. The spin densities of VC/H2O2-HM readily returned to the original value under relatively high humidity and oxic conditions. During this process, the HM-associated “unstable” free radicals released an electron to O2, inducing the formation of reactive oxygen species (ROS, i.e., OH and O2). The generated ROS promoted the degradation of polycyclic aromatic hydrocarbons based on the radical quenching measurements. The transformation rates followed the order naphthalene>phenanthrene>anthracene>benzo[a]pyrene. Our results provide valuable insight into the HM-induced transformation of organic contaminants under natural conditions.

  • RESEARCH ARTICLE
    Supaporn Phanwilai, Naluporn Kangwannarakul, Pongsak (Lek) Noophan, Tamao Kasahara, Akihiko Terada, Junko Munakata-Marr, Linda Ann Figueroa
    Frontiers of Environmental Science & Engineering, 2020, 14(6): 115. https://doi.org/10.1007/s11783-020-1374-2

    • Two IFAS and two MBBR full-scale systems (high COD:N ratio 8:1) were characterized.

    • High specific surface area carriers grew and retained slow-growing nitrifiers.

    • High TN removal is related to high SRT and low DO concentration in anoxic tanks.

    The relative locations of AOB, NOB, and DNB were examined for three different kinds of carriers in two types of hybrid biofilm process configurations: integrated fixed-film activated sludge (IFAS) and moving bed biofilm reactor (MBBR) processes. IFAS water resource recovery facilities (WRRFs) used AnodkalnessTM K1 carriers (KC) at Broomfield, Colorado, USA and polypropylene resin carriers (RC) at Fukuoka, Japan, while MBBR WRRFs used KC carriers at South Adams County, Colorado, USA and sponge carriers (SC) at Saga, Japan. Influent COD to N ratios ranged from 8:1 to 15:1. The COD and BOD removal efficiencies were high (96%–98%); NH4+-N and TN removal efficiencies were more varied at 72%–98% and 64%–77%, respectively. The extent of TN removal was higher at high SRT, high COD:N ratio and low DO concentration in the anoxic tank. In IFAS, RC with high specific surface area (SSA) maintained higher AOB population than KC. Sponge carriers with high SSA maintained higher overall bacteria population than KC in MBBR systems. However, the DNB were not more abundant in high SSA carriers. The diversity of AOB, NOB, and DNB was fairly similar in different carriers. Nitrosomonas sp. dominated over Nitrosospira sp. while denitrifying bacteria included Rhodobacter sp., Sulfuritalea sp., Rubrivivax sp., Paracoccus sp., and Pseudomonas sp. The results from this work suggest that high SRT, high COD:N ratio, low DO concentration in anoxic tanks, and carriers with greater surface area may be recommended for high COD, BOD and TN removal in WRRFs with IFAS and MBBR systems.

  • RESEARCH ARTICLE
    Xinyi Hu, Ting Yang, Chen Liu, Jun Jin, Bingli Gao, Xuejun Wang, Min Qi, Baokai Wei, Yuyu Zhan, Tan Chen, Hongtao Wang, Yanting Liu, Dongrui Bai, Zhu Rao, Nan Zhan
    Frontiers of Environmental Science & Engineering, 2020, 14(4): 66. https://doi.org/10.1007/s11783-020-1245-x

    • The total organic pollutant concentrations in sediment were 27.4-1620 ng/g.

    • The phenol concentrations were relatively high in the sediment of the Dianchi Lake.

    • Average total concentrations decreased as follows: Caohai>Waihai>Haigeng Dam.

    • 1,4-dichlorobenzene, 3- or 4-methylphenol, 1,2,4-trichlorobenzene might be risks.

    Organic pollutants are widespread environmental pollutants with high toxicity, persistence, and bioaccumulation. Our aim was to investigate the distribution of aromatic amines, phenols, chlorobenzenes, and naphthalenes in the surface sediment of the Dianchi Lake, China. Nineteen surface sediment samples were collected from the Dianchi Lake, and 40 types of organic pollutants were analyzed via gas chromatography–mass spectrometry. The total organic pollutant concentrations in the surface sediment of the Dianchi Lake varied from 27.4 to 1.62 × 103 ng/g. The concentrations of phenols were much higher than those in other water bodies but still within a controllable range, whereas the concentrations of the other organic pollutant classes were similar or even lower. The detection ratio of 3- or 4-methylphenol was the highest (100.00%) among the pollutants. The average total organic pollutant concentrations decreased in the following order: Caohai (540 ng/g)>the middle of Waihai (488 ng/g)>the edge of Waihai (351 ng/g)>Haigeng Dam (90.4 ng/g). Pearson analysis showed a strong correlation among 1-methylnaphthalene, 2-methylnaphthalene, 1,3-dinitronaphthalene, and 1,4-dinitronaphthalene (p<0.01). Caohai, the north lakeshore of Waihai and the south of Waihai showed higher risk because of high concentration; meanwhile, 1,4-dichlorobenzene, 3- or 4-methylphenol and 1,2,4-trichlorobenzene were more likely to cause risks.

  • RESEARCH ARTICLE
    Rongrong Zhang, Daohao Li, Jin Sun, Yuqian Cui, Yuanyuan Sun
    Frontiers of Environmental Science & Engineering, 2020, 14(4): 68. https://doi.org/10.1007/s11783-020-1247-8

    • FeS/carbon fibers were in situ synthesized with Fe-carrageenan hydrogel fiber.

    • The double helix structure of carrageenan is used to load and disperse Fe.

    • Pyrolyzing sulfate groups enriched carrageenan-Fe could easily generate FeS.

    • The adsorption mechanisms include reduction and complexation reaction.

    Iron sulfide (FeS) nanoparticles (termed FSNs) have attracted much attention for the removal of pollutants due to their high efficiency and low cost, and because they are environmentally friendly. However, issues of agglomeration, transformation, and the loss of active components limit their application. Therefore, this study investigates in situ synthesized FeS/carbon fibers with an Fe-carrageenan biomass as a precursor and nontoxic sulfur source to ascertain the removal efficiency of the fibers. The enrichment of sulfate groups as well as the double-helix structure in ι-carrageenan-Fe could effectively avoid the aggregation and loss of FSNs in practical applications. The obtained FeS/carbon fibers were used to control a Cr(VI) polluted solution, and exhibited a relatively high removal capacity (81.62 mg/g). The main mechanisms included the reduction of FeS, electrostatic adsorption of carbon fibers, and Cr(III)-Fe(III) complexation reaction. The pseudo-second-order kinetic model and Langmuir adsorption model both provided a good fit of the reaction process; hence, the removal process was mainly controlled by chemical adsorption, specifically monolayer adsorption on a uniform surface. Furthermore, co-existing anions, column, and regeneration experiments indicated that the FeS/carbon fibers are a promising remediation material for practical application.

  • RESEARCH ARTICLE
    Wenrui Guo, Yue Wen, Yi Chen, Qi Zhou
    Frontiers of Environmental Science & Engineering, 2020, 14(4): 57. https://doi.org/10.1007/s11783-020-1236-y

    • Fe(III) accepted the most electrons from organics, followed by NO3, SO42‒, and O2.

    • The electrons accepted by SO42‒ could be stored in the solid AVS, FeS2-S, and S0.

    • The autotrophic denitrification driven by solid S had two-phase characteristics.

    • A conceptual model involving electron acceptance, storage, and donation was built.

    • S cycle transferred electrons between organics and NO3 with an efficiency of 15%.

    A constructed wetland microcosm was employed to investigate the sulfur cycle-mediated electron transfer between carbon and nitrate. Sulfate accepted electrons from organics at the average rate of 0.84 mol/(m3·d) through sulfate reduction, which accounted for 20.0% of the electron input rate. The remainder of the electrons derived from organics were accepted by dissolved oxygen (2.6%), nitrate (26.8%), and iron(III) (39.9%). The sulfide produced from sulfate reduction was transformed into acid-volatile sulfide, pyrite, and elemental sulfur, which were deposited in the substratum, storing electrons in the microcosm at the average rate of 0.52 mol/(m3·d). In the presence of nitrate, the acid-volatile and elemental sulfur were oxidized to sulfate, donating electrons at the average rate of 0.14 mol/(m3·d) and driving autotrophic denitrification at the average rate of 0.30 g N/(m3·d). The overall electron transfer efficiency of the sulfur cycle for autotrophic denitrification was 15.3%. A mass balance assessment indicated that approximately 50% of the input sulfur was discharged from the microcosm, and the remainder was removed through deposition (49%) and plant uptake (1%). Dominant sulfate-reducing (i.e., Desulfovirga, Desulforhopalus, Desulfatitalea, and Desulfatirhabdium) and sulfur-oxidizing bacteria (i.e., Thiohalobacter, Thiobacillus, Sulfuritalea, and Sulfurisoma), which jointly fulfilled a sustainable sulfur cycle, were identified. These results improved understanding of electron transfers among carbon, nitrogen, and sulfur cycles in constructed wetlands, and are of engineering significance.

  • PREFACE
    Jinyong Liu, Yin Wang, Haoran Wei
    Frontiers of Environmental Science & Engineering, 2020, 14(5): 91. https://doi.org/10.1007/s11783-020-1270-9
  • REVIEW ARTICLE
    Zhengqing Cai, Xiao Zhao, Jun Duan, Dongye Zhao, Zhi Dang, Zhang Lin
    Frontiers of Environmental Science & Engineering, 2020, 14(5): 84. https://doi.org/10.1007/s11783-020-1263-8

    ▪ Overviewed evolution and environmental applications of stabilized nanoparticles.

    ▪ Reviewed theories on particle stabilization for enhanced reactivity/deliverability.

    ▪ Examined various in situ remediation technologies based on stabilized nanoparticles.

    ▪ Summarized knowledge on transport of stabilized nanoparticles in porous media.

    ▪ Identified key knowledge gaps and future research needs on stabilized nanoparticles.

    Due to improved soil deliverability and high reactivity, stabilized nanoparticles have been studied for nearly two decades for in situ remediation of soil and groundwater contaminated with organic pollutants. While large amounts of bench- and field-scale experimental data have demonstrated the potential of the innovative technology, extensive research results have also unveiled various merits and constraints associated different soil characteristics, types of nanoparticles and particle stabilization techniques. Overall, this work aims to critically overview the fundamental principles on particle stabilization, and the evolution and some recent developments of stabilized nanoparticles for degradation of organic contaminants in soil and groundwater. The specific objectives are to: 1) overview fundamental mechanisms in nanoparticle stabilization; 2) summarize key applications of stabilized nanoparticles for in situ remediation of soil and groundwater contaminated by legacy and emerging organic chemicals; 3) update the latest knowledge on the transport and fate of stabilized nanoparticles; 4) examine the merits and constraints of stabilized nanoparticles in environmental remediation applications; and 5) identify the knowledge gaps and future research needs pertaining to stabilized nanoparticles for remediation of contaminated soil and groundwater. Per instructions of this invited special issue, this review is focused on contributions from our group (one of the pioneers in the subject field), which, however, is supplemented by important relevant works by others. The knowledge gained is expected to further advance the science and technology in the environmental applications of stabilized nanoparticles.

  • RESEARCH ARTICLE
    Ragini Pirarath, Palani Shivashanmugam, Asad Syed, Abdallah M. Elgorban, Sambandam Anandan, Muthupandian Ashokkumar
    Frontiers of Environmental Science & Engineering, 2021, 15(1): 15. https://doi.org/10.1007/s11783-020-1307-0

    • Synthesized few-layered MoS2 nanosheets via surfactant-assisted hydrothermal method.

    • Synthesized MoS2 nanosheets show petal-like morphology.

    • Adsorbent showed 93% of mercury removal efficiency.

    • The adsorption of mercury is attributed to negative zeta potential (-21.8 mV).

    Recently, different nanomaterial-based adsorbents have received greater attention for the removal of environmental pollutants, specifically heavy metals from aqueous media. In this work, we synthesized few-layered MoS2 nanosheets via a surfactant-assisted hydrothermal method and utilized them as an efficient adsorbent for the removal of mercury from aqueous media. The synthesized MoS2 nanosheets showed petal-like morphology as confirmed by scanning electron microscope and high-resolution transmission electron microscopic analysis. The average thickness of the nanosheets is found to be about 57 nm. Possessing high stability and negative zeta potential makes this material suitable for efficient adsorption of mercury from aqueous media. The adsorption efficiency of the adsorbent was investigated as a function of pH, contact time and adsorbent dose. The kinetics of adsorption and reusability potential of the adsorbent were also performed. A pseudo-second-order kinetics for mercury adsorption was observed. As prepared MoS2 nanosheets showed 93% mercury removal efficiency, whereas regenerated adsorbent showed 91% and 79% removal efficiency in the respective 2nd and 3rd cycles. The adsorption capacity of the adsorbent was found to be 289 mg/g at room temperature.

  • RESEARCH ARTICLE
    Ying Cui, Feng Tan, Yan Wang, Suyu Ren, Jingwen Chen
    Frontiers of Environmental Science & Engineering, 2020, 14(6): 111. https://doi.org/10.1007/s11783-020-1290-5

    • Selective molecularly imprinted polymer (MIP) binding gel was prepared.

    • MIP-DGT showed excellent uptake performance for antibiotics.

    • In situ measurement of antibiotics in wastewaters via MIP-DGT was developed.

    • The MIP-DGT method was robust, reliable, and highly sensitive.

    Urban wastewater is one of main sources for the introduction of antibiotics into the environment. Monitoring the concentrations of antibiotics in wastewater is necessary for estimating the amount of antibiotics discharged into the environment through urban wastewater treatment systems. In this study, we report a novel diffusive gradient in thin films (DGT) method based on molecularly imprinted polymers (MIPs) for in situ measurement of two typical antibiotics, fluoroquinolones (FQs) and sulfonamides (SAs) in urban wastewater. MIPs show specific adsorption toward their templates and their structural analogs, resulting in the selective uptake of the two target antibiotics during MIP-DGT deployment. The uptake performance of the MIP-DGTs was evaluated in the laboratory and was relatively independent of solution pH (4.0–9.0), ionic strength (1–750 mmol/L), and dissolved organic matter (DOM, 0–20 mg/L). MIP-DGT samplers were tested in the effluent of an urban wastewater treatment plant for field trials, where three SA (sulfamethoxazole, sulfapyridine, and trimethoprim) and one FQ (ofloxacin) antibiotics were detected, with concentrations ranging from 25.50 to 117.58 ng/L, which are consistent with the results measured by grab sampling. The total removal efficiency of the antibiotics was 80.1% by the treatment plant. This study demonstrates that MIP-DGT is an effective tool for in situ monitoring of trace antibiotics in complex urban wastewaters.

  • REVIEW ARTICLE
    Lingchen Kong, Xitong Liu
    Frontiers of Environmental Science & Engineering, 2020, 14(5): 90. https://doi.org/10.1007/s11783-020-1269-2

    • Mechanisms for selective recovery of materials in electrochemical processes are discussed.

    • Wastewaters that contain recoverable materials are reviewed.

    • Application prospects are discussed from both technical and non-technical aspects.

    Recovering valuable materials from waste streams is critical to the transition to a circular economy with reduced environmental damages caused by resource extraction activities. Municipal and industrial wastewaters contain a variety of materials, such as nutrients (nitrogen and phosphorus), lithium, and rare earth elements, which can be recovered as value-added products. Owing to their modularity, convenient operation and control, and the non-requirement of chemical dosage, electrochemical technologies offer a great promise for resource recovery in small-scale, decentralized systems. Here, we review three emerging electrochemical technologies for materials recovery applications: electrosorption based on carbonaceous and intercalation electrodes, electrochemical redox processes, and electrochemically induced precipitation. We highlight the mechanisms for achieving selective materials recovery in these processes. We also present an overview of the advantages and limitations of these technologies, as well as the key challenges that need to be overcome for their deployment in real-world systems to achieve cost-effective and sustainable materials recovery.

  • RESEARCH ARTICLE
    Haiyan Mou, Wenchao Liu, Lili Zhao, Wenqing Chen, Tianqi Ao
    Frontiers of Environmental Science & Engineering, 2021, 15(4): 61. https://doi.org/10.1007/s11783-020-1353-7

    • Separate reduction and sintering cannot be effective for Cr stabilization.

    • Combined treatment of reduction and sintering is effective for Cr stabilization.

    • Almost all the Cr in the reduced soil is residual form after sintering at 1000°C.

    This study explored the effectiveness and mechanisms of high temperature sintering following pre-reduction with ferric sulfate (FeSO4), sodium sulfide (Na2S), or citric acid (C6H8O7) in stabilizing hexavalent chromium (Cr(VI)) in highly contaminated soil. The soil samples had an initial total Cr leaching of 1768.83 mg/L, and Cr(VI) leaching of 1745.13 mg/L. When FeSO4 or C6H8O7 reduction was followed by sintering at 1000°C, the Cr leaching was reduced enough to meet the Safety Landfill Standards regarding general industrial solid waste. This combined treatment greatly improved the stabilization efficiency of chromium because the reduction of Cr(VI) into Cr(III) decreased the mobility of chromium and made it more easily encapsulated in minerals during sintering. SEM, XRD, TG-DSC, and speciation analysis indicated that when the sintering temperature reached 1000°C, almost all the chromium in soils that had the pre-reduction treatment was transformed into the residual form. At 1000°C, the soil melted and promoted the mineralization of Cr and the formation of new Cr-containing compounds, which significantly decreased subsequent leaching of chromium from the soil. However, without reduction treatment, chromium continued to leach from the soil even after being sintered at 1000°C, possibly because the soil did not fully fuse and because Cr(VI) does not bind with soil as easily as Cr(III).

  • REVIEW ARTICLE
    Lijie Zhou, Hongwu Wang, Zhiqiang Zhang, Jian Zhang, Hongbin Chen, Xuejun Bi, Xiaohu Dai, Siqing Xia, Lisa Alvarez-Cohen, Bruce E. Rittmann
    Frontiers of Environmental Science & Engineering, 2021, 15(1): 16. https://doi.org/10.1007/s11783-020-1308-z

    5R (Recover, Reduce, Recycle, Resource and Reuse) approaches to manage urban water.

    5R harvests storm water, gray water and black water in several forms.

    5R offers promise for moving solutions for urban water scarcity in practice.

    Demand for water is expanding with increases in population, particularly in urban areas in developing countries. Additionally, urban water system needs a novel perspective for upgradation with urbanization. This perspective presents a novel 5R approach for managing urban water resources: Recover (storm water), Reduce (toilet flushing water), Recycle (gray water), Resource (black water), and Reuse (advanced-treated wastewater). The 5R generation incorporates the latest ideas for harvesting storm water, gray water, and black water in its several forms. This paper has briefly demonstrated each R of 5R generation for water treatment and reuse. China has the chance to upgrade its urban water systems according to 5R principles. Already, a demonstration project of 5R generation has been installed in Qingdao International Horticultural Exposition, and Dalian International Convention Center (China) has applied 5R, achieving over 70% water saving. The 5R offers promise for moving solutions for urban water scarcity from “hoped for in the future” to “realistic today”.

  • 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.

  • REVIEW ARTICLE
    Chao Lu, Kanglan Deng, Chun Hu, Lai Lyu
    Frontiers of Environmental Science & Engineering, 2020, 14(5): 82. https://doi.org/10.1007/s11783-020-1261-x

    • Dual-reaction-center (DRC) system breaks through bottleneck of Fenton reaction.

    • Utilization of intrinsic electrons of pollutants is realized in DRC system.

    • DRC catalytic process well continues Fenton’s story.

    Triggered by global water quality safety issues, the research on wastewater treatment and water purification technology has been greatly developed in recent years. The Fenton technology is particularly powerful due to the rapid attack on pollutants by the generated hydroxyl radicals (•OH). However, both heterogeneous and homogeneous Fenton/Fenton-like technologies follow the classical reaction mechanism, which depends on the oxidation and reduction of the transition metal ions at single sites. So even after a century of development, this reaction still suffers from its inherent bottlenecks in practical application. In recent years, our group has been focusing on studying a novel heterogeneous Fenton catalytic process, and we developed the dual-reaction-center (DRC) system for the first time. In the DRC system, H2O2 and O2 can be efficiently reduced to reactive oxygen species (ROS) in electron-rich centers, while pollutants are captured and oxidized by the electron-deficient centers. The obtained electrons from pollutants are diverted to the electron-rich centers through bonding bridges. This process breaks through the classic Fenton mechanism, and improves the performance and efficiency of pollutant removal in a wide pH range. Here, we provide a brief overview of Fenton’s story and focus on combing the discovery and development of the DRC technology and mechanism in recent years. The construction of the DRC and its performance in the pollutant degradation and interfacial reaction process are described in detail. We look forward to bringing a new perspective to continue Fenton’s story through research and development of DRC technology.

  • RESEARCH ARTICLE
    Ting Chen, Yingying Zhao, Xiaopeng Qiu, Xiaoyan Zhu, Xiaojie Liu, Jun Yin, Dongsheng Shen, Huajun Feng
    Frontiers of Environmental Science & Engineering, 2021, 15(2): 33. https://doi.org/10.1007/s11783-020-1325-y

    • Economics of food waste treatment projects at 29 pilot cities in China was examined.

    • Roles of location, population size, processing technique, and income were studied.

    • Economic benefits were limited with a profit to cost ratio of 0.08±0.37.

    • Service population size affects construction economics significantly (P = 0.016).

    • Choice of food waste processing technique affects operating economics notably.

    This study examines the economic benefits of food waste treatment projects in China and factors affecting them. National-level pilot projects for food waste treatment located in 29 cities were selected as samples. The economics of food waste recycling from the investors’ perspective, in terms of investment during the construction phase and cost and benefit during the operation phase, was assessed. Results indicate that the average tonnage investment of food waste treatment projects was RMB 700.0±188.9 thousand yuan, with a profit to cost ratio of 0.08±0.37. This ratio increased to 0.95±0.57 following the application of government subsidies. It highlights the limited economic benefits of food waste treatment facilities, which rely on government subsidies to maintain their operations in China. Further analysis using a multi-factor analysis model revealed that regional location, service population size, processing techniques, and urban income exerted varying impacts on the economy of food waste treatment. Population size exerted the highest impact (P = 0.016) during the construction stage, and processing techniques notably influenced the project economy during the operation stage. The study highlights the need to prioritize service population size and processing techniques during economic decision-making and management of food waste recycling projects. The results of this study can serve as a valuable practical reference for guiding future policies regarding food waste treatment and related planning.

  • RESEARCH ARTICLE
    Caihong Xu, Jianmin Chen, Zhikai Wang, Hui Chen, Hao Feng, Lujun Wang, Yuning Xie, Zhenzhen Wang, Xingnan Ye, Haidong Kan, Zhuohui Zhao, Abdelwahid Mellouki
    Frontiers of Environmental Science & Engineering, 2021, 15(3): 37. https://doi.org/10.1007/s11783-020-1329-7

    • Urban aerosols harbour diverse bacterial communities in Shanghai.

    • The functional groups were associated with nitrogen, carbon, and sulfur cycling.

    • Temperature, SO2, and wind speed were key drivers for the bacterial community.

    Airborne bacteria play key roles in terrestrial and marine ecosystems and human health, yet our understanding of bacterial communities and their response to the environmental variables lags significantly behind that of other components of PM2.5. Here, atmospheric fine particles obtained from urban and suburb Shanghai were analyzed by using the qPCR and Illumina Miseq sequencing. The bacteria with an average concentration of 2.12 × 103 cells/m3, were dominated by Sphingomonas, Curvibacter, Acinetobacter, Bradyrhizobium, Methylobacterium, Halomonas, Aliihoeflea, and Phyllobacterium, which were related to the nitrogen, carbon, sulfur cycling and human health risk. Our results provide a global survey of bacterial community across urban, suburb, and high-altitude sites. In Shanghai (China), urban PM2.5 harbour more diverse and dynamic bacterial populations than that in the suburb. The structural equation model explained about 27%, 41%, and 20%–78% of the variance found in bacteria diversity, concentration, and discrepant genera among urban and suburb sites. This work furthered the knowledge of diverse bacteria in a coastal Megacity in the Yangtze river delta and emphasized the potential impact of environmental variables on bacterial community structure.

  • RESEARCH ARTICLE
    Wei Fan, Qi Li, Mingxin Huo, Xiaoyu Wang, Shanshan Lin
    Frontiers of Environmental Science & Engineering, 2020, 14(4): 63. https://doi.org/10.1007/s11783-020-1242-0

    • The recharge pond dwelling process induced changes in cell properties.

    • Cell properties and solution chemistry exerted confounding effect on cell transport.

    E. coli cells within different recharge water displayed different spreading risks.

    Commonly used recharge water resources for artificial groundwater recharge (AGR) such as secondary effluent (SE), river water and rainfall, are all oligotrophic, with low ionic strengths and different cationic compositions. The dwelling process in recharge pond imposed physiologic stress on Escherichia coli (E. coli) cells, in all three types of investigated recharge water resources and the cultivation of E. coli under varying recharge water conditions, induced changes in cell properties. During adaptation to the recharge water environment, the zeta potential of cells became more negative, the hydrodynamic diameters, extracellular polymeric substances content and surface hydrophobicity decreased, while the cellular outer membrane protein profiles became more diverse. The mobility of cells altered in accordance with changes in these cell properties. The E. coli cells in rainfall recharge water displayed the highest mobility (least retention), followed by cells in river water and finally SE cells, which had the lowest mobility. Simulated column experiments and quantitative modeling confirmed that the cellular properties, driven by the physiologic state of cells in different recharge water matrices and the solution chemistry, exerted synergistic effects on cell transport behavior. The findings of this study contribute to an improved understanding of E. coli transport in actual AGR scenarios and prediction of spreading risk in different recharge water sources.