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    Bin Wang, Liping Heng, Qian Sui, Zheng Peng, Xuezhi Xiao, Minghui Zheng, Jianxin Hu, Heidelore Fiedler, Damià Barceló, Gang Yu
    Frontiers of Environmental Science & Engineering, 2023, 17(4): 52.

    The combustion of vinyl chloride (VC) after the train derailment accident in Ohio, USA in February, 2023 has caused widespread concern around the world. This paper tried to analyze several issues concerning the accident, including the appropriateness of the VC combustion in the emergency response in this accident, the meanings of so-called “controlled combustion”, the potential environmental risks caused by VC and combustion by-products, and follow-up work. In our view, this accident had surely caused environmental and health risks to some extent. Hence, a comprehensive environmental risk assessment is necessary, and then the site with risk should be comprehensively remediated, hazardous waste should be harmlessly treated as soon as possible. Finally, this accident suggests that further efforts should be taken to bridge the gap between chemical safety management and their environmental risk management.

    Shilpa, Nitai Basak, Sumer Singh Meena
    Frontiers of Environmental Science & Engineering, 2022, 16(12): 161.

    ● Health hazards of plastic waste on environment are discussed.

    ● Microbial species involved in biodegradation of plastics are being reviewed.

    ● Enzymatic biodegradation mechanism of plastics is outlined.

    ● Analytical techniques to evaluate the plastic biodegradation are presented.

    The abundance of synthetic polymers has increased due to their uncontrolled utilization and disposal in the environment. The recalcitrant nature of plastics leads to accumulation and saturation in the environment, which is a matter of great concern. An exponential rise has been reported in plastic pollution during the corona pandemic because of PPE kits, gloves, and face masks made up of single-use plastics. The physicochemical methods have been employed to degrade synthetic polymers, but these methods have limited efficiency and cause the release of hazardous metabolites or by-products in the environment. Microbial species, isolated from landfills and dumpsites, have utilized plastics as the sole source of carbon, energy, and biomass production. The involvement of microbial strains in plastic degradation is evident as a substantial amount of mineralization has been observed. However, the complete removal of plastic could not be achieved, but it is still effective compared to the pre-existing traditional methods. Therefore, microbial species and the enzymes involved in plastic waste degradation could be utilized as eco-friendly alternatives. Thus, microbial biodegradation approaches have a profound scope to cope with the plastic waste problem in a cost-effective and environmental-friendly manner. Further, microbial degradation can be optimized and combined with physicochemical methods to achieve substantial results. This review summarizes the different microbial species, their genes, biochemical pathways, and enzymes involved in plastic biodegradation.

    Xi Lu, Dan Tong, Kebin He
    Frontiers of Environmental Science & Engineering, 2023, 17(2): 14.

    ● China has pledged ambitious carbon peak and neutrality goals for mitigating global climate change.

    ● Major challenges to achieve carbon neutrality in China are summarized.

    ● The new opportunities along the pathway of China’s carbon neutrality are discussed from four aspects.

    ● Five policy suggestions for China are provided.

    China is the largest developing economy and carbon dioxide emitter in the world, the carbon neutrality goal of which will have a profound influence on the mitigation pathway of global climate change. The transition towards a carbon-neutral society is integrated into the construction of ecological civilization in China, and brings profound implications for China’s socioeconomic development. Here, we not only summarize the major challenges in achieving carbon neutrality in China, but also identify the four potential new opportunities: namely, the acceleration of technology innovations, narrowing regional disparity by reshaping the value of resources, transforming the industrial structure, and co-benefits of pollution and carbon mitigation. Finally, we provide five policy suggestions and highlight the importance of balancing economic growth and carbon mitigation, and the joint efforts among the government, the enterprises, and the residents.

    Han Qu, Hongting Diao, Jiajun Han, Bin Wang, Gang Yu
    Frontiers of Environmental Science & Engineering, 2023, 17(1): 12.

    Over the past decades, the plastic production has been dramatically increased. Indeed, a category of small plastic particles mainly with the shapes of fragments, fibers, or spheres, called microplastics (particles smaller than 5 mm) and nanoplastics (particles smaller than 1 μm) have attracted particular attention. Because of its wide distribution in the environment and potential adverse effects to animal and human, microplastic pollution has been reported as a serious environment problem receiving increased attention in recent years. As one of the commonly detected emerging contaminants in the environment, recent evidence indicates that the concentration of microplastics show an increasing trend, for the reason that up to 12.7 million metric tons of plastic litter is released into aquatic environment from land-based sources each year. Furthermore, microplastic exposure levels of model organisms in laboratory studies are usually several orders of magnitude higher than those found in environment, and the microplastics exposure conditions are also different with those observed in the environment. Additionally, the detection of microplastics in feces indicates that they can be excreted out of the bodies of animal and human. Hence, great uncertainties might exist in microplastics exposure and health risk assessment based on current studies, which might be exaggerated. Policies reduce microplastic emission sources and hence minimize their environmental risks are determined. To promote the above policies, we must first overcome the technical obstacles of detecting microplastics in various samples.

    Yang Zhang, Zheng Peng, Zhaomin Dong, Mujie Wang, Chen Jiang
    Frontiers of Environmental Science & Engineering, 2022, 16(12): 152.

    ● China’s implementation of the SC was systematically studied.

    ● Implementation process of the SC can be roughly divided into three stages.

    ● DDT and HCH concentrations in the air have been steadily decreasing.

    ● China has safely disposed of 6352.1 tons of pesticide POPs.

    Persistent organic pollutants (POPs) are extremely harmful to the environment and human health; the Stockholm Convention on Persistent Organic Pollutants was therefore adopted by the international community in 2001 to eliminate or reduce the production, use, and emissions of POPs. China is the largest developing country that has signed the Stockholm Convention, and thus plays an important role in its implementation. This paper systematically studies the practice and achievements of China since it signed the Stockholm Convention 20 years ago. China has established an implementation guarantee system including institutions, implementation mechanisms, policies, law enforcement, and scientific and technological support. During the 20 years since the implementation of the Stockholm Convention, dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (HCH) concentrations in the air have been steadily decreasing, and Perfluorooctane sulfonic acid/Perfluorooctane sulfonyl fluoride (PFOS/PFOSF) concentrations in water bodies have decreased. In the past 20 years, China has safely disposed of 6352.1 tons of pesticide persistent organic pollutants and 36998 sets of electrical equipment containing polychlorinated biphenyls (PCBs), with a disposal rate of 100%. In the future, China will further strengthen the construction of persistent organic pollutant monitoring networks, scientific research, publicity, education, and international cooperation to improve environmental quality, providing a reference for other countries to implement the Stockholm Convention.

    Yanfeng Yang, Ruina Zhang, Ziyang Lou
    Frontiers of Environmental Science & Engineering, 2022, 16(12): 158.

    ● The airborne bacteria in landfills were 4–50 times higher than fungi.

    ● Bioaerosols released from the working area would pose risk to on-site workers.

    ● The safe distance for the working area should be set as 80 m.

    Landfills are widely complained about due to the long-term odor and landfill gas emissions for local residents, while the bioaerosols are always neglected as another threat to on-site workers. In this study, bioaerosols samples were collected from the typical operation scenes in the large-scale modern landfill, and the emission levels of airborne bacteria, pathogenic species, and fungi were quantified and co-related. The corresponding exposure risks were assessed based on the average daily dose via inhalation and skin contact. It was found that the levels of culturable bacteria and fungi in all landfill samples were around 33–22778 CFU/m3 and 8–450 CFU/m3, and the active-working landfill area and the covered area were the maximum and minimum emission sources, respectively, meaning that the bioaerosols were mainly released from the areas related with the fresh waste operation. Acinetobacter sp., Massilia sp., Methylobacterium-Methylorubrum sp. and Noviherbaspirillum sp. were the main bacterial populations, with a percentage of 42.56%, 89.82%, 70.24% and 30.20% respectively in total bioaerosols measured. With regards to the health risk, the health risks via inhalation were the main potential risks, with four orders of magnitude higher than that of skin contact. Active-working area showed the critical point for non-carcinogenic risks, with a hazard quotient of 1.68, where 80 m protection distance is recommended for on-site worker protection, plus more careful protection measures.

    Yunpeng Xing, Boyuan Xue, Yongshu Lin, Xueqi Wu, Fang Fang, Peishi Qi, Jinsong Guo, Xiaohong Zhou
    Frontiers of Environmental Science & Engineering, 2022, 16(12): 155.

    ● A cellphone-based colorimetric multi-channel sensor for in-field detection.

    ● A universal colorimetric detection platform in the absorbance range of 400–700 nm.

    ● Six-fold improvement of sensitivity by introducing a transmission grating.

    ● Quantifying multiple water quality indexes simultaneously with high stability.

    The development of colorimetric analysis technologies for the commercial cellphone platform has attracted great attention in environmental monitoring due to the low cost, high versatility, easy miniaturization, and widespread ownership of cellphones. This work demonstrates a cellphone-based colorimetric multi-channel sensor for quantifying multiple environmental contaminants simultaneously with high sensitivity and stability. To improve the sensitivity of the sensor, a delicate optical path system was created by using a diffraction grating to split six white beams transmitting through the multiple colored samples, which allows the cellphone CMOS camera to capture the diffracted light for image analysis. The proposed sensor is a universal colorimetric detection platform for a variety of environmental contaminants with the colorimetry assay in the range of 400–700 nm. By introducing the diffraction grating for splitting light, the sensitivity was improved by over six folds compared with a system that directly photographed transmitted light. As a successful proof-of-concept, the sensor was used to detect turbidity, orthophosphate, ammonia nitrogen and three heavy metals simultaneously with high sensitivity (turbidity: detection limit of 1.3 NTU, linear range of 5–400 NTU; ammonia nitrogen: 0.014 mg/L, 0.05–5 mg/L; orthophosphate: 0.028 mg/L, 0.1–10 mg/L; Cr (VI): 0.0069 mg/L, 0.01–0.5 mg/L; Fe: 0.025 mg/L, 0.1–2 mg/L; Zn: 0.032 mg/L, 0.05–2 mg/L) and reliability (relative standard deviations of six parallel measurements of 0.37%–1.60% and recoveries of 95.5%–106.0% in surface water). The miniature sensor demonstrated in-field sensing ability in environmental monitoring, which can be extended to point-of-care diagnosis and food safety control.

    Yiqun Cao, Qingxin Ma, Biwu Chu, Hong He
    Frontiers of Environmental Science & Engineering, 2023, 17(4): 48.

    ● Recent advances in the photolysis of nitrate/HNO3 are reviewed.

    ● Mechanisms and key factors affecting the photolysis of nitrate/HNO3 are summarized.

    ● Atmospheric implications and future research recommendations are provided.

    Nitrate is an important component of atmospheric particulate matter and affects air quality, climate, human health, and the ecosystem. Nitrate was previously considered a permanent sink for nitrogen oxides (NOx). However, this viewpoint has been challenged in recent years because growing research evidence has shown the transformation of nitrate into NOx (i.e., renoxification). The photolysis of nitrate/HNO3, especially in the particulate phase or adsorbed on particles, can be a significant renoxification process in the atmosphere. The formation and photolysis of nitrate in aerosol not only change the diurnal variation of NOx, but also provide long-distance transport of NOx in the form of nitrate, which affects local and regional atmospheric chemistry and air quality. This review summarizes recent advances in the fundamental understanding of the photolysis of nitrate/HNO3 under various atmospheric conditions, with a focus on mechanisms and key factors affecting the process. The atmospheric implications are discussed and future research is recommended.

    Guannan Mao, Donglin Wang, Yaohui Bai, Jiuhui Qu
    Frontiers of Environmental Science & Engineering, 2023, 17(7): 82.

    ● Abundance of MAGs carrying ARG-VF pairs unchanged in rivers after WWTP upgrade.

    ● Upgrade of WWTPs significantly reduced diversity of pathogenic genera in rivers.

    ● Upgrade of WWTPs reduced most VF (ARG) types carried by potential pathogens in rivers.

    ● Upgrade of WWTPs narrowed the pathogenic host ranges of ARGs and VFs in rivers.

    Wastewater treatment plants (WWTPs) with additional tertiary ultrafiltration membranes and ozonation treatment can improve water quality in receiving rivers. However, the impacts of WWTP upgrade (WWTP-UP) on pathogens carrying antibiotic resistance genes (ARGs) and virulence factors (VFs) in rivers remain poorly understood. In this study, ARGs, VFs, and their pathogenic hosts were investigated in three rivers impacted by large-scale WWTP-UP. A five-year sampling campaign covered the periods before and after WWTP-UP. Results showed that the abundance of total metagenome-assembled genomes (MAGs) containing both ARGs and VFs in receiving rivers did not decrease substantially after WWTP-UP, but the abundance of MAGs belonging to pathogenic genera that contain both ARGs and VFs (abbreviated as PAVs) declined markedly. Genome-resolved metagenomics further revealed that WWTP-UP not only reduced most types of VFs and ARGs in PAVs, but also effectively eliminated efflux pump and nutritional VFs carried by PAVs in receiving rivers. WWTP-UP narrowed the pathogenic host ranges of ARGs and VFs and mitigated the co-occurrence of ARGs and VFs in receiving rivers. These findings underline the importance of WWTP-UP for the alleviation of pathogens containing both ARGs and VFs in receiving rivers.

    Peng Li, Lingqian Dong, Han Jin, Jingren Yang, Yonghui Tu, Chao Wang, Yiliang He
    Frontiers of Environmental Science & Engineering, 2022, 16(12): 159.

    ● A novel Al-MOF was successfully synthesized by a facile solvothermal method.

    ● Al-MOF showed superior performance for phosphate detection.

    ● High selectivity and anti-interference for detection were demonstrated.

    ● The high coordination between Al-O and PO43− was the key in fluorescence sensing.

    The on-site monitoring of phosphate is important for environmental management. Conventional phosphate detection methods are not appropriate to on-site monitoring owing to the use of complicated detection procedures, and the consequent high cost and maintenance requirements of the detection apparatus. Here, a highly sensitive fluorescence-based method for phosphate detection with a wide detection range was developed based on a luminescent aluminum-based metal-organic framework (Al-MOF). The Al-MOF was prepared by introducing amine functional groups to conventional MIL to enhance phosphate binding, and exhibited excellent fluorescence properties that originated from the ligand-to-metal charge transfer (LMCT). The detection limit was as low as 3.25 μmol/L (0.10 mg/L) and the detection range was as wide as 3–350 μmol/L (0.10–10.85 mg/L). Moreover, Al-MOF displayed specific recognition toward phosphate over most anions and metal cations, even for a high concentration of the co-existent ions. The mechanism of phosphate detection was analyzed through the characterization of the combination of Al-MOF and phosphate, and the results indicated the high affinity between Al-O and phosphate inhibited that the LMCT process and recovered the intrinsic fluorescence of NH2-H2BDC. The recovery of the developed detection method reached a satisfactory range of 85.1%–111.0%, and the feasibility of on-site phosphate detection was verified using a prototype sensor for tap water and lake water samples. It was demonstrated that the prepared Al-MOF is highly promising for on-site detection of phosphate in an aqueous environment.

    Yiting Chen, Jun Yan, Mengli Chen, Fucheng Guo, Tao Liu, Yi Chen
    Frontiers of Environmental Science & Engineering, 2022, 16(12): 157.

    ● Fermentation broth facilitates N removal and energy yields in tertiary CW-MFC.

    ● Carbon sources are preferred for nitrogen removal over electricity generation.

    ● A mutual promotion relationship exists between acetic and humic acid in N removal.

    ● Humic acid boosts the abundances of functional genes relate to nitrogen metabolism.

    Constructed wetlands (CWs) are widely used as a tertiary treatment technology, and the addition of carbon sources can significantly improve advanced nitrogen removal. However, excessive carbon sources would lead to an increase in the effluent chemical oxygen demand in CWs, and microbial fuel cells (MFCs) can convert these into electricity. In this study, constructed wetland-microbial fuel cells (CW-MFCs) were built to achieve simultaneous nitrogen removal and electricity generation, using wetland plant litter fermentation broths as carbon sources. The total nitrogen removal in the groups with fermentation broth addition (FGs) reached 83.33%, which was 19.64% higher than that in the CG (group without fermentation broth), and the mean voltages in the FGs were at least 2.6 times higher than that of the CG. Furthermore, two main components of the fermentation broths, acetic acid (Ac) and humic acid (HA), were identified using a three-dimensional excitation emission matrix and gas chromatograph and added to CW-MFCs to explore the influence mechanism on the treatment performance. Denitrification and electrogenesis presented the same tendency: Ac&HA > Ac > CG’ (groups without Ac and HA). These results indicate that Ac and HA increased the abundance of functional genes associated with nitrogen metabolism and electron transfer. This study demonstrated that CW-MFC fermentation broth addition can be a potential strategy for the disposal of secondary effluent and bioelectricity generation.

    Zhengheng Pu, Jieru Yan, Lei Chen, Zhirong Li, Wenchong Tian, Tao Tao, Kunlun Xin
    Frontiers of Environmental Science & Engineering, 2023, 17(2): 22.

    ● A novel deep learning framework for short-term water demand forecasting.

    ● Model prediction accuracy outperforms other traditional deep learning models.

    ● Wavelet multi-resolution analysis automatically extracts key water demand features.

    ● An analysis is performed to explain the improved mechanism of the proposed method.

    Short-term water demand forecasting provides guidance on real-time water allocation in the water supply network, which help water utilities reduce energy cost and avoid potential accidents. Although a variety of methods have been proposed to improve forecast accuracy, it is still difficult for statistical models to learn the periodic patterns due to the chaotic nature of the water demand data with high temporal resolution. To overcome this issue from the perspective of improving data predictability, we proposed a hybrid Wavelet-CNN-LSTM model, that combines time-frequency decomposition characteristics of Wavelet Multi-Resolution Analysis (MRA) and implement it into an advanced deep learning model, CNN-LSTM. Four models - ANN, Conv1D, LSTM, GRUN - are used to compare with Wavelet-CNN-LSTM, and the results show that Wavelet-CNN-LSTM outperforms the other models both in single-step and multi-steps prediction. Besides, further mechanistic analysis revealed that MRA produce significant effect on improving model accuracy.

    Yujun Zhou, Qinghua Ji, Chengzhi Hu, Huijuan Liu, Jiuhui Qu
    Frontiers of Environmental Science & Engineering, 2023, 17(1): 11.

    ● A novel hybrid fuel cell (F-HFC) was fabricated.

    ● Pollutant degradation and synchronous electricity generation occurred in F-HFC.

    ● BiOCl-NH4PTA photocatalyst greatly improved electron transfer and charge separation.

    ● Pollutant could act as substrate directly in ambient conditions without pretreatment.

    ● The mechanism of the F-HFC was proposed and elucidated.

    The development of highly efficient energy conversion technologies to extract energy from wastewater is urgently needed, especially in facing of increasing energy and environment burdens. Here, we successfully fabricated a novel hybrid fuel cell with BiOCl-NH4PTA as photocatalyst. The polyoxometalate (NH4PTA) act as the acceptor of photoelectrons and could retard the recombination of photogenerated electrons and holes, which lead to superior photocatalytic degradation. By utilizing BiOCl-NH4PTA as photocatalysts and Pt/C air-cathode, we successfully constructed an electron and mass transfer enhanced photocatalytic hybrid fuel cell with flow-through field (F-HFC). In this novel fuel cell, dyes and biomass could be directly degraded and stable power output could be obtained. About 87 % of dyes could be degraded in 30 min irradiation and nearly 100 % removed within 90 min. The current density could reach up to ~267.1 μA/cm2; with maximum power density (Pmax) of ~16.2 μW/cm2 with Rhodamine B as organic pollutant in F-HFC. The power densities were 9.0 μW/cm2, 12.2 μW/cm2, and 13.9 μW/cm2 when using methyl orange (MO), glucose and starch as substrates, respectively. This hybrid fuel cell with BiOCl-NH4PTA composite fulfills the purpose of decontamination of aqueous organic pollutants and synchronous electricity generation. Moreover, the novel design cell with separated photodegradation unit and the electricity generation unit could bring potential practical application in water purification and energy recovery from wastewater.

    Frontiers of Environmental Science & Engineering, 2022, 16(12): 162.
    Yuanxin Zhang, Fei Li, Chaoqiong Ni, Song Gao, Shuwei Zhang, Jin Xue, Zhukai Ning, Chuanming Wei, Fang Fang, Yongyou Nie, Zheng Jiao
    Frontiers of Environmental Science & Engineering, 2023, 17(2): 21.

    ● Used a double-stage attention mechanism model to predict ozone.

    ● The model can autonomously select the appropriate time series for forecasting.

    ● The model outperforms other machine learning models and WRF-CMAQ.

    ● We used the model to analyze the driving factors of VOCs that cause ozone pollution.

    Ozone is becoming a significant air pollutant in some regions, and VOCs are essential for ozone prediction as necessary ozone precursors. In this study, we proposed a recurrent neural network based on a double-stage attention mechanism model to predict ozone, selected an appropriate time series for prediction through the input attention and temporal attention mechanisms, and analyzed the cause of ozone generation according to the contribution of feature parameters. The experimental data show that our model had an RMSE of 7.71 μg/m3 and a mean absolute error of 5.97 μg/m3 for 1-h predictions. The DA-RNN model predicted ozone closer to observations than the other models. Based on the importance of the characteristics, we found that the ozone pollution in the Jinshan Industrial Zone mainly comes from the emissions of petrochemical enterprises, and the good generalization performance of the model is proved through testing multiple stations. Our experimental results demonstrate the validity and promising application of the DA-RNN model in predicting atmospheric pollutants and investigating their causes.

    Xiaoge Huang, Lihao Chen, Ziqi Ma, Kenneth C. Carroll, Xiao Zhao, Zailin Huo
    Frontiers of Environmental Science & Engineering, 2022, 16(12): 151.

    ● nZVI, S-nZVI, and nFeS were systematically compared for Cd(II) removal.

    ● Cd(II) removal by nZVI involved coprecipitation, complexation, and reduction.

    ● The predominant reaction for Cd(II) removal by S-nZVI and nFeS was replacement.

    ● A simple pseudo-second-order kinetic can adequately fit Fe(II) dissolution.

    Cadmium (Cd) is a common toxic heavy metal in the environment. Taking Cd(II) as a target contaminant, we systematically compared the performances of three Fe-based nanomaterials (nano zero valent iron, nZVI; sulfidated nZVI, S-nZVI; and nano FeS, nFeS) for Cd immobilization under anaerobic conditions. Effects of nanomaterials doses, initial pH, co-existing ions, and humic acid (HA) were examined. Under identical conditions, at varied doses or initial pH, Cd(II) removal by three materials followed the order of S-nZVI > nFeS > nZVI. At pH 6, the Cd(II) removal within 24 hours for S-nZVI, nFeS, and nZVI (dose of 20 mg/L) were 93.50%, 89.12% and 4.10%, respectively. The fast initial reaction rate of nZVI did not lead to a high removal capacity. The Cd removal was slightly impacted or even improved with co-existing ions (at 50 mg/L or 200 mg/L) or HA (at 2 mg/L or 20 mg/L). Characterization results revealed that nZVI immobilized Cd through coprecipitation, surface complexation, and reduction, whereas the mechanisms for sulfidated materials involved replacement, coprecipitation, and surface complexation, with replacement as the predominant reaction. A strong linear correlation between Cd(II) removal and Fe(II) dissolution was observed, and we proposed a novel pseudo-second-order kinetic model to simulate Fe(II) dissolution.

    Kaixuan Zheng, Xingshen Luo, Yiqi Tan, Zhonglei Li, Hongtao Wang, Tan Chen, Li Zhao, Liangtong Zhan
    Frontiers of Environmental Science & Engineering, 2022, 16(12): 156.

    ● A novel PRB configuration based on passive convergent flow effect was proposed.

    ● A 2D finite-difference hydrodynamic model, PRB-Flow, was developed.

    ● PC-PRB can significantly enhance the hydraulic capture capacity of PRB.

    ● The PRB geometric dimensions and materials cost are effectively reduced.

    ● The dominant influential factor of the PC-PRB capture width is pipe length, Lp.

    A novel permeable reactive barrier (PRB) configuration, the so-called passive convergence-permeable reactive barrier (PC-PRB), is proposed to overcome several shortcomings of traditional PRB configurations, such as high dependency to site hydrogeological characteristics and plume size. The PC-PRB is designed to make the plume converge towards the PRB due to the passive hydraulic decompression-convergent flow effect. The corresponding passive groundwater convergence (PC) system is deployed upstream of the PRB system, which consists of passive wells, water pipes, and a buffer layer. A two-dimensional (2D) finite-difference hydrodynamic code, entitled PRB-Flow, is developed to examine the hydraulic performance parameters (i.e., capture width (W) and residence time (t)) of PC-PRB. It is proved that the horizontal 2D capture width (Wh) and vertical 2D capture depth (Wv) of the PC-PRB remarkably increase compared to that of the continuous reactive barrier (C-PRB). The aforementioned relative growth values in order are greater than 50% and 25% in this case study. Therefore, the PRB geometric dimensions as well as the materials cost required for the same plume treatment lessens. The sensitivity analysis reveals that the dominant factors influencing the hydraulic performance of the PC-PRB are the water pipe length (Lp), PRB length (LPRB), passive well height (Hw), and PRB height (HPRB). The discrepancy between the Wh of PC-PRB and that of the C-PRB (i.e., ΔWh) has a low correlation with PRB parameters and mainly depends on Lp, which could dramatically simplify the PC-PRB design procedure. Generally, the proposed PC-PRB exhibits an effective PRB configuration to enhance hydraulic performance.

    Xiujuan Chen, Yunqiu Liu, Gordon Huang, Chunjiang An, Renfei Feng, Yao Yao, Wendy Huang, Shuqing Weng
    Frontiers of Environmental Science & Engineering, 2022, 16(12): 153.

    ● A PAA-ZnO-HDTMS flax fiber with UV-induced switchable wettability was developed.

    ● The property of flax fiber could be switched from hydrophobicity to hydrophilicity.

    ● The mechanism of the acquired UV-induced switchable wettability was discussed.

    ● The developed flax fiber was successfully used for multipurpose oil-water separation.

    The large number of oily wastewater discharges and oil spills are bringing about severe threats to environment and human health. Corresponding to this challenge, a functional PAA-ZnO-HDTMS flax fiber with UV-induced switchable wettability was developed for efficient oil-water separation in this study. The developed flax fiber was obtained through PAA grafted polymerization and then ZnO-HDTMS nanocomposite immobilization. The as-prepared PAA-ZnO-HDTMS flax fiber was hydrophobic initially and could be switched to hydrophilic through UV irradiation. Its hydrophobicity could be easily recovered through being stored in dark environment for several days. To optimize the performance of the PAA-ZnO-HDTMS flax fiber, the effects of ZnO and HDTMS concentrations on its switchable wettability were investigated. The optimized PAA-ZnO-HDTMS flax fiber had a large water contact angle (~130°) in air and an extremely small oil contact angle (~0°) underwater initially. After UV treatment, the water contact angle was decreased to 30°, while the underwater oil contact angle was increased to more than 150°. Based on this UV-induced switchable wettability, the developed PAA-ZnO-HDTMS flax fiber was applied to remove oil from immiscible oil-water mixtures and oil-in-water emulsion with great reusability for multiple cycles. Thus, the developed flax fiber could be further fabricated into oil barrier or oil sorbent for oil-water separation, which could be an environmentally-friendly alternative in oil spill response and oily wastewater treatment.

    Jinhui Liang, Peng Gao, Benhang Li, Longfei Kang, Li Feng, Qi Han, Yongze Liu, Liqiu Zhang
    Frontiers of Environmental Science & Engineering, 2022, 16(12): 150.

    ● The physicochemical and structural properties of DBC were characterized.

    ● The effects of DBC on DBPs and DBPFP generation during disinfection were evaluated.

    ● The DBPs and DBPFP generation during chlor(am)ination were compared.

    Dissolved black carbon (DBC) released from biochar can be one of the potential disinfection by-products (DBPs) precursors in the dissolved organic matter pool. However, the physiochemical and structural properties of DBC and the effects on the development of DBPs and DBP formation potential (DBPFP) during the disinfection process remain unclear. In this study, the characteristics of two kinds of DBC, namely, animal-derived DBC (poultry litter DBC, PL-DBC) and plant-derived DBC (wheat straw DBC, WS-DBC), were investigated. The effects of different kinds of DBC on the evolution of DBPs and DBPFP in chlorine and chloramine disinfection processes were compared with natural organic matter (NOM). The results showed that the total DBPs concentrations derived from PL-DBC, WS-DBC and NOM were similar during chlorination (i.e., 61.23 μg/L, 64.59 μg/L and 64.66 μg/L, respectively) and chloramination (i.e., 44.63 μg/L, 44.42 μg/L and 45.58 μg/L, respectively). The lower total DBPs and DBPFP concentrations in chloramination could be attributed to the fact that the introduction of ammonia in chloramine inhibited the breaking of the bond between the disinfectant and the active group of the precursor. Additionally, DBC presented much lower total DBPFP concentrations than NOM in both chlorination and chloramination. However, both kinds of DBC tended to form more monochloroacetic acids and haloacetamides than NOM, which could result from the higher organic strength, higher protein matter, and nitrogen-rich soluble microbial products of DBC.

    Xiaoying Wang, Haiguang Zhang, Xu Wang, Shuo Chen, Hongtao Yu, Xie Quan
    Frontiers of Environmental Science & Engineering, 2023, 17(1): 1.

    ● Electroconductive RGO-MXene membranes were fabricated.

    ● Wettable membrane channels were established between RGO and MXene nanosheets.

    ● Hydrophilic MXene reduces the resistance of water entering the membrane channels.

    ● Water permeance of RGO-MXene membrane is 16.8 times higher than that of RGO membrane.

    ● Electro-assistance can enhance the dye rejection performance of RGO-MXene membrane.

    Reduced graphene oxide (RGO) membranes are theoretically more conducive to the rapid transport of water molecules in their channels compared with graphene oxide (GO) membranes, as they have fewer oxygen-containing functional groups and more non-oxidized regions. However, the weak hydrophilicity of RGO membranes inhibits water entry into their channels, resulting in their low water permeability. In this work, we constructed wettable RGO-MXene channels by intercalating hydrophilic MXene nanosheets into the RGO membrane for improving the water permeance. The RGO-MXene composite membrane exhibits high pure water permeance of 62.1 L/(m2·h·bar), approximately 16.8 times that of the RGO membrane (3.7 L/(m2·h·bar)). Wettability test results and molecular dynamics simulations suggest that the improved water permeance results from the enhanced wettability of RGO-MXene membrane and increased rate of water molecules entering the RGO-MXene channels. Benefiting from good conductivity, the RGO-MXene membrane with electro-assistance exhibits significantly increased rejection rates for negatively charged dyes (from 56.0% at 0 V to 91.4% at 2.0 V for Orange G) without decreasing the permeate flux, which could be attributed to enhanced electrostatic repulsion under electro-assistance.

    Xianjun Tan, Zhenying Jiang, Yuxiong Huang
    Frontiers of Environmental Science & Engineering, 2023, 17(1): 3.

    ● Terminal carboxylate group activation is PFOA degradation’s rate-limiting step.

    ● Bi3O(OH)(PO4)2 with surface frustrated Lewis pairs (SFLPs) efficiently degrade PFOA.

    ● Photo-induced Lewis acidic sites and proximal surface hydroxyls constitute SFLPs.

    ● SFLPs act as collection centers to effectively adsorb PFOA.

    ● SFLPs endow accessible pathways for photogenerated holes rapid transfer to PFOA.

    Heterogeneous photocatalysis has gained substantial research interest in treating per- and polyfluoroalkyl substances (PFAS)-contaminated water. However, sluggish degradation kinetics and low defluorination efficiency compromise their practical applications. Here, we report a superior photocatalyst, defected Bi3O(OH)(PO4)2, which could effectively degrade typical PFAS, perfluorooctanoic acid (PFOA), with high defluorination efficiency. The UV light irradiation could in situ generate oxygen vacancies on Bi3O(OH)(PO4)2 through oxidation of the lattice hydroxyls, which further promotes the formation of Lewis acidic coordinately unsaturated bismuth sites. Then, the Lewis acidic sites couple with the proximal surface hydroxyls to constitute the surface frustrated Lewis pairs (SFLPs). With the in-depth spectroscopic analysis, we revealed that the photo-induced SFLPs act as collection centers to effectively adsorb PFOA and endow accessible pathways to transfer photogenerated holes to PFOA rapidly. Consequently, activation of the terminal carboxyl, a rate-limiting step for PFOA decomposition, could be easily achieved over the defected Bi3O(OH)(PO4)2 photocatalyst. These results suggest that SFLPs exhibit great potential in developing highly efficient photocatalysts to degrade persistent organic pollutants.

    Jaime A. Teixeira da Silva, Panagiotis Tsigaris
    Frontiers of Environmental Science & Engineering, 2023, 17(3): 39.

    James E. Lovelock, famed for his Gaia hypothesis, which views the Earth as a living integrated and interconnected self-regulating system whose equilibrium comes about from complex energy-based interactions and feedback loops, ultimately sustaining life, passed away at the end of July, 2022 at the age of 103. Not only are the adaptive mechanisms of Gaia central to the conversation of environmental homeostasis, they lie at the heart of climate change and global warming. Lovelock is also remembered as the co-inventor of the electron capture detector that eventually allowed for the sensitive detection of chlorofluorocarbons and pesticides. Finally, Lovelock’s free-spirited nature and research independence allow academia to rethink current research’s modus operandi.

    Yirong Hu, Wenjie Du, Cheng Yang, Yang Wang, Tianyin Huang, Xiaoyi Xu, Wenwei Li
    Frontiers of Environmental Science & Engineering, 2023, 17(5): 55.

    ● A machine learning model was used to identify lake nutrient pollution sources.

    ● XGBoost model showed the best performance for lake water quality prediction.

    ● Model feature size was reduced by screening the key features with the MIC method.

    ● TN and TP concentrations of Lake Taihu are mainly affected by endogenous sources.

    ● Next-month lake TN and TP concentrations were predicted accurately.

    Effective control of lake eutrophication necessitates a full understanding of the complicated nitrogen and phosphorus pollution sources, for which mathematical modeling is commonly adopted. In contrast to the conventional knowledge-based models that usually perform poorly due to insufficient knowledge of pollutant geochemical cycling, we employed an ensemble machine learning (ML) model to identify the key nitrogen and phosphorus sources of lakes. Six ML models were developed based on 13 years of historical data of Lake Taihu’s water quality, environmental input, and meteorological conditions, among which the XGBoost model stood out as the best model for total nitrogen (TN) and total phosphorus (TP) prediction. The results suggest that the lake TN is mainly affected by the endogenous load and inflow river water quality, while the lake TP is predominantly from endogenous sources. The prediction of the lake TN and TP concentration changes in response to these key feature variations suggests that endogenous source control is a highly desirable option for lake eutrophication control. Finally, one-month-ahead prediction of lake TN and TP concentrations (R2 of 0.85 and 0.95, respectively) was achieved based on this model with sliding time window lengths of 9 and 6 months, respectively. Our work demonstrates the great potential of using ensemble ML models for lake pollution source tracking and prediction, which may provide valuable references for early warning and rational control of lake eutrophication.

    Seo Won Cho, Haoran Wei
    Frontiers of Environmental Science & Engineering, 2023, 17(5): 57.

    ● Definition of emerging contaminants in drinking water is introduced.

    ● SERS and standard methods for emerging contaminant analysis are compared.

    ● Enhancement factor and accessibility of SERS hot spots are equally important.

    ● SERS sensors should be tailored according to emerging contaminant properties.

    ● Challenges to meet drinking water regulatory guidelines are discussed.

    Emerging contaminants (ECs) in drinking water pose threats to public health due to their environmental prevalence and potential toxicity. The occurrence of ECs in our drinking water supplies depends on their physicochemical properties, discharging rate, and susceptibility to removal by water treatment processes. Uncertain health effects of long-term exposure to ECs justify their regular monitoring in drinking water supplies. In this review article, we will summarize the current status and future opportunities of surface-enhanced Raman spectroscopy (SERS) for EC analysis in drinking water. Working principles of SERS are first introduced and a comparison of SERS and liquid chromatography-tandem mass spectrometry in terms of cost, time, sensitivity, and availability is made. Subsequently, we discuss the strategies for designing effective SERS sensors for EC analysis based on five categories—per- and polyfluoroalkyl substances, novel pesticides, pharmaceuticals, endocrine-disrupting chemicals, and microplastics. In addition to maximizing the intrinsic enhancement factors of SERS substrates, strategies to improve hot spot accessibilities to the targeting ECs are equally important. This is a review article focusing on SERS analysis of ECs in drinking water. The discussions are not only guided by numerous endeavors to advance SERS technology but also by the drinking water regulatory policy.

    Shuang Zhang, Shuai Liang, Yifan Gao, Yang Wu, Xia Huang
    Frontiers of Environmental Science & Engineering, 2023, 17(3): 30.

    ● A novel nonpolar super-aligned carbon nanotube (SACNT) membrane was prepared.

    ● SACNT membranes achieved smoother and more uniform structures.

    ● SACNT membranes have inert chemistry and unique nonpolar wetting feature.

    ● SACNT membranes exhibit superior separation and antifouling capabilities.

    ● SACNT membranes achieved superior oil/water separation efficiency.

    Membrane separation technology has made great progress in various practical applications, but the unsatisfactory separation performance of prevailing membrane materials hampers its further sustainable growth. This study proposed a novel nonpolar super-aligned carbon nanotube (SACNT) membrane, which was prepared with a layer-by-layer cross-stacking method. Through controlling the number of stacked SACNT layers, three kinds of SACNT membranes (SACNT_200, SACNT_300, and SACNT_400) were prepared. Systematic characterizations and filtration tests were performed to investigate their physico-chemical properties, surface wetting behavior, and filtration performance. Compared with two commercial membranes (Com_0.22 and Com_0.45), all the SACNT membranes achieved smoother and more uniform structures. Due to the hexagonal graphene structure of CNTs, the surface chemistry of the SACNT membranes is simple and inert, thereby potentially eliminating the covalent-bonding-induced membrane fouling. Besides, the SACNT membranes exhibited a typical nonpolar wetting behavior, with high contact angles for polar liquids (water: ~124.9°–126.5°; formamide: ~80.0°–83.9°) but low contact angles for nonpolar diiodomethane (~18.8°–20.9°). This unique nonpolar feature potentially leads to weak interactions with polar substances. Furthermore, compared with the commercial membranes, the SACNT membranes obtained a significantly higher selectivity while achieving a comparable or higher permeability (depending on the number of stacked layers). Moreover, the SACNT membranes exhibited superior separation performance in various application scenarios, including municipal wastewater treatment (> 2.3 times higher cleaning efficiency), electro-assistant fouling inhibition (or even self-cleaning), and oil/water separation (> 99.2 % of separation efficiency), suggesting promising application prospects in various fields.

    Zhijun Liu, Xi Luo, Senlin Shao, Xue Xia
    Frontiers of Environmental Science & Engineering, 2023, 17(4): 40.

    ● Pd-Cu modified CNT membranes were prepared successfully by electrodeposition method.

    ● The deposition voltage and deposition time were optimized for Pd-Cu co-deposition.

    ● NO3-N was removed efficiently from water by Pd-Cu modified CNT membranes.

    ● The presence of dissolved oxygen did not affect the nitrate reduction performance.

    ● Mass transfer rate was promoted significantly with the increase in membrane flux.

    Excessive nitrate in water is harmful to the ecological environment and human health. Electrocatalytic reduction is a promising technology for nitrate removal. Herein, a Pd-Cu modified carbon nanotube membrane was fabricated with an electrodeposition method and used to reduce nitrate in a flow-through electrochemical reactor. The optimal potential and duration for codeposition of Pd and Cu were −0.7 V and 5 min, respectively, according to linear scan voltammetry results. The membrane obtained with a Pd:Cu ratio of 1:1 exhibited a relatively high nitrate removal efficiency and N2 selectivity. Nitrate was almost completely reduced (~99 %) by the membrane at potentials lower than −1.2 V. However, −0.8 V was the optimal potential for nitrate reduction in terms of both nitrate removal efficiency and product selectivity. The nitrate removal efficiency was 56.2 %, and the N2 selectivity was 23.8 % for the Pd:Cu=1:1 membrane operated at −0.8 V. Nitrate removal was enhanced under acidic conditions, while N2 selectivity was decreased. The concentrations of Cl ions and dissolved oxygen showed little effect on nitrate reduction. The mass transfer rate constant was greatly improved by 6.6 times from 1.14 × 10−3 m/h at a membrane flux of 1 L/(m2·h) to 8.71 × 10−3 m/h at a membrane flux of 15 L/(m2·h), which resulted in a significant increase in the nitrate removal rate from 13.6 to 133.5 mg/(m2·h). These findings show that the Pd-Cu modified CNT membrane is an efficient material for nitrate reduction.

    Yujie Pan, Yalan Li, Hongxia Peng, Yiping Yang, Min Zeng, Yang Xie, Yao Lu, Hong Yuan
    Frontiers of Environmental Science & Engineering, 2023, 17(5): 56.

    ● This study systematically examined the relationship between groundwater Cd and UCL.

    ● The study covered 211 UCL and sociological characteristic from nine groundwater samples.

    ● We found a significant positive correlation between groundwater Cd and UCL.

    ● Smoking status and education level also significantly affected UCL.

    Cadmium (Cd) has received widespread attention owing to its persistent toxicity and non-degradability. Cd in the human body is mainly absorbed from the external environment and is usually assessed using urinary Cd. Hunan Province is the heartland of the Chinese non-ferrous mining area, where several serious Cd pollution events have occurred, including high levels of Cd in the urine of residents. However, the environmental factors influencing high urinary Cd levels (UCLs) in nearby residents remain unclear. Therefore, 211 nearby residents’ UCLs and the corresponding sociological characteristics from nine groundwater samples in this area were analyzed using statistical analysis models. Groundwater Cd concentration ranged from 0.02 to 1.15 μg/L, aligning with class III of the national standard; the range of UCL of nearby residents was 0.37–36.60 μg/L, exceeding the national guideline of 0–2.5 μg/L. Groundwater Cd levels were positively correlated with the UCL (P < 0.001, correlation coefficient 95 % CI = 9.68, R2 = 0.06). In addition, sociological characteristics, such as smoking status and education level, also affect UCL. All results indicate that local governments should strengthen the prevention and abatement of groundwater Cd pollution. This study is the first to systematically evaluate the relationship between groundwater Cd and UCL using internal and external environmental exposure data. These findings provide essential bases for relevant departments to reduce Cd exposure in regions where the heavy metal industry is globally prevalent.

    Fan Yang, Junpeng Li, Huan Wang, Xiaofeng Xiao, Rui Bai, Feng Zhao
    Frontiers of Environmental Science & Engineering, 2023, 17(2): 19.

    ● Term of manganese-oxidizing microorganisms should be reconsidered.

    ● Visible light induces heterotrophic bacteria to produce superoxide.

    ● Heterotrophic bacteria oxidize Mn(II) ions with a fast oxidation rate.

    ● Superoxide oxidizing Mn(II) ions is an unintended side reaction of bacteria.

    ● Superoxide is an important oxidation force of Mn(II) in the environment.

    Manganese oxides are widely distributed in soils and sediments, affecting the migration and transformation of heavy metals and organic pollutants. The microbial conversion of soluble Mn(II) into insoluble Mn(III/IV) oxides is considered to be the initial source of manganese oxides in the environment; however, whether this process is related to a physiological role remains unclear. Here, we explored the microbial manganese oxidation process under visible light by using coastal surface seawater microorganisms. Visible light greatly promotes the oxidation rate of Mn(II), and the average rate reaches 64 μmol/(L·d). The generated manganese oxides were then conducive to Mn(II) oxidation, thus the rapid manganese oxidation was the result of the combined action of biotic and abiotic, and biological function accounts for 88 % ± 4 %. Extracellular superoxide produced by microorganisms induced by visible light is the decisive factor for the rapid manganese oxidation in our study. But the production of these superoxides does not require the presence of Mn(II) ions, the Mn(II) oxidation process was more like an unintentional side reaction, which did not affect the growth of microorganisms. More than 70 % of heterotrophic microorganisms in nature are capable of producing superoxide, based on the oxidizing properties of free radicals, all these bacteria can participate in the geochemical cycle of manganese. What’s more, the superoxide oxidation pathway might be a significant natural source of manganese oxide.

    Jinyong Liu, Jinyu Gao
    Frontiers of Environmental Science & Engineering, 2023, 17(2): 26.

    ● Advances, challenges, and opportunities for catalytic water pollutant reduction.

    ● Cases of Pd-based catalysts for nitrate, chlorate, and perchlorate reduction.

    ● New functionalities developed by screening and design of catalytic metal sites.

    ● Facile catalyst preparation approaches for convenient catalyst optimization.

    ● Rational design and non-decorative effort are essential for future work.

    In this paper, we discuss the previous advances, current challenges, and future opportunities for the research of catalytic reduction of water pollutants. We present five case studies on the development of palladium-based catalysts for nitrate, chlorate, and perchlorate reduction with hydrogen gas under ambient conditions. We emphasize the realization of new functionalities through the screening and design of catalytic metal sites, including (i) platinum group metal (PGM) nanoparticles, (ii) the secondary metals for improving the reaction rate and product selectivity of nitrate reduction, (iii) oxygen-atom-transfer metal oxides for chlorate and perchlorate reduction, and (iv) ligand-enhanced coordination complexes for substantial activity enhancement. We also highlight the facile catalyst preparation approach that brought significant convenience to catalyst optimization. Based on our own studies, we then discuss directions of the catalyst research effort that are not immediately necessary or desirable, including (1) systematic study on the downstream aspects of under-developed catalysts, (2) random integration with hot concepts without a clear rationale, and (3) excessive and decorative experiments. We further address some general concerns regarding using H2 and PGMs in the catalytic system. Finally, we recommend future catalyst development in both “fundamental” and “applied” aspects. The purpose of this perspective is to remove major misconceptions about reductive catalysis research and bring back significant innovations for both scientific advancements and engineering applications to benefit environmental protection.

    Jianxun Yang, Qi Gao, Miaomiao Liu, John S. Ji, Jun Bi
    Frontiers of Environmental Science & Engineering, 2023, 17(2): 20.

    ● Emotional responses to visibility-reducing haze was assessed in a controlled lab.

    ● Valence and arousal have non-linear responses to pollution-caused low visibility.

    ● Repetitive exposure aggravates negative emotions in severely polluted conditions.

    ● Emotional bias to pollution relates with gender, decisiveness, attitude to clean air.

    A growing number of studies have shown that impaired visibility caused by particulate matter pollution influences emotional wellbeing. However, evidence is still scant on how this effect varies across individuals and over repetitive visual exposure in a controlled environment. Herein, we designed a lab-based experiment (41 subjects, 6 blocks) where participants were presented with real-scene images of 12 different PM2.5 concentrations in each block. Emotional valence (negative to positive) and arousal (calm to excited) were self-rated by participants per image, and the response time for each rating was recorded. We find that as pollution level increases from 10 to 260 µg/m3, valence scores decrease, whereas arousal scores decline first and then bounce back, following a U-shaped trend. When air quality deteriorates, individual variability decreases in hedonic valence but increases in arousal. Over blocks, repetitive visual exposure increases valence at a moderate pollution level but aggravates negative emotions in severely polluted conditions (> 150 µg/m3). Finally, we find females, people who are slow in making responses, and those who are highly aroused by clean air tend to express more negative responses (so-called negativity bias) to ambient pollution than their respective counterparts. These results provide deeper insights into individual-level emotional responses to dirty air in a controlled environment. Although the findings in our pilot study should only be directly applied to the conditions assessed herein, we introduce a framework that can be replicated in different regions to assess the impact of air pollution on local emotional wellbeing.