2023 Vol. 13, No. 4

Display Method:
Research trends and future prospects of constructed wetlands at home and abroad based on CiteSpace
HOU Yaojun, CHEN Qibin, WANG Chaoxu, WANG Yong, LI Zuochen, WANG Yawei, LI Yanan, CUI Jianguo
2023, 13(4): 1275-1286. doi: 10.12153/j.issn.1674-991X.20220788
Abstract(849) HTML (277) PDF(8408KB)(158)

Constructed wetlands have the advantages of low capital consumption and good treatment effect, etc., and it has been highly concerned by domestic and foreign scholars. The related research papers have grown significantly, but there is a relative lack of literature analysis in the field of constructed wetlands. The domestic and foreign papers on constructed wetlands in China National Knowledge Infrastructure (CNKI) core journal database and Web of Science (WoS) core collection database from 2000 to 2021 were statistically analyzed by the bibliometric methods using CiteSpace and other software. Based on the comparative analysis of the annual quantity of papers, publication countries, publication authors, research directions and research hotspot evolutions, the research trend differences at home and abroad were revealed. The results showed that from 2000 to 2021, the annual quantity of published papers on constructed wetlands research at home and abroad was on a rapid rise. The quantity of English papers published by Chinese scholars ranked first in the world in WoS core collection database. The main research direction in the field of foreign constructed wetlands also focused on the coupling of microbial fuel cell technology and the removal of emerging pollutants such as personal care products on the basis of traditional research. The main research direction in the field of domestic constructed wetlands revolved around four major categories of decontamination mechanism, decontamination efficiency, decontamination objects and their application. The use of gene sequencing technology to study constructed wetlands from a microscopic perspective, and the constructed wetland-microbial fuel cell coupling technology would be the research hotspots in the field of constructed wetlands in recent years. Constructed wetland technology had entered a mature stage, and was expected to be combined with more emerging fields in the future.

Design analysis of constructed wetlands for treatment of terminal effluent of wastewater treatment plants from technical standard perspective
MA Yuxin, CHEN Qibin, WANG Chaoxu, LI Zuochen, LI Weiqiang, SHEN Zhipeng, CUI Jianguo
2023, 13(4): 1287-1294. doi: 10.12153/j.issn.1674-991X.20220937
Abstract(350) HTML (905) PDF(955KB)(157)

The constructed wetlands (CWs) technology has been gradually applied to the upgrading and reconstruction of wastewater treatment plants (WWTPs) and the utilization of terminal effluent of WWTPs in China, and has become an important technical research field. Some national and local responsible departments and professional associations have promulgated and implemented several technical standards, which are used to guide and standardize the design and construction of CWs for treatment of terminal effluent of WWTPs. The application status of CWs projects for treatment of terminal effluent of WWTPs at home and abroad and the implementation of relevant technical standards guiding the design and construction of CWs were summarized, and the process selection and structure design parameters in the technical standards of CWs at different levels were compared and analyzed. By comparing the feasibility and economy of the carbon level control strategies of CWs and the accessibility of the actual project applications, it was found that the wetland structure optimization, process improvement and coupling process were the better strategies and pathways to optimize the design of CWs projects and enhance their nitrogen removal efficiency. Meanwhile, in order to ensure the safety and normal operation of CWs projects, it was suggested that the total water balance of wetlands should be calculated under the local hydrological conditions during the design of CWs projects. It was necessary to build a basic database based on substrates and aquatic plant selection, engineering operation monitoring and other aspects to strengthen the guiding role of technical standards in the whole life cycle of CWs.

Effect of external carbon addition on pollutants removal from the tail water of a sewage treatment plant by biochar-based subsurface flow constructed wetland
LIU Yongchao, CHEN Qibin, WANG Chaoxu, WANG Jiayong, SUN Zhaosen, ZHANG Yeguo, WEI Yang
2023, 13(4): 1295-1303. doi: 10.12153/j.issn.1674-991X.20220733
Abstract(341) HTML (188) PDF(4086KB)(73)

As a kind of multifunctional eco-friendly material, biochar has been widely used in sewage treatment by constructed wetlands in recent years, which can provide carbon source for heterotrophic denitrification and enhance nitrogen removal capacity of constructed wetland. To explore the effect of external carbon addition on deep purification of the tail water of a sewage treatment plant by biochar-based horizontal subsurface flow constructed wetland, two parallel indoor experimental units were set with quartz sand/almond shell biochar (volume ratio 7∶3) and quartz sand (the control) as the constructed wetland matrix, respectively. Moreover, in the later phase of operation, different C/N ratios were designed by external carbon addition and the operation modes of continuous flow and intermittent flow were adopted, respectively. Results showed that before external carbon addition, chemical oxygen demand (COD) removal rate of constructed wetland was negative, and total nitrogen (TN) and nitrate nitrogen (NO3 -N) removal rates continued to decrease during 41 days. However, COD removal rates of quartz sand and quartz sand/almond shell biochar units increased to 37.88%-90.44% and 73.60%-97.90%, respectively, and TN and NO3 -N removal rates also significantly increased after external carbon addition. The maximum removal rates of TN and NO3 -N in quartz sand/biochar unit were 65.61% and 74.20%, respectively, as the influent C/N ratio was increased to 8 by external carbon addition and the intermittent flow mode was running. Biochar addition increased the microbial biomass of the constructed wetland, and created the appropriate redox environment facilitating denitrification. Therefore, the removal rates of COD, TN, and NO3 -N of the wetland unit set with quartz sand/almond shell biochar increased by 5.66%-130.35%, 9.34%-54.03%, and 8.71%-63.04%, respectively, compared with the control. The external carbon addition and biochar application could be an effective measure to strengthen the denitrogenation efficiency of constructed wetland for tail water purification of sewage treatment plants.

Measurement of the development level and spatial-temporal differences of the National Ecological Civilization Construction Demonstration Areas in the Yellow River basin
XIONG Xiangyan, HAN Yongwei, MENG Xiaojie, LIU Lixiang, WANG Dewang
2023, 13(4): 1304-1314. doi: 10.12153/j.issn.1674-991X.20220805
Abstract(248) HTML (156) PDF(5140KB)(39)

Exploring the level, development trends and spatial differences of ecological civilization construction in the Yellow River basin has important guidance and reference significance for further advancing the construction of ecological civilization in the Yellow River basin. 21 indicators were selected from ecological background, green economy, living environment and institutional culture to construct the eco-civilization construction indices system for measuring the development level in the Yellow River basin, and the development level and spatial-temporal differences of the 36 National Ecological Civilization Construction Demonstration Areas (NECCDAs) in the Yellow River basin were comprehensively analyzed. The results showed that three indicators related to water resources had high weights, including the proportion of water quality reaching or better than Class Ⅲ of Environmental Quality Standards for Surface Water (GB 3838-2002), water consumption per unit of GDP, urban sewage treatment rate, which weights were 0.095 3, 0.069 9 and 0.060 6, respectively. Water resource utilization and management was the key factor affecting the construction of ecological civilization construction in the Yellow River basin. From 2016 to 2019, the ecological civilization construction of the 36 NECCDAs in the Yellow River basin made some progress. The ecological civilization index increased from 0.645 3 to 0.735 4, while the growth rate of living environment, institutional culture, ecological background and green economy indicators were 31.22%, 14.08%, 12.68% and 6.69%, respectively. The ecological civilization construction level of the upstream and middle reaches was similar and higher than the downstream in the basin. The ecological civilization construction emphasis of different areas should be different. The ecological protection and systematic treatment of the upstream should be paid more attention to, the pollution control and living environment of the midstream need to be strengthened, and the degree of economic greening in the downstream should be further advanced.

Construction and optimization of ecological security pattern in the source regions of the Yangtze River and the Yellow River in northwestern Sichuan
LIU Siyuan, LUO Yong, YU Hui, WANG Xiao, LI Zihan, DONG Wei
2023, 13(4): 1315-1324. doi: 10.12153/j.issn.1674-991X.20220792
Abstract(290) HTML (214) PDF(14047KB)(39)

Taking biodiversity protection as the starting point, the northwestern Sichuan region with fragile ecological environment and frequent earthquakes was focused on, to realize the construction and optimization of the ecological safety network in Aba Tibetan and Qiang Autonomous Prefecture (Aba Prefecture in short). Elevation, slope, land cover, vegetation coverage, susceptibility to geological disasters, distance from water system, and distance from construction land were selected as resistance surface factors, and weighted superposition was used to construct a comprehensive resistance surface. Based on circuit theory and using Linkage Mapper tool, the ecological corridors of Aba Prefecture were built, ecological nodes were identified, and then the ecological security pattern of Aba Prefecture was optimized. The results showed that 18 ecological sources were identified, with an area of 28553.83 km2, showing the characteristics of concentrated distribution in the south and north, and sporadic distribution pattern in the east and west. 39 ecological corridors were constructed, and 61 ecological nodes were identified. There were 35 pinch points and 26 obstacle points, showing a spatial pattern of long corridors in the central and western regions and short corridors in the east. 8 core ecological sources, 4 central ecological sources, and 6 general ecological sources were planned, with 9 first-level ecological corridors, 22 second-level ecological corridors, and 8 third-level ecological corridors, and with 17 first-level ecological nodes and 44 second-level ecological nodes. The ecological sources and ecological corridors were scientifically graded, and the pattern optimization system of "two districts, two belts, and three corridors" was proposed. Some suggestions were also provided, including developing high-quality tourism, improving species migration channels, and connecting river corridors, so as to effectively maintain the ecological security pattern of the source regions of the Yellow River in northwest Sichuan.

Identification of priority areas for ecological restoration based on evaluation of ecosystem service bundles:taking Changsha City as an example
JIANG Hongbo, QIN Menglin, WANG Zhengqiang, LUO Dingding, WU Xinyu
2023, 13(4): 1325-1333. doi: 10.12153/j.issn.1674-991X.20220983
Abstract(277) HTML (292) PDF(8443KB)(48)

In order to quickly and effectively divide the priority of ecological restoration in Changsha City, a research framework for identifying the priority areas of territory space ecological restoration in the system of "ecosystem service bundle-urbanization intensity" was constructed. By using the calculation model of ecosystem service value, cluster analysis, linear regression model and spatial statistics, the ecosystem service bundles in the study area were indentified, as well as the evolution of the comprehensive service capacity of ecosystem service bundles and the change of urbanization intensity were analyzed by spatial statistics. The priority areas of ecological restoration in the study area were identified in turn, and ecological restoration and protection strategies were put forward. The results showed that urban expansion heavily encroached on the surrounding land, resulting in 1821 grids (accounting for 20.15%) of the four ecosystem service bundles in the main urban area of Changsha City changing their service bundle types from 2000 to 2020. Urban expansion destroyed the original ecological environment and landscape pattern, which made urbanization always have a negative impact on the development of ecosystem service bundles, and the negative impact became more and more obvious with the acceleration of urbanization. Ecological restoration priority areas were divided into five grades, and 2609 grids (accounting for 28.87%) needed ecological restoration, of which 13.53% were classified as Grade Ⅰ ecological restoration priority areas, with Grade Ⅱ accounting for 0.58%, Grade Ⅲ accounting for 12.53%, and Grade Ⅳ accounting for 2.23%. Priority areas of Grade Ⅰ and Ⅲ ecological restoration paid attention to the promotion of key ecosystem services, while those of Grade Ⅱ and Ⅳ ecological restoration and ecological protection areas paid attention to the maintenance of existing ecosystem services. This method could quickly locate the areas where high-speed urbanization and ecosystem damage occurred at the same time, and provide reference for the formulation of different zoning restoration strategies, which can improve the ecosystem service capacity and reduce the negative impact of urbanization on the ecosystem.

Identification of key areas for ecological protection and restoration of county territorial space based on ecological security pattern: a case study in Yihuang County of Fuzhou City
HUANG Liping, XIANG Fangfang, CHEN Rongqing
2023, 13(4): 1334-1344. doi: 10.12153/j.issn.1674-991X.20221028
Abstract(267) HTML (163) PDF(16185KB)(47)

In order to effectively realize the ecological protection and restoration of the territorial space, it is of great significance to explore the methods of constructing the ecological security pattern of the territorial space and identifying the key areas of ecological protection and restoration. Taking Yihuang County of Fuzhou City as an example, based on the basic framework of "ecological source-landscape resistance surface-ecological corridor", the ecological security pattern of territorial space was constructed. The Morphological Spatial Pattern Analysis (MSPA) model was used to identify ecological sources, and the evaluation results of ecological conservation importance were used as one of the indicators to construct the landscape comprehensive resistance surface. The minimum cumulative resistance (MCR) model, gravity model and circuit theory were integrated to identify and extract ecological corridors. Then, based on the circuit theory, the ecological "pinch points" and obstacle points were identified, the key areas of ecological protection and restoration in the territorial space of Yihuang County were judged, the key areas to be repaired were partitioned, and restoration strategies were proposed. The results showed that there were 10 ecological sources and 19 ecological corridors, including 7 important ecological corridors and 12 general ecological corridors in Yihuang County. There were 20 ecological pinch points, 26 obstacle points and 38 key areas to be repaired, which were divided into 5 ecological restoration zones, including the ecological construction zone for agricultural land, the construction and maintenance area for urban green space, the river rehabilitation area, the maintenance and restoration area for ecological land, and the unimpeded area of road ecological corridor.

InVEST Model considering terrain and biodiversity and its application in the analysis of county biodiversity security pattern: a case study of Wengyuan County
CHEN Zhao, YANG Xianfang, CHEN Jindong, WANG Qi, LIU Ting, DENG Nanrong
2023, 13(4): 1345-1353. doi: 10.12153/j.issn.1674-991X.20220783
Abstract(296) HTML (170) PDF(2404KB)(54)

Detailed assessment of the county-level biodiversity security pattern can provide scientific reference for the planning, implementation and management of regional biodiversity conservation. Taking Wengyuan County in the mountainous area of Northern Guangdong Province as an example, InVEST habitat quality model was used to achieve a comprehensive assessment of the regional biodiversity security pattern, by combining with regional topography and biodiversity characteristics and applying the habitat quality index and the composite topography and biodiversity index as evaluation indicators. The results showed that the overall habitat quality index (HQI) of Wengyuan County was good, especially in the river system and forest areas with weak anthropogenic disturbance, and the areas with low HQI were concentrated in the those strongly influenced by human activities such as construction land and cultivated land. The distribution pattern of topographic diversity composite index (TDCI) was consistent with that of relief amplitude (RA) and slope position index (SPI), but opposite to that of the relative difference of topographic wetness index (RDW). The distribution pattern of biodiversity composite index (BCI) was affected by the interaction between species diversity background in Shannon-Wiener index (H') and biodiversity richness (BR), human footprint index (HF), biodiversity significance (BS) and total vegetation coverage. The distribution of biodiversity security pattern index (BSPI) was well consistent with that of HQI, BCI and TDCI. Low-risk/low-vulnerability areas were concentrated in the county areas with strong human activities, such as urban construction land, transportation and water conservancy, and cultivated land. High-risk/high-vulnerability areas were mainly distributed in the areas with weak anthropogenic disturbances, such as nature protection and drinking water sources in the north, northwest, southeast and northeast of Wengyuan County. Through the verification and analysis of the relevant data such as the ecological protection redline, it was shown that the improved and optimized evaluation results could reflect the biodiversity security pattern of the study area more precisely and objectively.

Pollution characteristics and ecological risk assessment of heavy metals in surface sediments of lakes along the east route of South-to-North Water Diversion Project
ZHANG Jiagen, HUANG Tianyin, CHEN Shuqin, WU Yusheng, PANG Yan, XU Qiujin
2023, 13(4): 1354-1363. doi: 10.12153/j.issn.1674-991X.20220913
Abstract(163) HTML (148) PDF(8907KB)(30)

Nansi Lake, Luoma Lake, Hongze Lake and Gaoyou Lake along the east route of South-to-North Water Diversion Project were taken as the research objects, the spatial distribution characteristics and ecological risks of seven heavy metals (Cr, Cu, Ni, Zn, Pb, Cd, As) in the surface sediments of the four lakes were analyzed by the multi-index comprehensive evaluation model (TOPSIS method) and the potential ecological risk index method, and were compared and analyzed with other lakes in the five geographic regions of China. The results showed that the concentration of heavy metals in the surface sediments of the four lakes was lower than that of Taihu Lake, Chaohu Lake, Dongting Lake and Poyang Lake in the Eastern Plain Lake Area, but higher than that of the lakes in Mengxin, Qinghai-Tibet, Northeast Mountain and Plain Lake areas, and the distribution of heavy metals in lake sediments in different regions had obvious differences. In addition to geological structural characteristics, human activities such as industrial and agricultural production were the main factors that led to differences in heavy metals in lake sediments. The comprehensive potential ecological risk level of heavy metals in the surface sediments of the four lakes was low, but the individual heavy metal of Cd had moderate to high potential ecological risks. It was recommended to strengthen the supervision of industrial and agricultural production discharge around the lakes along the east route of South-to-North Water Diversion Project, further adjust and optimize the industrial structure along each lake, and strictly control the input of heavy metal pollution, especially the control of heavy metal Cd and other human activities, to ensure the water environment safety of the lakes along the east route of South-to-North Water Diversion Project.

Research progress of agricultural non-point source pollution migration process and model in basins
HUANG Guoxian, NIE Yuxi, ZHANG Qinghuan, TONG Sichen, ZHAO Jian, LIANG Dongfang, CHEN Wei
2023, 13(4): 1364-1372. doi: 10.12153/j.issn.1674-991X.20220981
Abstract(791) HTML (266) PDF(2878KB)(164)

Agricultural non-point source pollution is still the main source of water pollution in China. It involves multi-disciplinary intersection of agriculture, water conservancy, environment and ecology, etc., and is one of the key issues of both national and international environmental pollution academic research and watershed pollution control and management. Different disciplines usually use different methods to study the generation and migration of agricultural non-point source pollution at different time and space scales. For example, agriculture focuses on processes such as water irrigation on fields-hillsides-watershed scale, fertilization for different crops at different life stages, nutrient transformation and absorption, soil pool budget, and the effect of microorganisms on nutrients. However, it is often overlooked the internal relationship between different scales or systems, and there are few studies on the integrated simulation of the transportation process. The agricultural non-point source pollution transportation process and its influencing factors from different typical spatial scales (from fields to hillsides, and then to watershed scales), as well as the agricultural non-point source pollution modeling methods in watershed, were summarized. It was proposed that in addition to deeply considering local hydrological processes and the yield, accumulation, release and transportation of pollutants at the typical scales of field and hillside in the model system, the hydrological and pollutant migration processes and the development of an integrated non-point source model, which covered fields-hillsides-watershed system, should be highlighted. Meantime, the existing research problems related to the scale transformation, modeling methods and model uncertainty research of agricultural non-point source pollution migration process were analyzed, and the future research directions were prospected.

Research progress of stable isotopes in source analysis of nitrate pollution in water
ZHANG Lieyu, MA Yangyang, LI Guowen, TANG Wenzhong, DU Caili
2023, 13(4): 1373-1383. doi: 10.12153/j.issn.1674-991X.20221103
Abstract(416) HTML (240) PDF(3675KB)(116)

Accurate identification of nitrate pollution sources in water bodies is crucial, and stable isotopes have been widely used in source analysis studies of nitrate pollution in water bodies. Still, there are few studies on the influence of isotope fractionation on the accuracy of source analysis results. The stable isotope analysis technology and its application in the analysis of nitrate pollution sources in water bodies were introduced, and by comparing the spatial and temporal variability of δ15N-NO3 and δ18O-NO3 in nitrogen transformations and the application of other technical methods in the source analysis of nitrate pollution, the limitations of the current stable isotope techniques in the source analysis of nitrate pollution were presented. The results showed that isotopic fractionation in nitrogen transformation had a strong influence on δ15N-NO3 and δ18O-NO3 in water, and the use of δ15N-NO3 and δ18O-NO3 of potential sources that met environmental characteristics was the key to ensure the accuracy of stable isotope model analysis results. Therefore, an in-depth study of microbial information related to nitrogen transformation in water bodies would help to further understand the characteristics of nitrate in migration transformation; the input of nitrate from soil layer or groundwater should be the key investigation end source for nitrate pollution source analysis in surface water bodies; the development of stable isotope models adapted to the geoclimatic characteristics of the study area in combination with machine learning was the future research direction to achieve accurate source tracing.

Research progress of antibiotic resistance genes in wastewater treatment plants
2023, 13(4): 1384-1394. doi: 10.12153/j.issn.1674-991X.20220847
Abstract(542) HTML (136) PDF(1650KB)(82)

Antibiotic resistance genes (ARGs) are emerging contaminants which pose a great threat to the environment and human health. As an important source and sink of ARGs, wastewater treatment plants (WWTPs) have great potential ecological risks. Therefore, the diversity, composition as well as transfer mechanism of ARGs in the wastewater treatment processes were systematically introduced. ARGs of beta-lactam, macrolide, tetracycline, sulfonamide and aminoglycoside were widely detected in global WWTPs. However, the abundance of different types of ARGs along treatment processes and dominant ARGs detected in each process were different. Horizontal transfer was the main transfer mechanism of ARGs. The effects of common factors such as environmental conditions, influent wastewater quality and operational parameters on the abundance and distribution of ARGs were also summarized. It was proposed that the focus of future research was identifying the representative ARGs and the most influencing factors, quantifying the effects of various factors on the abundance, compositions and horizontal transfer mechanisms of ARGs, and establishing a standard system for evaluating the risks of ARGs for monitoring and controlling the potential ecological risks of ARGs in WWTPs.

Changing characteristics and influencing factors of Manning's roughness coefficient along grass swales
WANG Jianlong, SUN Zheng, XIA Xu, WANG Wenhai, WU Xuelei
2023, 13(4): 1395-1403. doi: 10.12153/j.issn.1674-991X.20220840
Abstract(241) HTML (110) PDF(10077KB)(19)

With the rapid development of sponge cities, grass swales have been widely used. Recently, the Chezy formula is generally used to calculate the flow rate along the grass swales. There are differences between the application conditions of the Chezy formula and grass swales, which often cause remarkable calculation errors. One of the reasons for the errors is the Manning roughness coefficient variation. Assuming that the Chezy formula was appropriate, the variation characteristics of the Manning roughness coefficient of grass swales under different constant and variable inflow conditions were systematically researched through full-scale experiments, and the effect of vegetation height on the Manning roughness coefficient was further analyzed. The results showed that the flow rate and Manning roughness coefficient decreased with the increase of flow distance along the grass swale. Under different inflow conditions, the Manning roughness coefficient was closely related to the inflow rate, and the higher the flow rate, the greater the Manning roughness coefficient, with the maximum value being 0.22. In addition, the maximum Manning roughness coefficient of grass swale with different vegetation heights was 0.19-0.22 under different variable flow inflow conditions, and the vegetation height had little influence on the Manning roughness coefficient under the experimental conditions. Therefore, the Manning roughness coefficient of grass swale was markedly affected by runoff volume. The research results can provide reference for selecting the Manning roughness coefficient in the calculation of grass swale drainage capacity.

The interactive effects of titanium dioxide nanoparticles and phosphate on arsenic accumulation and biotransformation in Chlamydomonas reinhardtii
ZHANG Xin, YANG Fan, YU Ziyue, YAN Changzhou
2023, 13(4): 1404-1414. doi: 10.12153/j.issn.1674-991X.20220728
Abstract(159) HTML (93) PDF(3542KB)(15)

Nanomaterials can modify the environmental behavior of arsenic (As) due to their large specific surface area and high reaction activity, which may affect the absorption and metabolism of As in microalgae. In this study, Chlamydomonas reinhardtii was used as model organism to investigate the influence of titanium dioxide nanoparticles (nano-TiO2) on As(Ⅴ) accumulation and biotransformation in algal cells at different phosphate concentrations. The results showed that nano-TiO2 significantly promoted As accumulation in algae cells in 0.013, 0.100 and 0.500 mmol/L phosphate groups at the beginning of exposure (1 d), but the carrier effect of nano-TiO2 decreased with the extension of exposure time. After 8 days of exposure, in the nano-TiO2 addition groups, As(Ⅴ) in algal cells was not only reduced to As(Ⅲ) and methylated to dimethyl arsenic, but also further transformed to an unknown As compound, possibly arsenosugars. And the proportion of arsenosugars in algal cells gradually increased with the decrease of phosphate concentration, which might inhibit the efflux of As(Ⅲ). After 8 days of exposure, As(Ⅴ) and As(Ⅲ) were the main As species in the culture medium, and a small amount of dimethyl arsenic was also detected. The addition of nano-TiO2 decreased the proportions of As(Ⅲ) in the culture medium, especially in 0.5 and 1.0 mmol/L phosphate group. This study indicated that the interaction between nanomaterials and phosphate significantly affected the accumulation and metabolism of As in microalgae, which facilitates the application of microalgae in As remediation.

Progress in the application of atmospheric pressure plasma jets in environmental field
HAO Xiaolong, SHI Chaoyang, ZHANG Yibo
2023, 13(4): 1415-1424. doi: 10.12153/j.issn.1674-991X.20220815
Abstract(217) HTML (424) PDF(1641KB)(63)

Atmospheric pressure plasma jet (APPJ) is a new type of atmospheric pressure plasma discharge technology. It is generated under atmospheric pressure and has the advantages of low discharge temperature and excitation voltage, flexible discharge device, simple and safe operation. It can be produced in atmospheric environment, and has a wide range of application prospects in biomedicine, environmental health, material modification and other fields. The applications of APPJ in the environmental field such as environmental sanitation and pollution control at home and abroad in recent years were comprehensively summarized, especially the applications of environmental sterilization, environmental pollutant removal and environmental algae treatment, and its jet equipment, treatment styles, effects and mechanisms were elaborated. Based on the research status, the existing problems and solutions in the field of APPJ environment were discussed, including its sterilization and degradation mechanism, scale-up of test, design of plasma jet generator and development of plasma jet power supply. Finally, the future development direction and trend of the application of this technology in the field of environment were prospected.

Spray pyrolysis technology and its application in environmental pollution control
LIU Zhengang, SUN Yue, LUO Lei
2023, 13(4): 1425-1433. doi: 10.12153/j.issn.1674-991X.20221018
Abstract(253) HTML (66) PDF(4625KB)(32)

Spray pyrolysis, as a new pyrolysis technology for one-step, continuous, highly expandable, and large-scale preparation of environmental functional nanomaterials, has received the attention of researchers. The working principles, product characteristics, environmental applications and industrial challenges of spray pyrolysis technology were introduced in detail, and the hot spots of spray pyrolysis technology in the field of environmental pollution control were visually analyzed. The results show that spray pyrolysis is a technology for producing nanoparticles by decomposing precursor solutions at high temperature and its equipment mainly consists of atomizer, heating equipment and collection device. The product property of spray pyrolysis is influenced by precursor solution and pyrolysis parameters. By controlling precursor solution composition and pyrolysis process parameters, nanomaterials with desirable size and morphology can be obtained. Owing to the specific physicochemical properties, these environmental functional nanomaterials (e.g., powders or thin films) prepared by spray pyrolysis technology are highly effective for the removal of pollutants from both atmosphere and wastewater. Simultaneous, based on the research focus, the pyrolysis method, product characteristics, application fields and the main mechanism of pollutant removal of spray pyrolysis technology were analyzed. However, there are still many challenges in expanding the spray pyrolysis technology from laboratory scale to industrial application. The research can provide theoretical and technical support for the application of spray pyrolysis technology in the field of environmental pollution control.

Feasibility, technical status and prospects of lithium recovery from produced water in oil and gas fields
ZHAO Ziyi, ZHOU Xue, WANG Tiefu, LI Chengchen, SUN Guangdong, KONG Fanxin, YANG Demin, CHEN Jinfu, ZHANG Ying
2023, 13(4): 1434-1443. doi: 10.12153/j.issn.1674-991X.20221190
Abstract(464) HTML (229) PDF(4992KB)(82)

The contradiction between high demand and low production of lithium resources makes it urgent to develop new lithium resources. The produced water of oil and gas fields is rich in lithium elements, which is a potential liquid lithium resource. Therefore, it is of great practical significance to analyze the feasibility of lithium extraction from produced water of oil and gas field and propose a feasible technical route. First, the composition of produced water in oil and gas fields was analyzed, and the water quality characteristics of the produced water in oil and gas fields were defined. Then, the lithium resource endowment of major basins in China was analyzed, and the challenges of lithium extraction due to the high concentration of organic matter and rich ion composition in the complex organic-inorganic hybrid system were emphasized. Finally, the water characteristics, water treatment technology and high-efficient lithium extraction technology were comprehensively analyzed and the applicability of those lithium recovery technologies (precipitation, adsorption, extraction and membrane separation) for produced water was discussed. Combined with the practice of lithium extraction and the current situation of the industry, it was recommended to develop a lithium extraction technical route of "pretreatment + enrichment concentration (adsorption/extraction-membrane separation) + precipitation".

Spatio-temporal variation characteristics and influencing factors of ozone in three major urban agglomerations in China from 2015 to 2020
YE Shen, WANG Peng, SHE Yuanyang, DING Mingjun
2023, 13(4): 1444-1453. doi: 10.12153/j.issn.1674-991X.20221094
Abstract(359) HTML (88) PDF(8500KB)(55)

The spatio-temporal variation characteristics of ozone concentration in the three major urban agglomerations of Beijing-Tianjin-Hebei, Yangtze River Delta, and Pearl River Delta in China from 2015 to 2020 were analyzed, and the main factors affecting temporal and spatial changes were studied based on random forest model and geographical detector model. The results showed that: 1) From 2015 to 2020, the temporal and spatial evolution characteristics of ozone concentration values of the three urban agglomerations showed an increasing trend year by year, and the ozone variation rate showed a trend of "decreasing from the central to the south": Yangtze River Delta (3.4%) > Beijing-Tianjin-Hebei (2.9%) > Pearl River Delta (2.1%). The spatial variation characteristics of the average ozone concentration were "high in the north and low in the south": Beijing-Tianjin-Hebei (98.3 μg/m3) > Yangtze River Delta (96.7 μg/m3) > Pearl River Delta (90.5 μg/m3). 2) Temperature, wind speed, GDP, and energy consumption were not only the main factors affecting the temporal variation of ozone in the three urban agglomerations, but also had a threshold effect on ozone concentration. 3) Energy consumption and GDP were the main factors affecting the spatial change of ozone concentration in the three urban agglomerations, and their interpretation rates were more than 36%. Therefore, for ozone prevention and control in urban agglomerations more attention should be paid to economically developed areas, and key monitoring and early warning should be carried out in high energy consuming areas to achieve the effectiveness of ozone prevention and control in urban agglomerations.

Scenario analysis of motor vehicle emission trends and synergistic control in Beijing
YE Heyong, FAN Shoubin, LI Tingting, WANG Yazhou, LONG Teng
2023, 13(4): 1454-1463. doi: 10.12153/j.issn.1674-991X.20220917
Abstract(136) HTML (135) PDF(2475KB)(35)

In order to analyze the trends of motor vehicle emissions on the time scale of Beijing, the synergistic control effects of motor vehicle emissions of air pollutants and greenhouse gases were studied. COPERT 5 model was applied to construct the emission inventories of motor vehicle pollutants CO, NOx, VOCs, PM2.5 and greenhouse gases CO2, CH4 and N2O in Beijing from 2005 to 2020, and five emission reduction scenarios were set up to evaluate the emission reduction effects of motor vehicle pollutants under each scenario in 2025 with 2020 as the base year, and the synergistic emission reduction elasticity coefficient method and coordinate system method were applied to analyze the synergistic effects of air pollutants and greenhouse gases, respectively. The results showed that CO2 emissions increased significantly, with a growth rate of 85.25% in 2020 compared to 2005, while all the pollutants decreased compared to 2005. Under different control scenarios, the emissions of motor vehicle air pollutants and greenhouse gases in Beijing were reduced compared with the business-as-usual scenario (BAU), and the integrated control scenario (RIS) had the best emission reduction effect. From the results of the synergistic emission reduction elasticity coefficient method and coordinate system method, the synergistic effects of air pollutants and greenhouse gases under different control scenarios were observed, and the synergistic effects were optimal in the RIS scenario. In the future, Beijing should actively adopt comprehensive control measures and coordinate various emission reduction measures, laying the foundation for collaborative governance of pollution reduction and carbon reduction and green low-carbon economic and social transformation as soon as possible.

Pollution characteristics and source identification of heavy metals in farmland soils around a tailing pond in Zhejiang Province
LÜ Yujuan, WANG Qiuyue, SUN Xuemei, ZHANG Zhiwei, ZHANG Yimin, GAO Yuexiang
2023, 13(4): 1464-1475. doi: 10.12153/j.issn.1674-991X.20221193
Abstract(198) HTML (145) PDF(3915KB)(38)

The safety of the ecological environment around tailing ponds has received high attention, and soil heavy metal pollution is one of the risk sources of cultivated land management and protection. The concentrations of eight heavy metals Cd, Hg, As, Pb, Zn, Cu, Cr and Ni were measured in the soil of a copper mine tailing pond in Zhejiang Province, which was located in the hilly mountainous area of east Zhejiang Province, and the degree of soil heavy metal pollution and ecological risk around the tailing pond were evaluated by using the geo-accumulation index method, pollution index method, potential ecological risk index method and ecological risk warning index method. The sources of heavy metals in farmland soils were quantitatively analyzed by combining the positive definite matrix factor (PMF) receptor model. The results showed that: 1) The concentrations of Cd, Hg, Cu and Zn with a character of high variability in farmland soils in the study area were 5.36, 2.06, 8.19 and 5.36 times higher than the background values of soil elements, respectively. The pollution index showed that the percentage of heavy pollution of Cu, Zn and Cd all reached 10.5%, the percentage of moderate pollution was 5.26%, and 15.8% of the points near the tailing pond (<300 m) were in the severe pollution level. The geo-accumulation index indicated that Cd, Cu, Zn and Hg might have cumulative risks. 2) The results of the ecological risk index showed that Cd was with high potential ecological risk, Hg was with considerable potential ecological risk, Cu was with moderate ecological risk and the remaining heavy metals were minor risk. The comprehensive potential ecological risk index (RI) was 308.91, which belonged to high risk level. The results of the ecological risk warning index indicated Cu was severe warning, Cd and Zn were medium warning, Hg was mild warning, As was early warning, Pb, Cr and Ni were no warnings. The comprehensive ecological risk warning index (IER) was 16.06, which belonged to severe warning level. The spatial distribution patterns of RI and IER were similar, and Cd, Cu, Zn and Hg were the main warning elements and ecological risk factors in the study area. 3) The sources apportionment of heavy metals in the farmland soil based on PMF indicated that the heavy metal contamination in the area mainly came from three sources. Specifically, Cd, Zn and Cu pollution was mainly influenced by mixed of tailings from copper tailing pond and seepage water under the dam, and the corresponding contribution rate was 94.4%, 94.3% and 67.1%, respectively. Agricultural activities such as chemical fertilizer and pesticide application had the highest contribution to Hg, and its contribution rate was 61.5%. Natural parent material and transportation activities had the highest contribution to Cr, Ni, Pb and As, and the corresponding contribution rate was 89.7%, 82.7%, 75.0% and 68.3%, respectively.

Comprehensive evaluation and analysis of heavy metal pollution degree in typical electroplating sites
WANG Chunlin, JIANG Weiguo, SONG Jie, GENG Zhipeng
2023, 13(4): 1476-1485. doi: 10.12153/j.issn.1674-991X.20221104
Abstract(196) HTML (101) PDF(5779KB)(20)

In view of the problems of incomplete single index evaluation and insufficient spatial analysis in the pollution degree evaluation study, a comprehensive evaluation spatial model was built based on three pollution indexes to carry out research in the electroplating site. Based on the survey report of the electroplating site, remote sensing images and other data, a comprehensive evaluation spatial model was built to comprehensively evaluate the pollution degree and analyze the pollution distribution of the electroplating site. The results show that the concentration of Cr, Ni, Zn, and Cu elements in electroplating sites are relatively high, and the pollution exceeding standard is more prominent; The concentration of other heavy metal elements are relatively low, and there is no situation of exceeding the standard. The spatial distribution of different pollution indexes in different sites have high consistency, but there are also differences. In the spatial distribution of comprehensive evaluation values, there are significant differences in the distribution of functional areas among different sites, with the sewage treatment area and electroplating workshop area having higher comprehensive value. The evaluation content of a single index is relatively one-sided, and a comprehensive evaluation model can provide a more comprehensive analysis of the distribution of site pollution, providing a reference basis for future development of the site.

Status and prospect of in-situ remediation technologies applied in hexavalent chromium contaminated sites
HAN Wei, ZHAO Ruifeng, SHI Yichen, LIU Wanrong, WANG Yujing, NIE Jinglei
2023, 13(4): 1486-1496. doi: 10.12153/j.issn.1674-991X.20221240
Abstract(543) HTML (181) PDF(2057KB)(67)

Hexavalent chromium Cr(Ⅵ) is a typical heavy metal pollutant with a wide range of sources. Due to its diverse forms and valence states, the geo-chemical reaction process is extremely complicated. There are lots of Cr(Ⅵ) contaminated plots in China and the remediation of Cr(Ⅵ) contaminated sites is very challenging. In-situ remediation has gradually become the mainstream of remediation strategies for contaminated sites due to many advantages such as no excavation and less environmental interference. The latest research progress of different in-situ remediation technologies for Cr(Ⅵ) was reviewed. Based on a large number of in-situ remediation engineering cases at home and abroad, the application effects of in-situ biological, in-situ chemical and other remediation technologies and different injection methods were analyzed. The key parameters of different types of in-situ remediation technologies including applicable geological conditions, applicable concentration range, influence radius, remediation duration, remediation medium, agent type and dosage, and injection method were clarified. It played a key role to establish a precise contamination field concept model, and choose efficient chemicals and the best injection method or remediation process combinations for complex contaminated sites. The advantages and disadvantages of different in-situ remediation technologies of Cr(Ⅵ) were compared in examples, and their different applicable scenarios were explored. At the same time, the future development direction of technologies was prospected.

Application of in-situ horizontal barrier risk control technology in the treatment of a decommissioned industrial contaminated site
ZANG Changjuan, SUN Yuchao, LIU Zhiyang, JIANG Mengdi, GUO Baoman
2023, 13(4): 1497-1505. doi: 10.12153/j.issn.1674-991X.20220677
Abstract(189) HTML (82) PDF(4094KB)(40)

In order to meet the goal of human health risk control, targeted risk control schemes were designed for indoor and outdoor areas in combination with the working situation of later site development scenarios of a decommissioned industrial contaminated site. For the −2 m contaminated soil under the foundation of indoor regional buildings, the soil gas barrier control project was adopted. The soil gas was blocked by spraying a film between the foundation and the air guide layer of the building, and the negative pressure of the air guide layer below the building was controlled to be −5-−2 Pa. The soil gas was collected by the extraction system, which was treated by the tail gas treatment system to reach the standard before discharge. HDPE film (two cloth and one film) was used as a horizontal barrier for contaminated soil with an original ground elevation below −3 m in outdoor areas, and clean clay was used for cover and compaction above the barrier layer. The results of the risk control effectiveness evaluation carried out within one year after project completion showed that the engineering performance indicators and pollutant indicators of the indoor and outdoor areas met the evaluation standards and achieved the expected effect. The project passed the acceptance of the ecological environment department in December 2021 and entered the later stage of environmental supervision.

Influencing factors and thermal desorption performance of the coupled heating process of steam injection and electrical resistance heating
CHEN Zhikang, LIU Liujun, YUE Rui, SIMA Jingke, MAO Xuhui
2023, 13(4): 1506-1513. doi: 10.12153/j.issn.1674-991X.20220864
Abstract(217) HTML (148) PDF(3501KB)(23)

Aiming at the application limitations of single thermal desorption technology, a three-dimensional experimental system of the steam enhanced extraction and electrical resistance heating (SEE-ERH) coupled thermal desorption was constructed to study the influencing factors and desorption performance of the coupled heating process of thermal desorption technology. The results of the temperature field distribution experiments showed that water content, voltage intensity, steam injection amount and extraction rate could influence the heating effect. Within a certain range, the heating effect was positively correlated with the first three factors. The model established using COMSOL software could well simulate the heating process of the system. The pollution desorption experiment results showed that adding SEE to ERH could promote the desorption of pollutant components and accelerate the removal rate of pollutants. Under the condition of 20% moisture content, 80 V voltage, 1.00 L/min steam injection rate and 1.2 L/min extraction rate, the heating efficiency of SEE-ERH was good, and the desorption efficiency of phenanthrene could reach up to 99.0%.

Analysis of the time series difference of the material structure evolution of DOM and humic acid during composting of different materials
ZHAO Qin, CHENG Donghui, WANG Yan, ZHAO Xinyu, DANG Qiuling
2023, 13(4): 1514-1524. doi: 10.12153/j.issn.1674-991X.20221230
Abstract(349) HTML (103) PDF(3016KB)(42)

Dissolved organic matter (DOM) and humic acid (HA) were extracted from three composting processes of chicken manure without bacterial agent (CM), chicken manure with bacterial agent (CMB) and kitchen waste (FW). The material structure and transformation time sequence of DOM and HA were characterized by fluorescence spectrum parallel factor analysis and two-dimensional correlation spectrum analysis. The results showed that the humification index (HIX) value of DOM was CMB>CM>FW, FW compost had stronger autogenous source characteristics of organic matter, and CMB compost had the highest degree of organic matter humification. Compared to composting time, the spectral structural characteristics of DOM and HA had a stronger response to the type of compost; the relative contents of protein-like components in DOM of the three composts were CM>FW>CMB, and humus components showed CMB>FW>CM; the relative content of protein-like components in HA was CM>CMB(FW), and humus-like components showed CMB(FW)>CM. The two-dimensional correlation spectra showed that the evolution sequence of DOM components in chicken manure compost was as follows: humic acid-like>tyrosine-like>tryptophan-like>fulvic acid-like. The components of HA were as follows: tyrosine-like>fulvic acid-like>tryptophan-like; the evolution sequence of DOM components in kitchen waste was as follows: tryptophan-like>tyrosine-like>fulvic acid-like; the components of HA were as follows: humic acid-like>tyrosine-like>tryptophan-like>fulvic acid-like. Appropriate moisture content was conducive to the generation of humic-like substances in DOM. The decrease of ammonia nitrogen (NH4 +-N) content was related to the degradation of protein-like substances and the enhancement of humic degree in DOM, and nitro-nitrogen (NO3 -N) content was significantly positively correlated with humic-like components. A decrease in water-soluble organic carbon (DOC) and water content may signal increased HA humification during composting.

Preparation and performance study of a new type of steel slag-based non-fired ceramsite filter media
SHEN Xinyu, YAN Xiaoya, LIN Yang, XU Yueqing, LIU Rong
2023, 13(4): 1525-1534. doi: 10.12153/j.issn.1674-991X.20220709
Abstract(342) HTML (128) PDF(5573KB)(33)

The non-burning process was adopted to prepare ceramic granule filter media with steel slag as the main raw material. It was used to replace the cobblestone in the filter tank of the blast furnace bottom filtration water flushing slag process, providing a new idea for the resource utilization of steel slag. After determining the base ratio of steel slag to cement of 2.0, gypsum and water glass were selected as activators to study their impact on the performance of the filter media. Finally, an 8% gypsum addition was selected as the optimal preparation parameter for the filter material. At this time, the particle strength of filter media was increased to 4.14 MPa, the 1 h water absorption rate was 9.05%, the particle density was 1.49 g/cm3, the decrease in strength was only 3% after 25 times of cold and hot impacts, and the filtration speed was 5.92 mm/s. With the help of X-ray diffractometer (XRD) and scanning electron microscope (SEM), the physical composition and microscopic morphology of the filter media were characterized. It was found that the exciter used could promote the hydration reaction of the main minerals C3S and C2S in the steel slag to produce C—S—H type gels, and these hydration products intertwined and bonded to reduce the porosity inside the filter media and improve the filter media particle strength and 25 times of cold and hot impacts continuously. This series of filter media could also be used as construction ceramic pellets for building materials, such as aggregate.

Research progress on the application of steel slag for soil remediation
WANG An, WU Meiling, LI Zhongyuan, ZHOU Yuqiang, HUANG Zhanbin
2023, 13(4): 1535-1543. doi: 10.12153/j.issn.1674-991X.20230169
Abstract(315) HTML (149) PDF(1875KB)(50)

Steel slag is a by-product of the steel industry. A large amount of untreated steel slag waste is piled up, which not only seriously wastes resources but also occupies a large amount of land resources, thus causing pollution to the surrounding soil and environment, and even posing a major threat to human production and life. At present, the production of steel slag in China is increasing rapidly, but the comprehensive utilization rate of steel slag is only about 20%. Using steel slag for soil remediation is one of the important directions for combining solid waste disposal with ecological construction. Based on summarizing the physical and chemical properties of steel slag resources, the basic principles and status quo of using steel slag for soil remediation at home and abroad were summarized. The main functions of steel slag as a soil conditioner, soil fertilizer, and soil heavy metal passivator were systematically analyzed. Steel slag, as a soil conditioner, could not only improve acid soil but also effectively reduce greenhouse gas emissions. As a soil fertilizer, it could provide trace elements and nutrients for the soil, and as a soil heavy metal passivator, it could reduce the heavy metal content in soil. The potential of steel slag for soil remediation was pointed out, and the environmental impacts produced by steel slag used in agricultural soil were explored and the risk assessment was conducted. Finally, the future research direction for the application of steel slag in soil remediation was discussed.

Assessment of influencing factors and resource potential of scrap steel recycling in Shanxi Province
FENG Lin, YUAN Jin, HE Hong, DENG Tianlu
2023, 13(4): 1544-1551. doi: 10.12153/j.issn.1674-991X.20220824
Abstract(171) HTML (89) PDF(1609KB)(12)

Exploring the influencing factors and resource utilization potential of scrap steel in Shanxi Province is of positive significance for accelerating the development of circular economy and promoting the green and low-carbon transformation of the steel industry. Based on PEST (political, economic, social, technical) model, the principal component analysis method was used to identify the influencing factors of scrap steel recycling in Shanxi Province. Relying on the life cycle method, combined with GM (1,1) model and the system dynamics simulation model, the potential of scrap steel resource utilization in Shanxi Province from 2021 to 2035 was comprehensively evaluated. The results showed that the influencing factors of scrap steel recycling in Shanxi Province could be sumarized into three aspects, i.e. the comprehensive strength of enterprises, the industry policy environment and the industry market environment. Moreover, Shanxi Province had great potential for scrap steel recycling; the utilization of scrap steel resources would increase rapidly from 2021 to 2030 and stabilize after 2030. In order to improve the level of scrap steel resource utilization in Shanxi Province and promote the high-quality development of the industry, the following policy suggestions were proposed: cultivating standardized and large-scale scrap steel recycling enterprises; improving the level of intelligent information in the industry and enhancing the scientific and technological innovation ability of enterprises; strengthening market supervision and guiding the benign development of the market.

Biodiversity-oriented water ecological restoration effect in urban river with reclaimed water supply
MENG Tingting, DONG Yuequn, WEN Cheng, XUE Xiaofei, MAO Jianhua, HUANG Yue, LI Dan, WANG Yang, XU Kaixiang
2023, 13(4): 1552-1561. doi: 10.12153/j.issn.1674-991X.20221067
Abstract(481) HTML (255) PDF(3806KB)(100)

The monitoring and analysis of water ecological restoration effects are useful to improve the ecosystem health of rivers replenished by reclaimed water. The water ecological restoration covering all trophic levels was conducted, and the community structure, biodiversity indices and water quality were monitored for one year to judge the change of ecosystem health in the old river section of Xiaotaihou River in Beijing. As the results showed, although both the water environmental quality and water quantity suffered great decreasing during the experiment, the water ecological health and water environmental quality in the experimental zone all improved. After ecological restoration, species richness of zooplankton, zoobenthos, fish and birds increased to 6, 2, 3 and 2 times of the previous, respectively. The numbers of dominant species of zooplankton, zoobenthos and fish all increased significantly and the dominant species changed from pollution-tolerant species to a health indicator type. Shannon-Wiener diversity index, Pielou evenness index and Margalef abundance index of zoobenthos, fish and bird all increased. The dominant bird species changed from season to season. The top species of the food chain appeared. The average contents of total phosphorus, ammonia nitrogen and total nitrogen in the experimental zone were 35%, 31% and 30%, respectively, lower than those outside the experimental zone. In a word, the water ecosystem with a complete structure could resist external disturbances such as water quantity and quality changes and improve water environmental quality. Biodiversity indexes and community structures of biological communities could respond and indicate the change of the water environment well. The comprehensive evaluation of multiple biodiversity indexes was more comprehensive and objective than the individual index.

Study on the composition and influencing factors of microbial community in ecological restoration rivers
WANG Gelin, YU Luji, WANG Li, FAN Pengyu, LIU Mengshuo, LI Yahui, GU Likun
2023, 13(4): 1562-1572. doi: 10.12153/j.issn.1674-991X.20220876
Abstract(504) HTML (180) PDF(4420KB)(74)

In order to clarify the microbial community structure, function and influencing factors of ecological restoration rivers, the Qingyi River in Xuchang City was taken as an example, and high-throughput sequencing methods were used to study the influence of ecological restoration measures on the microbial community structure of river water and sediment, and then the purification effect of carbon, nitrogen and sulfur functional bacteria in ecological restoration measures and the distribution of waterborne pathogenic bacteria were analyzed. The results showed that: In the river sections with less human interference, the near-natural riverbank had a good interception effect on land-source pollution, and the interception and oxygenation capacity of ecological filter dams could help the river to remove chemical oxygen demand (COD). The water quality of the urban river section was greatly affected by human activities, and the purification effect of ecological restoration measures was not obvious. In the suburban river section, human interference was less, the river's self-purification capacity was improved, and the total phosphorus (TP) and ammonia nitrogen (NH4 +-N) indicators gradually returned to the original level. The microbial diversity and richness of the Qingyi River sediment were higher than that of the overlying water, and Proteobacteria was the dominant species in sediment and water. The relative abundance of Cyanobacteria, which participated in the nitrogen cycle, reached 4.7%, indicating that the Qingyi River still had eutrophic river sections. The most abundant pathogenic bacteria in the Qingyi River water was Acinetobacter, while the most abundant pathogenic bacteria in sediment were Clostridium, Flavobacterium and Bacteroidetes, among which Bacteroidetes was the most abundant in the urban section. Spearman correlation analysis showed that there was a significant correlation between microbial diversity in water and temperature (T), pH, COD (P<0.05). The main factors affecting the microbial community structure in the suburban sediment were NH4 +-N, total nitrogen (TN) and TP. The results showed that the abundance and diversity of microbes in the urban section of the ecologically restored river were high and the risk of pathogenicity was high; the abundance of carbon, nitrogen and sulfur functional bacteria in the suburban section was high, and it was the main place for material cycling.

Study on the characteristics of plant communities in different ecological restoration stages of Hulun Buir sandy grassland
HAO Haojing, GUAN Xiao, CAO Ming, LI Junsheng
2023, 13(4): 1573-1585. doi: 10.12153/j.issn.1674-991X.20220877
Abstract(264) HTML (169) PDF(3893KB)(43)

Artificial vegetation restoration is an important measure to slow down grassland desertification and ecological reconstruction. Understanding the succession characteristics and influencing factors of plant communities in different restoration stages is conducive to the sustainable restoration of vegetation in the sandy land. Taking the vegetation restoration of Ganzhuer sandy land in Hulun Buir as an example, the plant community structure characteristics and soil physical and chemical properties at different restoration stages in 9, 11, 13 and 15 years were investigated respectively, and the succession changes of artificial restoration plant communities and their responses to environmental factors were explored. It was found that 42 species of plants were found in the study area, belonging to 17 families and 35 genera, including 39 species of herbs, mainly Compositae, Gramineae, Rosaceae and Leguminosae. There were 3 kinds of shrubs, including Leguminosae and Compositae. The number of species in different recovery years varied from large to small, and the order was 28 species (15 a) > 25 species (13 a) > 19 species (9 a) > 16 species (11 a). Within each year, the number of perennial herbaceous species was significantly higher than that of annual and biennial plants. In different restoration stages, the dominant species, aboveground biomass and species diversity of herbaceous and shrub fluctuated. Specifically, among the herbaceous plants, Cynanchum thesioides, Corispermum hyssopifolium, Elymus dahuricus, Cleistogenes squarrosa, Leymus chinensis and Setaria viridis had higher dominance, and Cynanchum thesioides was the main dominant species of shrub. The aboveground biomass and total coverage of herbaceous plants did not change noticeably, but the overall trend was fluctuating and increasing. The total coverage of shrub in 15 a was significantly higher than that in 9 a, and the aboveground biomass showed a trend of gradual increase, which was significantly higher in 11, 13, 15 a than in 9 a. The species diversity index of the herbaceous had no significant difference in different restoration stages, and the species diversity of shrub layer was significantly higher in 15 a than in 9 a. The random forest model showed that the contribution of local climate and soil factors to the characteristics of plant community structure was different in the restoration process of desertification grassland. Soil total nitrogen, total potassium, organic matter, annual precipitation and average annual wind speed were the dominant factors affecting herbaceous diversity in Ganzhuer sandy land, and all of them were positively correlated except the average annual wind speed. Therefore, it was suggested to appropriately increase fertilizer containing nitrogen, potassium, organic matter and other nutrients in the sandy land vegetation restoration, so as to promote the plant community structure reconstruction and diversity restoration in the desertification ecosystem.

Characterizing the composition of dissolved organic matter in groundwater at a polluted site and its indicating significance for natural attenuation
ZHAO Meng, JIANG Yonghai, JIA Yongfeng, LIAN Xinying, SHANG Changjian, ZANG Yongge, FENG Fan
2023, 13(4): 1586-1594. doi: 10.12153/j.issn.1674-991X.20220813
Abstract(263) HTML (129) PDF(2003KB)(45)

Dissolved organic matter (DOM) affects the degradation and transformation of pollutants in groundwater, and the changes of DOM structural composition can reflect the migration and transformation process of external pollutants. Taking groundwater from a polluted site in Shandong Province as the research object, three-dimensional fluorescence spectroscopy (EEM), synchronous fluorescence spectroscopy (SFS) and fluorescence region volume integral method (FRI) were used to analyze the composition and structure of the groundwater DOM. The role of DOM spectral information in indicating the natural attenuation effect of groundwater organic pollution was investigated in combination with the natural attenuation capacity assessment methods, i.e. hydrogeochemical index analysis method and microbiological analysis method. The results showed that the content of both humus-like and protein-like substances in groundwater increased under the persistence of organic pollution in groundwater and long-term microbial action, and the proportion of protein-like substances gradually increased with the increasingly strong biodegradation. Based on FRI region theory, a substitute characterization index was proposed to quickly assess the effect of the biodegradation in the natural attenuation of organic pollution in groundwater: the ratio of relative contents of specific fluorescence regions [P(Ⅰ +Ⅱ) /P], that was, the ratio of the relative content of protein-like substances to humus-like substances. The larger the value of P(Ⅰ+Ⅱ) /P was, the stronger the biodegradation in natural attenuation was.

Passivation effect of Fe0 in the removal of Cr (Ⅵ) from groundwater and the optimization of electrochemical depassivation parameters
PENG Yue, FENG Yanping, LAN Weiwei, LIU Jian
2023, 13(4): 1595-1603. doi: 10.12153/j.issn.1674-991X.20221003
Abstract(146) HTML (108) PDF(4200KB)(28)

Zero-valent iron (Fe0) is widely used in the remediation of groundwater polluted by Cr(Ⅵ). However, there is a problem that passivation reduces the remediation efficiency. First of all, Fe0 was used to remove Cr (Ⅵ) in groundwater, and passivated iron filings with different passivation degrees were prepared. Subsequently, the electrochemical method was used to deactivate the passivated iron filings, and the effects of electrode setting, electrolysis voltage, electrolysis time and electrode distance on the depassivation effect were studied by single factor test and orthogonal test. Meanwhile, the depassivation solution and the iron filings before and after depassivation as well as the precipitate produced during the depassivation process were analyzed. The results showed that the depassivation effect was the best when passivated iron filings were used as anode. The depassivation effect first increased and then decreased with the increase of electrolysis voltage, decreased with the increase of electrode distance, and increased with the increase of electrolysis time. The influence of three factors on the depassivation effect from high to low was as follows: electrolysis time > electrolysis voltage > electrode distance. The results of the X-ray diffractometer, scanning electron microscope and energy dispersive spectroscopy analysis showed that the activity of passivated iron filings could be recovered effectively due to surface precipitation shedding under electrochemical action. The optimum conditions for depassivation of passivated iron filings were as follows: passivated iron filings for anode, electrolysis voltage = 10 V, electrolysis time = 60 min, electrode distance = 2 cm. Under these conditions, the removal rate of Cr (Ⅵ) by iron filings after depassivation could be restored to more than 90% of the original; Cr (Ⅲ) precipitate could not be dissolved, but the concentration of Fe in the solution could be increased during depassivation process. These research results could provide a useful reference for improving the remediation effect and material utilization rate of Cr (Ⅵ) polluted groundwater by Fe0.

Study on the characteristics and causes of groundwater pollution in coal gangue dumps
ZHAO Ziqian, SHA Haoqun, HUANG Jiu, HE Xiaosong, PAN Qi, LIU Xieyang
2023, 13(4): 1604-1613. doi: 10.12153/j.issn.1674-991X.20221129
Abstract(249) HTML (93) PDF(3943KB)(54)

The stock of coal gangue in China is large, and it still increases rapidly, posing a high risk on the environment. However, the effect of the self-ignition degree of coal gangue on the release of leachates pollutant is unclear, and the information on the natural attenuation of these leachate pollutants is limited. The coal gangue with different self-ignition degrees and the contaminated groundwater were collected from a typical coal gangue dump site in Taiyuan City, Shanxi Province. The composition and concentration of heavy metals, inorganic salts and organic compounds in coal gangue and groundwater were investigated, and the sources of groundwater pollution were explored based on statistical analysis. The results showed that the gangue extracts and groundwater flowing from the mountainside below the gangue dump were not contaminated by Cd, Pb, As, and Zn, though they had been lightly polluted by Cr and Ni. The concentrations of SO4 2−, Fe, and Mn were high in the extracts, with SO4 2− concentration of 5 982 mg/L and Fe and Mn concentrations of 1 081 and 19 times higher than the groundwater Ⅳ quality standard specified in Quality Standard for Ground (GB/T 14848-93), respectively. According to the pollution source analysis, it could be obtained that Na+, K+, Cl and NO3 in groundwater near the gangue dump sites mainly originated from soil and aquifer medium, while SO4 2−, Fe, Mn, Cd, Zn, As, Cr, and Ni were mainly released from gangue leaching. The pollution release of the coal gangue with different self-ignition degrees was as follows: burning gangue > burned gangue > fresh gangue. The self-ignition of coal gangue contributed to the release of pollution. Natural attenuation of heavy metal significantly occurred during the migration process of gangue leachates. However, the concentration of SO4 2−, Ni, and Mn still had certain risks, exceeding Class Ⅳ groundwater standard specified in GB/T 14848-93.

Nitrogen flow pattern and influencing factors of food production and consumption system in the Yangtze River Delta city cluster based on material flow model
DONG Li, ZOU Tiansen, XU Rui, ZHANG Zeqian, YANG Queping
2023, 13(4): 1614-1624. doi: 10.12153/j.issn.1674-991X.20210732
Abstract(227) HTML (114) PDF(3767KB)(27)

As an important growth pole, the release of reactive nitrogen from food production and consumption system of city clusters greatly affects regional nitrogen cycle. The material flow analysis model was introduced to quantitatively analyze the nitrogen flow patterns among cropland, livestock, aquaculture and human consumption subsystems in the Yangtze River Delta city cluster in 2019. The structure of nitrogen loss to the environment from each subsystem, the spatial distribution of nitrogen loss, and the main influencing factors of nitrogen loss intensity were also investigated. The results indicated that the total nitrogen input to the food production and consumption system was 3 472.56 Gg/a. The largest component of the total nitrogen input came from fertilizer application. The total nitrogen output from the system was 3 061.29 Gg/a, mainly represented by nitrogen loss (90.9%). The nitrogen use efficiency (NUE) of cropland, livestock, and aquaculture subsystems was 42.6%, 30.8%, and 40.1%, respectively. Moreover, nitrogen loss from cropland subsystem was the highest, which was 1 325.53 Gg/a, accounting for 47.6% of the total nitrogen loss, followed by that from human consumption subsystem, livestock subsystem and aquaculture subsystem. The spatial heterogeneity of nitrogen loss intensity among cities in the Yangtze River Delta was significant. Shanghai, Yangzhou and Yancheng rank the top three in terms of nitrogen loss intensity, which was 26.43, 23.20 and 22.26 kg/hm2, respectively, while the nitrogen loss intensity of Hangzhou, Xuancheng and Chizhou was low, being 6.14, 5.83 and 4.55 kg/hm2, respectively. The result of Pearson correlation analysis showed that the spatial heterogeneity of nitrogen loss intensity was significantly correlated with factors including economy, population, agricultural production, and land use (P<0.05 or 0.01), with the correlation coefficients ranging from 0.42 to 0.76.

Typical safety risk and long-term management strategies for post-remediation site reuse
SHI Pengfei, PENG Zheng, MA Yan, AI Shengji, CHENG Lu, WANG Lifang, YU Jingjing, LI Fasheng
2023, 13(4): 1625-1634. doi: 10.12153/j.issn.1674-991X.20220841
Abstract(182) HTML (234) PDF(2748KB)(47)

From the view of engineering practices at home and abroad, the reuse of heavily polluted and complex post-remediation site often poses safety risks to human health, ecological environment or engineering construction. Long-term stewardship is the core strategy to ensure the safe reuse of post-remediation sites. However, relevant studies in this field are still insufficient in China. Based on the statistical analysis of 550 cases of contaminated sites in China, the results showed that 58.7% of post-remediation sites were redeveloped for residential purposes. Two typical safety risk problems, including heavy metal re-release after solidification/stabilization and vapor intrusion of organic pollutants, were analyzed. Based on foreign advanced long-term stewardship experience and domestic practices, suggestions for long-term stewardship and improvement of the above typical safety risks were put forward from five aspects, including long-term monitoring, institutional control, regular review, public participation and site archives management.

Comparative analysis of the environmental impact of virgin and recycled PET fibers based on life cycle assessment
LIU Qiwen, BI Yingying, DONG Liming, DONG Li, LIU Jingyang
2023, 13(4): 1635-1642. doi: 10.12153/j.issn.1674-991X.20220835
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The recycled polyester filaments prepared from recycled polyethylene terephthalate (PET) bottles and virgin filaments prepared from refined terephthalic acid and ethylene glycol were used as the analysis objects. The whole life cycle assessment (LCA) method was used to quantitatively analyze the environmental impact and contribution of each stage of production, and some suggestions for reducing environmental impact were put forward. Five environmental impact categories, including global warming potential (GWP), acidification, abiotic depletions, photochemical oxidation and terrestrial ecotoxicity, were selected for classification and calculation. The results showed that the environmental impact contribution of melt spinning stage in the production process of recycled filament was greater than that of physical treatment stage. Through characterization analysis and normalization analysis, compared with the virgin filament, the global warming potential of recycled filament per 100 kg was reduced by 32.09 kg CO2 eq, and the acidification potential was reduced by 0.37 kg SO2 eq. The most important categories of environmental impact in the production of virgin filament and recycled filament were abiotic depletions. According to the comprehensive and intuitive assessment of five environmental impact categories by the life cycle polygon method, the environmental impact of recycled filament was smaller than that of virgin filament, and the environmental impact could be reduced from the aspects of energy optimization and process improvement.