Latest issue

Dec 2021, Volume 15 Issue 6
    
  • Select all
  • RESEARCH ARTICLE
    Yue Wang, Mengshuang Shi, Zhaofeng Lv, Huan Liu, Kebin He

    • Regional transportation contributed more than local emissions during haze episodes.

    • Short-range regional transportation contributed the most to the PM2.5 in the OIAs.

    • Low wind speeds and low PBLHs led to higher local contributions to Beijing.

    The 2022 Winter Olympics is scheduled to take place in Beijing and Zhangjiakou, which were defined as OIAs (Olympic infrastructure areas) in this study. This study presents the characteristics and source apportionment of PM2.5 in the OIAs, China. The entire region of mainland China, except for the OIAs, was divided into 9 source regions, including four regions in the BTH(Beijing-Tianjin-Hebei) region, the four provinces surrounding the BTH and the remaining areas. Using CAMx/PSAT, the contributions of the nine regions to the PM2.5 concentration in the OIAs were simulated spatially and temporally. The simulated source apportionment results showed that the contribution of regional transportation was 48.78%, and when PM2.5 concentration was larger than 75 μg/m3 central Hebei was the largest contributor with a contribution of 19.18%, followed by Tianjin, northern Hebei, Shanxi, Inner Mongolia, Shandong, southern Hebei, Henan and Liaoning. Furthermore, the contribution from neighboring regions of the OIAs was 47.12%, which was nearly twice that of long-range transportation. Haze episodes were analyzed, and the results presented the importance of regional transportation during severe PM2.5 pollution periods. It was also found that they were associated with differences in pollution sources between Zhangjiakou and Beijing. Regional transportation was the main factor affecting PM2.5 pollution in Zhangjiakou due to its low local emissions. Stagnant weather with a low planetary boundary layer height and a low wind velocity prevented the local emitted pollutants in Beijing from being transported outside, and as a result, local emissions constituted a larger contribution in Beijing.

  • RESEARCH ARTICLE
    Shuhan Li, Xin Zhou, Xiwei Cao, Jiabo Chen

    • Short-term effect of the pyridine exposure on the SAD process was investigated.

    • The SAA at 150 mg/L pyridine reduced by 56.7% of the maximum value.

    • Inhibition kinetics models and inhibitory parameters were indicated.

    • Collaboration of AnAOB, HDB and PDB promoted the SAD.

    • Possible metabolic pathways of nitrogen and pyridine were proposed.

    In-depth knowledge on the role of pyridine as a bottleneck restricting the successful application of anammox-based process treating refractory coking wastewater remains unknown. In this study, the effect of short-term pyridine addition on a simultaneous anammox and denitrification (SAD) system fed with 25–150 mg/L pyridine was explored. The short-term operation showed that the highest total nitrogen (TN) removal efficiency was achieved at 25–50 mg/L of pyridine. As the pyridine addition increased, the contribution of the anammox pathway in nitrogen removal decreased from 99.3% to 79.1%, while the denitrification capability gradually improved. The specific anammox activity (SAA) at 150 mg/L pyridine decreased by 56.7% of the maximum SAA. The modified non-competitive inhibition model indicated that the 50% inhibitory concentration (IC50) of pyridine on anammox was 84.18 mg/L and the substrate inhibition constant (Ki) of pyridine for self-degradation was 135.19 mg/L according to the Haldane model. Moreover, high-throughput sequencing confirmed the abundance of Candidatus Kuenenia as the amount of anammox species decreased, while the amounts of denitrifiers and pyridine degraders significantly increased as the pyridine stress increased. Finally, the possible pathways of nitrogen bioconversion and pyridine biodegradation in the SAD system were elucidated through metagenomic analysis and gas chromatography/mass spectrometry results. The findings of this study enlarge the understanding of the removal mechanisms of complex nitrogenous pyridine-containing wastewater treated by the SAD process.

  • RESEARCH ARTICLE
    Xiangyu Yang, Qiang He, Fucheng Guo, Xiaobo Liu, Yi Chen

    • Aquatic plants are more likely to absorb TiO2 NPs that are beneficial to them.

    • Ag NPs inhibited the growth of aquatic plants under both 5- and 60-day exposure.

    • CeO2 NPs had positive/negative impact on plant in 5/60-day exposure, respectively.

    • TiO2 NPs presence could enhance the photosynthesis and increase the plant biomass.

    • The ENPs changed plant activity, which resulted in changes of wetland performance.

    Engineered nanoparticles (ENPs) threaten the environment through wastewater discharging. Generally, constructed wetlands (CWs) are efficient methods for ENPs removal. However, the biotoxicity of ENPs on plants in CWs is unclear. Here, we investigated the distribution and bio-impacts of different ENPs (Ag NPs, TiO2 NPs, and CeO2 NPs) in plants under 5- and 60-day exposure to 1 and 50 mg/L concentrations. Results showed that ENPs appeared in the vascular bundle and mesophyll cell space, which induced the variation in antioxidase activities (e.g., superoxide dismutase [SOD], peroxidase [POD], and catalase [CAT] activities) as well as overproduction of malondialdehyde (MDA). Additionally, Ag NPs inhibited photosynthesis rate and root activity during two exposure phases. CeO2 NPs had positive and negative impacts on plants in 5- and 60-day exposure, respectively. Inversely, TiO2 NPs enhanced photosynthesis and root activity under 60-day exposure. Finally, the contents of the C, N, and P elements in plants fluctuated in response to ENPs stress. All results have a positive correlation with the wetland performance under ENPs exposure except for TiO2 NPs treatment. Overall, our study systematically reveals aquatic plants' responses to ENPs and provides a reference for building ecological treatment systems to purify wastewater containing ENPs.

  • RESEARCH ARTICLE
    Xiao Deng, Yixuan Chen, Yang Yang, Liang Peng, Luo Si, Qingru Zeng

    •Direct seeding (DS) method led to more distributed Cd in aerial parts of rice.

    •The Cd content was significantly higher in brown rice with planting mode of DS.

    •Using DS lessened the Fe plaque covering the root surface in all growth stages.

    •Transplantation mode should be considered as a priority in Cd-contaminated areas.

    Global rice production practices have gradually changed from a reliance on transplanting to direct seeding. Yet how this shift may alter cadmium (Cd) accumulation in rice is poorly known. Here we conducted field experiments with two rice genotypes cultivars that were planted using three methods: via direct seeding (DS), seedling throwing (ST), and manual transplanting (MT). Rice samples were collected during four growth stages. The formation and distribution of iron plaque were analyzed using DCB (dithionite-citrate-bicarbonate) extractions and observed under micro-XRF (micro X-ray fluorescence). The results revealed that, in each growth stage, DS rice was more apt to harbor Cd distributed in the plant’s aerial parts, and the Cd concentration of brown rice from DS was 21.8%–43.3% significantly higher than those from ST and MT at maturity stage (p<0.05). During the vegetative stages, the Cd uptake percentage was higher in DS than MT rice, and those plants arising from the DS method were capable of absorbing more Cd earlier in their growth and development. Conversely, using DS decreased the amount of iron plaque covering the root surface in every growth stage, especially in the critical period of Cd accumulation, such that the roots’ middle areas were distinguished by a near-complete absence of iron plaque, thus weakening its role as an effective barrier to Cd uptake from soil. Collectively, this study demonstrated that implementing the DS mode of planting will increase Cd’s distribution in the aboveground parts of rice, and heightening the risk of Cd contamination in grain.

  • RESEARCH ARTICLE
    Qiyun Zhu, April Gu, Dan Li, Tianmu Zhang, Lunhong Xiang, Miao He

    • UV-vis absorption analyzer was applied in drainage type online recognition.

    • The UV-vis spectrum of four drainage types were collected and evaluated.

    • A convolutional neural network with multiple derivative inputs was established.

    • Effects of different network structures and input contents were compared.

    Optimizing sewage collection is important for water pollution control and wastewater treatment plants quality and efficiency improvement. Currently, the urban drainage pipeline network is upgrading to improve its classification and collection ability. However, there is a lack of efficient online monitoring and identification technology. UV-visible absorption spectrum probe is considered as a potential monitoring method due to its small size, reagent-free and fast detection. Because the performance parameters of probe like optic resolution, dynamic interval and signal-to-noise ratio are weak and high turbidity of sewage raises the noise level, it is necessary to extract shape features from the turbidity disturbed drainage spectrum for classification purposes. In this study, drainage network samples were online collected and tested, and four types were labeled according to sample sites and environment situation. Derivative spectrum were adopted to amplify the shape features, while convolutional neural network algorithm was established to conduct nonlinear spectrum classification. Influence of input and network structure on classification accuracy was compared. Original spectrum, first-order derivative spectrum and a combination of both were set to be three different inputs. Artificial neural network with or without convolutional layer were set be two different network structures. The results revealed a convolutional neural network combined with inputs of first and zero-order derivatives was proposed to have the best classification effect on domestic sewage, mixed rainwater, rainwater and industrial sewage. The recognition rate of industrial wastewater was 100%, and the recognition rate of domestic sewage and rainwater mixing system were over 90%.

  • RESEARCH ARTICLE
    Hailan Wang, Baoyu Gao, Li’an Hou, Ho Kyong Shon, Qinyan Yue, Zhining Wang

    • The boron concentration in diluted DS can satisfy the irrigation water standard.

    • The boron concentration in diluted DS equaled that in two-pass RO permeate.

    • FDFO process SEC was slightly lower than the 2nd pass RO SEC.

    • FDFO has potential as an alternative to 2nd pass RO for irrigation water production.

    Agriculture is the largest consumer of freshwater. Desalinated seawater is an important alternative water source for sustainable irrigation. However, some issues of the current desalination technology hinder its use for agriculture irrigation, including low boron removal and high energy consumption. This study systematically explored the feasibility of employing fertilizer drawn forward osmosis (FDFO) as an alternative to 2nd pass reverse osmosis (RO) by considering the boron removal performance and specific energy consumption (SEC). Different operating conditions were investigated, such as the boron and NaCl concentrations in feed solution (FS), draw solution (DS) concentration, pH, the volume ratio of FS to DS, membrane orientation, flow rate, and operating temperature. The results indicated that a low boron concentration in FS and high pH DS (pH= 11.0) decreased the boron solute flux, and led to low final boron concentration in the DS. The other operating conditions had negligible influence on the final DS boron concentration. Also, a lower flow rate and higher specific water flux with certain permeate water volumes were conducive to reducing the SEC of the FDFO process. Overall, our study paves a new way of using FDFO in irrigation, which avoids the phytotoxicity and human health risk of boron. The results show the potential of FDFO as an alternative to 2nd pass RO for irrigation water production.

  • RESEARCH ARTICLE
    Farasat Ali, Ghulam Jilani, Leilei Bai, Chunliu Wang, Linqi Tian, Helong Jiang

    • Sediment desiccation alters morphological characteristics of aquatic sediment.

    • Alternation in morphological properties of sediment limiting root characteristics.

    • Fibrous-rooted macrophytes root properties extra favor nutrients removal.

    • Thick-rooted macrophytes exhibit higher life-span in two sediment types.

    Purpose of the current study was to investigate the effects of constantly wet and dried-rewetted sediments on root functional traits of emerged macrophytes and their nutrients removal abilities. It is based on the hypothesis that root characteristics and nutrients removal abilities of plants will be altered in the course of sediment desiccation. Four emerged macrophytes including two fibrous-root plants (Canna indica and Acorus calamus) and two thick-root plants (Alocasia cucullata and Aglaonema commutatum) were investigated for their root functional traits and rhizoperformance in both wet and dried-rewetted sediments. Results showed that sediment desiccation followed by rewetting substantially altered the root functional traits (root surface area, radial oxygen loss, and root activity) of plants due to adverse changes in morphological characteristics (porosity, bulk density, particle density) of dried-rewetted sediments than by wet sediments. Consequently, limited plants growth and removal of nitrogen (N), phosphorus (P) and dissolved organic carbon (DOC) were recorded in dried-rewetted sediments and their pore water than in wet sediments. Radial oxygen loss from plant roots correlated positively with root functional traits, plants growth, and removal of N, P and DOC from pore water and sediment in both sediment types. Among the macrophyte species, the fibrous-root plants having advantages root functional traits, greatly influenced the rhizospheric conditions (pH, dissolved oxygen and redox potential), and demonstrated higher N, P and DOC reduction from both sediment types. While, the thick-rooted plants with thick diameter roots (D > 1 mm) and higher rhizome exhibited longer life-span in both sediment types.

  • REVIEW ARTICLE
    Shaoyi Xu, Xiaolong Wu, Huijie Lu

    • 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.

  • RESEARCH ARTICLE
    Yingwu Wang, Ping Ning, Ruheng Zhao, Kai Li, Chi Wang, Xin Sun, Xin Song, Qiang Lin

    • Cu0.15-ACF performs the best for H2S and PH3 simultaneous removal.

    • 550°C and 90°C are separately calcination and reaction temperatures.

    • The reason why Cu0.15/ACF shows better performance was found.

    • The accumulation of H2PO4 and SO42−(H2O)6 is the deactivation cause of Cu0.15/ACF.

    Poisonous gases, such as H2S and PH3, produced by industrial production harm humans and damage the environment. In this study, H2S and PH3 were simultaneously removed at low temperature by modified activated carbon fiber (ACF) catalysts. We have considered the active metal type, content, precursor, calcination, and reaction temperature. Experimental results exhibited that ACF could best perform by loading 15% Cu from nitrate. The optimized calcination temperature and reaction temperature separately were 550°C and 90°C. Under these conditions, the most removal capacity could reach 69.7 mg/g and 132.1 mg/g, respectively. Characterization results showed that moderate calcination temperature (550°C) is suitable for the formation of the copper element on the surface of ACF, lower or higher temperature will generate more cuprous oxide. Although both can exhibit catalytic activity, the role of the copper element is significantly greater. Due to the exceptional dispersibility of copper (oxide), the ACF can still maintain the advantages of larger specific surface area and pore volume after loading copper, which is the main reason for better performance of related catalysts. Finally, increasing the copper loading amount can significantly increase the crystallinity and particle size of copper (oxide) on the ACF, thereby improving its catalytic performance. In situ IR found that the reason for the deactivation of the catalyst should be the accumulation of generated H2PO4 and SO42−(H2O)6 which could poison the catalyst.

  • RESEARCH ARTICLE
    Yuqing Xu, Zedong Lu, Wenjun Sun, Xiaohui Zhang

    • Pore structure affects biologically activated carbon performance.

    • Pore structure determines organic matter (OM) removal mechanism.

    • Microbial community structure is related to pore structure and OM removal.

    Optimizing the characteristics of granular activated carbon (GAC) can improve the performance of biologically activated carbon (BAC) filters, and iodine value has always been the principal index for GAC selection. However, in this study, among three types of GAC treating the same humic acid-contaminated water, one had an iodine value 35% lower than the other two, but the dissolved organic carbon removal efficiency of its BAC was less than 5% away from the others. Iodine value was found to influence the removal of different organic fractions instead of the total removal efficiency. Based on the removal and biological characteristics, two possible mechanisms of organic matter removal during steady-state were suggested. For GAC with poor micropore volume and iodine value, high molecular weight substances (3500–9000 Da) were removed mainly through degradation by microorganisms, and the biodegraded organics (soluble microbial by-products,<3500 Da) were released because of the low adsorption capacity of activated carbon. For GAC with higher micropore volume and iodine value, organics with low molecular weight (<3500 Da) were more easily removed, first being adsorbed by micropores and then biodegraded by the biofilm. The biomass was determined by the pore volume with pore diameters greater than 100 μm, but did not correspond to the removal efficiency. Nevertheless, the microbial community structure was coordinate with both the pore structure and the organic removal characteristics. The findings provide a theoretical basis for selecting GAC for the BAC process based on its pore structure.

  • RESEARCH ARTICLE
    Peidong Su, Xiangyu Gao, Junke Zhang, Ridha Djellabi, Bo Yang, Qi Wu, Zhen Wen

    • Mechanochemical treatment reduced the calcination temperature for biochar synthesis.

    • Biochar is converted to graphite after mechanochemical treatment.

    • Biochar was reduced to nanoscale after mechanochemical treatment.

    Biochar (BC) has been extensively studied as adsorbent for the treatment of water pollution. Despite the distinct advantages, the high calcination temperature and low adsorption capacity of pristine BC limit its practical applications. Most of the former studies focused on the structure and/or surface modification to improve the adsorption capacity of BC. However, the harsh experiment conditions involved in the biochar modification limited the application in industrial level. Herein, we introduced mechanical treatment into BC preparation to reduce the calcination temperature and improve the adsorption capacity simultaneously. The results indicated that the calcination temperature was reduced and the adsorption capacity of the treated BC was improved after mechanochemical treatment. Characterization of the samples disclosed that BCs were graphitized with the particle size reduced to nanoscale after treatment. Adsorption tests indicated that the mechanochemically treated BCs showed much better removal performance of organic contaminants than that of pristine BCs. For instance, among four pristine BCs (BC600, BC700, BC800, and BC900), only BC900 has strong adsorption capacity for MB, while BC600 has low adsorption capacity (1.2 mg/g). By comparison, the adsorption capacity of MB increased greatly to 173.96 mg/g by BC600-500/1 (treated at 500 r/min for 1 hour). To optimize the mechanochemical treatment, the effects of rotation speed and agitation duration were also investigated.

  • RESEARCH ARTICLE
    Jingke Song, Chenyang Li, Xuejiang Wang, Songsong Zhi, Xin Wang, Jianhui Sun

    • Bi doping in TiO2 enhanced the separation of photo-generated electron-hole.

    • The performance of photocatalytic degradation of MC-LR was improved.

    • Coexisting substances have no influence on algal removal performance.

    • The key reactive oxygen species were h+ and OH in the photocatalytic process.

    The increase in occurrence and severity of cyanobacteria blooms is causing increasing concern; moreover, human and animal health is affected by the toxic effects of Microcystin-LR released into the water. In this paper, a floating photocatalyst for the photocatalytic inactivation of the harmful algae Microcystis aeruginosa (M. aeruginosa) was prepared using a simple sol-gel method, i.e., coating g-C3N4 coupled with Bi-doped TiO2 on Al2O3-modified expanded perlite (CBTA for short). The impact of different molar ratios of Bi/Ti on CBTA was considered. The results indicated that Bi doping in TiO2 inhibited photogenerated electron-hole pair recombination. With 6 h of visible light illumination, 75.9% of M. aeruginosa (initial concentration= 2.7 × 106 cells/L) and 83.7% of Microcystin-LR (initial concentration= 100 μg/L) could be removed with the addition of 2 g/L CBTA-1% (i.e., Bi/Ti molar ratio= 1%). The key reactive oxygen species (ROSs) in the photocatalytic inactivation process are h+ and OH. The induction of the Bi4+/Bi3+ species by the incorporation of Bi could narrow the bandgap of TiO2, trap electrons, and enhance the stability of CBTA-1% in the solutions with coexisting environmental substances.

  • RESEARCH ARTICLE
    Mohammadtaghi Vakili, Wen Qiu, Giovanni Cagnetta, Jun Huang, Gang Yu

    • Solvent-free chitosan oxidation is obtained by rapid mechanochemical reaction.

    • Different oxidants induce very diverse physicochemical changes on chitosan.

    • Oxidized chitosan with persulfate or percarbonate has improved adsorption capacity.

    • Uptake on oxidized chitosan with persulfate is 125-fold faster than on pristine one.

    Oxidation has been profitably utilized to improve some properties of chitosan. However, only solvent-based oxidation procedures have been proposed so far, which are hardly feasible at industrial scale in an economic way because of product recovery cost. In this study, a solvent-free, rapid, and effective oxidation method is proposed. It is based on direct solid-state reaction between chitosan and oxidant powder in a mechanochemical reactor. Results prove that by short high energy ball milling (<3 h) it is possible to achieve diverse physicochemical modifications employing different reagents. Apart from polysaccharidic chain shortening, persulfate provokes high amorphization and induces formation of ketonic groups; percarbonate heightens deacetylation degree, preserving in part crystallinity; calcium peroxide merely deprotonates amino groups and increases amorphization degree. Adsorption tests with the azo-dye reactive red 2 show that adsorption capacity of chitosan co-milled with persulfate (974 mg/g milled product), which is the best performing adsorbent, is twice that of pristine chitosan, while adsorption rate is outstandingly boosted (125 times).

  • FEATURE ARTICLE
    Caihong Huang, Zhurui Tang, Beidou Xi, Wenbing Tan, Wei Guo, Weixia Wu, Caiyun Ma

    • ARGs were detected in livestock manure, sludge, food waste and fermentation dregs.

    • The succession of microbial community is an important factor affecting ARGs.

    • Horizontal transfer mechanism of ARGs during composting should be further studied.

    Antibiotic resistance genes (ARGs) have been diffusely detected in several kinds of organic solid waste, such as livestock manure, sludge, antibiotic fermentation residues, and food waste, thus attracting great attention. Aerobic composting, which is an effective, harmless treatment method for organic solid waste to promote recycling, has been identified to also aid in ARG reduction. However, the effect of composting in removing ARGs from organic solid waste has recently become controversial. Thus, this article summarizes and reviews the research on ARGs in relation to composting in the past 5 years. ARGs in organic solid waste could spread in different environmental media, including soil and the atmosphere, which could widen environmental risks. However, the conventional composting technology had limited effect on ARGs removal from organic solid waste. Improved composting processes, such as hyperthermophilic temperature composting, could effectively remove ARGs, and the HGT of ARGs and the microbial communities are identified as vital influencing factors. Currently, during the composting process, ARGs were mainly affected by three response pathways, (I) “Microenvironment-ARGs”; (II) “Microenvironment-microorganisms-ARGs”; (III) “Microorganisms-horizontal gene transfer-ARGs”, respectively. Response pathway II had been studied the most which was believed that microbial community was an important factor affecting ARGs. In response pathway III, mainly believed that MGEs played an important role and paid less attention to eARGs. Further research on the role and impact of eARGs in ARGs may be considered in the future. It aims to provide support for further research on environmental risk control of ARGs in organic solid waste.

  • REVIEW ARTICLE
    Noshan Bhattarai, Shuxiao Wang, Yuepeng Pan, Qingcheng Xu, Yanlin Zhang, Yunhua Chang, Yunting Fang

    • Challenges in sampling of NH3 sources for d15N analysis are highlighted.

    • Uncertainties in the isotope-based source apportionment of NH3 and NH4+ are outlined.

    • Characterizing dynamic isotopic fractionation may reduce uncertainties of NHx science.

    Agricultural sources and non-agricultural emissions contribute to gaseous ammonia (NH3) that plays a vital role in severe haze formation. Qualitative and quantitative contributions of these sources to ambient PM2.5 (particulate matter with an aerodynamic equivalent diameter below 2.5 µm) concentrations remains uncertain. Stable nitrogen isotopic composition (δ15N) of NH3 and NH4+15N(NH3) and δ15N(NH4+), respectively) can yield valuable information about its sources and associated processes. This review provides an overview of the recent progress in analytical techniques for δ15N(NH3) and δ15N(NH4+) measurement, sampling of atmospheric NH3 and NH4+ in the ambient air and their sources signature (e.g., agricultural vs. fossil fuel), and isotope-based source apportionment of NH3 in urban atmosphere. This study highlights that collecting sample that are fully representative of emission sources remains a challenge in fingerprinting δ15N(NH3) values of NH3 emission sources. Furthermore, isotopic fractionation during NH3 gas-to-particle conversion under varying ambient field conditions (e.g., relative humidity, particle pH, temperature) remains unclear, which indicates more field and laboratory studies to validate theoretically predicted isotopic fractionation are required. Thus, this study concludes that lack of refined δ15N(NH3) fingerprints and full understanding of isotopic fractionation during aerosol formation in a laboratory and field conditions is a limitation for isotope-based source apportionment of NH3. More experimental work (in chamber studies) and theoretical estimations in combinations of field verification are necessary in characterizing isotopic fractionation under various environmental and atmospheric neutralization conditions, which would help to better interpret isotopic data and our understanding on NHx (NH3 + NH4+) dynamics in the atmosphere.

  • VIEWS & COMMENTS
    Elvis Genbo Xu, Zhiyong Jason Ren
  • REVIEW ARTICLE
    Elham Abaie, Limeimei Xu, Yue-xiao Shen

    •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.

  • RESEARCH ARTICLE
    Yukun Zhang, Shuying Wang, Shengbo Gu, Liang Zhang, Yijun Dong, Lei Jiang, Wei Fan, Yongzhen Peng

    • Actual SAORs was determined using MLVSS and temperature.

    • Measured SAOR decreased with increasing MLVSS 1.1‒8.7 g/L.

    • Temperature coefficient (θ) decreased with increasing MLVSS.

    • Nitrification process was dynamically simulated based on laboratory-scale SBR tests.

    • A modified model was successfully validated in pilot-scale SBR systems.

    Measurement and predicted variations of ammonia oxidation rate (AOR) are critical for the optimization of biological nitrogen removal, however, it is difficult to predict accurate AOR based on current models. In this study, a modified model was developed to predict AOR based on laboratory-scale tests and verified through pilot-scale tests. In biological nitrogen removal reactors, the specific ammonia oxidation rate (SAOR) was affected by both mixed liquor volatile suspended solids (MLVSS) concentration and temperature. When MLVSS increased 1.6, 4.2, and 7.1-fold (1.3‒8.9 g/L, at 20°C), the measured SAOR decreased by 21%, 49%, and 56%, respectively. Thereby, the estimated SAOR was suggested to modify when MLVSS changed through a power equation fitting. In addition, temperature coefficient (θ) was modified based on MLVSS concentration. These results suggested that the prediction of variations ammonia oxidation rate in real wastewater treatment system could be more accurate when considering the effect of MLVSS variations on SAOR.

  • RESEARCH ARTICLE
    Xinyu Wang, Ye Jin, Weirui Chen, Ruini Zou, Jinxin Xie, Yiming Tang, Xukai Li, Laisheng Li

    •CeOx/GF-EP process had the better degradation efficiency than GF-EP process.

    •CeOx/GF-EP process had the flexible application in the pH range from 5.0 to 9.0.

    •CeOx could enhance surface hydrophilicity and reduce the charge-transfer resistance.

    •The interfacial electron transfer process was revealed.

    E-peroxone (EP) was one of the most attractive AOPs for removing refractory organic compounds from water, but the high energy consumption for in situ generating H2O2 and its low reaction efficiency for activating O3 under acidic conditions made the obstacles for its practical application. In this study, cerium oxide was loaded on the surface of graphite felt (GF) by the hydrothermal method to construct the efficient electrode (CeOx/GF) for mineralizing carbamazepine (CBZ) via EP process. CeOx/GF was an efficient cathode, which led to 69.4% TOC removal in CeOx/GF-EP process with current intensity of 10 mA in 60 min. Moreover, CeOx/GF had the flexible application in the pH range from 5.0 to 9.0, TOC removal had no obvious decline with decrease of pH. Comparative characterizations showed that CeOx could enhance surface hydrophilicity and reduce the charge-transfer resistance of GF. About 5.4 mg/L H2O2 generated in CeOx/GF-EP process, which was 2.1 times as that in GF-EP process. The greater ozone utility was also found in CeOx/GF-EP process. More O3 was activated into hydroxyl radicals, which accounted for the mineralization of CBZ. An interfacial electron transfer process was revealed, which involved the function of oxygen vacancies and Ce3+/Ce4+ redox cycle. CeOx/GF had the good recycling property in fifth times’ use.

  • RESEARCH ARTICLE
    Fei Xie, Bowei Zhao, Ying Cui, Xiao Ma, Xiao Zhang, Xiuping Yue

    • MFC promoted the nitrogen removal of anammox with Fe-C micro-electrolysis.

    • Reutilize pyrolysis waste tire as micro-electrolysis and electrode materials.

    • Total nitrogen removal efficiency of modified MFC increased to 85.00%.

    Candidatus kuenenia and SM1A02 were major genera responsible for nitrogen removal.

    In this study, microbial fuel cells (MFCs) were explored to promote the nitrogen removal performance of combined anaerobic ammonium oxidation (anammox) and Fe-C micro-electrolysis (CAE) systems. The average total nitrogen (TN) removal efficiency of the modified MFC system was 85.00%, while that of the anammox system was 62.16%. Additionally, the effective operation time of this system increased from six (CAE system alone) to over 50 days, significantly promoting TN removal. The enhanced performance could be attributed to the electron transferred from the anode to the cathode, which aided in reducing nitrate/nitrite in denitrification. The H+ released through the proton exchange membrane caused a decrease in the pH, facilitating Fe corrosion. The pyrolyzed waste tire used as the cathode could immobilize microorganisms, enhance electron transport, and produce a natural Fe-C micro-electrolysis system. According to the microbial community analysis, Candidatus kuenenia was the major genus involved in the anammox process. Furthermore, the SM1A02 genus exhibited the highest abundance and was enriched the fastest, and could be a novel potential strain that aids the anammox process.

  • RESEARCH ARTICLE
    Shiguan Yang, Xinrui Fan, Ji Liu, Wei Zhao, Bin Hu, Qiang Lu

    • Possible formation pathways of H2S were revealed in thiophene pyrolysis.

    • The influence of hydrogen radicals on thiophene pyrolysis was examined.

    • Thiophene decomposition starts with hydrogen transfer between adjacent C atoms.

    • The presence of hydrogen radicals significantly promotes the formation of H2S.

    Pyrolysis is an efficient and economical method for the utilization of waste rubber, but the high sulfur content limits its industrial application. Currently, the migration and transformation of the element S during pyrolysis of waste rubber is far from well known. In this work, a density functional theory (DFT) method was employed to explore the possible formation pathways of H2S and its precursors (radicals HS· and S·) during the pyrolysis of thiophene, which is an important primary pyrolytic product of rubber. In particular, the influence of reactive hydrogen radicals was carefully investigated in the thiophene pyrolysis process. The calculation results indicate that the decomposition of thiophene tends to be initiated by hydrogen transfer between adjacent carbon atoms, which needs to overcome an energy barrier of 312.4 kJ/mol. The optimal pathway to generate H2S in thiophene pyrolysis involves initial H migration and S-C bond cleavage, with an overall energy barrier of 525.8 kJ/mol. In addition, a thiol intermediate that bears unsaturated C-C bonds is essential for thiophene pyrolysis to generate H2S, which exists in multiple critical reaction pathways. Moreover, the presence of hydrogen radicals significantly changes the decomposition patterns and reduces the energy barriers for thiophene decomposition, thus promoting the formation of H2S. The current work on H2S formation from thiophene can provide some theoretical support to explore clean utilization technologies for waste rubber.

  • RESEARCH ARTICLE
    Tao Liu, Yudong Song, Zhiqiang Shen, Yuexi Zhou

    • The inhibition of the main organic pollutions in CMW was demonstrated.

    • Variations of AK and BK showed a high correlation with the SAA of Ac and n-Bu.

    • The inhibitory degree was in the order of Ac>n-Bu for individual toxicants.

    • Biodegradation products of the main toxicants were analyzed.

    This work aims to investigate the inhibitory effect of crotonaldehyde manufacture wastewater (CMW) on biological acidification. To reveal the inhibitory effect of wastewater to the anaerobic granular sludge (AnGS), variations of the specific acidogenic activity (SAA) and activities of key enzymes were investigated. The results indicated that the dosage of CMW causing a 50% effect concentration (EC50) on the activity of total volatile fatty acids (TVFA) production was 380 mg COD/g VSS. The inhibitory effect of individual toxicants in CMW on the activity of TVFA production were in the order of crotonaldehyde>ethyl sorbate>(E,E)-2,4-hexadienal, and their inhibitory degrees on individual VFA products were acetic acid (Ac)>n-butyric acid (n-Bu), which could correspond to the variations in the activities of acetate kinase (AK) and butyrate kinase (BK). Furthermore, the combined effect of three toxicants on the activity of TVFA production was significantly higher than that of any individual toxicant, and the contribution of the relative toxicity to CMW was 77.27%. Additionally, the biodegradation products of the main toxicants indicated that the removal of crotonaldehyde and (E,E)-2,4-hexadienal was primarily due to the hydrogenation of alkene and aldehyde and the oxidation of aldehyde. Nevertheless, the removal of ethyl sorbate was primarily based on adsorption. In conclusion, biological acidification has a limited ability to treatment CMW, therefore, a further pretreatment technology should be used to remove the main toxicant of wastewater.

  • RESEARCH ARTICLE
    Congren Yang, Xianlai Zeng, Haodong Li, Zuyuan Tian, Wei Liu, Wenqing Qin, Jinhui Li

    • US tin use decreases as the GDP value added by manufacturing sector increases.

    • Global and China’s tin use increases as the GDP added by manufacturing increases.

    • A sigmoid curve can fit the US tin use data well.

    • US tin use patterns is not due to the finite tin reserves or resources.

    • Policies, substitutions, etc. play key roles in the changing tin use patterns.

    Tin is of key importance to daily life and national security; it is considered an essential industrial metal. The United States (US) is the world’s largest economy and consumer of natural resources. Therefore, the analysis of historical tin use in the US is helpful for understanding future tin use trends in the world as a whole and in developing countries. Time series analysis, regression analysis with GDP or GDP/capita, and historical data fitted with logistic and Gompertz models are employed in this study. Historical tin use in the US shows three stages—increase-constant-decrease, as GDP per capita has increased. Tin use in the US is negatively correlated with the GDP value added by the manufacturing sector, while the use of tin worldwide and in China continues to increase along with the GDP value added by the manufacturing sector. Although a sigmoid curve can fit the US tin use data well, that use is not directly related to the limited tin reserves or resources. Rather, policies, economic restructuring, substitutions, new end-use markets, etc. have played key roles in the changing tin use patterns. This work contributes to understanding future tin use at both the global and national levels: tin use will continue to increase with GDP at the global level, but use patterns of tin at the national level can be changed through human intervention.

  • RESEARCH ARTICLE
    Jiqin Wang, Xiaoxia Yi, Xiangfei Zeng, Shuyuan Chen, Rui Wang, Jiancheng Shu, Mengjun Chen, Zhengxue Xiao

    • Copper fractal growth was observed during WPCBs recycling by slurry electrolysis.

    • Dendrites fractal growth could be controlled by additive during electrodeposition.

    • Additive was proved to be an effective way to refine the copper crystal.

    • These findings contribute to enrich the study of slurry electrolysis.

    Superfine copper particles could be directly prepared from waste printed circuit boards by slurry electrolysis. Meanwhile, copper fractal growth could be observed. To better understand this phenomenon, the factors that affect copper dendrites in a point-cathode system were discussed in detail. These results showed that the fractal degree of copper dendrites increased as the increase of applied voltage and the decrease of copper sulfate and gelatin concentrations. Sodium lauryl sulfate and hydrochloric acid concentrations could not significantly impact the fractal degree of copper dendrites, while gelatin concentration could. The minimum copper fractal dimension was 1.069 when gelatin and copper sulfate concentration was 120 mg/L and 0.1 mol/L, respectively with an applied voltage of 11 V. Moreover, the results diffusion-limited aggregation model demonstrated that particle translational speed, particle numbers and binding probability significantly affected copper dendrite patterns. The scanning electron microscopy results indicated that the three additives greatly affected the refinement of the copper crystal. These findings contribute to enrich the theoretical study on metals recovery from e-waste by slurry electrolysis.

  • RESEARCH ARTICLE
    Fanling Meng, Yunxue Xia, Jianshuai Zhang, Dong Qiu, Yaozhu Chu, Yuanyuan Tang

    • Cu and Cr can be mostly incorporated into CuFexAlyCr2xyO4 with a spinel structure.

    • Spinel phase is the most crucial structure for Cu and Cr co-stabilization.

    • Compared to Al, Fe and Cr are easier to be incorporated into the spinel structure.

    • ‘Waste-to-resource’ by thermal process at attainable temperatures can be achieved.

    Chromium slag usually contains various heavy metals, making its safe treatment difficult. Glass-ceramic sintering has been applied to resolve this issue and emerged as an effective method for metal immobilization by incorporating heavy metals into stable crystal structures. Currently, there is limited knowledge about the reaction pathways adopted by multiple heavy metals and the co-stabilization functions of the crystal structure. To study the Cu/Cr co-stabilization mechanisms during thermal treatment, a simulated system was prepared using a mixture with a molar ratio of Al2O3:Fe2O3:Cr2O3:CuO= 1:1:1:3. The samples were sintered at temperatures 600–1300°C followed by intensive analysis of phase constitutions and microstructure development. A spinel phase (CuFexAlyCr2xyO4) started to generate at 700°C and the incorporation of Cu/Cr into the spinel largely complete at 900°C, although the spinel peak intensity continued increasing slightly at temperatures above 900°C. Fe2O3/Cr2O3 was more easily incorporated into the spinel at lower temperatures, while more Al2O3 was gradually incorporated into the spinel at higher temperatures. Additionally, sintered sample microstructures became more condensed and smoother with increased sintering temperature. Cu / Cr leachability substantially decreased after Cu/Cr incorporation into the spinel phase at elevated temperatures. At 600°C, the leached ratios for Cu and Cr were 6.28% and 0.65%, respectively. When sintering temperature was increased to 1300°C, the leached ratios for all metal components in the system were below 0.2%. This study proposes a sustainable method for managing Cu/Cr co-exist slag at reasonable temperatures.

  • RESEARCH ARTICLE
    Yangyang Liang, Qingbin Song, Naiqi Wu, Jinhui Li, Yuan Zhong, Wenlei Zeng

    • 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.

  • RESEARCH ARTICLE
    Mengjun Chen, Oladele A. Ogunseitan

    • 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.

  • RESEARCH ARTICLE
    Fu Chen, Qi Zhang, Jing Ma, Qianlin Zhu, Yifei Wang, Huagen Liang

    • A new EK-BIO technology was developed to decontaminate e-waste contaminated soil.

    • Adding sodium citrate in electrolyte was a good choice for decontaminating the soil.

    • The system has good performance with low cost.

    This work investigates the influence of electrokinetic-bioremediation (EK-BIO) on remediating soil polluted by persistent organic pollutants (POPs) and heavy metals (mainly Cu, Pb and Ni), originated from electronic waste recycling activity. The results demonstrate that most of POPs and metals were removed from the soil. More than 60% of metals and 90% of POPs in the soil were removed after a 30-day EK-BIO remediation assisted by citrate. A citrate sodium concentration of 0.02 g/L was deemed to be suitable because higher citrate did not significantly improve treatment performance whereas increasing dosage consumption. Citrate increased soil electrical current and electroosmotic flow. After remediation, metal residues mainly existed in stable and low-toxic states, which could effectively lower the potential hazard of toxic metals to the surrounding environment and organisms. EK-BIO treatment influenced soil microbial counts, dehydrogenase activity and community structure.

  • RESEARCH ARTICLE
    Yanxiao Si, Fang Zhang, Hong Chen, Guanghe Li, Haichuan Zhang, Dun Liu

    • With the same charge, current density had little effect on As(III) removal in ACEC.

    • ACEC had the lowest energy consumption compared with EC/O2 or EC/N2.

    • There was a trade-off relationship between energy consumption and removal time.

    • The ·OH concentration in ACEC was 1.5 times of that in the EC/O2 system.

    Naturally occurring arsenic enrichment in groundwater poses a huge threat to human health. Air cathode electrocoagulation (ACEC) has recently been proposed to enhance As(III) oxidation and lower energy consumption. In this study, ACEC, EC/O2 and EC/N2 were evaluated with different current densities from 1 to 8 mA/cm2 to investigate the effect on As(III) removal in different redox environments. Current density had no appreciable effect on arsenic removal efficiency given the same charge in ACEC because the concentration ratio of Fe/H2O2 under different current densities remained stable. However, in EC/O2 and EC/N2, As(III) removal was inhibited at higher current densities (4–8 mA/cm2), likely because more Fe(II) competed with As(III) for the oxidant, leading to less effective oxidation of As(III). In all EC systems, the ·OH units generated per power consumption reached the highest value at the lowest current density. Compared with other EC systems, the ACEC system showed lower energy consumption at all current densities due to the low energy consumption of the electrode reaction and more free radical generation. A lower current density saved more energy at the expense of time, showing the trade-off relationship between energy consumption and removal time. The operation costs for As(III) removal under optimal conditions were calculated as 0.028 $/m3 for ACEC, 0.030 $/m3 for EC/O2, and 0.085 $/m3 for EC/N2

  • RESEARCH ARTICLE
    Zongqun Chen, Wei Jin, Hailong Yin, Mengqi Han, Zuxin Xu

    • A way for overflow control based on on-site coagulation/flocculation was proposed.

    • Coagulant and flocculant dose were optimized based on pollutant removal performance.

    • Settling time of 5 min is enough in a proper transmission distance.

    • Fast removal of particulate pollutants could be achieved under varied flow.

    The pollution caused by wet weather overflow in urban drainage systems is a main factor causing blackening an odorization of urban rivers. The conventional overflow treatment based on coagulation/flocculation in terminal drainage systems requires relatively large space and long retention time demand that makes it not applicable in crowded urban drainage systems or under heavy rains. On-site coagulation/flocculation in terminal drainage pipes was proposed in this study which was aimed to transfer the coagulation/flocculation process to the inside of pipes at the terminal drainage system to save space and reduce the retention time of the coagulation/flocculation process. The optimized dose of chemicals was studied first which was 80 mg/L of coagulant and 0.8 mg/L of flocculant. Settling for only 5 min can remove most of the pollutants at 406.5 m of transmission distance. In addition, the relation of wet weather overflow rate and concentration of pollution load on the on-site coagulation/flocculation process was investigated, which indicated that high removal of pollutant was gained at a large range of flow velocity and pollutant concentration. Finally, the study confirmed electric neutralization, bridging, and net capture as the major mechanisms in this process, and further optimization was proposed. The proposed process can reduce much turbidity, chemical oxygen demand, and total phosphorous, but hardly remove soluble ammonia and organics. This work provides scientific guidance to address wet weather overflow in terminal drainage pipes.