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Aluminium(Al)-rich (0.2 mg/L) groundwater has received more concerns because of its harmful to human beings. Origins of large-scale occurrence on Al-rich groundwater in urbanized areas such as the Pearl River Delta (PRD) are still little known. The current work was conducted to investigate spatial distribution of Al-rich groundwater in the PRD, and to discuss its origins in various aquifers. For that, 265 groundwater samples and 15 river water samples were collected, and 21 hydrochemical parameters including Al were analyzed by using conventional analytical procedures. The results showed that groundwater Al concentrations were up to 22.64 mg/L, and Al-rich groundwater occurred in 15% of the area occupied by the PRD. Al-rich groundwater in the coastal-alluvial aquifer was about 2 times those in alluvial-proluvial and fissured aquifers, whereas the karst aquifer was absent. In the coastal-alluvial aquifer, Al-rich groundwater in the peri-urban area was 2 or more times those in urbanized and agricultural areas, whereas the remaining area was absent. By contrast, in the alluvial-proluvial aquifer, Al-rich groundwater in the remaining area was 1.5-3.5 times that in other areas; in the fissured aquifer, the distribution of Al-rich groundwater was independent of land-use types. The infiltration of wastewater from township enterprises was main anthropogenic source for Al-rich groundwater in urbanized and peri-urban areas, whereas irrigation of Al-rich river water was the main one in the agricultural area. Naturally dissolution of Al-rich minerals in soils/rocks, triggered by both of pH decrease resulted from nitrification of contaminated ammonium (e.g., sewage leakage, the use of nitrogen fertilizer) and acid deposition, was the main geogenic source for Al-rich groundwater in the PRD. The contribution of anthropogenic sources to Al-rich groundwater in the coastal-alluvial aquifer was more than that in alluvial-proluvial and fissured aquifers, whereas the contribution of geogenic sources was opposite. In conclusion, the discharge of township enterprises wastewater and ammonium-rich sewage, the emission of nitrogen-containing gas, and the use of nitrogen fertilizer should be preferentially limited to decrease the occurrence of Al-rich groundwater in urbanized areas such as the PRD.

Identifying nitrate sources and their temporal evolution in different land use is important for the sustainable management of groundwater resources. In this study, groundwater dating (

Knowledge on driving forces controlling natural background levels (NBLs) of geogenic contaminants (GCs) in groundwater of coastal urbanized areas are still limited because of complex hydrogeological conditions and anthropogenic activities. This study assesses NBLs of two GCs including arsenic (As) and manganese (Mn) in four groundwater units of the Pearl River Delta (PRD) with large scale urbanization by using a preselection method composed of the chloride/bromide mass ratio versus chloride concentration and the oxidation capacity with the combination of Grubbs' test. More importantly, driving factors controlling NBLs of As/Mn in groundwater of the PRD are discussed. Results showed that groundwater As/Mn concentrations in residual datasets were independent of land-use types, while those in original datasets in different land-use types were distinct because of various human activities, indicating that the used preselection method in this study is valid for NBLs-As/Mn assessment in groundwater of the PRD. NBL-As in coastal-alluvial aquifers was6 times that in other groundwater units. NBL-Mn in coastal-alluvial aquifers was 1.4 times that in alluvial-proluvial aquifers, and both were4 times that in other two groundwater units. High NBLs-As/Mn in coastal-alluvial aquifers is mainly attributed to reduction of FeMn oxyhydr(oxides) induced by mineralization of organic matter in Quaternary sediments. Elevated pH also contributes higher NBL-As in coastal-alluvial aquifers. By contrast, higher NBL-Mn in alluvial-proluvial aquifers than in other two groundwater units mainly ascribes to reduction of FeMn oxyhydr(oxides) in Quaternary sediments triggered by irrigation of reducing river waters. In addition, more occurrence of As/Mn-rich sediments and the infiltration of As/Mn-rich river water are also important factors for high NBLs-As/Mn in coastal-alluvial aquifers. This study shows that revealing natural driving factors of GCs-rich groundwater in coastal urbanized areas on the basis of identification of contaminated groundwaters via the used preselection methods is acceptable.

Cadmium (Cd)-contaminated paddy soils are a big concern. However, the effect of irrigation with acid water on the migration and transformation of Cd and the effect of alternating redox conditions caused by intermittent irrigation on Cd aging processes in different depths of paddy soils are unclear. This study revealed Cd fractionation and aging in a Cd-contaminated paddy soil under four irrigation periods with acid water and four drainage periods, by applying a soil columns experiment and a sequential extraction procedure. The results showed that the dynamic changes of soil pH, oxidation reduction potential (ORP), iron (Fe) oxides and dissolved organic carbon (DOC) throughout the intermittent irrigation affected the transformation of Cd fractions. After 32 days, the proportion of exchangeable Cd (F1) to the total Cd decreased with a reduction of 24.4% and 20.1% at the topsoil and the subsoil, respectively. The labile fractions of Cd decreased, and the more immobilizable fractions of Cd increased in the different depths of soils due to the aging process. Additionally, the redistribution of the Fe and Mn oxide-bound Cd (F3) and organic matter and secondary-sulfide-bound Cd (F4) occurred at different depths of soils during the incubation time. Overall, the bioaccessibility of Cd in the subsoil was higher than that in the topsoil, which was likely due to the leaching and accumulation of soluble Cd in the deep soil. In addition, the aging processes in different depths of soils were divided into three stages, which can be mainly described as the transformation of F1 into F3 and F4.

As the most important graphene derivate, graphene oxide (GO) is a high-efficient adsorbent for the removal of heavy metals in aquatic environment due to its abundant oxygen functional groups, enormous specific area, and strong hydrophilia. However, there are some drawbacks, such as easily aggregating and difficult separation, restricting the environmental application of GO. GO is not a suitable adsorbent by itself. Hence, some materials were used to synthesize GO composites, and GO composites are commonly characterized by high adsorption capacity to overcome the above drawbacks. This review discusses five main GO composites-GO-chitosan, GO-alginate, GO-SiO2, NZVI-rGO, and magnetic GO composites-and summarizes the synthesis methods of GO composites and its application for the removal of heavy metals in aquatic environments. The influencing factors, adsorption capacities, and mechanisms related to the removal of heavy metals by GO composites are highlighted. Lastly, the application potentials and challenges of GO composites for aqueous environmental remediation are discussed. Graphical abstract.

Fe-rich (0.3 mg/L) groundwater is generally present in areas where organic matter-rich fluvial, lacustrine, or marine sedimentary environments occur. The Pearl River Delta (PRD) that marine sediments is common, where a large scale of Fe-rich groundwater was distributed but disappearing in recent decade. This study aims to investigate the change of Fe-rich groundwater in the PRD, and to discuss the genesis controlling Fe-rich groundwater in the PRD during the past dozen years. A total of 399 and 155 groundwater samples were collected and analyzed at 2006 and 2018, respectively. Results showed that Fe-rich groundwater of the PRD was from 19.3% at 2006 dropped to 1.3% at 2018. Fe-rich groundwater in coastal-alluvial aquifers was more than 2 times that in other aquifers at 2006. Both of anthropogenic and geogenic sources were contributed to the widely distribution of Fe-rich groundwater in the PRD at 2006. The infiltration of industrial wastewater and the irrigation of Fe-rich surface water were the major anthropogenic driving forces for the occurrence of Fe-rich groundwater in the PRD at 2006. The reductive dissolution of Fe minerals in aquifer sediments, associated with the degradation of organic matter in marine sediments and the sewage infiltration, was the main driving force for the enrichment of groundwater Fe in coastal-alluvial aquifers at 2006. The intrusion of sewage triggering the reductive dissolution of Fe minerals in terrestrial sediments and the reductive dissolution of Fe minerals in carbon-rich rocks induced by sewage leakages were the major driving forces for the occurrence of Fe-rich groundwater in alluvial-proluvial and fissured aquifers at 2006. All these driving forces were weaker or even not work at 2018 because of the large decrease of untreated wastewater discharge in the PRD during 2006-2018. Therefore, limiting untreated wastewater discharge is the first choice to improve the groundwater quality in urbanized areas.

The experimental and simulated investigations on electrostatic spraying with twin capillaries are carried out. The starting electric voltage required for the cone-jet and the deposition characteristics of the droplets are measured. The whole spraying process, which includes jet and droplet motions, is simulated and the simulated results on the motions of jet and droplet are basically consistent with the experiments. According to the simulated results, the contributions of various electric forces to droplet movement are quantitatively analyzed and the droplet dynamic characteristics, especially the interaction mechanism between two sprays, are revealed. The test results on the droplet deposition characteristics partially support the simulated results on the droplet motion. The present work is useful for a better understanding on the interaction between sprays in double or multi-capillary system.

Groundwater pollution in urbanized areas (UAs) is commonly complicated due to various human activities. This chapter discussed the groundwater pollution in the Pearl River Delta (PRD) where high levels of urbanization and industrialization are. High levels of manganese, iron, ammonium, iodide, nitrate, and arsenic in groundwater often occur in the PRD. The reductive dissolution of iron/manganese (oxyhydr)oxides, the release of arsenic and iodide adsorbed onto iron/manganese (oxyhydr)oxides, and the mineralization of organic matter in strata are mainly responsible for high levels of manganese, iron, arsenic, iodide, and ammonium in groundwater. By contrast, high level of nitrate in groundwater originated mainly from the leakage of domestic sewage and industrial wastewater. About 5% groundwater was detected 18 organic pollutants, and naphthalene was the most frequently detected organic pollutant with detection rate of 2.51%. The occurrence of organic pollutants in groundwater originated mainly from the industrialization.

Establishment of natural background levels (NBL) of groundwater in urbanized areas such as the Pearl River Delta (PRD) is challenging. Pre-selection methods are the most common approaches for NBL assessment, but it will overestimate (or underestimate) contaminated groundwater in urbanized areas by using present pre-selection methods with empirical definite values because of complicated human activities. Unlike present pre-selection methods, this study aims to establish a new pre-selection method with the indicative of Cl/Br ratios to identify contaminated groundwaters with convincing evidences. Specifically, this new method consists of indicatives of the oxidation capacity and the Cl/Br ratio combining with contaminated-markers. In addition, factors controlling NBL of Cl and NO3 in groundwater in various hydrogeological units in the PRD were also discussed. Main procedures of this new method: contaminated-markers in various hydrogeological units are extracted by a hierarchical cluster analysis, thereby determining threshold values of Cl/Br ratios and Cl concentration in various hydrogeological units for identifying contaminated groundwater; After that, groundwater chemical datasets was selected by the oxidation capacity, and then tested by Grubbs' test until normal distributions. Groundwater Cl and NO3 concentrations in datasets before and after this new method are dependent and independent of urbanization levels, respectively, indicating that the new method is useful for groundwater NBL assessment in urbanized areas such as the PRD. Both the seawater intrusion and the diffusion of Cl from marine deposits are likely to be responsible for the much higher NBL-Cl in coastal-alluvial and marine aquifers than in other hydrogeological units. Groundwater Cl enrichment resulted from groundwater recharge and evaporation is mainly responsible for the higher NBL-Cl in alluvial-proluvial aquifers than in lacustrine aquifers, fissured aquifers, as well as karst aquifers. More than double times NBL-NO3 in alluvial-proluvial and fissured aquifers than in other hydrogeological units is probably attributed to more oxidizing conditions of their vadose zones and groundwaters.

Efficient identification of groundwater contamination is a major issue in the context of groundwater use and protection. This study used a new approach of multi-hydrochemical indicators, including the Cl-Br mass ratio, the hydrochemical facies, and the concentrations of nitrate, phosphate, organic contaminants, and Pb in groundwater to identify groundwater contamination in the Pearl River Delta (PRD) where there is large scale urbanization. In addition, the main factors resulting in groundwater contamination in the PRD were also discussed by using socioeconomic data and principal component analysis. Approximately 60% of groundwater sites in the PRD were identified to be contaminated according to the above six indicators. Contaminated groundwaters commonly occur in porous and fissured aquifers but rarely in karst aquifers. Groundwater contamination in porous aquifers is positively correlated with the urbanization level. Similarly, in fissured aquifers, the proportions of contaminated groundwater in urbanized and peri-urban areas were approximately two times that in non-urbanized areas. Groundwater contamination in the PRD was mainly attributed to the infiltration of wastewater from township-village enterprises on a regional scale. In addition, livestock waste was also an important source of groundwater contamination in the PRD. Therefore, in the future, the supervision of the wastewater discharge of township-village enterprises and the waste discharge of livestock should be strengthened to protect against groundwater contamination in the PRD.

Groundwater contamination with heavy metal (loid)s occurs worldwide. Permeable reactive barriers (PRBs) have been widely accepted as an alternative to traditional ex-situ removal technologies for sustainable in-situ remediation of heavy metal (loid) contaminated groundwater. Reactive media play a key role in efficiently removing target metal (loid) ions with PRBs. The past few decades have seen the rapid development of reactive media within PRBs for the removal of heavy metal (loid)s in groundwater. Recently, more complicated and multifunctional are the up-to-date characteristics of reactive media within PRBs through modifications toward traditional material. This review summarizes recent findings regarding reactive media within PRBs for the removal of heavy metal (loid)s in groundwater. Reactive media are classified into three classes, namely emerging single material, mixed materials, and core-shell materials. The characteristics of metal (loid)s and representative applied-materials for particular metal (loid) remediation with PRBs are presented. The primary mechanisms and factors influencing the reaction of reactive media with heavy metal (loid)s in groundwater are also summarized, and, the regeneration of used materials and the shortcomings of current reactive media investigated in laboratory-to-field application are highlighted. Finally, developmental directions and exploration highlights for PRB material applied to remove heavy metal (loid)s from groundwater in the future are highlighted. This review provides up-to-date insights into the removal of heavy metal (loid)s using reactive media within PRB and collates references for future research and field-scale applications.

Regional-scale nitrate and organic contaminants in the shallow groundwater were investigated in the Piedmont region of Taihang Mountains (PRTM), but the information of the microbial communities is limited. However, microorganisms provide a dominated contribution to indicate and degrade the contaminants in the aquifer. Therefore, this study investigates the microbial diversity and contamination microbial indicators of groundwater samples with different contaminated types to better understand the contamination in the PRTM. Seventy-six samples were collected between two rivers in the Tang-Dasha River Basin covering 4000 km2 in the PRTM. High-throughput sequencing was employed to determine the samples&rsquo, DNA sequences. The samples were divided into four groups: background (B), nitrate contamination (N), organic contamination (O) and organic-nitrate contamination (O_N) based on the cumulative probability distribution and the Chinese groundwater standard levels of NO3&minus, COD and DO concentrations. Then, the microbial diversity and contamination microbial indicators were studied in the four groups. The results showed that the O group exhibited lower diversity than other groups. Bacteria detected in these four groups covered 531 families, 987 genera, and 1881 species. Taxonomic assignment analysis indicated that Rhodobacter, Vogesella, Sphingobium dominated in the O_N group, N group, and O group, and accounted for 18.05%, 17.74%, 16.45% in each group at genus level, respectively. Furthermore, these three genera were identified as contamination microbial indicators to the three types of contamination, respectively. The results provide a potential molecular microbiological method to identity contamination in shallow groundwater, and established a strong foundation for further investigation and remediation in the PRTM.

Redox conditions and arsenic (As) loads may affect the aging mechanisms of As in soils. A batch experiment of one wastewater-irrigated soil under four different conditions was performed to investigate the impact of redox conditions and As loads on the aging mechanisms of As in soils in this study. The results showed that the aerobic condition substantially decreased the more labile fractions and increased the less mobilizable or immobilizable fractions in soils over time, which was likely due to the oxidation of As(III) to As(V) and the decomposition of organic matter. The redistribution of the strongly adsorbed and organically bound fraction (F4) occurred in all soils during the aging process, and both low As load and aerobic conditions accelerated this redistribution. The aging processes of As were characterized by three stages in various soils except the low As load soil with two stages within 180 days: The transformations of As fractions were from three former fractions to three later ones in all soils in the first stage (0 day–10 days), while the main transformations after 10 days were from F4 to bound to Fe and Mn/Al oxides fraction (F5) and from water soluble fraction (F1) to F5 in soils with low and high As loads, respectively; In contrast, the main transformations in the second stage were from F1 to F4 and from F1 to F5 in soils at low oxygen and aerobic conditions, respectively, and were from F4 to F5 in the third stage in both redox conditions. The bioaccessibility of As in the low As load soil decreased markedly from approximately 40% down to 70% down to

Groundwater quality assessment is essential for drinking from a security point of view. In this paper, a new evaluation method called toxicity combined fuzzy evaluation (TCFE) has been put forward, which is based on the fuzzy synthetic evaluation (FSE) method and the toxicity data from Agency for Toxic Substances and Disease Registry. The comparison of TCFE and FSE in the groundwater quality assessment of Guangzhou region also has been done. The assessment results are divided into 5 water quality levels; level I is the best while level V is the worst. Results indicate that the proportion of level I, level II, and level III used by the FSE method was 69.33% in total. By contrast, this proportion rose to 81.33% after applying the TCFE method. In addition, 66.7% of level IV samples in the FSE method became level I (50%), level II (25%), and level III (25%) in the TCFE method and 29.41% of level V samples became level I (50%) and level III (50%). This trend was caused by the weight change after the combination of toxicity index. By analyzing the changes of different indicators' weight, it could be concluded that the better-changed samples mainly exceeded the corresponding standards of regular indicators and the deteriorated samples mainly exceeded the corresponding standards of toxic indicators. The comparison between the two results revealed that the TCFE method could represent the health implications of toxic indicators reasonably. As a result, the TCFE method is more scientific in view of drinking safety.

The objective of this study is to investigate the impacts of anthropogenic and natural processes on the granular aquifer (GA) and the fractured rock aquifer (FRA) in the central region of Guangzhou city. Results indicate that 47.8% and 30.4% of samples in GA are not suitable for drinking and industrial purposes respectively, mainly due to the high concentrations of Fe and NH4+. In contrast, 48.3% and 41.4% of samples in FRA are not suitable for drinking and industrial purposes respectively, mainly due to the high concentrations of Al, NO3−, NH4+, Fe, and Pb. The contributions of Pb, Al, and NO3− to groundwater quality in GA are lower than those in FRA, while the contributions of Na+, Cl−, SO42−, and TDS to groundwater quality in GA and FRA are similar. High concentrations of Pb, Al, Na+, Cl−, SO42−, TDS, and NO3− in groundwater of both GA and FRA are mainly ascribed to human activities such as urbanization and industrialization, while high concentrations of Fe and NH4+ in groundwater of GA are mai...

Iodine-rich groundwater is a cause for concern because it is harmful to human health, and determining the sources of groundwater iodine in coastal urbanized areas is complicated. This study aims to delineate the spatial distribution of groundwater iodide in various shallow and unconfined aquifers, as well as in areas with different urbanization levels in the Pearl River Delta (PRD), and to identify the origins of iodide-rich (>0.08 mg/L) groundwater in this region. Approximately 400 groundwater samples, 10 surface water samples, and 9 leachate samples were collected, and a total of 17 chemicals were analyzed. The result showed that iodide-rich groundwater was present in 13.95% of shallow granular aquifers and 6.82% of shallow fissured aquifers; however, it was not present in karst aquifers. In shallow granular aquifers, the proportions of iodide-rich groundwater in areas with different urbanization levels were similar. On the other hand, in shallow fissured aquifers, iodide-rich groundwater mostly appeared in urbanized areas, and its proportion was more than three times that of non-urbanized areas; however, it was not present in peri-urban areas. The reductive dissolution of iodine-loaded Fe/Mn (oxy)hydroxides and decomposition of iodine-rich organic matter in sediments were likely the main sources of iodide-rich groundwater in shallow granular aquifers. Urbanization accompanied by wastewater leakage was also a significant source for iodide-rich groundwater in granular aquifers of urbanized areas. In contrast, the degradation of organic matter in carbonate-rich rocks and urbanization accompanied by leakage of reductive sewage were most likely responsible for the occurrence of iodide-rich groundwater in shallow fissured aquifers. The leakage of landfill leachate was also a significant source for iodide-rich groundwater in the fissured aquifers of non-urbanized areas.

The fate of phosphorus in groundwater needs to be understood because phosphorus-rich groundwater is discharged into surface water bodies, which causes eutrophication, especially in urbanized areas. The present study investigated the spatial distributions and driving forces related to the groundwater phosphate levels in various aquifers in the Pearl River Delta (PRD), which has undergone three decades of urbanization, as well as the relationship between groundwater phosphate and arsenic was also discussed. The results showed that most of the high-phosphate (>1.53 mg/L) groundwater occurred in granular aquifers. The proportion of high-phosphate groundwater in granular aquifers was more than four times that in fissured aquifers, whereas high-phosphate groundwater was not observed in karst aquifers in the PRD. High-phosphate groundwater primarily occurred in urbanized areas in the PRD, and the proportion of high-phosphate groundwater had a significant positive correlation with the urbanization level. In granular aquifers, reductive environment and alkalization led to enrichment of the groundwater with phosphate. Anthropogenic sources such as wastewater from township-village enterprises (TVE) and animal wastes were the main sources of high-phosphate groundwater in urbanized areas, and the external input of phosphate enriched the groundwater arsenic levels in urbanized areas. By contrast, geogenic sources such as the release of phosphate from the reduction of Fe/Mn (hydr)oxides and the seawater intrusion accompanied by the release of phosphate from secondary minerals were mainly responsible for the occurrence of high-phosphate groundwater in peri-urban and non-urbanized areas, respectively. The high concentrations of both phosphate and arsenic in groundwater in fissured aquifers were mainly attributed to the infiltration of wastewater from TVEs. In contrast to the granular aquifers, the groundwater Eh and pH conditions were not conductive to the occurrence of high-phosphate groundwater in fissured aquifers.

High nitrogen loading in aquifers is an important issue because of its harmful effects on human health; its origins are often complicated, especially in urbanized areas. This study aims to investigate the distributions of nitrate, nitrite, and ammonium in various aquifers in the Pearl River Delta, and to identify their main sources using hydrochemical and socioeconomic data and principal component analysis. The results show that groundwater with high nitrate (>20 mg/L as N), high nitrite (>1 mg/L as N), and high ammonium (>0.5 mg/L as N) appeared in 7.0%, 4.3%, and 20.5% of granular aquifers, and in 8.3%, 0.8%, and 5.3% of fissured aquifers, respectively, but did not appear in karst aquifers. The proportions of high-nitrate and high-ammonium groundwater in urbanized areas were nearly or more than twice those in non-urbanized areas. High nitrate levels in both granular and fissured aquifers originated mainly from the wastewater leakage of township-village enterprises during the industrialization. Urbanization accompanied by leakage of domestic sewage was another main driving force for high nitrate levels in fissured aquifers. Housing construction aggravated groundwater nitrate contamination in newly urbanized areas. Nitrate contamination in granular aquifers was reduced via denitrification in urbanized areas developed in 1988–1998, whereas that in fissured aquifers was increased by nitrification in urbanized areas developed before 1998. High ammonium levels in granular aquifers in urbanized areas originated mainly from mineralization of organic nitrogen in overlying aquitards, whereas that in peri-urban areas and non-urbanized areas originated mainly from urbanization accompanied by leakage of domestic sewage and irrigation using ammonium-rich river water, respectively. By contrast, high ammonium levels in fissured aquifers are attributed mainly to mineralization of organic nitrogen in carbon-rich strata, which was enhanced by urbanization accompanied by a relatively anoxic environment. Our study implies that nitrate and ammonium contaminations in this area will worsen in the future owing to a lack of effective control and treatment in these rapidly urbanized areas. Naturally originating high-ammonium groundwater in this area can be used as a nitrogen resource, for example, as a nitrogen fertilizer in agricultural irrigation.

High concentration of manganese (Mn) in groundwater is a major concern because of its harmful to human health, and the origin of which in urbanized areas is often complicated. The present study aims to delineate spatial distributions of groundwater Mn in various aquifers and in areas with different urbanization levels in the Pearl River Delta (PRD), and to identify the origins of groundwater Mn in this region. Nearly 400 groundwater samples collected, and 14 chemicals were analyzed. The results show that approximately 20% groundwater in granular aquifers showed elevated-Mn (>0.4 mg/L), and was more than two times of that in fissured aquifers, while that in karst aquifers was absent. The proportions of elevated-Mn groundwater in urbanized areas and peri-urban areas were higher than that in non-urbanized areas. The decomposition of organic matter and reduction of Fe (hydr)oxides in sediments with reducing condition was likely to be the main factor controlling elevated-Mn groundwater in granular aquifers at a regional scale. By contrast, elevated-Mn groundwater in fissured aquifers was likely mainly affected by the urbanization accompanied with the leakage of low-oxygen domestic sewage and the industrialization accompanied by the leakage of industrial wastewater. In addition, Mn-rich surface water was also probably an important source for groundwater Mn in river network areas. Therefore, it is necessary to make a long-term monitoring for groundwater Mn in granular aquifers, especially in urbanized areas and river network areas, because of the high proportion of elevated-Mn.

Urbanization and industrialization have increased groundwater resource demands, and may drive the change of heavy metal(loid)s and organic chemicals in groundwater in the Pearl River Delta (PRD), southern China. Thus, a comprehensive understanding of the distributions, sources, and driving forces of heavy metal(loid)s and organic chemicals in groundwater in the PRD is vital for water resource management in this region. In this study, eight heavy metal(loid)s and fifty-five organic chemicals in groundwater across the PRD were investigated. The results show that undrinkable groundwater related to heavy metal(loid)s was mainly due to high concentrations of Fe (19.3%) and As (6.8%). Eighteen organic contaminants were detected in groundwater in the PRD, where the most frequently detected organic contaminant was naphthalene, and its detection rate was 2.51%. In 5.3% of all groundwater samples, one or more organic contaminants were found. All detected organic contaminants, except ones without allowable limits, in groundwater were at concentrations below allowable limits of China. The mean concentrations of heavy metal(loid)s in granular aquifers were higher than those in fissured and karst aquifers, especially for Fe and As. Except Se, the mean concentrations of other heavy metal(loid)s and the frequency of detection of organic contaminants in groundwater in urbanized and peri-urban areas were higher than those in non-urbanized areas, especially for Hg, Co, and organic contaminants. Fe, As, and Se in groundwater mainly originated from the release of Fe/As/Se rich sediments. The former two were driven by reduction reactions, while the latter was driven by oxidation resulting from the infiltration of NO3-. In contrast, other five heavy metal(loid)s and organic contaminants in groundwater mainly originated from the anthropogenic sources, such as the infiltration of industrial sewage. It is evident that urbanization and industrialization are two powerful driving forces for heavy metal(loid)s and organic contaminants in groundwater in the PRD.

The present study focused on the influence of temperature variation on the aging mechanisms of arsenic in soils. The results showed that higher temperature aggravated the decrease of more mobilizable fractions and the increase of less mobilizable or immobilizable fractions in soils over time. During the aging process, the redistribution of both carbonate-bound fraction and specifically sorbed and organic-bound fraction in soils occurred at various temperatures, and the higher temperature accelerated the redistribution of specifically sorbed and organic-bound fraction. The aging processes of arsenic in soils at different temperatures were characterized by several stages, and the aging processes were not complete within 180 days. Arsenic bioaccessibility in soils decreased significantly by the aging, and the decrease was intensified by the higher temperature. In terms of arsenic bioaccessibility, higher temperature accelerated the aging process of arsenic in soils remarkably.

Fuel spray and atomization characteristics play an important role in the performance of internal combustion engines. Experimental and numericalatomization studies of the fuel injector used in IGC (Inner Guide-vane Combustor) under various assembly and operation conditions have been performed in order to determine the configurations of the fuel injector proposed for use in IGC.Droplet Sauter MeanDiameter (SMD) distributions were measured with Phase Doppler Analyzer (PDA) at differentoperating conditions and used to evaluate the atomization performance. Computational Fluid Dynamic (CFD)study has also been conducted based on Discrete Particle Model (DPM).Current work examines optimizing the atomizer location and assembly condition of these vanes and the cavity within them. Results reveal thatthe distribution of droplet SMDvaries with the assembly and operation condition. The further results showed that fuel injector used in IGC with single slot, forward injection direction and ‘

Using by sequential extraction procedures to obtain the chemical forms of arsenic in soils can provide useful information for the assessment of arsenic mobility and bioavailability in soils. However, sample pretreatments before the extraction probably have some effects on the fractionation of arsenic in soils. Impact of sample pretreatments (freeze-drying, oven-drying, air-drying, and the fresh soil) on the fractionation of arsenic in anoxic soils was investigated in this study. The results show that there are some differences for arsenic fractions in soils between by drying pretreatments and by the fresh soil, indicating that the redistribution among arsenic fractions in anoxic soils occurs after drying pretreatments. The redistribution of arsenic fractions in anoxic soils is ascribed to the oxidation of organic matter and sulfides, the crystallization of iron (hydr)oxides, the ageing process, and the diffusion of arsenic into micropores. The freeze-drying is the best drying method to minimize the effect on the fractionation of arsenic in anoxic soils, while air-drying is the worst one. Drying pretreatments are not recommended for the fractionation of arsenic in anoxic soils with high concentration of iron.

The distribution of arsenic (As) in shallow groundwater of eastern Chancheng District in Foshan City as a function of season and water table was investigated, and the influence of hydrochemical factors on the As distribution was discussed. The groundwater samples were collected from 20 sites in dry season and 9 sites in wet season. As concentrations in 20% groundwater samples exceeded value of the WHO guideline (10 μg/L), and the highest As concentration of 23.5 μg/L occurred in dry season. It is observed that groundwater As concentration decreased with the increase of depth of water table in dry season, and were generally higher in wet season than that in dry season, indicating that ground surface As might be one of the main sources for shallow groundwater As in study area, especially in wet season. Groundwater As concentration in study area had significantly positive correlation with the concentration of Fe, Mn, NH4, F, and COD, and was positively correlated to pH, but negatively correlated to Eh and K, indicating that reductive dissolution of Fe and Mn (oxy)hydroxides might be one of the main control mechanisms for groundwater As mobilization, while pH and F also played an important role in controlling the groundwater As mobilization in study area.

Anthropogenic factors resulted from the urbanization may affect the groundwater As in urbanized areas. Groundwater samples from the Guangzhou city (South China) were collected for As and other parameter analysis, in order to assess the impact of urbanization and natural processes on As distribution in aquifers. Nearly 25.5 % of groundwater samples were above the WHO drinking water standard for As, and the As concentrations in the granular aquifer (GA) were generally far higher than that in the fractured bedrock aquifer (FBA). Samples were classified into four clusters by using hierarchical cluster analysis. Cluster 1 is mainly located in the FBA and controlled by natural processes. Anthropogenic pollution resulted from the urbanization is responsible for high As concentrations identified in cluster 2. Clusters 3 and 4 are mainly located in the GA and controlled by both natural processes and anthropogenic factors. Three main mechanisms control the source and mobilization of groundwater As in the study area. Firstly, the interaction of water and calcareous rocks appears to be responsible for As release in the FBA. Secondly, reduction of Fe/Mn oxyhydroxides and decomposition of organic matter are probably responsible for high As concentrations in the GA. Thirdly, during the process of urbanization, the infiltration of wastewater/leachate with a high As content is likely to be the main source for groundwater As, while NO3 − contamination diminishes groundwater As.

To elucidate the distribution of arsenic in shallow aquifers of the Guangzhou region (South China), 85 groundwater samples were collected and 18 chemical parameters of them were analyzed. The arsenic concentration of groundwater ranged from below detection limit to 0.13 mg/L. The results showed that those areas with high arsenic concentration were characterized by porous aquifers, low-lying, relief topography and close proximity to fault belt and rivers. The reductive dissolution of Fe (hydr)oxides is the main control mechanism for arsenic enrichment in the river delta region where groundwater is mainly characterized by a reducing environment. This mechanism was well embodied in the areas with these geological and geographical features. Agricultural fertilizer could produce high levels of nitrate in groundwater and the reduction of it could restrain the enrichment of arsenic. Industrial effluents, sewage irrigation and the probable leakage from sewers could promote the arsenic content in groundwater by lateral flow and infiltration. In addition, the effect of ion competition between phosphate and arsenic occurred in sewer leakage areas characterized by middle-high construction leading to the elevation of arsenic concentrations. The arsenic distribution in groundwater was caused by these natural and anthropogenic factors jointly.

Industrialization and urbanization expansion may change the groundwater quality in the Pearl River Delta (PRD). The aims of this study were to evaluate the groundwater quality in various aquifers and areas with different urbanization levels in the PRD, to extract the main impact indicators, and to discuss the driving forces for the groundwater quality. Nearly 400 groundwater samples were collected and 23 indicators were analyzed. In the PRD, 83% groundwater was drinkable (good-quality) by using a fuzzy synthetic evaluation method. Groundwater in karst aquifers was drinkable, and its quality was better than those in granular and fissured aquifers. In the latter two aquifer types, groundwater quality in non-urbanized areas was much better than those in peri-urban and urbanized areas. In granular aquifers, Mn + Fe, I− + Ni + Mn, and Mn + As + I− were the main impact indicators for poor-quality groundwater in urbanized areas, peri-urban areas, and non-urbanized areas, respectively. Correspondingly, reductive dissolution of Fe/Mn (oxy)hydroxides, infiltration of industrial wastewater and reductive dissolution of I− and Mn, and reductive dissolution of Mn, As, and I− were likely responsible for poor-quality groundwater in these areas, respectively. By contrast, in fissured aquifers, NO3−, NO3− + Pb, and I− were the main impact indicators for poor-quality groundwater in urbanized areas, peri-urban areas, and non-urbanized areas, respectively. Correspondingly, infiltration of domestic sewage, infiltration of domestic sewage and industrial wastewater, and mineralization of I-rich organic matter were probably responsible for poor-quality groundwater in these areas, respectively. Industrialization was one of the main driving forces for groundwater quality in granular and fissured aquifers in peri-urban areas, while urbanization was one of the main driving forces for groundwater quality in fissured aquifers in urbanized and peri-urban areas in the PRD.

The present work investigates the adsorption of As (III) on a soil irrigated by sewage, as a function of reaction time, initial As (III) concentrations, pH, phosphate, and humic acid. The results show that As (III) adsorption onto the soil takes place in two processes: a fast one that takes place in less than 1 h and a slow one that takes place in about 6 h, and the rate data are best described by the pseudo second-order kinetic model at pH 7.5. As (III) adsorption can be better described by the Freundlich isotherm model, although Langmuir, Temkin and Dubinin–Radushkevich isotherm models can also give a good fit for the adsorption of As (III) onto the soil. The maximum adsorption amount of As (III) derived from Langmuir isotherm for the soil is 0.368 mg/g. The adsorption of As (III) decreases slightly at final pH 1.21–4.3 due to the decrease of net positive charge for the soil and the apparent species transformation of As, then increases rapidly up to pH about 7 and decreases again as pH continues to increase. The presence of phosphate or humic acid prevents the adsorption of As (III) onto the soil, and the inhibition efficiencies of phosphate for As (III) adsorption onto the soil with the initial phosphate/As (III) molar ratio ≥ 1 are higher than that with the initial phosphate/As (III) molar ratio

Groundwater quality is the critical factor that affects human health and the quality of industrial products in Foshan City, South China. Multivariate statistical techniques, including hierarchical cluster analysis (HCA) and principal component analysis (PCA), were applied to evaluate and interpret the complex groundwater quality in eastern Chancheng district, Foshan City. During the dry and wet seasons, 60% and 11% of the total groundwater samples (respectively) are suitable for drinking purposes; other samples can be used for drinking after being treated for pH, Fe, Mn, Al, NH4, and NO3. Similarly, during the dry and wet seasons, 75% and 33% of the total groundwater samples (respectively) are suitable for industrial purposes; other samples can be used for industrial purposes after being treated for NH4 and NO3. Five principal components are extracted from PCA and used to explain 81.78% of the variance in groundwater. The indicators to groundwater quality assessment are EC, Na, Cl, Fe, Mn, NH4, pH, Eh, PO4, HCO3, and K from PCA. HCA reveals that groundwater samples in the study area can be classified into three groups: one reflecting the interaction of groundwater and sediment medium along with the role of cation exchange; another reflecting the role of anion exchange between phosphate and carbonate; and the final reflecting the reducing environment.

Methods based on two-point geostatistics have been routinely used to interpolate random variables such as groundwater level and concentration and to estimate their values at un-sampled locations. These methods use the observed data to analyze spatial two-point correlations and ignore the higher order moments that may play a key role in the characterization of complex patterns. In this work, a multiple-point geostatistics method is applied to interpolate groundwater level data. To do this, the ensemble simulated groundwater level maps after modeling full physics are used as training images to derive the multiple correlations. An example shows the advantages of using multiple-point geostatistics compared with the traditional two-point geostatistics methods (such as Kriging) for the interpolation of groundwater level data in a complex geological formation.

Broad applications of graphene oxide (GO) will result in the release of GO into aquatic environments, where clay minerals and metal (hydr)oxides are commonly present. Thereby the interactions between GO and a binary system containing clay minerals and metal (hydr)oxides can occur. We investigated the aggregation of GO with kaolinite and kaolinite-goethite associations (KGAs) in aquatic systems under different pHs, ionic strengths, and GO concentrations. GO suspension was unstable at low pHs, and the aggregation of GO occurred in the presence of KGA-4% and KGA-10% until pH 5 and 6, respectively. Kaolinite decreased the critical coagulation concentration (CCC) of GO at pH 5.5 from around 50 to 20 mM NaCl due to the reduced energy barrier. Heteroaggregation of GO with KGAs was extremely sensitive to ionic strength at pH 5.5, and the CCC of GO in the presence of KGA-10% increased from less than 1 mM NaCl to 5 mM NaCl with the increase of pH from 5.5 to 9. The heteroaggregation extent of GO with KGAs was enhanced firstly, then reduced with the increase of GO concentrations at pH 5.0, which is likely because KGA plates were more efficiently wrapped by large-size GO sheets with increasing GO concentrations. These findings are useful for understanding and predicting the fate of GO in the relatively complicated aquatic and soil environments where binary minerals co-exist.

The aim of the present work is to investigate the distribution and possible sources of phthalate esters (PAEs) in groundwater and surface water of a subtropical Dongguan city, South China. Groundwater and surface water samples were collected from fifty-six and nine sampling sites in 2006, respectively. Concentrations of six PAE compounds (Σ6PAEs) in groundwater and surface water range from below detection limit (BDL) to 6.7 µg/L and from BDL to 33.8 µg/L, with an average value of 0.9 µg/L and 11.1 µg/L, respectively. Of the six PAE compounds in groundwater and surface water, di (2ethylhexyl) phthalate (DEHP) and di-n-butyl phthalate (DnBP) are the main compounds of PAEs. DnBP and DEHP are predictive indicators for the Σ 6 PAEs in surface water (r = 0.803, p < 0.01) and groundwater (r = 0.726, p < 0.01), respectively. Most of high Σ6PAEs in groundwater are measured near the boundary of Dongguan city. In contrast, the Σ6PAEs in groundwater samples are BDL in the center of Dongguan city. The concentration of DnBP in groundwater is negatively correlated with groundwater table (R = 0.6496, p < 0.05), while there is no correlation between DEHP concentration and table in groundwater. Our results indicate the high Σ6PAEs in surface water and the good hydraulic connection between surface water and groundwater. Thus, the PAEs in surface water may be one of the main sources for those in groundwater in the study area.

The aim of the present work is to investigate the distribution of arsenic (As) in sewage irrigation area, to deduce the migration and transformation mechanism of As in soil and groundwater, and to infer the source of As in soil and groundwater. This study is carried out in a sewage irrigation area of the Pearl River Delta, China. Surface water samples, soil samples, and groundwater samples from sewage irrigation area were analyzed for As and other elements. As contents in water samples were analyzed by hydride generation-atomic fluorescence spectroscopy, and As fractionation in soil samples was extracted using a seven-step sequential extraction method according to a seven fraction scheme: water soluble, ion exchangeable, bound to carbonate, weakly bound to organic matter, associated with oxides of iron (Fe) and manganese (Mn), strongly bound to organic matter, and the residual fraction. Waste water has content of As up to 16.8 μg/L in the study area. Soil has enriched As due to the irrigation of soil with waste water, and the total content of As in soil is about 0.7 times higher than the background value. Sequential extraction method reveals that the mean content of residual fraction in soil is more than 70%, releasable fraction (weakly organic fraction, Fe-Mn oxide fraction, and carbonate fraction) is about 20%–30%, whereas strongly organic and mobile fractions (water soluble and ion exchangeable) are within 0.2%. In the soil profile, the contents of water soluble, ion exchangeable, and carbonate fraction decrease with the depth, whereas the contents of other fractions are irregular with the depth. Using correlation analysis, it is concluded that water soluble fraction is easy to change into ion exchangeable and carbonate fraction, ion exchangeable fraction is easy to change into carbonate and Fe-Mn oxide fraction, and carbonate fraction is easy to change into weakly organic and Fe-Mn oxide fraction in the soil of study area. Organic matter and (hydr)oxides of Fe and aluminium (Al) in soil play an important role in controlling the distribution and mobility of As in soil. As concentrations in groundwater range from 2.8 to 21.0 μg/L, and it is inferred that As from waste water and the release of high As sediment (soil and aquifer medium) are the main sources for high As groundwater in study area. Using cluster analysis, it is concluded that reducing groundwater with slightly alkaline is beneficial to enrichment of As in groundwater, and hydroxides of Fe, Mn, and Al also play a key role for the enrichment of As in groundwater of the study area.

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

The moving of manufacturing industry from developed countries to Dongguan, China, promoted the semi-urbanization and rural industrialization in this area. It is urgent to acquire the impact of the enhanced anthropogenic pressure on the evolution of groundwater chemistry in this area. The objectives, in this study, were to understand the evolution of groundwater chemistry in Dongguan area based on the comparison of hydrochemical data variations and land use changes during the urbanization, to distinguish the impact of natural processes and anthropogenic activities on the groundwater chemistry by using principal components analysis (PCA) and hierarchical cluster analysis (HCA), and to discuss the origins of trace elements in groundwater. Eighteen physico-chemical parameters were investigated at 73 groundwater sites during July 2006. By analyzing the hydrochemical data, it shows that lateral flow from rivers and agricultural irrigation are the mechanisms controlling the groundwater chemistry in the river network area where the cation exchange of Na(+) in sediments taken up by the exchanger Ca(2+) occurs. Seawater intrusion is the mechanism controlling the groundwater chemistry in the coast area where the cation exchange of Ca(2+) in sediments taken up by the exchanger Na(+) occurs. The ion exchange reaction for fissured aquifer is weak in the study area. In addition, the comparison of hydrochemical data between in 2006 and in 1980 shows that anthropogenic activities such as excessive application of agricultural fertilizers, inappropriate emissions of domestic sewage and excessive emissions of SO2 are responsible for the occurrences of groundwater with NO3(-), SO4(2-) and Mg(2+) types. Four principal components (PCs) were extracted from PCA, which explain 80.86% of the total parameters in water chemistry: PC1, the seawater intrusion and As contamination; PC2, the water-rock interaction, surface water recharge and acidic precipitation; PC3, heavy metal pollution from industry; and PC4, agricultural pollution and sewage intrusion. Four clusters were generated from HCA: cluster 1 is mainly influenced by the industrialization; cluster 2 is mainly affected by the water-rock interaction and the irrigation and lateral flow of river water; cluster 3 is mainly influenced by the seawater intrusion; and cluster 4 is mainly influenced by the sewage intrusion and agricultural pollution. The results show that both natural processes such as seawater intrusion, water-rock interaction and lateral flow of river water and anthropogenic activities such as industrialization, sewage intrusion and agricultural pollution are the two major factors for the evolution of groundwater chemistry in Dongguan area.

Through testing the pH values of over two thousand groups of groundwater samples from the Pearl River Delta, water acidification was found to be one of the most outstanding groundwater environmental problems in the region. 76.3% of the whole region was covered by the acidic groundwater. The pH value distribution of the groundwater in the region was characterized by obvious regional differences. The groundwater in hilly areas was mainly acidic with the pH values centralized between 5.6 and 6.4; while the groundwater in the plain areas was generally neutral with the pH values between 6.4 and 7.2. The main factors affecting the pH values of the groundwater were acid rains, soils, rivers and seawater tides. In hilly areas, the acid rains had a high infiltration intensity, and the soils had a weak buffering capacity against acid, which played important roles in the low pH values of the groundwater. The increase of pH values of the groundwater was caused by the influences of the thick clay layer in plain areas, the weakened infiltration intensity of acid rains, the frequent water exchanges between rivers and groundwater as well as the invasion of salty tides and seawater into the groundwater.

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.

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.

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.

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.

The contents and characteristics of ten heavy metals in surface sediments from Yangzonghai Lake in Yunnan, China were analyzed. Ecological risk index presented by Hakanson 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.