In this paper, a sensitive atomic emission spectrometer (AES) based on a new low power and low argon consumption (<8 W, 100 mL min–1) miniature direct current (dc) atmospheric pressure glow discharge (APGD) plasma (3 mm × 5 mm) excitation source was developed for the determination of arsenic in water samples. In this method, arsenic in water was reduced to AsH3 by hydride generation (HG), which was then transported to the APGD source for excitation and detected by a compact CCD (charge-coupled device) microspectrometer. Different parameters affecting the APGD and the hydride generation reactions were investigated. The detection limit for arsenic with the proposed APGD-AES was 0.25 μg L–1, and the calibration curves were found to be linear up to 3 orders of magnitude. The proposed method was successfully applied to the determination of certified reference material (GBW08605), tap water, pond water, groundwater, and hot spring samples. Measurements from the APGD analyzer showed good agreement with the certified value/values obtained with well-established hydride generation atomic fluorescence spectrometry (HG-AFS). These results suggest that the developed robust, cost-effective, and fast analyzer can be used for field based arsenic determination and may provide an important tool for arsenic contamination and remediation programs.

This study proposed a new and previously unconsidered reaction mechanism in the activation of peroxymonosulfate. We report that singlet oxygen (1O2) rather than ˙OH or SO4˙− was the dominant reactive oxygen species towards the efficient degradation of ofloxacin and phenol, demonstrating a promising application in real wastewater treatment.

•Fourteen antibiotics were investigated in aquatic environment over three seasons.•Total concentrations of antibiotics in two water matrixes were highest in spring.•The vertical variations of antibiotic residues in groundwater were not unified.•Surface water and groundwater accumulated different kind of dominant antibiotics.•Algae was the most sensitive to the antibiotics compared to the daphnids and fish.The occurrence of 14 antibiotics (fluoroquinolones, tetracyclines, macrolides and sulfonamides) in groundwater and surface water at Jianghan Plain was investigated during three seasons. The total concentrations of target compounds in the water samples were higher in spring than those in summer and winter. Erythromycin was the predominant antibiotic in surface water samples with an average value of 1.60 μg/L, 0.772 μg/L and 0.546 μg/L respectively in spring, summer and winter. In groundwater samples, fluoroquinolones and tetracyclines accounted for the dominant proportion of total antibiotic residues. The vertical distributions of total antibiotics in groundwater samples from three different depths boreholes (10 m, 25 m, and 50 m) exhibited irregular fluctuations. Consistently decreasing of antibiotic residues with increasing of depth was observed in four (G01, G02, G03 and G05) groundwater sampling sites over three seasons. However, at the sampling sites G07 and G08, the pronounced high concentrations of total antibiotic residues were detected in water samples from 50 m deep boreholes instead of those at upper aquifer in winter sampling campaign, with the total concentrations of 0.201 μg/L and 0.100 μg/L respectively. The environmental risks posed by the 14 antibiotics were assessed by using the methods of risk quotient and mixture risk quotient for algae, daphnids and fish in surface water and groundwater. The results suggested that algae might be the aquatic organism most sensitive to the antibiotics, with the highest risk levels posed by erythromycin in surface water and by ciprofloxacin in groundwater among the 14 antibiotics. In addition, the comparison between detected antibiotics in groundwater samples and the reported effective concentrations of antibiotics on denitrification by denitrifying bacteria, indicating this biogeochemical process driven by microorganisms won’t be inhibitory influenced by the antibiotic residues in groundwater.

•High iodine contents are observed in soil/sediment with higher TOC contents.•Iodide exhibited lower affinities on all (un)treated soil/sediment samples.•A rod-like mineral rich in metal hydroxides is responsible for iodate adsorption.•Organic-mineral complexes are the dominant factor controlling iodine mobilization.•Iodine species in shallow/deep aquifers are dominated by iodate/iodide, respectively.Characterizing the properties of main host of iodine in soil/sediment and the geochemical behaviors of iodine species are critical to understand the mechanisms of iodine mobilization in groundwater systems. Four surface soil and six subsurface sediment samples were collected from the iodine-affected area of Datong basin in northern China to conduct batch experiments and to evaluate the effects of NOM and/or organic-mineral complexes on iodide/iodate geochemical behaviors. The results showed that both iodine contents and kf-iodate values had positive correlations with solid TOC contents, implying the potential host of NOM for iodine in soil/sediment samples. The results of chemical removal of easily extracted NOM indicated that the NOM of surface soils is mainly composed of surface embedded organic matter, while sediment NOM mainly occurs in the form of organic-mineral complexes. After the removal of surface sorbed NOM, the decrease in kf-iodate value of treated surface soils indicates that surface sorbed NOM enhances iodate adsorption onto surface soil. By contrast, kf-iodate value increases in several H2O2-treated sediment samples, which was considered to result from exposed rod-like minerals rich in Fe/Al oxyhydroxide/oxides. After chemical removal of organic-mineral complexes, the lowest kf-iodate value for both treated surface soils and sediments suggests the dominant role of organic-mineral complexes on controlling the iodate geochemical behavior. In comparison with iodate, iodide exhibited lower affinities on all (un)treated soil/sediment samples. The understanding of different geochemical behaviors of iodine species helps to explain the occurrence of high iodine groundwater with iodate and iodide as the main species in shallow (oxidizing conditions) and deep (reducing conditions) groundwater.Download high-res image (256KB)Download full-size image

Almost 20 years’ multi-disciplinary study on geogenic high arsenic (As) groundwater systems in China has greatly improved our understanding of the major processes controlling hydrogeochemical behavior of As in the subsurface environment. Among them, sorption by Fe(III) oxide/hydroxides was found to be one of the dominant processes retaining As in the aquifer matrix. Managed Aquifer Rehabilitation (MAR) by enhancing Fe(II) oxidation to promote As sorption was proposed and tested in a pilot-scale field experiment. Periodical injection of Fe(II) and ClO− into a high As sandy aquifer triggered formation of new Fe(III) (hydr)oxides coating on sediment particles via advanced heterogeneous oxidation of Fe(II) and concurrent oxidative adsorption of As(III) via co-precipitation and surface complexation with Fe(III) (hydr)oxides. Monitoring results indicate that aqueous As concentration decreased from the initial average value of 78.0 μg/L to 9.8 μg/L over the 25-day amendment period and leveled off below 10 μg/L for the following 30 days. MAR is thus proved to be a cost-effective approach for remediating high As aquifers.

•The effects of colloids on groundwater iodine mobilization were unraveled.•Reducing conditions favored colloidal iodine release into groundwater.•The increase of pH enhanced iodine desorption from colloids.•Fe-OM colloids controlled iodine behavior in large grain size fractions.The geochemical behaviors of colloids in aquifers played an important role in determining the fate of iodine in groundwater system. To decipher the impact of colloids on iodine mobilization in aquifers, three successive pore-sized colloids filtration (0.45 μm, 30 kDa and 5 kDa) were conducted on in-situ during groundwater sampling. The results showed that the distribution ratios (f) of total iodine (IT) and iron in the dissolved solution (i.e., 5 kDa ultrafiltered) were from 0.78 to 0.99 and from 0.56 to 0.94, respectively. Natural organic matter (NOM) in the colloidal fractions obtained the f values ranging from 0.14 to 1.00. The decreased Eh values from recharge area to discharge area indicated redox potential of groundwater system changed from oxidizing to reducing along groundwater flowpath, and interestingly, the corresponding iodine fractions in groundwater were decreasing in dissolved solution and increasing in colloidal fractions. Inverse correlation between Fe and DOC and positive correlation between iodine and DOC suggested the occurrence of reductive dissolution of iron oxyhydroxides and degradation of organic iodine in groundwater system. Iodine distribution increased in dissolved solution and decreased in colloids with pH increase. Moreover, as pH increased, f (Fe) and f (DOC) decreased in dissolved solution and increased in colloids. Relatively weak correlation of f (IT) with f (Fe) and strong relationship between f (IT) and f (DOC) in the large grain size fractions suggested the Fe-OM complexes controlled iodine distribution in groundwater, which depends on the presence of Fe bridges. Negligible association of iodine with Fe and NOM in the small grain size fractions might be attributed to the effects of abundant OH− content in groundwater.Download high-res image (168KB)Download full-size image

•Field test of high As groundwater remediation in reducing aquifers was explored.•As can be sequestered by stimulating the in-situ formation of Fe(II) sulfides.•Managed aquifer rehabilitation is promising for large-scale As decontamination.Severe health problems due to elevated arsenic (As) in groundwater have made it urgent to develop cost-effective technologies for As removal. This field experimental study tested the feasibility of in-situ As immobilization via As incorporation into newly formed biogenic Fe(II) sulfides in a typical As-affected strongly reducing aquifer at the central part of Datong Basin, China. After periodic supply of FeSO4 into the aquifer for 25 d to stimulate microbial sulfate reduction, dissolved sulfide concentrations increased during the experiment, but the supplied Fe(II) reacted quickly with sulfide to form Fe(II)-sulfides existing majorly as mackinawite as well as a small amount of pyrite-like minerals in sediments, thereby restricting sulfide build-up in groundwater. After the completion of field experiment, groundwater As concentration decreased from an initial average value of 593 μg/L to 159 μg/L, with an overall As removal rate of 73%, and it further declined to 136 μg/L adding the removal rate up to 77% in 30 d after the experiment. The arsenite/Astotal ratio gradually increased over time, making arsenite to be the predominant species in groundwater residual As. The good correlations between dissolved Fe(II), sulfide and As concentrations, the increased abundance of As in newly-formed Fe sulfides as well as the reactive-transport modeling results all indicate that As could have been adsorbed onto and co-precipitated with Fe(II)-sulfide coatings once microbial sulfate reduction was stimulated after FeSO4 supply. Under the strongly reducing conditions, sulfide may facilitate arsenate reduction into arsenite and promote As incorporation into pyrite or arsenopyrite. Therefore, the major mechanisms for the in-situ As-contaminated groundwater remediation can be As surface-adsorption on and co-precipitation with Fe(II) sulfides produced during the experimental period.Download high-res image (200KB)Download full-size image

•Hollow zeolite spheres were synthesized by one-step organic-free hydrothermal method from natural minerals.•The diameters of the microsphere were controlled with potassium cation concentration.•A possible K-induced Ostwald ripening reversed crystal growth process was proposed.A novelty hierarchical hollow nitrate cancrinite zeolite microspheres (HNCMs) with micro-plate crystals act as sphere shell and wrapped with large number of nanorods crystal in the center of the microspheres were synthesized by a simple organic-free hydrothermal synthesis methods. With the adjustment of potassium cation concentration in synthetic system, nitrate cancrinite zeolites realize morphology tunable architectures from nanorod to HNCMs. A systematic investigation of the crystal growth over different crystallization stages indicates a stepwise crystallization progress of HNCMs. First, the primitive nitrate cancrinite nanoplatelets self assembled to yield solid spherical clusters. Then the spherical clusters undergo a surface to core crystallization progress which was supposed to be the reason for the formation of hollow cores. This work provides an alternative strategy for the synthesis of spherical hollow zeolite materials with tunable architectures, which may potentially be used in the field of separation, catalysis and biomedicine.

Advanced oxidation processes as a green technology have been adopted by combining the semiconductor catalyst MoSe2 with H2O2 under visible radiation. And novel three-dimensional self-assembled molybdenum diselenide (MoSe2) hierarchical microspheres from nanosheets were produced by using organic, selenium cyanoacetic acid sodium (NCSeCH2COONa) as the source of Se. The obtained products possess good crystallinity and present hierarchical structures with the average diameter of 1 μm. The band gap of MoSe2 microspheres is 1.68 eV and they present excellent photocatalytic activity under visible light irradiation in the MoSe2–H2O2 system. This effective photocatalytic mechanism was investigated in this study and can be attributed to visible-light-driven advanced oxidation processes.

A cost-effective K1.5Mg/SiO2 catalyst with a K2MgSiO4 component was employed to help transfer several hexoses into hydroxylmethylfurfural (HMF) in a biphasic water/butanol system. The solid catalysts with rod-like structures and moderate base sites could promote the aldose–ketose isomerization of glucose and have potential for the synthesis of lactic acid via a retro-aldol condensation. In the presence of sulfonated titania/mordenite solid acid, the K1.5Mg/SiO2 catalyst presented heat-stability and prolonged activity in the one-pot conversion of glucose to HMF, leading to an optimal yield of 62.2%. The one-pot catalysis of saccharides from the enzymatic hydrolysate of poplar sawdust achieved a high HMF yield of 56.9% at a glucose conversion of 91.6%.

The hydrogeochemical and isotopic investigations of high fluoride (up to 8.26 mg L−1) groundwater in the Datong Basin, Northern China were carried out in order to evaluate the geochemical controls on fluoride enrichment. The groundwater fluoride concentration tends to increase along with the regional groundwater flow path away from the basin margins, towards the central parts of the basin. Groundwater with high F concentrations has a distinctive major ion chemistry, being generally HCO3−-rich, Na-rich, Ca-poor, and having weak alkaline pH values (7.2 to 8.2) and Na–HCO3 waters. These data indicate that variations in the groundwater major ion chemistry and possibly pH, which are controlled by water–rock interaction processes in the aquifer, are important in mobilizing F. Positive correlations between fluoride with lithogenic sodium (LNa) and HCO3− in groundwater show that the high fluoride content and alkaline sodic characteristics of groundwater result from dissolution of fluorine-bearing minerals. The occurrence and behavior of fluorine in groundwater are mainly controlled by fluorite precipitation as a function of Ca2+ concentration. A positive correlation between fluoride and δ18O, low F-/Cl- ratios, and the low tritium level in the fluoride-rich groundwater indicate the effects of long-term water–rock interactions and intensive evapotranspiration.

A hydrogeochemical investigation using integrated methods of stable isotopes (18O, 2H), 87Sr/86Sr ratios, Cl/Br ratios, chloride-mass balance, mass balance and hydrogeochemical modeling was conducted to interpret the geochemical evolution of groundwater salinity in Datong basin, northern China. The δ2H, δ18O ratios in precipitation exhibited a local meteoric water line of δ2H = 6.4 δ18O −5 (R2 = 0.94), while those in groundwater suggested their meteoric origin in a historically colder climatic regime with a speculated recharge rate of less than 20.5 mm overall per year, in addition to recharge from a component of deep residual ancient lake water enriched with Br. According to the Sr isotope binary mixing model, the mixing of recharges from the Shentou karst springs (24%), the western margins (11%) and the eastern margins (65%) accounts for the groundwater from the deep aquifers of the down-gradient parts in the central basin is a possible mixing mechanism. In Datong, hydrolysis of silicate minerals is the most important hydrogeochemical process responsible for groundwater chemistry, in addition to dissolution of carbonate and evaporites. In the recharge areas, silicate chemical weathering is typically at the bisiallitization stage, while that in the central basin is mostly at the monosiallitization stage with limited evidence of being in equilibrium with gibbsite. Na exchange with bound Ca, Mg prevails at basin scale, and intensifies with groundwater salinity, while Ca, Mg exchange with bound Na locally occurs in the east pluvial and alluvial plains. Although groundwater salinity increases with the progress of water-rock/sediment interactions along the flow path, as a result of carbonate solubility control and continuous evapotranspiration, Na–HCO3 and Na–Cl–SO4 types of water are usually characterized respectively in the deep and the shallow aquifers of an inland basin with a silicate terrain in an arid climatic regime.

31 topsoil samples were collected by grid method in Xiaodian sewage irrigation area, Taiyuan City, North of China. The concentrations of 16 kinds of polycyclic aromatic hydrocarbons (PAHs) were determined by gas chromatograph coupled with mass spectrum. Generally speaking, the distribution order of PAHs in the area is: those with five and six rings > those with four rings > those with two and three rings. Source apportionment shows a significant zonation of the source of PAHs: the civil coal pollution occurred in the north part, the local and far factory pollution happened in the middle area and the mixed pollution sources from coal and wood combustion, automotive emission, presented in the south area. The distribution of PAHs has a definite relationship with the sewage water flow and soil adsorption. The related coefficient between PAHs and physicochemical property showed there was a negative correlation between pH, silt, clay and PAHs while there was a positive correlation between total organic carbon, sand and PAHs.

High iodine concentrations in groundwater have seldom been reported and there have been few systematic studies on high iodine groundwater worldwide. To better understand the sources and processes responsible for iodine enrichment in the groundwater of the Datong Basin, the hydrochemical characteristics of groundwater and geochemical features of aquifer sediments were studied. High iodine groundwater mainly occurs in the center of the Datong Basin with iodine concentrations ranging between 3.31 and 1890 μg L−1. Most samples with iodine concentrations higher than 500 μg L−1 are from wells with depths between 75 and 120 m. High pH and a reducing environment are favorable for iodine enrichment in the groundwater, with iodide as the dominant species that accounts for 63.2–99.3% of the total iodine. Sediment samples from a borehole specifically drilled for this study contain 0.18–1.46 mg kg−1 iodine that is moderately correlated with total organic carbon (TOC). The results of sequential extraction experiments show that iodine is mostly bound to iron oxyhydroxides and organic matter in the sediments. The mobilization processes of iodine are proposed to include reductive dissolution of iron oxyhydroxides and transformations among iodide, iodate and organic iodine driven by microbial activities under alkaline and reducing conditions.

In this study, the content and speciation of arsenic in coal waste and gas condensates from coal waste fires were investigated, respectively, using the digestion and sequential extraction methods. The fresh and fired-coal waste samples were collected from Yangquan, which is one of the major coal production regions in northern China. High-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) was used to determine the concentrations of four major arsenic species [As(III), As(V), monomethylarsonic acid (MMA) and dimethylarsenic acid (DMA)] in the extracts, while ICP-MS was used to measure total As content. Arsenic content in the investigated coal wastes and the condensate ranges between 23.3 and 69.3 mg/kg, which are higher than its reported average content in soils. Arsenic in coal waste exists primarily in the residual fraction; this is followed in decreasing order by the organic matter-bound, Fe–Mn oxides-bound, exchangeable, carbonates-bound, and water-soluble fractions. The high content of arsenic in the condensates indicates that combustion or spontaneous combustion is one of the major ways for arsenic release into the environment from coal waste. About 15% of the arsenic in the condensate sample is labile and can release into the environment under leaching processes. The water extractable arsenic (WEA) in the fresh coal waste, fired coal wastes, and the condensate varied between 14.6 and 341 μg/kg, with As(V) as the major species. Furthermore, both MMA and DMA were found in fresh coal wastes, fired coal wastes, and the condensate.

Discharge of huge amount of liquid slag from phosphorus-smelting electric furnace has posed serious threat to the environment. In this study, a novel approach of directly recycling the liquid slag to prepare cast stone as decorative building material was proposed and experimentally tested. In our lab experiments, 76 wt.% water-quenched slag was re-melted at 1400 °C for 0.5 h (thus simulating liquid slag from phosphorus-smelting electric furnace), and then mixed with 18 wt.% quartz powder and 6 wt.% calcined kaolinitic clay, and subsequently melted together at 1450 °C for 1 h into modified liquid slag which was cast, heat-treated, annealed and transformed into cast stone. The optimal temperature for heat-treating cast stone ranges from 850 to 900 °C. And as-prepared samples present excellent properties of bending strength, acid resistance and alkali resistance. ESEM images show that their microstructures are composed of spherical granules with particle sizes of about 0.2–0.4 μm, which are non-crystalline as indicated by the results of XRD analysis. EDS results show that the contents of major elements in the granule are different from those in its background area. Results of TCLP test show that heavy metals from raw slag have been solidified in the cast stone. The practical feasibility of the new technology was examined further by on-site experiments, in which fresh liquid slag from phosphorus-smelting electric furnace was directly mixed with quartz and kaolinitic clay to produce cast stone. The results were quite stable and consistent with those of lab experiments, proving that the proposed approach of direct utilization of both energy and material of liquid phosphorus slag to produce cast stone as decorative building material is feasible, cost-effective and environment-friendly.

Coagulation/flocculation process was applied in the polishing treatment of molasses wastewater on a bench-scale. Important operating variables, including coagulant type and dosage, solution pH, rapid mixing conditions as well as the type and dosage of polyeletrolytes were investigated based on the maximum removal efficiencies of chemical oxygen demand (COD) and color, residual turbidity and settling characteristics of flocs. HPSEC was utilized to evaluate the removal of molecular weight fractions of melanoidins-dominated organic compounds. Experimental results indicate that ferric chloride was the most effective among the conventional coagulants, achieving 89% COD and 98% color eliminations; while aluminum sulfate was the least effective, giving COD and color reductions of 66% and 86%, respectively. In addition to metal cations, counter-ions exert significant influence on the coagulation performance since Cl−-based metal salts attained better removal efficiency than SO42−-based ones at the optimal coagulant dosages. Coagulation of molasses effluent is a highly pH-dependent process, with better removal efficiency achieved at lower pH levels. Rapid mixing intensity, rather than rapid mixing time, has relatively strong influence on the settling characteristics of flocs formed. Lowering mixing intensity resulted in increasing settling rate but the accumulation of floating flocs. When used as coagulant aids, synthetic polyelectrolytes showed little effects on the improvement in organic removal. On the other hand, cationic polyacrylamide was observed to substantially enhance the settleability of flocs as compared to anionic polyacrylamide. The effects of rapid mixing conditions and polymer flocculants on the coagulation performance were discussed.

Co-firing coal and the residue from acid hydrolysis of Discorea zingiberensis is an efficient approach for the residue disposal. This paper reports the results of our experimental work on chlorine release in co-firing coal and the residue. The experimental work was done in two steps: to determine the amount of Cl release from different fuel types at different temperatures first, and then to determine the optimum amount of calcium based sorbents to reduce HCl emissions in flue gases. Different types of fuel were tested, including pure residue, pure coal, and coal-residue mixture. Coal briquette that was a 1:1 (mass ratio) mixture of coal and residue and contained 2% (mass) CaO was prepared under compaction at 5 MPa. Chlorine emission can be reduced by adjusting the ratio of residue to coal in the mixture, and effectively controlled when the ratio is between 1:1 (50%) and 1:5 (16.7%). The fuel composition and calcium based sorbents also have great impacts on chlorine retention. The most efficient sorbent is calcium acetate. Although the retention ratio of chlorine increases with the increase in the amount of calcium sorbent added, the mass ratio of around 5% CaO should be the best choice.

•The ratio of Stable stable isotopes of water and strontium isotope ratios illustrate the mixing of surface and ground and surface water during flooding.•The contents of major elements in groundwater were significantly changed during flooding.•The concentrations of arsenic in groundwater were evidently elevated after flooding.Hydrogeological and geochemical approaches were combined to investigate the impact of a short-term artificial flooding event on arsenic and associated hydrogeochemisty at a field monitoring site of high arsenic aquifers in Datong Basin, northern China. The groundwater levels fluctuated in response to the flooding (the surface water level and groundwater level fluctuated with time in a range of over 80 cm and 30 cm, respectively), indicating groundwater–surface water interaction. Redox indices, major ions, trace element concentrations, O, H and Sr isotope compositions for surface water and groundwater were determined before and after the flooding. δ2H and δ18O values for all water samples plot close to the global meteoric water line (GMWL); a subset of the samples (shallow wells) averagely increased from − 11.78 to − 11.26 for δ18O and from − 86.59 to − 83.49 for δ2H, commensurate with mixing with ~ 10% surface water. The relationship between compositions of strontium isotope 87Sr/86Sr ratios and Mg concentration also clearly indicates the effect of mixing between groundwater and surface water. Before and after the flooding, there were obvious variations in water chemistry, including arsenic concentrations. Increases and positive correlations between Cl− and Na+, Mg2 +, Ca2 + and SO42 − following flooding revealed surface water infiltration into groundwater, plus additional input from dissolution of evaporate minerals and/or evaporated pore-water. Organic matter and oxygen are carried into groundwater together with surface water; oxidation of organic matter leads to exhaustion of oxygen and consumption of terminal electron acceptors (e.g. ferric iron, sulfate, nitrate) inducing a more reducing groundwater environment (indicated by decreased ORP values). Consequently, reductive dissolution of iron oxides/hydroxides resulted in an observed elevation of HS, NH4-N, Fe(II), with the concentrations increasing from 5 μg/L to 10 μg/L, from 0.19 mg/L to 0.68 mg/L and from 0.06 mg/L to 1.86 mg/L, respectively. This may explain that the As concentrations were enhanced after surface water flooding (from mean value of 22.6 μg/L to 31 μg/L). However, a positive correlation was observed between enhance values of As and Cl in the groundwater after flooding is interpreted as reflecting re-dissolution of evaporate crusts and/or saline pore water during infiltration, and this may alone explain the increase in As observed in the groundwater. Surface water As concentration increased to a minor degree following flooding also (from 14 μg/L to 15.1 μg/L), possibly reflecting return flow of the high As groundwater during a temporary switch to gaining conditions.

•A geological filtration system was developed for arsenic removal in situ.•A mixture of natural Fe-mineral and limestone (2:1) was the most effective material.•The system reduced groundwater arsenic from 400 μg/L to below 10 μg/L in the field.•It is operational for 365,000 L drinking water of 5 persons for 5 years in rural areas.An effective and low-cost in-situ geological filtration system was developed to treat arsenic-contaminated groundwater in remote rural areas. Hangjinhouqi in western Hetao Plain of Inner Mongolia, China, where groundwater contains a high arsenic concentration, was selected as the study area. Fe-mineral and limestone widely distributed in the study area were used as filter materials. Batch and column experiments as well as field tests were performed to determine optimal filtration parameters and to evaluate the effectiveness of the technology for arsenic removal under different hydrogeochemical conditions. A mixture containing natural Fe-mineral (hematite and goethite) and limestone at a mass ratio of 2:1 was found to be the most effective for arsenic removal. The results indicated that Fe-mineral in the mixture played a major role for arsenic removal. Meanwhile, limestone buffered groundwater pH to be conducive for the optimal arsenic removal. As(III) adsorption and oxidation by iron mineral, and the formation of Ca–As(V) precipitation with Ca contributed from limestone dissolution were likely mechanisms leading to the As removal. Field demonstrations revealed that a geological filter bed filled with the proposed mineral mixture reduced groundwater arsenic concentration from 400 μg/L to below 10 μg/L. The filtration system was continuously operated for a total volume of 365,000 L, which is sufficient for drinking water supplying a rural household of 5 persons for 5 years at a rate of 40 L per person per day.

To better understand the occurrence of high F and As in groundwater of the Datong basin, a total of 486 groundwater samples were collected for hierarchical cluster analysis (HCA) of eighteen hydrochemical parameters. Groundwater samples can be divided into thirty-six and nineteen groups for shallow and deep groundwater, respectively. Results show that high F samples in shallow groundwater contain F as high as 22 mg/L and mainly occur in the discharge area in the basin center, and the highest F concentration of deep groundwater samples is 8.3 mg/L which mainly occur in the western mountain front area. The groundwater with elevated HCO3 concentration favors F enrichment in the Datong basin. Nearly all of the high F samples are oversaturated with respect to calcite and undersaturated with respect to fluorite, indicating that fluorite solubility is a limit for F enrichment. Besides, evapotranspiration has a stronger effect on fluoride enrichment, especially for the shallow groundwater. For the both F and As enrichment samples in deep groundwater, the desorption of Fe-(hydr)oxides is suggested to be the major mechanism. High As samples of shallow and deep groundwater mainly occur between Senggan River and Huangshui River. The highest arsenic concentration reaches up to 469 μg/L, and all samples of high arsenic groundwater have low concentrations of NO3 and SO4, indicating the prevailing reducing conditions in the aquifer system at Datong. The reductive dissolution of Fe-(hydr)oxides driven by sulfate reduction and biodegradation of organic matters is postulated to be the major process controlling arsenic enrichment in groundwater.Highlights► Hierarchical cluster analysis is used to classify groundwater from the Datong basin. ► Both F and As enrichment samples are distinguished in deep groundwater. ► Iron oxides trend to be the source of arsenic for high arsenic groundwater. ► F concentration in groundwater is controlled by different predominant processes.

China produces almost half of ceramic tiles in the world. However, serious air pollution and high energy consumption in the preparation of ceramic press-powders by traditional wet process (WP) have become major barriers for the sustainable development of ceramic tile manufacturing industry. A novel cleaner production process, named by the authors as Droplet-Powder Granulation Process (DPGP), was proposed and tested in this work. Droplet-powder granulator, a key facility of DPGP, was designed. In the granulator, ceramic suspension was directly sprayed to form fine suspension droplets and ceramic dry powder was simultaneously jetted and dispersed to enwrap, insulate and adsorb the suspension droplets so as to form coarse granules that were then rolled, tamped and dried into press-powders. Lab experiments of preparing press-powders by DPGP were carried out. The as-prepared DPGP press-powders consist of solid granules with nearly spherical shape and approximately normal grain size distribution, and present favorable flowability and relatively high bulk density, with the similar properties of the press-powders as those prepared by WP. Moreover, as compared with WP, DPGP can reduce both pollutant emission of 98% dust, 65% sulfur oxides and 71% nitrogen oxides and resource consumption of 24% energy and 69% water. Therefore, DPGP is an innovative approach for cleaner production of ceramic press-powders.

•Effects of sulfur redox cycling on As enrichment were clarified in Datong.•Co-increase in aqueous As and sulfide content occurred without Fe(II) build-up.•Sulfide-driven Fe mineral transformations promotes As mobilization.Sulfur redox cycling potentially exerts important influences on arsenic (As) fate in shallow groundwater systems. Hydrochemical and sediment geochemical analysis combined with thermodynamic modeling study were conducted at Datong Basin to elaborate the effects of sulfur redox cycling on As speciation and mobilization under a strongly reducing environment. Dissolved As and sulfide concentration in 32 groundwater samples with depths of 19–40 m below the land surface varied from 8 to 2700 μg/L and from <5 to 490 μg/L, respectively, while dissolved Fe(II) was relatively low ranging from <20 to 280 μg/L. The apparent co-increase in dissolved sulfide and As concentration, especially for samples with As content larger than 500 μg/L, indicates that sulfidogenesis may significantly contribute to the mobilization of As via sulfide-induced reduction of both As-bearing Fe(III) oxide minerals and As(V). Thermodynamic calculations indicate that groundwater As might be also thiolated in the presence of high-level sulfide, particularly to a large extent for As(V) speciation, instead of sequestration by As-sulfide precipitates. Results of sequential extraction and scanning electron microscopy array on sediments indicate the presence of Fe(II) sulfide mineral phases and an appreciable amount of co-existent As in the sediments, suggesting the precipitation of Fe(II) sulfides can restrict the build-up of dissolved Fe(II) and sequester As from groundwater, but not strongly enough, thereby lowering down As to a moderate level of about 500 μg/L. Thus, redox processes involving As, S and Fe species under sulfidic conditions as observed in Datong Basin not only facilitate the enrichment of As(III) species and As(V) potentially existing as thiolated species, but also the depletion of Fe(II) concentration in groundwater due to Fe(II) sulfide formation.

•Spatial distribution characteristics of aqueous As species were investigated.•Reduction of Fe minerals and As(V) can enhance As(III) enrichment in groundwater.•Microbial sulfate reduction may promote As(V) transformation into As(III).To elaborate primary geochemical factors controlling the enrichment and spatial distribution of arsenic (As) species in groundwater systems, multilevel hydrogeochemical monitoring was conducted at an As-contaminated site in central part of Datong Basin, northern China. Aqueous As concentration was highly variable, ranging from 5.47 to 2690 μg/L. High As groundwater was characterized by elevated HCO3−, Fe(II), HS−, NH4+ and dominated by As(III) species. The positive correlation between As and Fe contents was observed in easily-reducible Fe pool, indicating that poorly crystalline Fe minerals served as an important As sink via chemical adsorption and/or co-precipitation. Under moderately reducing and weakly alkaline conditions (Eh ≥ 100 mV and pH between 7.69 and 8.04), As mobilization could be controlled by pH-dependent desorption process. The relationships of aqueous As(V) and As(III) versus Fe(II) concentration confirm that reductive dissolution of As-bearing Fe oxides/hydroxides and reductive desorption of As(V) could be responsible for As enrichment and As(III) predominance in groundwater under more reducing conditions (Eh ≤ 100 mV). The co-presence of elevated As(III) and sulfide indicates that microbial sulfate reduction may promote As(V) transformation into thioarsenate and/or thioarsenite and further into As(III). However, the correlations of As(V) and As(III) concentration versus saturation indices of mackinawite suggest that decrease in aqueous As concentration may be due to re-sequestration of both As(V) and As(III) by Fe(II)-sulfide precipitates.

•The effect of dissolved organic matter (DOM) on As transport has been identified;•Coupling the biodegradation of DOM with reductive dissolution of minerals promotes As mobilization; minerals promotes with of DOM•DOM biodegradation and sulfate reduction could result in As sequestration.To understand the effects of natural dissolved organic matter (DOM) on microbially catalyzed As mobilization, the chemical properties and transformation of DOM as well as the hydrochemical characteristics of high As groundwater from the Datong Basin of northern China have been studied. Hydrochemical results indicated that As concentration in groundwater ranged from 18.0 to 182 μg/L with an average value of 58.4 μg/L. Dissolved Fe(II), sulfide and dissolved organic carbon (DOC) concentrations were high in the elevated As groundwater. The As contents in both the bulk sediments and extractable fractions show an obvious positive correlation with the Fe contents, demonstrating that As is strongly associated with Fe-bearing minerals via adsorption and/or co-precipitation. The DOM in the shallow groundwater mainly contained terrestrially and microbially derived humic substances, and most of the quinone-like humic substances were in the oxidized state. By contrast, the DOM in the deep groundwater was predominantly microbially derived and had a higher concentration of labile DOM, and the quinone-like humic substances were more reduced. The strong linear correlation between DOC and HCO3− suggests that the high concentration of HCO3− may be related to the microbially mediated oxidation of DOM into HCO3− using Fe(III) or SO42 − as electron acceptor in the anoxic groundwater. The relationships of As species with Fe(II), DOC concentrations, redox index and SUVA values of DOM indicate that abundant labile DOM may serve as an important electron donor to promote the microbially mediated reductions of Fe(III) oxides/hydroxides, SO42 − and As(V). Furthermore, the quinone-like humic substances act as electron shuttles to transfer electrons from labile DOM to Fe(III), SO42 −, and As(V) adsorbed on the surfaces of Fe minerals, hence enhancing the mobilization of As (particularly As(III)) into groundwater. However, the observed negative correlations of dissolved sulfide with As and Fe(II) concentrations in groundwater demonstrate that dissolved As is most likely scavenged via co-precipitation with Fe(II) sulfides or As-bearing sulfides. Therefore, reductive dissolution of Fe(III) oxides/hydroxides coupled to microbial oxidation of natural DOM may serve as the primary geochemical process controlling As mobilization in groundwater systems, while the formation of Fe(II) sulfides due to microbially mediated sulfate reduction and DOM oxidization could sequester As from groundwater.

•High iodine groundwater was observed in both shallow and deep groundwater.•Intense water-sediment interaction was identified by groundwater Sr isotope.•The stratification of 18O and 2H isotope indicates the vertical mixing by irrigation.•Extra O2/NO3/SO4 introduction by irrigation promotes iodine release into groundwater.High iodine concentrations in groundwater have caused serious health problems to the local residents in the Datong basin, northern China. To determine the impact of water-sediment interaction and irrigation practices on iodine mobilization in aquifers, isotope (2H, 18O and 87Sr/86Sr) and hydrogeochemical studies were conducted. The results show that groundwater iodine concentrations vary from 14.4 to 2180 μg/L, and high iodine groundwater (>150 μg/L) mainly occurs in the central area of the Datong basin. Sediment iodine content is between <0.01 and 1.81 mg/kg, and the co-occurrence of high iodine and high DOC/TOC concentrations of groundwater and sediment samples in the deeper aquifer indicates that the sediment enriched in iodine and organic matter acts as the main source of groundwater iodine. The 87Sr/86Sr values and groundwater chemistry suggest that aluminosilicate hydrolysis is the dominant process controlling hydrochemical evolution along groundwater flowpath, and the degradation of TOC/iodine-rich sediment mediated by microbes potentially triggers the iodine release from the sediment into groundwater in the discharge area. The vertical stratification of groundwater 18O and 2H isotope reflects the occurrence of a vertical mixing process driven by periodic surface irrigation. The vertical mixing could change the redox potential of shallow groundwater from sub-reducing to oxidizing condition, thereby affecting the iodine mobilization in shallow groundwater. It is postulated that the extra introduction of organic matter and O2/NO3/SO4 could accelerate the microbial activity due to the supplement of high ranking electron acceptors and promote the iodine release from the sediment into shallow groundwater.Download high-res image (158KB)Download full-size image

Poor water quality has become a public health issue as cases of fluorosis in Datong Basin, Northern China are increasing. This paper investigates the origin and the geochemical mechanisms of fluoride enrichment in groundwater at Datong Basin. The fluoride concentration in the groundwater samples from 70 wells selected for this study ranges from 0.1 to 8.3 mg/L (mean 2.2 mg/L), with 51% of the samples containing fluoride concentrations that exceed the WHO drinking water guideline value of 1.5 mg/L. High fluoride groundwaters are characterized by hydrochemical types HCO3Na(Mg), HCO3·SO4Na(Mg) and SO4·ClNa(Mg), with low Ca2+ and high HCO3− and Na+, and occurred in transition areas between the alluvial–pluvial mountain front plain and the alluvial–lacustrine plain of Datong Basin. Conditions favorable for fluoride enrichment in groundwater include weakly alkaline pH condition (7.2–8.2), moderate TDS, and HCO3− and Na+ as the dominant ions. The hydrolysis of F-bearing minerals in aquifer sediments is the dominant process for F− release, and facilitated by alkaline conditions and long residence time of groundwater. Calcite and fluorite are the main solubility-control minerals controlling the aqueous geochemistry of high fluoride groundwater. Evapotranspiration also favors fluoride enrichment in groundwater.Highlights► Geochemical mechanisms of high fluoride groundwater at Datong were investigated. ► High fluoride groundwater is of transitional hydrochemical types. ► pH alone seems not to be a dominant factor controlling F− enrichment. ► The hydrolysis of F-bearing minerals is the dominant process affecting F− levels. ► The evaporation to a moderate extent favors F− enrichment, but is limited.

Mineralogical, geochemical and zircon U–Pb dating studies were carried out to identify the sources of arsenic in the shallow aquifers of Datong Basin in northern China. A sediment sample from 18 m depth containing 10.3 mg/kg arsenic showed a Zircon U–Pb concordant age of 2528 ± 20 to 271 ± 4 Ma that can be divided into two groups (2528 ± 20 to 1628 ± 21 Ma and 327 ± 4 to 271 ± 4 Ma) and is comparable to that of the sedimentary rocks of Taiyuan (upper Carboniferous) and Shanxi Formation (lower Permian) outcropping to the west of Datong Basin. In contrast, a sediment sample from 22.5 m depth containing 5.7 mg/kg arsenic displayed a Zircon U–Pb concordant age ranging from 2561 ± 21 to 1824 ± 26 Ma that is comparable to that of the Hengshan Complex (Ne-Archaean Precambrian) outcropping to the east of .Electron microscope analysis of the rock samples of Taiyuan and Shanxi Formations revealed that iron oxides and sulfides occurred unevenly in a matrix of clay and organic matter. Arsenic was elevated in the iron oxides with a mean of 660 mg/kg (n = 11) and 970 mg/kg (n = 4) for Shanxi and Taiyuan Formations, respectively. Except one pyrite grain, arsenic contents were lower than the detection limit (1 mg/kg) in other pyrite grains. Arsenic in iron oxides from Shanxi and Taiyuan Formations contributed to high arsenic in aquifer sediment of Datong Basin. The low arsenic sediment of Datong Basin is likely to be derived from weathering of the Hengshan Complex with low arsenic content (ranging from 0.37 to 4.14 mg/kg).Research highlights► Zircon U–Pb ages have been used to determine the sources of arsenic in aquifer sediment at Datong Basin. ► We present arsenic contents in various type of bedrock samples. ► Zircon U–Pb ages in sediments and bedrocks helped to discriminate arsenic sources.

High fluoride groundwater with F− concentration up to 6.20 mg/L occurs in Taiyuan basin, northern China. The high fluoride groundwater zones are mainly located in the discharge areas, especially in places where shallow groundwater occurs (the groundwater depth is less than 4 m). Regional hydrogeochemical investigation indicates that processes including hydrolysis of silicate minerals, cation exchange, and evaporation should be responsible for the increase in average contents of major ions in groundwater from the recharge areas to the discharge areas. The concentration of F− in groundwater is positively correlated with that of HCO3− and Na+, indicating that groundwater with high HCO3− and Na+ contents help dissolve some fluoride-rich minerals. The water samples with high F− concentration generally have relatively higher pH value, implying that alkaline environment favors the replacement of exchangeable F− in fluoride-rich minerals by OH− in groundwater. In addition, the mixing of karst water along the western mountain front and the evaporation may also be important factors for the occurrence of high fluoride groundwater. The inverse geochemical modeling using PHREEQC supports the results of hydrogeochemical analyses. The modeling results show that in the recharge and flow-through area of the northern Taiyuan basin, interactions between groundwater and fluoride-rich minerals are the major factor for the increase of F− concentration, whereas in the discharge area of the northern basin, the evaporation as well as the mixing of karst water has greater contribution to the fluoride enrichment in groundwater.

Strontium isotopic compositions and major ion chemistry were used to delineate flow paths in an arsenic affected groundwater flow system in the Datong basin, China. Total of 28 samples including one spring and one river water were collected for major ions and strontium isotopic compositions and concentration analysis. The ion ratios indicate that dissolution of silicates and carbonates is the dominant geochemical process controlling the hydrochemistry of groundwater from two recharge areas at the basin margins, while the water chemistry in the center of the basin is affected by the dissolution of evaporites (including gypsum and halite). Groundwater from eastern and western margin areas have relatively high 87Sr/86Sr values ranging from 0.72114 to 0.72604 and from 0.71119 to 0.71151, which are consistent with expected values for groundwater dominantly affected by dissolution of silicates. However, in the discharge area, the groundwater samples had lower 87Sr/86Sr values and varied between 0.71016 and 0.71753. The contour map of δ87Sr in groundwater shows the general tendency of decrease from the western and eastern margin areas to the discharge area. The plot of 87Sr/86Sr vs. Sr/Na indicates that interactions between Quaternary aquifer sediment and groundwater in the recharge areas along the flow paths control the hydrochemistry and strontium isotopic compositions of groundwater. By contrast, groundwater samples from the discharge area are plotted on the mixing line, indicating that mixing of groundwater from recharge area with low 87Sr/86Sr values groundwater could be the controlling factor on their hydrochemistry and strontium isotopic compositions. Four main flow paths of groundwater were inferred from hydrochemical and isotopic data. The results of PHREEQC inverse modeling matched quite well with the results of strontium isotopic and ion compositions along the flow paths. The distribution of high arsenic groundwater in this area could be attributed to the combined effect of the vertical flow and local groundwater flow on the redox conditions of the groundwater system.Highlights► We delineate the flow paths in high arsenic groundwater aquifer system. ► We model the evolution of chemical and Sr isotopic composition along the flow paths. ► Groundwater flow regime has effect on arsenic enrichment in groundwater.

Environment isotopes (δ18O and δ2H) and Cl/Br ratios in groundwater have been used to trace groundwater recharge and geochemical processes for arsenic contamination in Datong Basin. The arsenic concentrations of groundwater samples ranged from 0.4 to 434.9 μg/L with the average of 51.2 μg/L, which exceeded China’s drinking water standard (10 μg/L). All the groundwater samples are plotted on or close to the meteoric water line of the δ18O vs. δ2H plot, indicating their meteoric origin. The relationship between δ18O values and Cl/Br ratios and Cl concentrations demonstrate that leaching and mixing are the dominant processes affecting the distribution of high arsenic groundwater in this area. The observed non-linearity in the trend between δ18O and arsenic concentration is due to combined effects of mixing and leaching. The similarity of the trend in Cl/Br ratios and δ18O values for high arsenic groundwater demonstrate that extensive leaching of irrigation return and salt flushing water flow could be the dominant process driving arsenic mobilization in the groundwater system. Moreover, the long term irrigation practice can cause the drastic change of the biogeochemical and redox condition of in the aquifer system, which in turn promotes the mobilization of arsenic. Therefore, groundwater pumping for irrigation in this area of waterborne endemic arsenic poisoning should be under strict control to protect groundwater quality in this area.Highlights► We test the applicability of δ2H, δ18O and Cl/Br ratios in delineating groundwater recharge. ► Vertical recharge by irrigation returns can be discerned by δ2H, δ18O and Cl/Br ratios. ► The correlation between As and δ18O indicating irrigation affects the As mobilization.

Hangjinhouqi is one of the most serious endemic arsenic and fluorosis areas in Hetao Plain, China. Groundwater samples (n=97) and two sediment cores issued from boreholes were collected to characterize the hydrogeochemistry of groundwater and sediment lithology of aquifers. Results showed that arsenic and fluoride content in groundwater range from 1 to 1093 μg/L and from 0.30 to 6.01 mg/L, respectively. The highest concentrations are mainly found in the flat areas of the Yin Mountains. As and F are not correlated, suggesting that their origin and/or geochemical processes leading to their release to groundwater are different. Between 15 and 45m of depth, both arsenic and fluoride are more easily released into groundwater. The external environment of high As and high F groundwater formation consisted of a lake-based geographical environment in a long term and closed geological structure, arid and semi-arid climatic conditions, as well as hydrogeological characteristics.

A microbial strain (Datong-1) was isolated from high arsenic aquifer sediments from the Datong Basin. The strain Datong-1 was identified as an Arthrobacter sp. based on 16S rDNA phylogenetic relationships, and is most closely related to DQ320481.1 and EU 196326.1 within the Arthrobacter genus. Batch experiments with sediment samples were carried out in order to study the arsenite oxidizing ability of Datong-1. These experiments indicate that strain Datong-1 can rapidly oxidize As(III) to As(V). Cell growth was concurrent with the variation of concentration levels of As(V) and As(III) in the suspension, indicating the impact of microbial activity on As(III) oxidization. Therefore, the Datong-1 strain, which can oxidize As(III), is a potential candidate for remediating arsenic contaminated groundwater in the Datong Basin in the future.

•Natural high iodine and fluoride concentrations were observed at North China Plain.•Groundwater fluoride was gradually increasing along groundwater flowpaths.•Under reducing condition of Bay area, groundwater had high iodine concentration.•Groundwater pH condition is the main factor controlling fluoride mobilization.•Variation of redox potential and pH co-controls iodine mobilization in groundwater.To better understand the enrichment of fluoride and iodine in groundwater at North China Plain (NCP), speciation analysis and geochemical modeling were conducted to identify the key hydrochemical processes controlling their mobilization in groundwater system. Groundwater fluoride and iodine concentrations ranged from 0.18 to 5.59 mg/L and from 1.51 to 1106 μg/L, respectively, and approximately 63% and 32.3% of groundwater fluoride and iodine were higher than the guidelines for drinking water (1.5 mg/L and 150 μg/L). High fluoride concentration (> 1.5 mg/L) can be detected in groundwater from the flow-through and discharge areas of NCP, and high iodine groundwater (> 150 μg/L) is mainly scattered in the coastal area. Na-HCO3/Cl type water resulted from water-rock interaction and seawater intrusion favors fluoride and iodine enrichment in groundwater. Speciation analysis results indicate that (1) fluoride complexes in groundwater are dominated by free fluoride, the negative charge of which favors fluoride enrichment in groundwater under basic conditions, and (2) iodide, iodate and organic iodine co-occur in groundwater at NCP with iodide as the dominant species. The geochemical modeling results indicate that groundwater fluoride is mainly associated with the saturation states of fluorite and calcite, as well as the adsorption equilibrium onto goethite and gibbsite, including the competitive adsorption between fluoride and carbonate. Groundwater iodine is mainly controlled by redox potential and pH condition of groundwater system. Reducing condition favors the mobilization and enrichment of groundwater iodide, which has the highest mobility among iodine species. Under reducing condition, reductive dissolution of iron (oxy)hydroxides is a potential geochemical process responsible for iodine release from sediment into groundwater. Under (sub)oxidizing condition, as groundwater pH over the ‘point of zero charge’ of iron (oxy)hydroxides, the lowering adsorption capacity of groundwater iodide/iodate on minerals leads to the release of sediment iodine into groundwater.Download high-res image (260KB)Download full-size image

•Geothermal waters are divided into two groups based on geochemical characteristics.•Hydrogen and oxygen isotopes indicate two groups of geothermal waters are main origin from meteoric water.•Three sources of elements supply for geothermal water: atmospheric deposition, bedrock and seawater.•Chlorine stable isotope shows a great potential to trace dissolved Cl in geothermal water.Geothermal energy is abundant in Guangdong Province of China, however, majority of it is still unexploited. To take full advantage of this energy, it is essential to know the information of geothermal system. Here, physical parameters such as pH and temperature, major ion (Na+, Ca2 +, Mg2 +, Cl−, SO42 − and HCO3−), trace elements (Br−, Sr2 +, Li+ and B3 +) and stable isotopes (2H, 18O and 37Cl) in geothermal water, non-geothermal water (river water, cold groundwater) and seawater were used to identify the origin and evolution of geothermal water in coastal plain of Southwest of Guangdong. Two separate groups of geothermal water have been identified in study area. Group A, located in inland of study area, is characterized by Na+ and HCO3−. Group B, located in coastal area, is characterized by Na+ and Cl−. The relationships of components vs. Cl for different water samples clearly suggest the hydrochemical differences caused by mixing with seawater and water–rock interactions. It's evident that water–rock interactions under high temperature make a significant contribution to hydrochemistry of geothermal water for both Group A and Group B. Besides, seawater also plays an important role during geothermal water evolution for Group B. Mixing ratios of seawater with geothermal water for Group B are calculated by Cl and Br binary diagram, the estimated results show that about < 1% to < 35% of seawater has mixed into geothermal water, and seawater might get into the geothermal system by deep faults. Molar Na/Cl ratios also support these two processes. Geothermal and non-geothermal water samples plot around GMWL in the δ2H vs. δ18O diagram, indicating that these samples have a predominant origin from meteoric water. Most of geothermal water samples display δ37Cl values between those of the non-geothermal water and seawater samples, further reveals three sources of elements supply for geothermal water, including atmospheric deposition, bedrocks and seawater, which show a great potential to trace source of dissolved Cl− in geothermal water. Estimated reservoir temperatures show that geothermal reservoirs in study area are mid-low temperature geothermal reservoirs.Download full-size image

The pigments (melanoidins) in molasses wastewater are refractory to conventional biological treatment. Ferric chloride was used as coagulant to remove color and chemical oxygen demand (COD) from molasses effluent. Using jar test procedure, main operating conditions such as pH and coagulant dosage were investigated. Under the optimum conditions, up to 86% and 96% of COD and color removal efficiencies were achieved. Residual turbidity in supernatant was less than 5 NTU and Fe3+ concentration was negligible because of effective destabilization and subsequent sedimentation. The results of high performance size exclusion chromatography (HPSEC) show that low molecular weight (MW) fraction of melanoidins is more reactive than high MW fraction and increase in the concentration of the lowest MW organic group is related to the capacity of charge neutralization. Aggregate size measurement reveals the size effect on the settleability of flocs formed, with larger flocs settling more rapidly. Charge neutralization and co-precipitation are proposed as predominant coagulation mechanism under the optimum conditions.

More than 100 million people in Asia are presently exposed to groundwater with arsenic (As) concentrations exceeding the World Health Organization standard of 10 μg L−1. Arsenic contaminated groundwater within basins of the central portion of the Yangtze River has recently been reported, but the processes controlling arsenic concentrations have yet to be resolved. We examined the hydrologic and geochemical factors controlling arsenic within the Jianghan Plain, an inland sedimentary basin of the Yangtze River, where arsenic concentrations exhibit strong seasonal variability driven by surface and groundwater mixing (Schaefer et al., 2016). Hydrologic fluctuations alter redox conditions in the aquifer, leading to oscillations between arsenic/iron reduction and oxidation. Here we investigate the depth-distribution of solid and aqueous phase iron and arsenic species and, through a series of laboratory manipulations, constrain the biogeochemical processes controlling seasonal changes in groundwater arsenic concentrations. In sediment incubations from ∼20 m below the surface, where solid-phase arsenic concentrations exceed 100 mg kg−1, both unamended and glucose-amended sediment samples result in arsenic release to the aqueous phase. In situ carbon was capable of promoting As release in the sediment. In contrast, sediment batch incubations from other depths resulted in limited As release. Solid phase arsenic in the enriched zone was relatively oxidized but may become reduced over short time periods. In sediments below the As-enriched zone, glucose amendment resulted in arsenic reduction, but arsenic release to the aqueous phase was restricted by the subsequent formation of arsenic sulfide minerals. Buried sedimentary arsenic coupled with anaerobic microbial respiration of subsurface organic carbon within the Jianghan Plain aquifer leads to rapid release of As to groundwater. Arsenic release from sediments at ∼20 m depth is sufficient to explain arsenic concentrations throughout the aquifer, and provides a mechanism to explain how shifts in hydrology result in seasonally variable arsenic concentrations in groundwater.

The highly dispersed iron layered double hydroxide (Fe-LDH) nanoplates supported on sepiolite (SEP) nanofibers have been successfully prepared via in situ co-precipitation of an iron salt precursor. The as-obtained hierarchical dendrite-like Fe-LDH/SEPs possess high specific area, and exhibit excellent removal ability for arsenic, demonstrating promising potential in environment applications.

The coexistence of arsenic and fluoride in groundwater has attracted extensive attention worldwide, and it is of crucial importance to efficiently remove them. In this study, hierarchically meso-/macroporous MgO using nanosheets as building blocks and with pore size distribution in the range of 10 to 150 nm was synthesized. The maximum adsorption capacities for As(III) and F were found to be about 540.9 mg g−1 (7.22 mmol g−1) and 290.67 mg g−1 (15.30 mmol g−1), respectively. Research indicated that a broad and multimodal pore size distribution provided suitable channels for ion diffusion, which were conducive to the proximity of contaminants to the internal surfaces of the adsorbent. Thermodynamic adsorption models demonstrated that two types of active sites coexisted on the MgO surface. The adsorption mechanisms of As(III) and F were proposed to include surface complexation as well as exchanges with hydroxyl and carbonate groups. Moreover, the removal rates of As(III) and F for a co-contaminated groundwater sample were determined to be 98.9% and 95%, respectively.

This study proposed a new and previously unconsidered reaction mechanism in the activation of peroxymonosulfate. We report that singlet oxygen (1O2) rather than ˙OH or SO4˙− was the dominant reactive oxygen species towards the efficient degradation of ofloxacin and phenol, demonstrating a promising application in real wastewater treatment.

A hydrogeochemical investigation using integrated methods of stable isotopes (18O, 2H), 87Sr/86Sr ratios, Cl/Br ratios, chloride-mass balance, mass balance and hydrogeochemical modeling was conducted to interpret the geochemical evolution of groundwater salinity in Datong basin, northern China. The δ2H, δ18O ratios in precipitation exhibited a local meteoric water line of δ2H = 6.4 δ18O −5 (R2 = 0.94), while those in groundwater suggested their meteoric origin in a historically colder climatic regime with a speculated recharge rate of less than 20.5 mm overall per year, in addition to recharge from a component of deep residual ancient lake water enriched with Br. According to the Sr isotope binary mixing model, the mixing of recharges from the Shentou karst springs (24%), the western margins (11%) and the eastern margins (65%) accounts for the groundwater from the deep aquifers of the down-gradient parts in the central basin is a possible mixing mechanism. In Datong, hydrolysis of silicate minerals is the most important hydrogeochemical process responsible for groundwater chemistry, in addition to dissolution of carbonate and evaporites. In the recharge areas, silicate chemical weathering is typically at the bisiallitization stage, while that in the central basin is mostly at the monosiallitization stage with limited evidence of being in equilibrium with gibbsite. Na exchange with bound Ca, Mg prevails at basin scale, and intensifies with groundwater salinity, while Ca, Mg exchange with bound Na locally occurs in the east pluvial and alluvial plains. Although groundwater salinity increases with the progress of water-rock/sediment interactions along the flow path, as a result of carbonate solubility control and continuous evapotranspiration, Na–HCO3 and Na–Cl–SO4 types of water are usually characterized respectively in the deep and the shallow aquifers of an inland basin with a silicate terrain in an arid climatic regime.

High iodine concentrations in groundwater have seldom been reported and there have been few systematic studies on high iodine groundwater worldwide. To better understand the sources and processes responsible for iodine enrichment in the groundwater of the Datong Basin, the hydrochemical characteristics of groundwater and geochemical features of aquifer sediments were studied. High iodine groundwater mainly occurs in the center of the Datong Basin with iodine concentrations ranging between 3.31 and 1890 μg L−1. Most samples with iodine concentrations higher than 500 μg L−1 are from wells with depths between 75 and 120 m. High pH and a reducing environment are favorable for iodine enrichment in the groundwater, with iodide as the dominant species that accounts for 63.2–99.3% of the total iodine. Sediment samples from a borehole specifically drilled for this study contain 0.18–1.46 mg kg−1 iodine that is moderately correlated with total organic carbon (TOC). The results of sequential extraction experiments show that iodine is mostly bound to iron oxyhydroxides and organic matter in the sediments. The mobilization processes of iodine are proposed to include reductive dissolution of iron oxyhydroxides and transformations among iodide, iodate and organic iodine driven by microbial activities under alkaline and reducing conditions.

The hydrogeochemical and isotopic investigations of high fluoride (up to 8.26 mg L−1) groundwater in the Datong Basin, Northern China were carried out in order to evaluate the geochemical controls on fluoride enrichment. The groundwater fluoride concentration tends to increase along with the regional groundwater flow path away from the basin margins, towards the central parts of the basin. Groundwater with high F concentrations has a distinctive major ion chemistry, being generally HCO3−-rich, Na-rich, Ca-poor, and having weak alkaline pH values (7.2 to 8.2) and Na–HCO3 waters. These data indicate that variations in the groundwater major ion chemistry and possibly pH, which are controlled by water–rock interaction processes in the aquifer, are important in mobilizing F. Positive correlations between fluoride with lithogenic sodium (LNa) and HCO3− in groundwater show that the high fluoride content and alkaline sodic characteristics of groundwater result from dissolution of fluorine-bearing minerals. The occurrence and behavior of fluorine in groundwater are mainly controlled by fluorite precipitation as a function of Ca2+ concentration. A positive correlation between fluoride and δ18O, low F-/Cl- ratios, and the low tritium level in the fluoride-rich groundwater indicate the effects of long-term water–rock interactions and intensive evapotranspiration.