Yuxi Zhang

Driving mechanism and sources of groundwater nitrate contamination in the rapidly urbanized region of south China

Nitrate contamination of groundwater has become an environmental problem of widespread concern in China. We collected 899 groundwater samples from a rapidly urbanized area, in order to identify the main sources and driving mechanisms of groundwater nitrate contamination. The results showed that the land use has a significant effect on groundwater nitrate concentration (P<0.001). Landfill leakage was an important source of nitrate in groundwater in the PRD (Pearl River Delta) region, since landfill yielded the highest nitrate concentration (38.14 mg/L) and the highest ratio of exceeded standard (42.50%). In this study, the driving mechanism of groundwater nitrate contamination was determined to be urban construction and the secondary and tertiary industrial development, and population growth. This study revealed that domestic wastewater and industrial wastewater were the main sources of groundwater nitrate pollution. Therefore, the priority method for relieving groundwater nitrate contamination is to control the random discharge of domestic and industrial wastewater in regions undergoing rapid urbanization. Capsule abstract. The main driving mechanism of groundwater nitrate contamination was determined to be urban construction and the secondary and tertiary industrial development, and population growth.

Distribution and Mobility of Heavy Metals in Soil of Sewage Irrigation Area in Pearl River Delta, China

The research reveals the mobility and distribution of heavy metals (Cd, Cu, Zn, Mn, Ni, and Cr) in soil of sewage irrigation area in Pearl River Delta. Samples were collected from topsoil (0-10cm) and subsoil (30-40cm), and the total concentration and available concentration of heavy metals were extracted by HNO3–HF–HClO4 and DTPA respectively. The mean total concentrations for all of the heavy metals in topsoil are higher than that in subsoil in study area. Cd has the best mobility in soil of study area due to soil has lower retention for Cd than for other metals, while Ni has the poorest mobility in soil of study area. The total concentrations of Zn, Cu and Cd decrease with the depth of soil profile, while the total concentrations of Cr and Ni have little change with the depth of soil profile, only the total concentration of Mn has a little decrease at first and then increased rapidly with the depth of soil profile.

Heavy Metal Contamination and Potential Ecological Risk Assessment of Sediments in Yangzonghai Lake

The contents and characteristics of ten heavy metals in surface sediments from Yangzonghai Lake in Yunnan, China were analyzed. Ecological risk index presented by Håkanson to assess the potential ecological risk of Yangzonghai Lake was utilized. The results showed that the average concentrations of titanium(Ti), manganese(Mn), zinc(Zn), vanadium(V), chromium(Cr), copper(Cu), nickel(Ni), cobalt(Co), lead(Pb) and arsenic(As) in surface sediments of Yangzonghai Lake were up to 9413.1, 617.9, 149.2, 189.6, 145.8, 97.6, 55.1, 27.4, 40.3 and 31.4mg/kg, respectively, which are higher than their natural background values. Pearson’s correlation analysis indicated that Zn, Cr, Pb and As were highly correlated, and the similar distributions in sediment indicated that they might originate from activities. Ti, Mn, V, Cu, Ni, and Co were also well correlated, and the distributions indicated that they were mainly from natural factors. The evaluation of pollution index revealed a clear accumulation of the 10 heavy metals, all reaching the level of moderate pollution. As, Cu and Cr were the most important environmental contaminants in Yangzonghai Lake. As a whole, heavy metals reached the level of low ecological risks, and in some parts, they reached the moderate level. Heavy metals in Yangzonghai Lake in the descending order of their ecological risks were As, Cu, Co, Ni, Pb, Cr, V, Zn, Mn and Ti. As was more prominent than other heavy metals in terms of the ecological risk and thus the most important factor of potential ecological risk in surface sediment of Yangzonghai Lake.

Natural Background Levels of Fe and Mn in Groundwater of Pearl River Delta

As scientific references of evaluation on the groundwater contamination, natural background levels about chemical indexes TFe and Mn of shallow groundwater in Pearl River Delta was derived with SPSS statistical software, and its spatial distribution regularities and the controlling factor were discussed. The results show that the regularity in Pearl River Delta is primarily controlled by topography, redox environment, property of the cover, and groundwater flow conditions.

Hydrochemical Evolution of Shallow and Deep Groundwater in Tongchuan City, China

ABSTRACT Zhang, Y.; Liu, J., and Zhang, Y., 2015. Hydrochemical evolution of shallow and deep groundwater in Tongchuan city, China. In order to reveal the formation mechanism of hydrochemical characteristics in Tongchuan City, we collected and detected 39 samples of underground water. Correlation analytical method, hydrochemical method and ion ratio coefficient method were employed to investigate the hydrochemical characteristics, influencing factors and principles of changing. Results demonstrate that the main factors, controlling the shallow water salinization, are the SO42−, NO3−, Cl− and K+. The contents of SO42−, NO3− and Cl− are in great differences and other indexes are in relatively stable. The values of γNa/γCl demonstrate that the Na+ is released from the aquifer of soil in the process of runoff. There is an exchange between the Ca2+ in water and Na+ in soil, which leads to γNa>γCl. As the exchange time in deep water is longer than that of shallow water, the exchange and adsorption of ions are more sufficient. The value of γNa/(γNa+γCl) demonstrates that with the increasing of ground water depth, the level of cation exchange enhances, which leads to the dominant cation turns to Ca2+ from to Na+. The value of γHCO3+γSO4/γCa+γMg demonstrates the shallow water is mainly from atmospheric rainfall and the influence of cation exchange is more obvious on deep water. The types of shallow water in Tongchuan City are mainly HCO3·SO4-Ca. Its classification is relatively complex. Whereas, the deep water is mainly HCO3-Na and the category of underground water is simple. As for shallow water, the contents of alkaline earth metal is larger that of alkali metal. For the deep water, the content of weak acid group is larger than that of strong acid group. In the region of upper reaches, the feature of both shallow water and deep water are mainly weak acid and alkaline earth metal. The chemical composition mainly consists of carbonate leaching. With the flowing of underground water, the shallow water turns to be strong acid and alkaline earth metal and the deep water turn to be weak acid and alkali metal.

Study on Application of Two-stage Bio-contact Oxidation Technology in Municipal Wastewater Treatment in Alpine Region

Following the introduction of characteristic of wastewater and correlated project in the Alpine Region, the problems were pointed out which should be noticed in wastewater treatment process selection in this specific area. Some suggestions about key design parameters were proposed, and the Two-stage Bio-contact Oxidation Technology was been selected and applied in wastewater treatment plant in north suburb of Dongsheng District, Erdos City. Through project application, it was indicated that when average value of COD, BOD5 and SS was 483.2mg/L, 244.4mg/L and 258.4mg/L respectively during 10 days at about 12 ° in influent wastewater, average value in effluent water reached up to 57.1mg/L, 23.8mg/L and 26.5mg/L and removal rate of each contaminant was up to 88.2%, 90.3% and 89.7% respectively. It gained preferable results and this successful project also provided references for other similar wastewater treatment plant for future.

A New Automatic On-Situ Sampling and Monitoring Method for Water

In view of the fact that some difficulties exist in automatic and depthset sampling and monitoring for water, a new sampling system is developed. Firstly, the future sampler design ingredients are analyzed. Then the sampling system structure and operating principles are introduced in detail. A model machine is designed and several experiments have been carried on. The results indicate that this sampling system can perform automatic sampling effectively and efficiently; it could sample water as deep as 30m, and the depth error is less than 0.5m; water parameters such as temperature, pH and electrical conductivity (EC) can be measured on-site and the accuracy is 0.1∘C, 0.01 and 1μS/cm respectively. Besides, the sampler can reduce volatile organic components loss effectively and is also suitable to collect water sample for inorganic component analysis.

Characteristic and Speciation of Beryllium in Shallow Groundwater in the Pearl River Delta

The Distribution of shallow groundwater containing beryllium were summarized and the major factors influencing beryllium enrichment were discussed in this paper, based on chemical data of Be, aluminum and pH from more than 900 groundwater samples in the Pearl River Delta. The results show that Be concentration ranges from less than 0.02µg•L-1 to 40.3µg•L-1, with the majority less than 0.05µg•L-1 and the mean Be content of 0.66µg•L-1. The samples of Be content exceeding the upper limit for drinking water in China were scatteredly found in Guangzhou, Shenzhen, Dongguan, Foshan and Huizhou, with the over proof rate of 2.24%. The distribution of Be contamination in groundwater is characterized by local punctate type. The pH and Al are the major factors influencing distribution of beryllium in groundwater. Acidic and high Al content in groundwater and soil provide favorable conditions for migration of Be. Rock weathering and natural soil formation is one of the origins of Be in groundwater, and pollution caused by human activities is the other important source of Be in groundwater, especially in the severely contaminated sites.

Relationship and Enrichment of Heavy Metals in Soil of Sewage Irrigation Area in Guangdong Province, China

The research reveals the relationship and enrichment of heavy metals in soil of sewage irrigation area in Guangdong province, southern China. Samples were collected from topsoil (0-10cm) and subsoil (30-40cm), and the total concentrations of heavy metals were extracted by HNO3-HF-HClO4. It is concluded that Cu, Zn, Cd, and Pb may be homologous or combined pollution, and Mn and Cr may be also homologous in soil. According to the result of cluster analysis, it is shown that Se and As may have the similar environmental geochemical behavior in topsoil, because the existing forms of them in environment are mainly acid anions. We can conclude that a significant degree of metal pollution exists in soil of sewage irrigation area, particularly for Cd, Cu, Pb and Zn. The degrees of contamination of heavy metals in topsoil (CF of Cd 8.1, Cu 7.0, Zn 5.9, Pb 3.6, Ni 2.1, As 1.8, Cr 1.6, Se 1.5) were higher than that in subsoil (CF of Cd 6.0, Cu 3.4, Zn 3.7, Pb 2.7, Ni 2.0, As 1.6, Cr 1.5, Se 1.4). EF values show deficiency enrichment with Ni, Se, Cr and As, low enrichment with Cu, Zn and Pb, and moderate enrichment with Cd in topsoil in study area, while deficiency enrichment with Ni, Se, Cr, Pb and As, and low enrichment with Cu, Zn and Cd in subsoil in study area.It should be recognized that the hazards posed by food production in sewage irrigation areas may become a common hazard for human.

Distribution of Heavy Metals in Groundwater of Sewage Irrigation Area in Guangdong Province, China

The research reveals the distribution and correlation of heavy metals in groundwater of sewage irrigation area in Guangdong province. 14 groundwater samples were collected in August 2008, and the groundwater samples were filtrated through 0.45 µm membranes and acidified in the field. Determinations of Cd, Cu, Zn, Pb, Ni, and Cr in all the samples were performed using ICP-OES, and determinations of As and Se in all the samples were performed employing HG-AFS. The result shows that the groundwater of sewage irrigation area has been contaminated with As and Ni, whereas the concentrations of other heavy metals (Pb, Zn, Cu, Cr, Cd, Se) in groundwater did not reach the upper limit for drinking water in China. High As concentrations in groundwater may due to the weak alkaline character of groundwater in sewage irrigation area, because groundwater with weak alkaline is beneficial to enrichment of As. According to correlation and cluster analysis, it is shown that Ni, Se, Zn and Cd may have the common source (sewage irrigation) or by chemical similarity in groundwater, Pb and Cu may have the similar environmental geochemical behavior in groundwater since they are chalcophile elements, whereas As is out of other heavy metals due to the pH of groundwater, because groundwater with weak alkaline is beneficial to enrichment of As, in contrast, for Pb, Cu, Zn etc. In addition, weak correlation relationships between pH and heavy metals concentrations in groundwater of study area suggest that heavy metals concentrations in groundwater of sewage irrigation area are not governed by simple relationships with pH.