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  • RESEARCH ARTICLE
    Zhe Wang, Wenjuan Zhang, Zhiwei Wang, Jing Chang
    Frontiers of Environmental Science & Engineering, 2023, 17(5): 54. https://doi.org/10.1007/s11783-023-1654-8

    p- CNB and IBP were selected, to explore factors determining ozonation outcomes.

    ● •OH contributed only 50 % to IBP removal, compared to the 90 % for p -CNB removal.

    ● IBP achieved fewer TOC removal and more by-product types and quantities.

    ● A longer ring-opening distance existed during the degradation of IBP.

    ● Multiple positions on both branches of IBP were attacked, consuming more oxidants.

    For aromatic monomer compounds (AMCs), ozonation outcomes were usually predicted by the substituents of the benzene ring based on the electron inductive effect. However, the predicted results were occasionally unreliable for complex substituents, and other factors caused concern. In this study, p-chloronitrobenzene (p-CNB) and ibuprofen (IBP) were selected for ozonation. According to the electron inductive theory, p-CNB should be less oxidizable, but the opposite was true. The higher rates of p-CNB were due to various sources of assistance. First, the hydroxyl radical (•OH) contributed 90 % to p-CNB removal at pH 7.0, while its contribution to IBP removal was 50 %. Other contributions came from molecular O3 oxidation. Second, p-CNB achieved 40 % of the total organic carbon (TOC) removal and fewer by-product types and quantities, when compared to the results for IBP. Third, the oxidation of p-CNB started with hydroxyl substitution reactions on the benzene ring; then, the ring opened. However, IBP was initially oxidized mainly on the butane branched chain, with a chain-shortening process occurring before the ring opened. Finally, the degradation pathway of p-CNB was single and consumed fewer oxidants. However, both branches of IBP were attacked simultaneously, and three degradation pathways that relied on more oxidants were proposed. All of these factors were determinants of the rapid removal of p-CNB.

  • RESEARCH ARTICLE
    Xinjie Yan, Xunyu Shen, Jipeng Wang, Jinlong Zhuang, Yu Wang, Jinchi Yao, Hong Liu, Yongdi Liu, James P. Shapleigh, Wei Li
    Frontiers of Environmental Science & Engineering, 2023, 17(4): 50. https://doi.org/10.1007/s11783-023-1650-z

    ● N2O emissions from a denitrifying SBR were 23 times higher than that of the CSTR.

    ● Feast famine conditions in SBR uniquely lead to producing undesirable levels of N2O.

    ● An MAG closely related to previously identified Thauera is likely a major N2O driver.

    ● Post-transcriptional regulation may be linked to higher N2O production in SBR.

    Nitrous oxide (N2O) is a potent greenhouse gas that can be emitted during the biological treatment of wastewater. In this study, a comparison of the long-term performance characteristics and N2O production of sequencing batch reactors (SBR) and continuous stirred tank reactors (CSTR) during nitrite-based denitrification was undertaken. It was found that both reactors had NO2-N removal efficiencies over 99.9 %, but the N2O-N emissions from the SBR reached ~2.3 % of the removal nitrite-N load, while in the CSTR it never exceeded 0.1 %. High frequency sampling during one operation cycle of the SBR demonstrated that the N2O accumulation ratio was ~0.1 % during the feast period, increased to ~1.9 % in the first five hours of the famine period, and then gradually reached ~2.3 % at the end of famine. Batch experiments showed that limiting extracellular electron donor is required for N2O accumulation in cells from the SBR-famine period and that cells from the CSTR do not accumulate N2O when either nitrite or carbon is limiting. Another notable difference in the two reactor communities was the high level of accumulation of intracellular granules, most likely polyhydroxybutyrate (PHB), in cells during the feast period in the SBR. Metagenome assembly and binning found that one genome (PRO1), which is a Thauera, accounted for over half the metagenomic reads in both reactors. Neither shifts in gene regulation nor community composition explained the observed differences in reactor performance suggesting some post-transcriptional regulation obligatorily linked to antecedent conditions underly increased N2O production in the SBR.

  • RESEARCH ARTICLE
    Zeou Dou, Maria Vitoria Bini Farias, Wensi Chen, Dongjing He, Yuhang Hu, Xing Xie
    Frontiers of Environmental Science & Engineering, 2023, 17(5): 53. https://doi.org/10.1007/s11783-023-1653-9

    ● A controlled-release fertilizer was developed based on chitosan biopolymer scaffold.

    ● Chitosan-MMT scaffold achieved a well-controlled nutrient release.

    ● Highly water-absorbing chitosan-MMT hydrogels enhanced the soil water retention.

    ● Physically crosslinked chitosan-MMT hydrogels exhibited excellent degradability.

    Fertilizer consumption is increasing drastically along with the rapid expansion of farming in response to the ever-growing population. However, a significant portion of the nutrients in traditional fertilizers is lost during leaching and runoff causing economic loss and environmental threats. Polymer-modified controlled-release fertilizers provide an opportunity for mitigating adverse environmental effects and increasing the profitability of crop production. Here, we present a cheap and easy-to-fabricate controlled-release fertilizer excipient based on hydrogels scaffolded by safe and biodegradable chitosan and montmorillonite (MMT) nanoclays. By introducing elastic and flexible physical crosslinking induced by 2-dimensional (2D) MMT nanoflakes into the chitosan hydrogel, highly swellable and degradable chitosan-MMT nanocomposites were fabricated. The addition of MMT into the chitosan hydrogels enhanced the total release of phosphorous (P) and potassium (K), from 22.0 % to 94.9 % and 9.6% to 31.4 %, respectively, compared to the pure chitosan gel. The chitosan-MMT nanocomposite hydrogel achieved a well-controlled overall fertilizer release in soil. A total of 55.3 % of loaded fertilizer was released over 15 d with a daily release of 2.8 %. For the traditional fertilizer podwer, 89.2 % of the fertilizer was washed out during the first irrigation under the same setup. In the meantime, the nanocomposites improved the water retention of the soil, thanks to its excellent water absorbency. Moreover, the chitosan-MMT nanocomposite hydrogels exhibited high degradation of 57 % after swelling in water for 20 d. Such highly degradable fertilizer excipient poses minimal threat to the long-term fertility of the soil. The engineered Chitosan-MMT biopolymer scaffold as a controlled-release fertilizer excipient provides a promising opportunity for advancing sustainable agriculture.

  • RESEARCH ARTICLE
    Yinghui Mo, Liping Sun, Lu Zhang, Jianxin Li, Jixiang Li, Xiuru Chu, Liang Wang
    Frontiers of Environmental Science & Engineering, 2023, 17(4): 49. https://doi.org/10.1007/s11783-023-1649-5

    ● MnO x /Ti flow-through anode was coupled with the biofilm-attached cathode in ECBR.

    ● ECBR was able to enhance the azo dye removal and reduce the energy consumption.

    ● MnIV=O generated on the electrified MnO x /Ti anode catalyzed the azo dye oxidation.

    ● Aerobic heterotrophic bacteria on the cathode degraded azo dye intermediate products.

    ● Biodegradation of intermediate products was stimulated under the electric field.

    Dyeing wastewater treatment remains a challenge. Although effective, the in-series process using electrochemical oxidation as the pre- or post-treatment of biodegradation is long. This study proposes a compact dual-chamber electrocatalytic biofilm reactor (ECBR) to complete azo dye decolorization and mineralization in a single unit via anodic oxidation on a MnOx/Ti flow-through anode followed by cathodic biodegradation on carbon felts. Compared with the electrocatalytic reactor with a stainless-steel cathode (ECR-SS) and the biofilm reactor (BR), the ECBR increased the chemical oxygen demand (COD) removal efficiency by 24 % and 31 % (600 mg/L Acid Orange 7 as the feed, current of 6 mA), respectively. The COD removal efficiency of the ECBR was even higher than the sum of those of ECR-SS and BR. The ECBR also reduced the energy consumption (3.07 kWh/kg COD) by approximately half compared with ECR-SS. The advantages of the ECBR in azo dye removal were attributed to the synergistic effect of the MnOx/Ti flow-through anode and cathodic biofilms. Catalyzed by MnIV=O generated on the MnOx/Ti anode under a low applied current, azo dyes were oxidized and decolored. The intermediate products with improved biodegradability were further mineralized by the cathodic aerobic heterotrophic bacteria (non-electrochemically active) under the stimulation of the applied current. Taking advantage of the mutual interactions among the electricity, anode, and bacteria, this study provides a novel and compact process for the effective and energy-efficient treatment of azo dye wastewater.

  • RESEARCH ARTICLE
    Jie Liu, Junjun Ma, Weizhang Zhong, Jianrui Niu, Zaixing Li, Xiaoju Wang, Ge Shen, Chun Liu
    Frontiers of Environmental Science & Engineering, 2023, 17(4): 51. https://doi.org/10.1007/s11783-023-1651-y

    ● We have provided an activated method to remove the toxicity of antibiotic residue.

    ● PFRB can greatly improve the salt adsorption capacity of MCDI.

    ● The hierarchical porous and abundant O/N-doped played the key role for the high-capacity desalination.

    ● A new field of reuse of penicillin fermentation residue has been developed.

    Membrane capacitive deionization (MCDI) is an efficient desalination technology for brine. Penicillin fermentation residue biochar (PFRB) possesses a hierarchical porous and O/N-doped structure which could serve as a high-capacity desalination electrode in the MCDI system. Under optimal conditions (electrode weight, voltage, and concentration) and a carbonization temperature of 700 °C, the maximum salt adsorption capacity of the electrode can reach 26.4 mg/g, which is higher than that of most carbon electrodes. Furthermore, the electrochemical properties of the PFRB electrode were characterized through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) with a maximum specific capacitance of 212.18 F/g. Finally, biotoxicity tests have showed that PFRB was non-biotoxin against luminescent bacteria and the MCDI system with the PFRB electrode remained stable even after 27 adsorption–desorption cycles. This study provides a novel way to recycle penicillin residue and an electrode that can achieve excellent desalination.

  • RESEARCH ARTICLE
    Kaige Yang, Zhouyi Zhang, Kangdie Hu, Bo Peng, Weiwei Wang, Hong Liang, Chao Yan, Mingyuan Wu, Yan Wang
    Frontiers of Environmental Science & Engineering, 2023, 17(3): 28. https://doi.org/10.1007/s11783-023-1628-x

    ● Metabolome can distinguish pregnant women exposure to PFOA at different degrees.

    ● Metabolome can reveal the metabolic changes of pregnant women exposure to PFOA.

    ● PFOA exposure degrees could affect the GSH metabolism of pregnant women.

    ● PFOA exposure degrees could change the microbiota metabolism of pregnant women.

    Perfluorooctanoic acid (PFOA) is a novel type of persistent synthetic organic pollutant, and its exposure on pregnant women can cause some adverse effects, such as pregnancy-induced hypertension, gestational diabetes mellitus, and preeclampsia. Therefore, understanding the metabolic changes caused by PFOA exposure is of great significance to protect pregnant women from its adverse effects. In this study, the metabolomes from the urine samples of pregnant women exposure to PFOA at different degrees were analyzed by GC-MS and LC-MS. The samples in different groups were distinguished and the differential metabolites were screened based on the VIP value, FC, and P-value of each comparison group through multivariate statistical analysis. The pathways related to differential metabolites were searched to reveal the effects of PFOA exposure on metabolic changes in pregnant women at different degrees. Finally, the ROC of differential metabolites was performed, and the differential metabolites with large area under the curve (AUC) values were selected and compared to identify the mutually differential metabolites. Meanwhile, these metabolites were fitted with a multivariable to explore if they could be used to distinguish different groups. The quantitative comparison of mutually differential metabolites revealed that the levels of L-cysteine, glycine, and 5-aminovaleric acid were positively correlated with the degree of PFOA exposure, indicating that different degrees of PFOA exposure could affect the synthesis or degradation of GSH and change the metabolism of oral or intestinal microbiota. Additionally, they may cause oxidative stress and abnormal fat metabolism in pregnant women.

  • REVIEW ARTICLE
    Yiqun Cao, Qingxin Ma, Biwu Chu, Hong He
    Frontiers of Environmental Science & Engineering, 2023, 17(4): 48. https://doi.org/10.1007/s11783-023-1648-6

    ● 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.

  • REVIEW ARTICLE
    Hanqing Fan, Yuxuan Huang, Ngai Yin Yip
    Frontiers of Environmental Science & Engineering, 2023, 17(2): 25. https://doi.org/10.1007/s11783-023-1625-0

    ● IEM ion/ion selectivities of charge, valence, & specific ion are critically assessed.

    ● Ion/molecule selectivities of ion/solvent and ion/uncharged solute are reviewed.

    ● Approaches to advance the selectivities through sorption and migration are analyzed.

    ● The permeability-selectivity tradeoff appears to be pervasive.

    ● Ion/molecule selectivities are comparatively underdeveloped and poorly understood.

    Ion-exchange membranes (IEMs) are utilized in numerous established, emergent, and emerging applications for water, energy, and the environment. This article reviews the five different types of IEM selectivity, namely charge, valence, specific ion, ion/solvent, and ion/uncharged solute selectivities. Technological pathways to advance the selectivities through the sorption and migration mechanisms of transport in IEM are critically analyzed. Because of the underlying principles governing transport, efforts to enhance selectivity by tuning the membrane structural and chemical properties are almost always accompanied by a concomitant decline in permeability of the desired ion. Suppressing the undesired crossover of solvent and neutral species is crucial to realize the practical implementation of several technologies, including bioelectrochemical systems, hypersaline electrodialysis desalination, fuel cells, and redox flow batteries, but the ion/solvent and ion/uncharged solute selectivities are relatively understudied, compared to the ion/ion selectivities. Deepening fundamental understanding of the transport phenomena, specifically the factors underpinning structure-property-performance relationships, will be vital to guide the informed development of more selective IEMs. Innovations in material and membrane design offer opportunities to utilize ion discrimination mechanisms that are radically different from conventional IEMs and potentially depart from the putative permeability-selectivity tradeoff. Advancements in IEM selectivity can contribute to meeting the aqueous separation needs of water, energy, and environmental challenges.

  • RESEARCH ARTICLE
    Haojun Lei, Kaisheng Yao, Bin Yang, Lingtian Xie, Guangguo Ying
    Frontiers of Environmental Science & Engineering, 2023, 17(4): 46. https://doi.org/10.1007/s11783-023-1646-8

    ● 38 PhACs and 2 pesticides were detected in the three rivers of the Pearl River basin.

    ● Anti-inflammatory/analgesics drugs were the predominant PhACs.

    ● The concentrations of PhACs showed seasonal and spatial variation.

    ● Diazepam and ibuprofen were the two PhACs with a moderate environmental risk.

    The occurrence, fate, and environmental risk of 40 pharmaceutically active compounds (PhACs) from surface waters and sediments were comprehensively investigated in the Beijiang River, Xijiang River, and Maozhou River of the Pearl River basin, South China. Salicylic acid and diclofenac (anti-inflammatory drugs), gemfibrozil (a lipid regulator), carbamazepine (an antiepileptic drug), diazepam (a psychoactive drug), and 2-methyl-4-chloro-phenoxyacetic acid (MCPA, a pesticide) were the most ubiquitous compounds in the studied region. The average concentrations of detected PhACs in surface waters and sediments ranged from 0.17 to 19.1 ng/L and 0.10 to 10.4 ng/g, respectively. Meanwhile, PhACs concentration in surface waters and sediments varied greatly among and within the Beijiang River, Xijiang River, and Maozhou River. The largest annual flux of PhACs of the Xijiang River and Beijiang River was more than 11 000 kg per annum, whereas only 25.7 kg/a in the Maozhou River. In addition, the estimated emissions of PhACs in the Beijiang River, Xijiang River, and Maozhou River ranged respectively from 0.28 to 4.22 kg/a, 0.12 to 6.72 kg/a, and 6.66 to 91.0 kg/a, and the back-estimated usage varied with a range from 12.0 to 293 kg/a, 6.79 to 944 kg/a, 368 to 17 459 kg/a. Moreover, the emissions of PhACs showed a close relationship with the gross domestic product (GDP) of each city along the Pearl River. The environmental risk assessment suggested that diazepam and ibuprofen had a moderate risk in this region.

  • REVIEW ARTICLE
    Jinyong Liu, Jinyu Gao
    Frontiers of Environmental Science & Engineering, 2023, 17(2): 26. https://doi.org/10.1007/s11783-023-1626-z

    ● 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.

  • RESEARCH ARTICLE
    Haoshu Wang, Yong Qin, Liqing Xin, Changxun Zhao, Zhuang Ma, Jian Hu, Weixiang Wu
    Frontiers of Environmental Science & Engineering, 2023, 17(4): 47. https://doi.org/10.1007/s11783-023-1647-7

    ● Decentralized composting (DC) is a profitable KW treating technology.

    ● SAC and BEC were economically attractive in rural area, while HDC was unprofitable.

    ● KW handling subsidy plays a vital role in making DC profitable.

    ● SAC and BEC have great potential in promoting rural KW treatment.

    This study was designed to evaluate whether the decentralized rural kitchen waste (KW) composting technologies used in China can be widely applied. To this end, we completed a techno-economic analysis of three typical types of KW compositing, namely solar-assisted (SAC), bio-enhanced (BEC), and heat-dewatering composting (HDC). These evaluations revealed that all three technologies produce composting products that meet China’s organic fertilizer standard and that both SAC and BEC are economically self-sustaining and generate net profits (18824.94 and 17791.52 US$/a) and positive net present values (32133.11 and 25035.93 US$). Subsequent sensitivity analysis demonstrated that the KW-handling subsidy plays a critical role in making decentralized composting economically attractive. Based on these analyses, we believe that reducing the coverage area of SAC, reducing the operating cost of BEC and HDC, upgrading composting products, and strengthening secondary pollution control would aid in supporting the technological improvement of these processes. Moreover, providing appropriate subsidies and promulgating specific standards and policies for KW fertilizer are key strategies for decentralized rural KW composting management.

  • REVIEW ARTICLE
    Rui Liang, Chao Chen, Akash Kumar, Junyu Tao, Yan Kang, Dong Han, Xianjia Jiang, Pei Tang, Beibei Yan, Guanyi Chen
    Frontiers of Environmental Science & Engineering, 0: 44. https://doi.org/10.1007/s11783-023-1644-x

    ● State-of-the-art applications of machine learning (ML) in solid waste (SW) is presented.

    ● Changes of research field over time, space, and hot topics were analyzed.

    ● Detailed application seniors of ML on the life cycle of SW were summarized.

    ● Perspectives towards future development of ML in the field of SW were discussed.

    Due to the superiority of machine learning (ML) data processing, it is widely used in research of solid waste (SW). This study analyzed the research and developmental progress of the applications of ML in the life cycle of SW. Statistical analyses were undertaken on the literature published between 1985 and 2021 in the Science Citation Index Expanded and Social Sciences Citation Index to provide an overview of the progress. Based on the articles considered, a rapid upward trend from 1985 to 2021 was found and international cooperatives were found to have strengthened. The three topics of ML, namely, SW categories, ML algorithms, and specific applications, as applied to the life cycle of SW were discussed. ML has been applied during the entire SW process, thereby affecting its life cycle. ML was used to predict the generation and characteristics of SW, optimize its collection and transportation, and model the processing of its energy utilization. Finally, the current challenges of applying ML to SW and future perspectives were discussed. The goal is to achieve high economic and environmental benefits and carbon reduction during the life cycle of SW. ML plays an important role in the modernization and intellectualization of SW management. It is hoped that this work would be helpful to provide a constructive overview towards the state-of-the-art development of SW disposal.

  • REVIEW ARTICLE
    Rui Liang, Chao Chen, Akash Kumar, Junyu Tao, Yan Kang, Dong Han, Xianjia Jiang, Pei Tang, Beibei Yan, Guanyi Chen
    Frontiers of Environmental Science & Engineering, 2023, 17(4): 44. https://doi.org/10.1007/s11783-023-1644-x

    ● State-of-the-art applications of machine learning (ML) in solid waste (SW) is presented.

    ● Changes of research field over time, space, and hot topics were analyzed.

    ● Detailed application seniors of ML on the life cycle of SW were summarized.

    ● Perspectives towards future development of ML in the field of SW were discussed.

    Due to the superiority of machine learning (ML) data processing, it is widely used in research of solid waste (SW). This study analyzed the research and developmental progress of the applications of ML in the life cycle of SW. Statistical analyses were undertaken on the literature published between 1985 and 2021 in the Science Citation Index Expanded and Social Sciences Citation Index to provide an overview of the progress. Based on the articles considered, a rapid upward trend from 1985 to 2021 was found and international cooperatives were found to have strengthened. The three topics of ML, namely, SW categories, ML algorithms, and specific applications, as applied to the life cycle of SW were discussed. ML has been applied during the entire SW process, thereby affecting its life cycle. ML was used to predict the generation and characteristics of SW, optimize its collection and transportation, and model the processing of its energy utilization. Finally, the current challenges of applying ML to SW and future perspectives were discussed. The goal is to achieve high economic and environmental benefits and carbon reduction during the life cycle of SW. ML plays an important role in the modernization and intellectualization of SW management. It is hoped that this work would be helpful to provide a constructive overview towards the state-of-the-art development of SW disposal.

  • REVIEW ARTICLE
    Rui Liang, Chao Chen, Akash Kumar, Junyu Tao, Yan Kang, Dong Han, Xianjia Jiang, Pei Tang, Beibei Yan, Guanyi Chen
    Frontiers of Environmental Science & Engineering, 0: 44. https://doi.org/10.1007/s11783-023-1644-x

    ● State-of-the-art applications of machine learning (ML) in solid waste (SW) is presented.

    ● Changes of research field over time, space, and hot topics were analyzed.

    ● Detailed application seniors of ML on the life cycle of SW were summarized.

    ● Perspectives towards future development of ML in the field of SW were discussed.

    Due to the superiority of machine learning (ML) data processing, it is widely used in research of solid waste (SW). This study analyzed the research and developmental progress of the applications of ML in the life cycle of SW. Statistical analyses were undertaken on the literature published between 1985 and 2021 in the Science Citation Index Expanded and Social Sciences Citation Index to provide an overview of the progress. Based on the articles considered, a rapid upward trend from 1985 to 2021 was found and international cooperatives were found to have strengthened. The three topics of ML, namely, SW categories, ML algorithms, and specific applications, as applied to the life cycle of SW were discussed. ML has been applied during the entire SW process, thereby affecting its life cycle. ML was used to predict the generation and characteristics of SW, optimize its collection and transportation, and model the processing of its energy utilization. Finally, the current challenges of applying ML to SW and future perspectives were discussed. The goal is to achieve high economic and environmental benefits and carbon reduction during the life cycle of SW. ML plays an important role in the modernization and intellectualization of SW management. It is hoped that this work would be helpful to provide a constructive overview towards the state-of-the-art development of SW disposal.

  • RESEARCH ARTICLE
    Weiyi Liu, Ting Pan, Hang Liu, Mengyun Jiang, Tingting Zhang
    Frontiers of Environmental Science & Engineering, 2023, 17(4): 41. https://doi.org/10.1007/s11783-023-1641-0

    ● Small molecular chains formed on photo-aged polylactic acid microplastics (MPs).

    ● Oxygen-containing functional groups generated on photo-aged polyamide MPs.

    ● Photo-aging has the opposite influence on the imidacloprid adsorption on two MPs.

    ● Electrostatic interactions and hydrogen bonds were the main mechanisms.

    ● High pH value and low ionic strength increase the adsorption capacity.

    The photo-aging behavior of microplastics (MPs) in natural environment has become a global concern. The ultraviolet radiation has enough energy to change the polymer structure and physical-chemical properties of MPs. Less attention has focused on the interactions of the photo-aged polar and biodegradable MPs with organic pollutants. This work investigated the structural properties of aged polar polyamide (PA) MPs and biodegradable polylactic acid (PLA) MPs exposed to ultraviolet irradiation and their adsorption behavior and mechanism for neonicotinoid insecticide imidacloprid (IMI). The results showed that the MPs had extensive changes in surface morphology and chemical properties after photo-aging. The C–N bond of PA MPs was disrupted to form more carbonyl groups. The oxygen-containing functional groups on the surface of aged PLA MPs were broken and generated relatively smaller molecules. The adsorption capacity of IMI on PA MPs decreased by 19.2 %, while the adsorption capacity of IMI on PLA MPs increased by 41.2 % after photo-aging. This depended on the natural structure of the MPs and their ability to absorb ultraviolet light. The electrostatic interactions, hydrogen bonds, van der Waals interactions, and polar-polar interactions were the main adsorption mechanisms of IMI on MPs. High initial solution pH and low ionic strength favored the adsorption of IMI by altering charge distribution on the MPs surface. The formation of the humic acid-IMI complexes decreased the concentration of IMI in the water phase and further decreased the adsorption on MPs. These results are enlightening for a scientific comprehension of the environmental behavior of the polar MPs.