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    Qinghui Sun, Juan Li, Chen Wang, Anqi Chen, Yanli You, Shupeng Yang, Huihui Liu, Guibin Jiang, Yongning Wu, Yanshen Li
    Frontiers of Environmental Science & Engineering, 2022, 16(1): 1.

    • Microplastics are widely found in both aquatic and terrestrial environments.

    • Cleaning products and discarded plastic waste are primary sources of microplastics.

    • Microplastics have apparent toxic effects on the growth of fish and soil plants.

    • Multiple strains of biodegradable microplastics have been isolated.

    Microplastics (MPs) are distributed in the oceans, freshwater, and soil environment and have become major pollutants. MPs are generally referred to as plastic particles less than 5 mm in diameter. They consist of primary microplastics synthesized in microscopic size manufactured production and secondary microplastics generated by physical and environmental degradation. Plastic particles are long-lived pollutants that are highly resistant to environmental degradation. In this review, the distribution and possible sources of MPs in aquatic and terrestrial environments are described. Moreover, the adverse effects of MPs on natural creatures due to ingestion have been discussed. We also have summarized identification methods based on MPs particle size and chemical bond. To control the pollution of MPs, the biodegradation of MPs under the action of different microbes has also been reviewed in this work. This review will contribute to a better understanding of MPs pollution in the environment, as well as their identification, toxicity, and biodegradation in the ocean, freshwater, and soil, and the assessment and control of microplastics exposure.

    Bin Wang, Gang Yu
    Frontiers of Environmental Science & Engineering, 2022, 16(6): 81.

    Since the concept of emerging contaminants (ECs) was first proposed in 2001, the global scientific research of ECs has developed rapidly. In the past decades, great progress has been achieved in the scientific research of ECs in China, including the establishment of EC analysis method system, the evaluation of the pollution status, pollution characteristics and environmental risk of ECs in typical regions of China, and establishment of EC control technology system. Continuous progress in scientific research of ECs promoted China’s action on EC control. It is planned that the environmental risk of ECs will be generally controlled by 2035 in China. Priority ECs should be screened for environmental management. Although great efforts have been made, the EC control in China still faces tremendous challenges. It is necessary to bridge the gap between scientific research and decision-making management. Based on the science and technology study, various measures such as engineering, policy management and public participation should be combinedly adopted for EC control.

    Elham Abaie, Limeimei Xu, Yue-xiao Shen
    Frontiers of Environmental Science & Engineering, 0: 124.

    •The history of biological and artificial water channels is reviewed.

    •A comprehensive channel characterization platform is introduced.

    •Rationale designs and fabrications of biomimetic membranes are summarized.

    •The advantages, limitations, and challenges of biomimetic membranes are discussed.

    •The prospect and scalable solutions of biomimetic membranes are discussed.

    Bioinspired and biomimetic membranes that contain biological transport channels or attain their structural designs from biological systems have been through a remarkable development over the last two decades. They take advantage of the exceptional transport properties of those channels, thus possess both high permeability and selectivity, and have emerged as a promising solution to existing membranes. Since the discovery of biological water channel proteins aquaporins (AQPs), extensive efforts have been made to utilize them to make separation membranes–AQP-based membranes, which have been commercialized. The exploration of AQPs’ unique structures and transport properties has resulted in the evolution of biomimetic separation materials from protein-based to artificial channel-based membranes. However, large-scale, defect-free biomimetic membranes are not available yet. This paper reviews the state-of-the-art biomimetic membranes and summarizes the latest research progress, platform, and methodology. Then it critically discusses the potential routes of this emerging area toward scalable applications. We conclude that an appropriate combination of bioinspired concepts and molecular engineering with mature polymer industry may lead to scalable polymeric membranes with intrinsic selective channels, which will gain the merit of both desired selectivity and scalability.

    Tingwei Gao, Kang Xiao, Jiao Zhang, Wenchao Xue, Chunhai Wei, Xiaoping Zhang, Shuai Liang, Xiaomao Wang, Xia Huang
    Frontiers of Environmental Science & Engineering, 2022, 16(4): 49.

    • Retrofitting from CAS to MBR increased effluent quality and environmental benefits.

    • Retrofitting from CAS to MBR increased energy consumption but not operating cost.

    • Retrofitting from CAS to MBR increased the net profit and cost efficiency.

    • The advantage of MBR is related to the adopted effluent standard.

    • The techno-economy of MBR improves with stricter effluent standards.

    While a growing number of wastewater treatment plants (WWTPs) are being retrofitted from the conventional activated sludge (CAS) process to the membrane bioreactor (MBR) process, the debate on the techno-economy of MBR vs. CAS has continued and calls for a thorough assessment based on techno-economic valuation. In this study, we analyzed the operating data of 20 large-scale WWTPs (capacity≥10000 m3/d) and compared their techno-economy before and after the retrofitting from CAS to MBR. Through cost-benefit analysis, we evaluated the net profit by subtracting the operating cost from the environmental benefit (estimated by the shadow price of pollutant removal and water reclamation). After the retrofitting, the removal rate of pollutants increased (e.g., from 89.0% to 93.3% on average for NH3-N), the average energy consumption increased from 0.40 to 0.57 kWh/m3, but the operating cost did not increase significantly. The average marginal environmental benefit increased remarkably (from 0.47 to 0.66 CNY/g for NH3-N removal), leading to an increase in the average net profit from 19.4 to 24.4 CNY/m3. We further scored the technical efficiencies via data envelopment analysis based on non-radial directional distance functions. After the retrofitting, the relative cost efficiency increased from 0.70 to 0.73 (the theoretical maximum is 1), while the relative energy efficiency did not change significantly. The techno-economy is closely related to the effluent standard adopted, particularly when truncating the extra benefit of pollutant removal beyond the standard in economic modeling. The modeling results suggested that MBR is more profitable than CAS given stricter effluent standards.

    Yangyang Liang, Qingbin Song, Naiqi Wu, Jinhui Li, Yuan Zhong, Wenlei Zeng
    Frontiers of Environmental Science & Engineering, 0: 115.

    • Implication of COVID-19 on medical waste and MSW generation is studied.

    • Challenges and effective strategy of solid waste generation is reviewed.

    • 2.9 million tons of COVID-19 related medical waste has been generated until Sep. 22.

    • The pandemic has postponed policies related to the reduction of plastic use.

    • Blockade resulted in a significant drop in waste generation in some regions.

    It has been over ten months since the beginning of the 2019 coronavirus disease (COVID-2019), and its impact on solid waste management, especially medical waste, is becoming clearer. This study systematically reviews the potential influences of the COVID-19 pandemic on medical waste, personal protection equipment waste and municipal solid waste (MSW), and discusses the corresponding measures and policies of solid waste management in typical countries. The results show that the generation of medical waste from the pandemic increased significantly, with 18%‒425% growth. It is estimated that the daily output of COVID-19 medical waste increased from 200 t/d on Feb. 22 to over 29000 t/d at the end of September 2020 throughout the world. The use of personal protective equipment will continue to grow in the long-term, while the blockade and isolation measures greatly reduced the volume of commercial waste, especially for tourist cities, and part of this waste was transferred to household waste. Residents’ attitudes and behavior toward food waste have changed due to the COVID-19 pandemic. In response to the pandemic, international organizations and several countries have issued new policies and guidelines and adjusted their management strategies for medical waste and MSW treatment. The pandemic has brought specific challenges to the disposal capacity of medical waste worldwide. It has also brought about the stagnation of policies related to the reduction of plastic products and waste recycling. This study will provide some useful information for managers and governmental officials on effective solid waste management during and after the COVID-19 pandemic.

    Kehui Liu, Xiaojin Guan, Chunming Li, Keyi Zhao, Xiaohua Yang, Rongxin Fu, Yi Li, Fangming Yu
    Frontiers of Environmental Science & Engineering, 2022, 16(6): 73.

    • The overall global perspective of the PHMCS field was obtained.

    • PHMCS research has flourished over the past two decades.

    • In total, 8 clusters were obtained, and many new hot topics emerged.

    • “Biochar,” “Drought,” “Nanoparticle,” etc., may be future hot topics.

    • Five future directions are proposed.

    In total, 9,552 documents were extracted from the Web of Science Core Collection and subjected to knowledge mapping and visualization analysis for the field of phytoremediation of HM-contaminated soil (PHMCS) with CiteSpace 5.7 R3 software. The results showed that (1) the number of publications increased linearly over the studied period. The top 10 countries/regions, institutions and authors contributing to this field were exhibited. (2) Keyword co-occurrence cluster analysis revealed a total of 8 clusters, including “Bioremediation,” “Arsenic,” “Biochar,” “Oxidative stress,” “Hyperaccumulation,” “EDTA,” “Arbuscular mycorrhizal fungi,” and “Environmental pollution” clusters (3) In total, 334 keyword bursts were obtained, and the 25 strongest, longest duration, and newest keyboard bursts were analyzed in depth. The strongest keyword burst test showed that the hottest keywords could be divided into 7 groups, i.e., “Plant bioremediation materials,” “HM types,” “Chelating amendments,” “Other improved strategies,” “Bioremediation characteristics,” “Risk assessment,” and “Other.” Almost half of the newest topics had emerged in the past 3 years, including “biochar,” “drought,” “health risk assessment,” “electrokinetic remediation,” “nanoparticle,” and “intercropping.” (4) In total, 9 knowledge base clusters were obtained in this study. The studies of Ali et al. (2013), Blaylock et al. (1997), Huang et al. (1997), van der Ent et al. (2013), Salt et al. (1995), and Salt (1998), which had both high frequencies and the strongest burst scores, have had the most profound effects on PHMCS research. Finally, future research directions were proposed.

    Jiuhui Qu, Hongqiang Ren, Hongchen Wang, Kaijun Wang, Gang Yu, Bing Ke, Han-Qing Yu, Xingcan Zheng, Ji Li
    Frontiers of Environmental Science & Engineering, 0: 13.
    Shaoyi Xu, Xiaolong Wu, Huijie Lu
    Frontiers of Environmental Science & Engineering, 2021, 15(6): 133.

    • AOA and comammox bacteria can be more abundant and active than AOB/NOB at WWTPs.

    • Coupled DNRA/anammox and NOx-DAMO/anammox/comammox processes are demonstrated.

    • Substrate level, SRT and stressors determine the niches of overlooked microbes.

    • Applications of overlooked microbes in enhancing nitrogen removal are promising.

    Nitrogen-cycling microorganisms play key roles at the intersection of microbiology and wastewater engineering. In addition to the well-studied ammonia oxidizing bacteria, nitrite oxidizing bacteria, heterotrophic denitrifiers, and anammox bacteria, there are some other N-cycling microorganisms that are less abundant but functionally important in wastewater nitrogen removal. These microbes include, but not limited to ammonia oxidizing archaea (AOA), complete ammonia oxidation (comammox) bacteria, dissimilatory nitrate reduction to ammonia (DNRA) bacteria, and nitrate/nitrite-dependent anaerobic methane oxidizing (NOx-DAMO) microorganisms. In the past decade, the development of high-throughput molecular technologies has enabled the detection, quantification, and characterization of these minor populations. The aim of this review is therefore to synthesize the current knowledge on the distribution, ecological niche, and kinetic properties of these “overlooked” N-cycling microbes at wastewater treatment plants. Their potential applications in novel wastewater nitrogen removal processes are also discussed. A comprehensive understanding of these overlooked N-cycling microbes from microbiology, ecology, and engineering perspectives will facilitate the design and operation of more efficient and sustainable biological nitrogen removal processes.

    Ying Cai, Jun Wu, Jian Lu, Jianhua Wang, Cui Zhang
    Frontiers of Environmental Science & Engineering, 2022, 16(7): 96.

    • Fate of microplastics in integrated membrane system for water reuse was investigated.

    • Integrated membrane system has high removal efficiency (>98%) for microplastics.

    • Microplastics (>93%) were mainly removed through membrane bioreactor treatment.

    • Small scale fiber plastics (<200 μm) could break through reverse osmosis (RO) system.

    • The flux of microplastics maintained at 2.7 × 1011 MPs/d after the RO treatment.

    Rare information on the fate of microplastics in the integrated membrane system (IMS) system in full-scale wastewater treatment plant was available. The fate of microplastics in IMS in a coastal reclaimed water plant was investigated. The removal rate of microplastics in the IMS system reached 93.2% after membrane bioreactor (MBR) treatment while that further increased to 98.0% after the reverse osmosis (RO) membrane process. The flux of microplastics in MBR effluent was reduced from 1.5 × 1013 MPs/d to 10.2 × 1011 MPs/d while that of the RO treatment decreased to 2.7 × 1011 MPs/d. Small scale fiber plastics (<200 μm) could break through RO system according to the size distribution analysis. The application of the IMS system in the reclaimed water plant could prevent most of the microplastics from being discharged in the coastal water. These findings suggested that the IMS system was more efficient than conventional activated sludge system (CAS) for the removal of microplastics, while the discharge of small scale fiber plastics through the IMS system should also not be neglected because small scale fiber plastics (<200 μm) could break through IMS system equipped with the RO system.

    Lihui Gao, Yijun Cao, Lizhang Wang, Shulei Li
    Frontiers of Environmental Science & Engineering, 2022, 16(6): 77.

    • The sustainable approaches related to Fenton sludge reuse systems are summarized.

    • Degradation mechanism of Fenton sludge heterogeneous catalyst is deeply discussed.

    • The efficient utilization directions of Fenton sludge are proposed.

    The classical Fenton oxidation process (CFOP) is a versatile and effective application that is generally applied for recalcitrant pollutant removal. However, excess iron sludge production largely restricts its widespread application. Fenton sludge is a hazardous solid waste, which is a complex heterogeneous mixture with Fe(OH)3, organic matter, heavy metals, microorganisms, sediment impurities, and moisture. Although studies have aimed to utilize specific Fenton sludge resources based on their iron-rich characteristics, few reports have fully reviewed the utilization of Fenton sludge. As such, this review details current sustainable Fenton sludge reuse systems that are applied during wastewater treatment. Specifically, coagulant preparation, the reuse of Fenton sludge as an iron source in the Fenton process and as a synthetic heterogeneous catalyst/adsorbent, as well as the application of the Fenton sludge reuse system as a heterogeneous catalyst for resource utilization. This is the first review article to comprehensively summarize the utilization of Fenton sludge. In addition, this review suggests future research ideas to enhance the cost-effectiveness, environmental sustainability, and large-scale feasibility of Fenton sludge applications.

    Shansi Wang, Siwei Li, Jia Xing, Jie Yang, Jiaxin Dong, Yu Qin, Shovan Kumar Sahu
    Frontiers of Environmental Science & Engineering, 2022, 16(2): 26.

    •Strong ENSO influence on AOD is found in southern China region.

    •Low AOD occurs in El Niño but high AOD occurs in La Niña events in southern China.

    •Angstrom exponent anomalies reveals the circulation pattern during each ENSO phase.

    •ENSO exerts large influence (70.5%) on annual variations of AOD during 2002–2020.

    •Change of anthropogenic emissions is the dominant driver for AOD trend (2002–2020).

    Previous studies demonstrated that the El Niño–Southern Oscillation (ENSO) could modulate regional climate thus influencing air quality in the low-middle latitude regions like southern China. However, such influence has not been well evaluated at a long-term historical scale. To filling the gap, this study investigated two-decade (2002 to 2020) aerosol concentration and particle size in southern China during the whole dynamic development of ENSO phases. Results suggest strong positive correlations between aerosol optical depth (AOD) and ENSO phases, as low AOD occurred during El Niño while high AOD occurred during La Niña event. Such correlations are mainly attributed to the variation of atmospheric circulation and precipitation during corresponding ENSO phase. Analysis of the angstrom exponent (AE) anomalies further confirmed the circulation pattern, as negative AE anomalies is pronounced in El Niño indicating the enhanced transport of sea salt aerosols from the South China Sea, while the La Niña event exhibits positive AE anomalies which can be attributed to the enhanced import of northern fine anthropogenic aerosols. This study further quantified the AOD variation attributed to changes in ENSO phases and anthropogenic emissions. Results suggest that the long-term AOD variation from 2002 to 2020 in southern China is mostly driven (by 64.2%) by the change of anthropogenic emissions from 2002 to 2020. However, the ENSO presents dominant influence (70.5%) on year-to-year variations of AOD during 2002–2020, implying the importance of ENSO on varying aerosol concentration in a short-term period.

    Xiaoqiang Gong, Jinbiao Li, Scott X. Chang, Qian Wu, Zhengfeng An, Chengpeng Huang, Xiangyang Sun, Suyan Li, Hui Wang
    Frontiers of Environmental Science & Engineering, 2022, 16(3): 39.

    • Earthworms increase CO2 and N2O emissions in agricultural and forest soil.

    • 10% biochar suppresses CO2 and N2O emissions in forest soil.

    • Biochar interacted with earthworm to significant affect CO2 and N2O emissions.

    The application of manure-derived biochar offers an alternative to avoid the direct application of manure to soil causing greenhouse gas emission. Soil fauna, especially earthworms, can markedly stimulate carbon dioxide (CO2) and nitrous oxide (N2O) emissions from soil. This study therefore investigated the effect of cattle manure biochar (added at rates of 0, 2%, or 10%, coded as BC0, BC2 and BC10, respectively) application, with or without earthworm Aporrectodea turgida, on emissions of CO2 and N2O and changes of physic-chemical properties of agricultural and forest soils in a laboratory incubation experiment. The BC10 treatment significantly enhanced cumulative CO2 emissions by 27.9% relative to the untreated control in the agricultural soil. On the contrary, the BC2 and BC10 treatments significantly reduced cumulative CO2 emissions by 16.3%–61.1% and N2O emissions by 92.9%–95.1% compared to the untreated control in the forest soil. The addition of earthworm alone significantly enhanced the cumulative CO2 and N2O fluxes in agricultural and forest soils. Cumulative CO2 and N2O fluxes were significantly increased when BC2 and BC10 were applied with earthworm in the agricultural soil, but were significantly reduced when BC10 was applied with earthworm in the forest soil. Our study demonstrated that biochar application interacted with earthworm to affect CO2 and N2O emissions, which were also dependent on the soil type involved. Our study suggests that manure biochar application rate and use of earthworm need to be carefully studied for specific soil types to maximize the climate change mitigation potential of such management practices.

    Wei Shan, Bingbing Li, Haichuan Zhang, Zhenghao Zhang, Yan Wang, Zhiyang Gao, Ji Li
    Frontiers of Environmental Science & Engineering, 2022, 16(1): 6.

    • MPs were analyzed throughout three WWTPs with mixed domestic–industrial influents.

    • White polyethylene granules from plastic manufacturing were the most dominant MPs.

    • MPs abundance in random grab-sampling was lower than that in daily dense sampling.

    • The production of MPs such as microbeads need to be restricted from the source.

    In wastewater treatment plants (WWTPs), microplastics (MPs) are complex, especially with mixed domestic–industrial influents. Conventional random grab sampling can roughly depict the distribution and characteristics of MPs but can not accurately reflect their daily fluctuations. In this study, the concentration, shape, polymer type, size, and color of MPs were analyzed by micro-Raman spectroscopy (detection limit of 0.05 mm) throughout treatment stages of three mixed domestic–industrial WWTPs (W1, W2, and W3) in Wuxi City, China, and the daily fluctuations of MPs were also obtained by dense grab sampling within 24 h. For influent samples, the average MP concentration of 392.2 items/L in W1 with 10% industrial wastewater was much higher than those in W2 (71.2 items/L with 10% industrial wastewater) and W3 (38.3 items/L with 60% industrial wastewater). White polyethylene granules with a diameter less than 0.5 mm from plastic manufacturing were the most dominant MPs in the influent of W1, proving the key role of industrial sources in MPs pollution. In addition, the daily dense sampling results showed that MP concentration in W1 influent fluctuated widely between 29.1 items/L and 4617.6 items/L within a day. Finally, few MPs (less than 4.0 items/L) in these WWTPs effluents were attributed to the effective removal of wastewater treatment processes. Thus, further attention should be paid to regulating the primary sources of MPs.

    Malan Yi, Yao Fang, Guoping Hu, Shufeng Liu, Jinren Ni, Tang Liu
    Frontiers of Environmental Science & Engineering, 2022, 16(6): 79.

    • Season and landform influenced spatiotemporal patterns of abundant and rare taxa.

    • Different stochastic processes dominated abundant and rare subcommunity assembly.

    • River flow and suspended solids regulated assembly processes of rare taxa.

    The rare microbial biosphere provides broad ecological services and resilience to various ecosystems. Nevertheless, the biogeographical patterns and assembly processes of rare bacterioplankton communities in large rivers remain uncertain. In this study, we investigated the biogeography and community assembly processes of abundant and rare bacterioplankton taxa in the Yangtze River (China) covering a distance of 4300 km. The results revealed similar spatiotemporal patterns of abundant taxa (AT) and rare taxa (RT) at both taxonomic and phylogenetic levels, and analysis of similarities revealed that RT was significantly influenced by season and landform than AT. Furthermore, RT correlated with more environmental factors than AT, whereas environmental and spatial factors explained a lower proportion of community shifts in RT than in AT. The steeper distance–decay slopes in AT indicated higher spatial turnover rates of abundant subcommunities than rare subcommunities. The null model revealed that both AT and RT were mainly governed by stochastic processes. However, dispersal limitation primarily governed the AT, whereas the undominated process accounted for a higher fraction of stochastic processes in RT. River flow and suspended solids mediated the balance between the stochastic and deterministic processes in RT. The spatiotemporal dynamics and assembly processes of total taxa were more similar as AT than RT. This study provides new insights into both significant spatiotemporal dynamics and inconsistent assembly processes of AT and RT in large rivers.

    Neha Badola, Ashish Bahuguna, Yoel Sasson, Jaspal Singh Chauhan
    Frontiers of Environmental Science & Engineering, 2022, 16(1): 7.

    • Physical, chemical and biological methods are explored for MPs removal.

    • Physical methods based on adsorption/filtration are mostly used for MPs removal.

    • Chemical methods of MPs removal work on coagulation and flocculation mechanism.

    • MBR technology has also shown the removal of MPs from water.

    • Global policy on plastic control is lacking.

    Microplastics are an emerging threat and a big challenge for the environment. The presence of microplastics (MPs) in water is life-threatening to diverse organisms of aquatic ecosystems. Hence, the scientific community is exploring deeper to find treatment and removal options of MPs. Various physical, chemical and biological methods are researched for MPs removal, among which few have shown good efficiency in the laboratory. These methods also have a few limitations in environmental conditions. Other than finding a suitable method, the creation of legal restrictions at a governmental level by imposing policies against MPs is still a daunting task in many countries. This review is an effort to place all effectual MP removal methods in one document to compare the mechanisms, efficiency, advantages, and disadvantages and find the best solution. Further, it also discusses the policies and regulations available in different countries to design an effective global policy. Efforts are also made to discuss the research gaps, recent advancements, and insights in the field.

    Mengjun Chen, Oladele A. Ogunseitan
    Frontiers of Environmental Science & Engineering, 2021, 15(6): 114.

    • Copyrights on electronic products are impediments in promoting circular economy.

    • Manufacturers antagonize refurbishment and remanufacturing to maximize profit.

    • International harmonization of copyright laws will aid repair and remanufacture.

    • Blockchain–digital immutable ledgers–can promote trust among stakeholders.

    The concept of zero waste is an ideal situation that will require different solutions for different categories of waste. Electronic waste (E-waste), the fastest growing category of solid hazardous waste presents various unique challenges. Electronic product repair, reuse and remanufacture (3re) are crucial for effective source reduction of E-waste and the integration of the electronics industry into a circular or zero-waste economy framework. Increasingly, 3re implementation is restricted by regulatory difficulties, particularly the invocation of copyright laws. Here, we use the examples of electronic printer cartridges and restored compact discs (CDs) to identify the challenges and to explore solutions for managing the risks associated with E-waste through circular economy and the opportunities presented by innovative Blockchain solutions. A set of international consensuses on judicial definitions, such as 3re, refurbish fake/counterfeit product and copyright exhaustion, are proposed to accelerate source reduction in E-waste management toward the goal of zero waste.

    Shengdong Liu, Enxiang Shang, Jingnan Liu, Yining Wang, Nanthi Bolan, M.B. Kirkham, Yang Li
    Frontiers of Environmental Science & Engineering, 2022, 16(1): 8.

    • Fluorescence staining provides a fast and easy method to quantify microplastics.

    • Factors that influence staining are summarized to obtain an optimum staining effect.

    • Natural organic matter can be stained by dye and interfere with quantification.

    • Fluorescence staining is applied in both field and laboratory studies.

    • Future work involves developing new dyes and automated image-analysis methods.

    Understanding the fate and toxicity of microplastics (MPs,<5 mm plastic particles) is limited by quantification methods. This paper summarizes the methods in use and presents new ones. First, sampling and pretreatment processes of MPs, including sample collection, digestion, density separation, and quality control are reviewed. Then the promising and convenient staining procedures and quantification methods for MPs using fluorescence dyes are reviewed. The factors that influence the staining of MPs, including their physicochemical properties, are summarized to provide an optimal operation procedure. In general, the digestion step is crucial to eliminate natural organic matter (NOM) to avoid interference in quantification. Chloroform was reported to be the most appropriate solvent, and 10–20 μg/mL are recommended as optimal dye concentrations. In addition, a heating and cooling procedure is recommended to maintain the fluorescence intensity of MPs for two months. After staining, a fluorescence microscope is usually used to characterize the morphology, mass, or number of MPs, but compositional analysis cannot be determined with it. These fluorescence staining methods have been implemented to study MP abundance, transport, and toxicity and have been combined with other chemical characterization techniques, such as Fourier transform infrared spectroscopy and Raman spectroscopy. More studies are needed to focus on the synthesis of novel dyes to avoid NOM’s interference. They need to be combined with other spectroscopic techniques to characterize plastic composition and to develop image-analysis methods. The stability of stained MPs needs to be improved.

    Yan Guo, Zibin Luo, Junhao Shen, Yu-You Li
    Frontiers of Environmental Science & Engineering, 2022, 16(7): 84.

    • The PNA, denitratation/anammox, and DAMO/anammox process are reviewed together.

    • Denitratation/anammox-based process is promising in mainstream treatment.

    • DAMO and denitratation processes realize the higher nitrogen removal efficiency.

    • The utilization of metabolism diversity of functional microbe is worth exploring.

    • An effective waste treatment system concept is proposed.

    Anammox technology has been widely researched over the past 40-year from the laboratory-scale to full-scale. It is well-known that in actual applications, the solo application of anammox is not feasible. Since both ammonium and nitrite are prerequisites based on the reaction mechanism, the pre-treatment of wastewater is necessary. With the combination of anammox process and other pre-treatment processes to treat the actual wastewater, many types of anammox-based processes have been developed with distinct nitrogen removal performance. Thus, in order to heighten the awareness of researchers to the developments and accelerate the application of these processes to the treatment of actual wastewater, the main anammox-based processes are reviewed in this paper. It includes the partial nitritation/anammox process, the denitratation/anammox (PD/A) process, the denitrifying anaerobic methane oxidation/anammox (DAMO/A) process, and more complex deuterogenic processes. These processes have made the breakthroughs in the application of the anammox technology, such as the combination of nitrification and PD/A process can achieve stability and reliability of nitrogen removal in the treatment of mainstream wastewater, the PD/A process and the DAMO/A have brought about further improvements in the total nitrogen removal efficiency of wastewater. The diversity of functional microbe characteristics under the specific condition indicate the wide application potential of anammox-based processes, and further exploration is necessary. A whole waste treatment system concept is proposed through the effective allocation of above mentioned processes, with the maximum recovery of energy and resources, and minimal environmental impact.

    Hua Long, Yang Liao, Changhao Cui, Meijia Liu, Zeiwei Liu, Li Li, Wenzheng Hu, Dahai Yan
    Frontiers of Environmental Science & Engineering, 2022, 16(4): 51.

    • Municipal solid waste (MSW) was fermented, screened, gasified, then co-processed.

    • Co-processing MSW in cement kilns could cause excessive pollutant emissions.

    • Bypass flue gas can be disposed of through the main flue system.

    • Popular MSW co-processing methods do not affect cement quality.

    Cement kiln co-processing techniques have been developed in the past 20 years in China, and more than 60 factories now use fermentation, screening, and gasification pre-treatment techniques to co-process municipal solid waste (MSW). There three complete MSW pre-treatment techniques, co-processing procedures, and environmental risk assessments have been described in few publications. In this study, we assessed the effectiveness of each technique. The results suggested that the pollutant content released by each pre-treatment technology was lower than the emission standard. To reveal the mechanisms of pollutant migration and enrichment, the substances in the kiln and kiln products are investigated. The input of co-processing materials (Co-M) produced by fermentation caused formation of polychlorinated dibenzo-p-dioxins and dibenzofuran (PCDD/Fs) in the bypass flue gas (By-gas) in excess of the regulatory standard. The Co-M input produced by the screening and gasifier technologies caused the total organic carbon (TOC) concentration to exceed the standard. In addition, the NOx, TOC, and PCDD/Fs in the By-gas exceeded the regulatory standard. Raw meal was the primary chlorine and heavy metals input stream, and clinker (CK) and cement kiln dust (CKD) accounted for>90% of the total chlorine output stream. Flue gas and CKD were the primary volatile heavy metal (Hg) output streams. Greater than 70% of the semi-volatile heavy metals (Cd, Pb, Tl and Se) distributed in hot raw meal and bypass cement kiln dust. The low-volatility heavy metals were concentrated in the CK. These results indicated that co-processing techniques used in China still require improvement.

    Yali Liu, Jianqing Du, Boyang Ding, Yuexian Liu, Wenjun Liu, Anquan Xia, Ran Huo, Qinwei Ran, Yanbin Hao, Xiaoyong Cui, Yanfen Wang
    Frontiers of Environmental Science & Engineering, 2022, 16(3): 28.

    •Considering evenness provides a more accurate assessment of sustainable development.

    •Water resource conservation drives industrial transformation.

    •Synergy between economic development and environmental protection is achieved.

    •Regional collaboration over water could promote sustainable development in drylands.

    Water resource availability is the major limiting factor for sustainable development in drylands. Climate change intensifies the conflicting water demands between people and the environment and highlights the importance of effective water resource management for achieving a balance between economic development and environmental protection. In 2008, Inner Mongolia, typical dryland in northern China, proposed strict regulations on water exploitation and utilization aimed at achieving sustainable development. Our study is the first to investigate the effectiveness and performance of these long-standing water conservation regulations. Our analyses found that the regulations drove industrial transformation, evidenced by the decreasing proportion of environmentally harmful industries such as coal and steel, and the increasing proportion of tertiary industries (especially tourism). Following industrial transformation, economic development decoupled from industrial water consumption and subsequently led to reduced negative environmental impacts. Based on these results, adaptive strategies were developed for 12 cities by revealing and integrating their development pathways and relative status in achieving sustainable development. Integration and cooperation between cities were proposed, e.g., a water trade agreement between eastern Inner Mongolia (an economically underdeveloped region with relatively abundant water resources) and central Inner Mongolia (an economically developed region with high water stress). Such an agreement may enable the holistic achievement of sustainable development across regions. By integrating the findings of our research, our study presents a reproducible framework for water-management-based sustainable development strategies in drylands.

    Qinjun Liang, Yu Gao, Zhigang Li, Jiayi Cai, Na Chu, Wen Hao, Yong Jiang, Raymond Jianxiong Zeng
    Frontiers of Environmental Science & Engineering, 2022, 16(4): 42.

    • MES was constructed for simultaneous ammonia removal and acetate production.

    • Energy consumption was different for total nitrogen and ammonia nitrogen removal.

    • Energy consumption for acetate production was about 0.04 kWh/g.

    • Nitrate accumulation explained the difference of energy consumption.

    • Transport of ammonia and acetate across the membrane deteriorated the performance.

    Microbial electrosynthesis (MES) is an emerging technology for producing chemicals, and coupling MES to anodic waste oxidation can simultaneously increase the competitiveness and allow additional functions to be explored. In this study, MES was used for the simultaneous removal of ammonia from synthetic urine and production of acetate from CO2. Using graphite anode, 83.2%±5.3% ammonia removal and 28.4%±9.9% total nitrogen removal was achieved, with an energy consumption of 1.32 kWh/g N for total nitrogen removal, 0.45 kWh/g N for ammonia nitrogen removal, and 0.044 kWh/g for acetate production. Using boron-doped diamond (BDD) anode, 70.9%±12.1% ammonia removal and 51.5%±11.8% total nitrogen removal was obtained, with an energy consumption of 0.84 kWh/g N for total nitrogen removal, 0.61 kWh/g N for ammonia nitrogen removal, and 0.043 kWh/g for acetate production. A difference in nitrate accumulation explained the difference of total nitrogen removal efficiencies. Transport of ammonia and acetate across the membrane deteriorated the performance of MES. These results are important for the development of novel electricity-driven technologies for chemical production and pollution removal.

    Elvis Genbo Xu, Zhiyong Jason Ren
    Frontiers of Environmental Science & Engineering, 2021, 15(6): 125.
    Wen Zhang, Qi Wang, Hao Chen
    Frontiers of Environmental Science & Engineering, 2022, 16(1): 11.

    Plastic pollution has been a legacy environment problems and more recently, the plastic particles, especially those ultrafine or small plastics particles, are widely recognized with increasing environmental and ecological impacts. Among small plastics, microplastics are intensively studied, whereas the physicochemical properties, environmental abundance, chemical states, bioavailability and toxicity toward organisms of nanoplastics are inadequately investigated. There are substantial difficulties in separation, visualization and chemical identification of nanoplastics due to their small sizes, relatively low concentrations and interferences from co-existing substances (e.g., dyes or natural organic matters). Moreover, detection of polymers at nanoscale is largely hampered by the detection limit or sensitivity for existing spectral techniques such as Transformed Infrared Spectroscopy (FTIR) or Raman Spectroscopy. This article critically examined the current state of art techniques that are exclusively reported for nanoplastic characterization in environmental samples. Based on their operation principles, potential applications and limitations of these analytical techniques are carefully analyzed.

    Hui Hu, Lei Jiang, Longli Sun, Yanling Gao, Tian Wang, Chenguang Lv
    Frontiers of Environmental Science & Engineering, 2022, 16(2): 21.

    • A ZnO-biochar hybrid composite was prepared by solvothermal-pyrolysis synthesis.

    • The superhydrophobic composite is suitable for selective recovery of Re(VII).

    • The adsorption mechanism is elucidated by experiments and material characterization.

    The recovery of scattered metal ions such as perrhenate (Re(VII)) from industrial effluents has enormous economic benefits and promotes resource reuse. Nanoscale-metal/biochar hybrid biosorbents are attractive for recovery but are limited by their insufficient stability and low selectivity in harsh environments. Herein, a superstable biochar-based biosorbent composed of ZnO nanoparticles with remarkable superhydrophobic features is fabricated, and its adsorption/desorption capabilities toward Re(VII) in strongly acidic aqueous solutions are investigated. The ZnO nanoparticle/biochar hybrid composite (ZBC) exhibits strong acid resistance and high chemical stability, which are attributable to strong C-O-Zn interactions between the biochar and ZnO nanoparticles. Due to the advantages of its hydrolytic stability, superhydrophobicity, and abundance of Zn-O sites, the ZBC proves suitable for the effective and selective separation of Re(VII) from single, binary and multiple ion systems (pH= 1), with a maximum sorption capacity of 29.41 mg/g. More importantly, this material also shows good recyclability and reusability, with high adsorption efficiency after six adsorption-desorption cycles. The findings in this work demonstrate that a metal/biochar hybrid composite is a promising sorbent for Re(VII) separation.

    Zhuqiu Sun, Jinying Xi, Chunping Yang, Wenjie Cong
    Frontiers of Environmental Science & Engineering, 2022, 16(7): 87.

    • Quorum sensing enhancement and inhibition methods are summarized.

    • Effects of quorum sensing regulation on biofilm are reviewed.

    • Current knowledge gaps and research challenges are proposed.

    Quorum sensing (QS) plays an important role in microbial aggregation control. Recently, the optimization of biological waste treatment systems by QS regulation gained an increasing attention. The effects of QS regulation on treatment performances and biofilm were frequently investigated. To understand the state of art of QS regulation, this review summarizes the methods of QS enhancement and QS inhibition in biological waste treatment systems. Typical QS enhancement methods include adding exogenous QS molecules, adding QS accelerants and cultivating QS bacteria, while typical QS inhibition methods include additions of quorum quenching (QQ) bacteria, QS-degrading enzymes, QS-degrading oxidants, and QS inhibitors. The specific improvements after applying these QS regulation methods in different treatment systems are concluded. In addition, the effects of QS regulation methods on biofilm in biological waste treatment systems are reviewed in terms of biofilm formation, extracellular polymeric substances production, microbial viability, and microbial community. In the end, the knowledge gaps in current researches are analyzed, and the requirements for future study are suggested.

    Shuangyang Zhao, Chengxin Chen, Jie Ding, Shanshan Yang, Yani Zang, Nanqi Ren
    Frontiers of Environmental Science & Engineering, 2022, 16(3): 36.

    • BiVO4/Fe3O4/rGO has excellent photocatalytic activity under solar light radiation.

    • It can be easily separated and collected from water in an external magnetic field.

    • BiVO4/Fe3O4/0.5% rGO exhibited the highest RhB removal efficiency of over 99%.

    • Hole (h+) and superoxide radical (O2) dominate RhB photo-decomposition process.

    • The reusability of this composite was confirmed by five successive recycling runs.

    Fabrication of easily recyclable photocatalyst with excellent photocatalytic activity for degradation of organic pollutants in wastewater is highly desirable for practical application. In this study, a novel ternary magnetic photocatalyst BiVO4/Fe3O4/reduced graphene oxide (BiVO4/Fe3O4/rGO) was synthesized via a facile hydrothermal strategy. The BiVO4/Fe3O4 with 0.5 wt% of rGO (BiVO4/Fe3O4/0.5% rGO) exhibited superior activity, degrading greater than 99% Rhodamine B (RhB) after 120 min solar light radiation. The surface morphology and chemical composition of BiVO4/Fe3O4/rGO were studied by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV–visible diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The free radicals scavenging experiments demonstrated that hole (h+) and superoxide radical (O2) were the dominant species for RhB degradation over BiVO4/Fe3O4/rGO under solar light. The reusability of this composite catalyst was also investigated after five successive runs under an external magnetic field. The BiVO4/Fe3O4/rGO composite was easily separated, and the recycled catalyst retained high photocatalytic activity. This study demonstrates that catalyst BiVO4/Fe3O4/rGO possessed high dye removal efficiency in water treatment with excellent recyclability from water after use. The current study provides a possibility for more practical and sustainable photocatalytic process.

    Jinkai Xue, Seyed Hesam-Aldin Samaei, Jianfei Chen, Ariana Doucet, Kelvin Tsun Wai Ng
    Frontiers of Environmental Science & Engineering, 2022, 16(5): 58.

    • 23 available research articles on MPs in drinking water treatment are reviewed.

    • The effects of treatment conditions and MP properties on MP removal are discussed.

    • DWTPs with more steps generally are more effective in removing MPs.

    • Smaller MPs (e.g.,<10 μm) are more challenging in drinking water treatment.

    Microplastics (MPs) have been widely detected in drinking water sources and tap water, raising the concern of the effectiveness of drinking water treatment plants (DWTPs) in protecting the public from exposure to MPs through drinking water. We collected and analyzed the available research articles up to August 2021 on MPs in drinking water treatment (DWT), including laboratory- and full-scale studies. This article summarizes the major MP compositions (materials, sizes, shapes, and concentrations) in drinking water sources, and critically reviews the removal efficiency and impacts of MPs in various drinking water treatment processes. The discussed drinking water treatment processes include coagulation-flocculation (CF), membrane filtration, sand filtration, and granular activated carbon (GAC) filtration. Current DWT processes that are purposed for particle removal are generally effective in reducing MPs in water. Various influential factors to MP removal are discussed, such as coagulant type and dose, MP material, shape and size, and water quality. It is anticipated that better MP removal can be achieved by optimizing the treatment conditions. Moreover, the article framed the major challenges and future research directions on MPs and nanoplastics (NPs) in DWT.

    Feng Chen, Shihao Guo, Yihao Wang, Lulu Ma, Bing Li, Zhimin Song, Lei Huang, Wen Zhang
    Frontiers of Environmental Science & Engineering, 2022, 16(5): 57.

    • A high-efficiency N-doped porous carbon adsorbent for Cr(VI) was synthesized.

    • The maximum adsorption capacity of Cr(VI) reached up to 285.71 mg/g at 318K.

    • The potential mechanism for Cr(VI) adsorption by NHPC was put forward.

    • DFT analyzed the adsorption energy and interaction between NHPC and Cr(VI).

    To develop highly effective adsorbents for chromium removal, a nitrogen-doped biomass-derived carbon (NHPC) was synthesized via direct carbonation of loofah sponge followed by alkali activation and doping modification. NHPC possessed a hierarchical micro-/mesoporous lamellar structure with nitrogen-containing functional groups (1.33 at%), specific surface area (1792.47 m2/g), and pore volume (1.18 cm3/g). NHPC exhibited a higher Cr(VI) adsorption affinity than the HPC (without nitrogen doping) or the pristine loofah sponge carbon (LSC) did. The influence of process parameters, including pH, dosage, time, temperature, and Cr(VI) concentration, on Cr(VI) adsorption by NHPC were evaluated. The Cr(VI) adsorption kinetics matched with the pseudo-second-order model (R2≥0.9983). The Cr(VI) adsorption isotherm was fitted with the Langmuir isotherm model, which indicated the maximum Cr(VI) adsorption capacities: 227.27, 238.10, and 285.71 mg/g at 298K, 308K, and 318K, respectively. The model analysis also indicated that adsorption of Cr(VI) on NHPC was a spontaneous, endothermal, and entropy-increasing process. The Cr(VI) adsorption process potentially involved mixed reductive and adsorbed mechanism. Furthermore, computational chemistry calculations revealed that the adsorption energy between NHPC and Cr(VI) (−0.84 eV) was lower than that of HPC (−0.51 eV), suggesting that nitrogen doping could greatly enhance the interaction between NHPC and Cr(VI).

    Yingbin Hu, Ning Li, Jin Jiang, Yanbin Xu, Xiaonan Luo, Jie Cao
    Frontiers of Environmental Science & Engineering, 2022, 16(7): 90.

    • The autotrophic nitrogen removal combining Feammox and Anammox was achieved.

    • Activated carbon can be used as an electron shuttle to enhance Feammox activity.

    • Fe(III) was reduced to Fe(II) and the secondary Fe(II) mineral (FeOOH) was obtained.

    • The iron-reducing bacteria and Anammox consortium was enriched simultaneously.

    Ferric iron reduction coupled with anaerobic ammonium oxidation (Feammox) is a novel ferric-dependent autotrophic process for biological nitrogen removal (BNR) that has attracted increasing attention due to its low organic carbon requirement. However, extracellular electron transfer limits the nitrogen transformation rate. In this study, activated carbon (AC) was used as an electron shuttle and added into an integrated autotrophic BNR system consisting of Feammox and anammox processes. The nitrogen removal performance, nitrogen transformation pathways and microbial communities were investigated during 194 days of operation. During the stable operational period (days 126–194), the total nitrogen (TN) removal efficiency reached 82.9%±6.8% with a nitrogen removal rate of 0.46±0.04 kg-TN/m3/d. The contributions of the Feammox, anammox and heterotrophic denitrification pathways to TN loss accounted for 7.5%, 89.5% and 3.0%, respectively. Batch experiments showed that AC was more effective in accelerating the Feammox rate than the anammox rate. X-ray photoelectron spectroscopy (XPS) analyses showed the presence of ferric iron (Fe(III)) and ferrous iron (Fe(II)) in secondary minerals. X-ray diffraction (XRD) patterns indicated that secondary iron species were formed on the surface of iron-AC carrier (Fe/AC), and Fe(III) was primarily reduced by ammonium in the Feammox process. The phyla Anaerolineaceae (0.542%) and Candidatus Magasanikbacteria (0.147%) might contribute to the Feammox process, and Candidatus Jettenia (2.10%) and Candidatus Brocadia (1.18%) were the dominative anammox phyla in the bioreactor. Overall, the addition of AC provided an effective way to enhance the autotrophic BNR process by integrating Feammox and anammox.

    Xianying Ma, Xinhui Zhou, Mengjie Zhao, Wenzhuo Deng, Yanxiao Cao, Junfeng Wu, Jingcheng Zhou
    Frontiers of Environmental Science & Engineering, 2022, 16(1): 3.

    • PP-MPs reduced the adsorption capacity of the bulk soil for Cd in aqueous medium.

    • The responses of the POM, OMC and mineral fractions to PP-MPs were different.

    • PP-MPs reduced the adsorption of POM and OMC fractions to Cd.

    • PP-MPs increased the adsorption of mineral fraction to Cd.

    • Effect of MPs on soil may be controlled by proportion of POM, OMC and mineral fractions.

    Microplastics (MPs) are widely present in a variety of environmental media and have attracted more and more attention worldwide. However, the effect of MPs on the the interaction between heavy metals and soil, especially in soil fraction level, is not well understood. In this study, batch experiments were performed to investigate the adsorption characteristics of Cd in bulk soil and three soil fractions (i.e. particulate organic matter (POM), organic-mineral compounds (OMC), and mineral) with or without polypropylene (PP) MPs. The results showed that the addition of PP-MPs reduced the Cd adsorption capacity of the bulk soil in aqueous solution, and the effects varied with PP-MPs dose and aging degree. Whereas, the responses of the three fractions to PP-MPs were different. In presence of PP-MPs, the POM and OMC fractions showed negative adsorption effects, while the mineral fraction showed positive adsorption. For the bulk soil, POM and OMC fractions, the adsorption isotherm fitted to the Langmuir model better than the Freundlich model, whereas, the Freundlich isotherm model is more fitted for the mineral fraction. Combined with the comprehensive analysis of the partitioning coefficients, XRD and FTIR results, it was found that OMC fraction extremely likely play a leading role in the bulk soil adsorption of Cd in this study. Overall, the effect of MPs on adsorption capacity of the bulk soil for Cd may be determined by the proportion of POM, OMC, and mineral fractions in the soil, but further confirmation is needed.