•NOR degradation performance in nZVI/H2O2 Fenton-like system was investigated under various experimental conditions.•Solution pH and temperature had a significant effect on NOR degradation.•The rate constants of NOR degradation was fitted well with pseudo-second-order kinetic equation.•The intermediates and possible pathway of NOR degradation were identified and confirmed.In this study, nanoscale zero-valent iron (nZVI) was synthesized in the laboratory by the borohydride reduction method. nZVI was characterized by transmission electron microscopy (TEM), scan electronic microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). In addition, the degradation performance of norfloxacin (NOR) in nZVI/H2O2 Fenton-like system was investigated in detail under various experimental conditions. It was found that the removal of NOR depended on its initial concentration, initial pH, temperature, H2O2 concentration and nZVI dose. At the ambient temperature, the degradation rate of NOR by nZVI/H2O2 Fenton-like reaction under the acidic medium (pH = 3–4) was more than 95% within 40 min of the reaction time, and the mineralization degree was around 50% in terms of total organic carbon (TOC) measurement. Optimal temperature for NOR removal was 308 K, and higher temperature would cause useless decomposition of H2O2 and consequently reduction of NOR degradation. The degradation rate and total removal efficiency of NOR were favored by increasing the nZVI and H2O2 dosages. The optimal conditions for NOR degradation were: initial pH = 4.0, H2O2 concentration = 20 mmol/L, nZVI dose = 100 mg/L, temperature = 308 K. The rate constants (Kobs) of NOR degradation could be fitted well with a pseudo-second-order kinetic equation. Several degradation intermediates of NOR were detected and confirmed, including C15H20FN3O (m/z 278), C9H11FN2 (m/z 167), C7H7FN2 (m/z 139), and C7H8FN (m/z 126), respectively. Based on the identified intermediates and the Gaussian quantum statistics molecular bonding energy calculation, the possible pathway for NOR degradation under nZVI/H2O2 Fenton-like reaction was discussed.

•Titanium speciation had important effects on sludge conditioning efficiency.•Sludge flocs formed with TSC0.5 were larger and more resistant to break.•Fe2O3 nanoparticles functioned as skeleton builders and further enhance floc strength.•Particles aggregation and regrowth were improved with addition of nano-Fe2O3.In this study, the effects of chemical conditioning using titanium salt coagulants (TSCs) of different hydrolysis speciation in combination with magnetic nano-particles on dewatering performance of waste activated sludge were evaluated by means of specific resistance to filtration (SRF) and capillary suction time (CST). The morphological and extracellular polymeric substances (EPS) properties under chemical conditioning were investigated in detail to understand the reaction mechanisms involved. The results showed that the TSC with basicity of 0.5 performed better in improving sludge dewatering performance than other TSCs. Sludge floc formed by TSC0.5 treatment was characterized by larger floc size and higher floc strength than that conditioned by other TSCs. EPS compression and densification were the major mechanisms of sludge conditioning, and TSC0.5 had better performance in compressing EPS structure. In addition, reduction of soluble EPS concentration, especially protein-like substances contributed to improvement of sludge filterability under conditioning. Furthermore, addition of Fe2O3 nanoparticles could further improve dewatering performance and decrease compressibility of sludge system by acting as skeleton builders and enhancing floc strength. The sludge particles aggregation efficiency was effectively improved with addition of nano-Fe2O3. They also were able to bind with protein-like substance in EPS component, which might contribute to promotion of sludge filterability.Download high-res image (180KB)Download full-size image

In order to investigate the environmental conditions of groundwater in Xincai River Basin, and further contribute more to rational development and utilization as well as scientific management of groundwater, we analyzed hydrochemical characteristics of groundwater using descriptive statistics, correlation matrices and ion ratio coefficients, and on that basis, assessed the quality of groundwater with revised Nemerow comprehensive pollution index method. The results showed that the major cations and anions in groundwater are Ca2+ and HCO3-, respectively, and the average values and coefficient variations of groundwater parameters are relatively large (except pH), which means high concentration and large spatial variation. The average value of rCl-/rCa2+ ratios is small, indicating a good hydrodynamic condition. Strong correlation exists between NH4+ and Ca2+, implying they may have the same origin, and strong correlations also exist between TDS and the major elements, implying that the major elements contribute much to the salinity of groundwater and the tendencies among them follow a similar trend. The groundwater quality assessment results show that the shallow groundwater quality in Xincai River Basin is relatively poor, and about half of the shallow groundwater is not suitable for drinking, which may be caused by excessive use of chemical fertilizers.

REEs (rare trace elements) are potential tracer for evolution of water system. In this study, dissolved REEs of different waters (salt lake water, intercrystalline brine, surface water and groundwater in Golmud River) from Qaidam Basin were investigated. The results show that ∑REE in different water samples are very inhomogeneous and consistent with TDS very well, which suggest REEs have a same main source with other major ions in these waters. Most samples are characterized by flat REE patterns (slightly enriched in heavy REEs) and obvious Eu positive anomaly. Eu-anomalies in aqueous inherit the characteristic of host rock, indicates that dissolution of host rock is main material source for basin. While Ce anomalies reflect source difference and processes that occurred during transport of water.

Muddy sediment is one of the most common aquitards. During the burial compaction of mud, the pressure and temperature of strata increased with depth, in which some complex physical, chemical and biological reactions occurred. Meanwhile, a large amount of porewater, which interacts with microbes, organic matter and minerals in mud, would be discharged into adjacent aquifers. Numerous previous efforts by geologists have put forward some evidences, indicating that a portion of components (such as ions and nutrient) in groundwater are from muddy sediments. This paper provides a brief overview of efforts on different reactions in pore water in which environments change from oxidation to reduction and interfaces between the aquitard and the aquifer. Then, in the view of geological evolution, an idea is proposed that mud provided not only water but also material source for adjacent aquifer during its compaction and burial. In order to further understand the genesis of natural groundwater, especially natural inferior groundwater and brine, the diagenetic reaction and mineralization, water-rock interaction during the compaction of sediment should be considered, which will be of great significance in hydrogeology.

•BDE-47 and BDE-209 have unique δ13C and δ81Br values.•Difference of isotopic compositions might be non-significant.•Source identification by isotopic characteristics faces challenges.Typical brominated organic pollutants poly brominated diphenyl ethers (PBDEs) might be characterized by their stable carbon and bromine isotopic compositions. Currently, there are no published reports concerning the two-dimensional isotopic (δ13C and δ81Br) values of PBDEs. To assess the significance of carbon and bromine isotopes in the source identification of PBDEs, EA-IRMS and off-line-IRMS methods were employed to measure the δ13C and δ81Br values of the typical PBDE congeners, 2,2′,4,4′-tetrabromodiphenyl ethers (BDE-47) and decabromodiphenyl ether (BDE-209) from different suppliers. The results show that individual PBDE congeners (three BDE-47 samples and three BDE-209 samples) have unique δ13C and δ81Br values, possibly due to differences in the precursors and manufacturing processes, indicating that the isotope composition is a promising probe to determine the source of PBDEs in the environment. While it is worth noting that some challenges might exist during practical application of this method, such as the similar isotopic compositions of PBDEs from different source. Thus, source identification associated with isotopic signatures should be used cautiously. This study provides a basis for further research into the source identification of PBDEs in the environment by examining their isotopic characteristics.

•Bacterial community structures are distinctly different along groundwater flow path.•Bacterial activities play key roles in groundwater redox transformation.•NO3− reduction process inhibits arsenic release, while SO42 − process doesn't.•Reductive desorption of As(V) is an important process in weakly alkaline groundwater.Studies have shown that arsenic is desorbed/released into groundwater as a result of bacterial reduction of As(V) and Fe(III). However, bacterial activities like sulfate reduction process can also reduce the content of arsenic in groundwater. In this study, we examined the effects of different biogeochemical processes (e.g. NO3− and SO42 − reduction) on arsenic, by investigating the chemical characteristics and bacterial community structure of groundwater in the Datong Basin, northern China. Along the groundwater flow path, arsenic concentration increased from < 1 to 947.6 μg/L with dominant bacteria change from aerobic (Fluviicola, Rhodococcus) to denitrifying bacteria (Thauera, Gallionella), and then to sulfate reducing bacteria (Desulfosporosinus). According to the groundwater redox sensitive indicators (Eh, NO3−, SO42 −/Cl− and Fe2 +) concentrations (or ratios), the sampling points were approximately divided into three zones (I, I′’ and II). Variation in features of these indicators suggested that the groundwater evolved from a weakly oxidizing environment (Zone I, Eh average 93.3 mV, respectively) to strong reducing environment (Zone II, Eh average − 101.8 mV). In Zone I, bacteria mainly consuming O2 or NO3− were found which inhibits Fe(III) and As(V) reduction reaction, resulting in a low As zone (< 1 to 3.3 μg/L). However, in Zone II, where O2 and NO3− have been depleted, SO42 − reduction appears to be the dominant process, and the Fe(III) and As(V) reduction processes are also occurring and hence, enrichment of As in the groundwater (2.8 to 947.6 μg/L, average 285.6 μg/L). Besides, bacterial Fe(III) reduction process was retarded due to the weakly alkaline conditions (pH 7.60–8.11, average 7.83), but abiotic Fe(III) reduction by HS− may be continued. Therefore, we conclude that the Fe(III) and As(V) reduction processes contributed to arsenic enrichment in the groundwater, and the reductive desorption of arsenate is the main occurring process especially in the weakly alkaline environment. Moreover, NO3− reduction process can significantly restrain the release of arsenic, but the process of SO42 − reduction is insignificant for arsenic concentration decline in natural groundwater.Download high-res image (384KB)Download full-size image

High levels of ammonium from anthropogenic sources threaten the quality of surface waters and groundwaters in some areas worldwide, but elevated ammonium levels of natural sources also have been identified. High levels of ammonium have been detected in both surface water and shallow groundwater of the Jianghan Plain, an alluvial plain of the Yangtze River. This study used N isotopes coupled with ancillary chemistry to identify ammonium in this region. Ammonium in the Tongshun River (up to 10.25 mg L−1) showed a sharp accumulation in the upstream and gradual attenuation in the downstream. The δ15N values of ammonium in the TSR were high and ranged narrowly from +12.5 to +15.4‰, suggesting an anthropogenic source that was septic effluent from industrial waste discharge. Sorption and nitrification were likely to respectively serve as the principal processes contributing to ammonium attenuation in different reaches of the downstream TSR. In shallow groundwater, high levels of ammonium (up to 14.10 mg L−1) occurred in a reducing environment. The narrow δ15N variation with low values (+2.3 to +4.5‰) in the lower aquifer suggested a natural source that was organic N mineralization. The δ15N values in the shallow aquitard exhibited a wide range from −1.8 to +9.4‰, owing to various sources. Two types of water in the shallow aquitard could be identified: (1) type-1 water with relatively longer residence time was similar to those in the aquifer where ammonium was mainly sourced from organic N mineralization; (2) type-2 water with shorter residence time was jointly affected by surface input, chemical attenuation and mineralization of organic N. The aquitard prevents prompt ammonium exchange between the surface and aquifer, and the shallower part of the aquitard provides a sufficient reaction time and an active reaction rate for ammonium removal.

Sewage irrigation is one of the best options to reduce the stress on limited fresh water and to meet the nutrient requirement of crops. Environment pollution caused by volatile halogenated hydrocarbons (VHCs) associated with sewage irrigation has received increasing attention due to the toxicological importance in ecosystem. The aim of this study was to discuss the spatial distribution characteristics of VHCs in unsaturated zone under sewage irrigation and their migration in the environment. Soil samples were collected from XiaoDian district of TaiYuan city and measured for the major VHCs including of chloroform (CHCl3), tetrachloromethane (CCl4), trichloroethylene (C2HCl3), tetrachloroethylene(C2Cl4), pentachlorobenzene (C6HCl5), hexachlorobenzene (C6Cl6). Results showed that VHCs were accumulated in the unsaturated zone with long-term sewage irrigation. The contents of VHCs in the unsaturated zone of the study area were 34, 2, 3, 1.5, 8.3, 4.8 times higher than the background value respectively. Soils with long-term irrigation of sewage showed higher contents of VHCs than that with short-term irrigation of sewage. Not only the irrigation time, soil physical properties (e.g. soil texture) also played an important role on VHCs accumulation in soil.

A precise analytical methodology for bromine stable isotope was established by GasBench II-IRMS. The bromine isotope analytical technique consists of two key links: the separation and purification of bromine and mass spectrometry of bromine stable isotope. The separation and purification of bromine aims at extracting bromine from natural waters containing a mass of chlorine and then precipitating bromide in form of silver bromide. By reacting with methyl iodide, silver bromide is converted to methyl bromide, which is analyzed by GasBench II-IRMS next. GasBench II-IRMS is mainly composed of a multipurpose online gas preparation device (GasBench II) containing CP-PoraPlot-Q chromatographic column and a gas stable isotope ratio mass spectrometer (MAT253). By mass spectrometry, the internal precision and external precision for this method can be reached at better than ±0.03‰ (n = 12) and ±0.06‰ (n = 8) with analysis time of 15 min,which achieved the international top level. Applying this method to measure bromine isotope compositions of typical geothermal groundwater, oilfield water, saline groundwater and salt lake water in China, different fractionation effect between bromine and chlorine and remarkable bromine isotope fractionation effect from different sources and evolutionary processes were observed.Graphical abstractHighlights► A precise analytical method for bromine stable isotopes was established by GasBench II-IRMS. ► A recovery rate of 100% was achieved during the extraction of bromine. ► The internal and external precision can be reached at better than ±0.03% and ±0.06% with analysis time of 15 min. ► Some conclusions were achieved by applying the method in a set of natural waters.

•DCMD-APZ technology shows ability to immobilize and reduce arsenic respectively.•Optimum conditions for high distillate flux production are depicted.•Fast adsorption kinetics at t1/2 ≤ 30 min was observed for arsenic immobilization.•XPS, wet chemistry, and adsorption models confirm immobilization and reduction of As.A highly effective novel system of direct contact membrane distillation (DCMD) integrated with acid-purged zero-valent iron (APZ) technology has been developed. Compared to conventional processes of arsenic removal which reconstitute secondary contamination at disposal site, this system proves capable of simultaneous removal and immobilization of arsenic from contaminated water with great efficiency and improved water flux. Using composite microporous membranes of polytetrafluoroethylene (PTFE) and polypropylene (PP) integrated with APZ in a DCMD-APZ configuration, varying residual arsenic concentrations were injected anoxically into ≤2 g acid-washed Fuchen (XK 13-201) reduced Fe powder at a flow rate of 0.33 mL/min and pH 6 ± 1.0 at 60 °C. Results from this unique configuration show advantages including maximum distillate flux production of 55.5 kg/m2 h with greater than 95% arsenic rejection efficiency using PTFE/PP composite membrane, fast adsorption and immobilization of rejected arsenic on APZ at t1/2 ≤ 30 min, and electrochemical reduction of As(V) and/or As(III) to sparsely soluble As(0) as confirmed by macroscopic wet chemistry, adsorption kinetic model and X-ray photoelectron spectroscopic (XPS) analysis conducted within 5 days of experimental period. Since the arsenic adsorption/reduction process is a thermodynamically assisted phenomenon, integrated configuration of the DCMD-APZ technology stands out as a promising technique to mitigate the unresolved challenges of arsenic contamination and re-dissolution in groundwater.

Hydrochemical characteristics of groundwater, the lithological features of the aquifer sediments and fluoride in rocks were studied to determine the distribution and genesis of high fluoride groundwater (> 1.5 mg/L) in Hangjinhouqi, which is an endemic fluorosis areas. Groundwater with high fluoride (> 1.5 mg/L) is mainly of HCO3–Na or HCO3–Cl–Na type for both fresh and brackish water. Different from other halide ions of Cl−, Br− and I−, F− in groundwater decreased with the TDS. Analysis of fluorine in rocks showed that the average of total fluorine in rocks in Hangjinhouqi (1278.84 mg/kg) is much higher than the background value of Inner Mongolia (316.2 mg/kg). During long-term water–rock interaction, fluoride in these rocks from Yin Mountains will be released out and then accumulated in the groundwater of sand or clay (silty clay) aquifers in the Hangjinhouqi area. All the water samples fall below the Ksp curve of CaF2. Due to CaF2 solubility control, Na-predominant water is favorable for F enrichment, that's why groundwater with high fluoride displayed low TDS in the study area.Highlights► High fluoride shallow groundwater in Hangjinhouqi is of HCO3–Na or HCO3–Cl–Na type. ► Unlike Cl−, Br− and I−, F− in groundwater decreases with increasing salinity. ► Elevated F in rocks from Yin Mountain is a source of F to sediment.

•The δ81Br in Quaternary shallow groundwater was systematacially surveyed for the first time.•The δ81Br values in groundwater decreased gradually from inland to shore.•Based on δ81Br and hydrochemistry, brine originated from seawater evaporation, rather than salt dissolution.•Mixing process occurred between brine and fresh water based on δ81Br and hydrochemistry.•Marine aerosol input was a potential process contributing to the enrichment of 81Br in brackish water.In the south coast of Laizhou Bay, due to intensive groundwater extraction since the 1970s, salt water intrusion has occurred seriously, which increased the stress on regional fresh water resources. It is of great importance to understand origin of salinity and salinization process in coastal aquifers. To trace source and transport of dissolved bromide as a perfect representative of salinity and reveal genesis of salinized groundwater in regional aquifer system, Br stable isotopes of the sampled waters were surveyed coupled with hydrochemistry and stable H/O isotopes along the direction from inland to shore. The results show that groundwater salinity, hydrochemistry and stable isotopes exhibit regular variation from inland to shore. The TDS values of the groundwater increase gradually ranging from 0.52 to 133.74 g/L, the chemical types transform from Cl–Ca and HCO3–Ca to Cl–Na, 2H and 18O are getting more and more enriched, and the δ81Br values decrease gradually, from inland to shore. Trends of major ions versus bromide and Br isotope signatures for brine indicate brine originated from seawater evaporation followed by some water–rock interaction processes. The hydrogen and oxygen isotope signatures of the brine indicate the dilution by fresh water of meteoric origin was a probable process during or after brine formation. The δ81Br values of brine samples show good anticorrelation to both δ2H and δ18O values, probably confirming the addition of fresh water. The potential contribution of evaporate dissolution as a primary process to the brine was ruled out based on their Br isotope signatures. Trends of major ions versus bromide and H/O stable isotopes for brackish water reveal brine intrusion has occurred and mixed with fresh water inland, and Br stable isotopic composition of brackish water indicates that marine aerosol input could enrich the dissolved bromide in brackish water except for brine intrusion. Other processes, such as diffusion, subaerial evaporation and anthropogenic activities may change the budget of dissolved Br−, but are not primary processes responsible for behavior of Br stable isotope in shallow brackish water. Major contribution of meteoric water in deep fresh water and more influence by brine in deep saline water were revealed based on the Br isotopic results.

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.

•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