Unlocking the potential of surface modification with phosphate on ball milled zero-valent iron reactivity:Implications for radioactive metal ions removal.

Numerous investigations have illuminated the profound impact of phosphate on the adsorption of uranium, however, the effect of phosphate-mediated surface modification on the reactivity of zero-valent iron (ZVI) remained enigmatic. In this study, a phosphate-modified ZVI (P-ZVIbm) was prepared with a facile ball milling strategy, and compared with ZVIbm, the U(VI) removal amount (435.2 mg/g) and efficiency (3.52×10-3 g·mg-1·min-1) of P-ZVIbm were disclosed nearly 2.0 and 54 times larger than those of ZVIbm respectively. The identification of products revealed that the adsorption mechanism dominated the removal process for ZVIbm, while the reactive modified layer strengthened both the adsorption pattern and reduction performance on P-ZVIbm. DFT calculation result demonstrated that the binding configuration shifted from bidentate binuclear to multidentate configuration, further shortening the Fe-U atomic distance. More importantly, the electron transferred is more accessible through the surface phosphate layer, and selectively donated to U(VI), accounting for the elevated reduction performance of P-ZVIbm. This investigation explicitly underscores the critical role of ZVI's surface microenvironment in the domain of radioactive metal ion mitigation and introduces a novel methodology to amplify the sequestration of U(VI) from aqueous environments.

Co-migration behavior of toluene coupled with trichloroethylene and the response of the pristine groundwater ecosystems - A mesoscale indoor experiment.

Experimental scale and sampling precision are the main factors limiting the accuracy of migration and transformation assessments of complex petroleum-based contaminants in groundwater. In this study, a mesoscale indoor aquifer device with high environmental fidelity and monitoring accuracy was constructed, in which dissolved toluene and trichloroethylene were used as typical contaminants in a 1.5-year contaminant migration experiment. The process was divided into five stages, namely, pristine, injection, accumulation, decrease, and recovery, and characteristics such as differences in contaminant migration, the responsiveness of environmental factors, and changes in microbial communities were investigated. The results demonstrated that the mutual dissolution properties of the contaminants increased the spread of the plume and confirmed that toluene possessed greater mobility and natural attenuation than trichloroethylene. Attenuation of the contaminant plume proceeded through aerobic degradation, nitrate reduction, and sulfate reduction phases, accompanied by negative feedback from characteristic ion concentrations, dissolved oxygen content, the oxidation-reduction potential and microbial community structure of the groundwater. This research evaluated the migration and transformation characteristics of typical petroleum-based pollutants, revealed the response mechanism of the ecosystem to pollutant, provided a theoretical basis for predicting pollutant migration and formulating control strategies.

Core-Shell MnFe Nanocatalyst Derived from Prussian Blue Analogs for Peroxymonosulfate Activation: Nonradical Mechanism and Bimetallic Valence Cycle.

Sulfamethazine (SAT) is widely present in sediment, soil, rivers, and groundwater. Unfortunately, traditional water treatment technologies are inefficient at eliminating SAT from contaminated water. Therefore, developing an effective and ecologically friendly treatment procedure to effectively remove SAT is critical. This has raised concerns about its potential impact on the environment and human health. In this study, metal-organic-inorganic composites consisting of graphene-encapsulated Fe-Mn metal catalyst (Mn3Fe1-NC) were synthesized by calcining MnFe Prussian blue analogs (PBA) under a nitrogen atmosphere. The composites were applied to activate peroxymonosulfate (PMS) and facilitate the degradation of SAT in aquatic environments. The Mn3Fe1-NC, dosed with 5 mg, in combination with PMS, dosed with 1.5 mmol L-1, achieved a 91.8% degradation efficiency of SAT. The transformation of the CN skeleton led to the formation of a carbon shell structure, which consequently reduced metal ion leaching from the material. At various pH levels, the iron and manganese ions were observed to leach out at levels lower than 0.1392 and 0.0580 mg L-1, respectively. In contrast, the Mn3Fe1-NC was found to be minimally impacted by pH levels and coexisting ions present in the aqueous environment. Radical burst experiments and electrochemical analysis tests verified that degradation primarily occurs through the nonradical pathway of electron transfer. The active sites responsible for this process were identified as the Mn (IV) and graphitic-N atoms on the material, which facilitate direct electron transfer. Additionally, the presence of Fe atoms promotes the valence cycling of Mn atoms. This study introduces new insights into the reaction mechanism and the constitutive relationship of catalytic centers in nonradical oxidation reactions.

Diurnal variation in the urban thermal environment and its relationship to human activities in China: a Tencent location-based service geographic big data perspective.

The main factor of the formation and deterioration in China's urban thermal environment is human activity, which is difficult to describe and measure. A new perspective on the effect of human activity on the urban thermal environment can be obtained by examining the interaction between location-based service (LBS) data and the urban thermal environment in China. However, relevant research is still limited. In this study, we used Tencent LBS data, Terra/Aqua MODIS land surface temperature (LST) data, and land use data to investigate the relationship between LBS and the urban thermal environment, specifically the LST and surface urban heat island intensity (SUHII) across China and its provinces. Our results showed that (1) in summer, the heat island effect was an issue in 94% of the urban areas in China, which was worse during the day. The high- and low-value periods of LBS data on a given day coincided with the acquisition times of MODIS LST products during the day and at night, respectively. (2) During both the day and at night, there was a significant connection between LBS data and the urban thermal environment in China. The highest correlation coefficient (r) between LBS data and the LST could reach 0.55 (p < 0.01) at the provincial level, and the highest correlation coefficient (r) between LBS data and the SUHII could reach 0.78 (p < 0.01) at the provincial level. (3) The urban thermal environment diurnal difference and LBS data exhibited a significant relationship. The ΔLBS diurnal differences were significantly positively related to the SUHII diurnal differences in China. The overall study findings revealed that LBS data constitute an important parameter to represent the human activity intensity when investigating the formation of the urban thermal environment in China.

Natural phosphorus-ferromanganese ore-based composites for the simultaneous remediation of arsenic- and lead-co-contaminated groundwater: synergistic effectiveness, kinetics, and mechanisms.

Natural phosphorus-ferromanganese ore (NPO-NFMO) based composites by mechanical ball milling method, applying for the simultaneous remediation of arsenic (As) and lead (Pb) co-contaminated groundwater. Kinetic behavior adopted pseudo-second-order adsorption mechanism attaining equilibrium in 120 min over a wide pH range (2.0-6.0). NPO-NFMO realized higher adsorption capacity for As(III) (6.8 mg g-1) and Pb(II) (26.5 mg g-1) than those of single NPO (1.7 and 7.8 mg g-1) and NFMO (2.9 and 5.1 mg g-1), indicating that synergistic effects of NPO and NFMO considerably enhanced the adsorption capacity in mixed adsorption system. Fresh and used NPO-NFMO were characterized, and indicated that NPO-NFMO formed stable minerals of PbAs2O6 and PbFe2(AsO4)2(OH)2. The underlying adsorption mechanism indicated that As(III) and Pb(II) removal was involved with multiple mechanisms, including electrostatic adsorption, oxidation, complexation, and coprecipitation. The effects of key reaction parameters including mass ratios of NPO and NFMO, initial metal ion concentration, dosage, solution pH, and co-existing anions in groundwater were systematically investigated. The novel designed NPO-NFMO-based composites can be deemed as a promising amendment for simultaneous immobilization of As(III) and Pb(II) in co-contaminated soil and groundwater.

Anthropogenic perturbation enhances the release of geogenic Mn to groundwater: Evidence from hydrogeochemical characteristics.

High geogenic Mn groundwater is widespread around the world and has also proved to be harmful to human health, especially to the IQ of Children. The natural release of Mn from aquifer sediments in slightly reducing condition is believed to be the primary cause. However, there isn't enough evidence to prove that anthropogenic activities promote the reductive release of Mn. Here a Historical Petrochemical Waste Storage Site (HPWSS) was studied to evaluate its impact on groundwater quality. Significantly elevated Mn, as well as elevated TDS, anionic surfactants, and organic pollutants, were found in the shallow aquifer (9-15 m) groundwater compared to the surrounding area. The Mn was believed to be generated in-situ, while others are caused by anthropogenic pollution. The good correlations between Mn and NH4+, HCO3-, I, As, Co, V, Ti, respectively, showed the Mn mobilization was mainly attributed to the reductive dissolution of Mn oxides/hydroxides. The potential processes leading to this enhanced Mn release are discussed, including 1) the infiltration of high salinity water which solubilized sediment organic matter (OM); 2) the anionic surfactants that promoted the dissolution and mobilization of surface-derived organic pollutants as well as sediment OM. Any of these processes may have provided a C source to stimulate the microbial reduction of Mn oxides/hydroxides. This study showed the input of pollutants could change the redox and dissolution conditions of the vadose zone and aquifer, causing a secondary geogenic pollution risk in groundwater. Since Mn is easily mobilized in suboxic condition as well as its toxicity, the enhanced release due to anthropogenic perturbation merits more attention.

Characteristics of persulfate gel materials in groundwater remediation: Column and tank experiments investigations.

Using persulfate and environment-friendly gel solution as raw materials, persulfate gel sustained-release material (PGSR) and persulfate gelatin gel sustained-release material (G-PGSR) were developed. The main purpose of this study was to evaluate the potential of PGSR and G-PGSR in sustained release, migration and removal performance through column and tank experimental investigations. Results showed that the maximum release rates of PGSR and G-PGSR in water columns were 1.34 and 0.58 mg min-1 and the cumulative release amounts achieved 2950 and 2818 mg within 75 h, representing release efficiencies of 98.3 % and 93.9 %, respectively. In three sand columns, the maximum release rate was 0.32, 0.21, and 0.16 mg min-1 and the cumulative release achieved 473, 426, and 359 mg within 90 h with release efficiencies of 94.7 %, 85.3 %, and 71.7 %, respectively. Release time and rate of PGSR and G-PGSR are constrained by the permeability of porous media. G-PGSR in the sand tank exhibited migration and release characteristic with the slow-release diffusion effect. Lateral diffusion produced higher S2O82- concentration far beyond what was allowed in the tank. The saturated hydraulic conductivity decreased from 4.9 × 10-3, 1.1 × 10-3, and 4.9 × 10-4 cm s-1 to 2.4 × 10-3, 7.4 × 10-4, and 2.1 × 10-4 cm s-1 in columns filled with medium, fine, and silt, respectively. G-PGSR injection did not significantly change the order of magnitude of hydraulic conductivity. 2,4-dinitrotoluene removal performance was affected with the inlet flow rates, which decreased from 92 %, 82 %, and 78 % to 42 %, 28 %, and 8 % during 24 PV at the flow rate of 0.5, 1.5, and 4.5 mL min-1, respectively. Moreover, the removal efficiency was enhanced by G-PGSR with activated carbon as an activator. This study expands our understanding and ability of persulfate gel materials for groundwater remediation and provides a certain research basis for practical applications.

A novel thermosensitive persulfate controlled-release hydrogel based on agarose/silica composite for sustained nitrobenzene degradation from groundwater.

The increasing risk of organic contamination of groundwater poses a serious threat to the environment and human health, causing an urgent need to develop long-lasting and adaptable remediation materials. Controlled-release materials (CRMs) are capable of encapsulating oxidants to achieve long-lasting release properties in aquifers and considered to be effective strategies in groundwater remediation. In this study, novel hydrogels (ASGs) with thermosensitive properties were prepared based on agarose and silica to achieve controlled persulfate (PS) release. By adjusting the composition ratio, the gelation time and internal pore structure of the hydrogels were regulated for groundwater application, which in turn affected the PS encapsulated amount and release properties. The hydrogels exhibited significant temperature responsiveness, with 6.8 times faster gelation rates and 2.8 times longer controlled release ability at 10 â„ƒ than at 30 â„ƒ. The ASGs were further combined with zero-valent iron to achieve long-lasting degradation of the typical nitrobenzene compound 2,4-dinitrotoluene (2,4-DNT), and the degradation performance was maintained at 50 % within 14 PV, which was significantly improved compared with that of the PS/ZVI system. This study provided new concepts for the design of controlled-release materials and theoretical support for the remediation of organic contamination.

Exogenous-organic-matter-driven mobilization of groundwater arsenic.

The potential release capacity of arsenic (As) from sediment was evaluated under a high level of exogenous organic matter (EOM) with both bioreactive and chemically reactive organic matters (OMs). The OMs were characterized by FI, HIX, BIX, and SUVA254 fluorescence indices showing the biological activities were kept at a high level during the experimental period. At the genus level, Fe/Mn/As-reducing bacteria (Geobacter, Pseudomonas, Bacillus, and Clostridium) and bacteria (Paenibacillus, Acidovorax, Delftia, and Sphingomonas) that can participate in metabolic transformation using EOM were identified. The reducing condition occurs which promoted As, Fe, and Mn releases at very high concentrations of OM. However, As release increased during the first 15-20 days, followed by a decline contributed by secondary iron precipitation. The degree of As release may be limited by the reactivity of Fe (hydro)oxides. The EOM infiltration enhances As and Mn releases in aqueous conditions causing the risk of groundwater pollution, which could occur in specific sites such as landfills, petrochemical sites, and managed aquifer recharge projects.

Efficient utilization of biogenic manganese oxides in bioaugmentation columns for remediation of thallium(I) contaminated groundwater.

Little attention has been paid to the in situ-generated biogenic manganese oxides (BMnOx) for practical implementation in continuous groundwater remediation systems. The enrichment effects of manganese oxidizing bacteria (MOB) in bioaugmentation columns and the in situ-generated BMnOx for continuous thallium(I) (Tl(I)) removal from groundwater were investigated. Results indicated that Pseudomonas Putida MnB1 (strain MnB1) attached on the groundwater sediments (GS) can achieve a maximum of 97.37 % Mn(II) oxidation and generate 29.6 mg/L BMnOx, which was superior than that of traditional quartz sand (QS). The in situ-generated BMnOx in MOB_GS column effectively removed 10-100 µg/L Tl(I) under the interference of high concentrations of Fe(II) and Mn(II) in groundwater. Distinctive microbial enrichment effects occurred in the bioaugmentation columns under the competition of indigenous microbes in groundwater. The release of Mn(II) from the BMnOx inhibited with the decrease in Tl(I) removal efficiency. XAFS analysis revealed Tl(I) was effectively adsorbed by BMnOx and Mn-O octahedra with Tl-O tetrahedral coordination existed in BMnOx. This study provides an in-depth understanding of the in situ-generated BMnOx for the Tl(I) removal and contributes to the application of BMnOx in groundwater remediation.

Preparation and properties of the persulfate gel materials and application for the remediation of 2,4-dinitrotoluene contaminated groundwater.

This study aims to develop persulfate new gel sustaining-release material (PGSR) and gelatin-gel sustaining-release material (G-PGSR) that can be injected into aquifers and slowly release S2O82- to groundwater. Compatibility and miscibility of colloidal silica gels and gelatin with S2O82- were tested. Morphologies of the as-prepared PGSR and G-PGSR were observed by scanning electron microscope (SEM) and Fourier transform infrared spectrometer (FT-IR). Release characteristics of PGSR containing variable persulfate concentrations (from 1.25 wt% to 5 wt%), silica sol (from 30 wt% to 40 wt%), and gelatin (from 0.5 wt% to 2.0 wt%) were monitored. Viscosities of PGSR solution increased from 5 to 112 cP with increasing silica sol from 30 wt% to 40 wt% during the first 10 min. Viscosities of PGSR solution in 40 wt% silica sol increased to 346 cP within the 30 min and rapidly increased to 8000 cP within the next 30 min followed by the gelation phase. Gelation rates of the PGSR solution increased with increased persulfate concentrations from 1.25 wt% to 5.0 wt%. The maximum release rates achieved at 5 h in G-PGSR were 1.98 mg of S2O82- per min similar to that in PGSR. The release persulfate concentrations in G-PGSR suggested that gelatin and colloidal silica were both compatible and miscible with S2O82-. Meanwhile, the PGSR exhibits a characteristic two-phase increase in viscosity with increased silica sol concentrations, persulfate concentrations, and gelatin concentrations. Compared with the persulfate only system, the degradation efficiency of 2,4-dinitrotoluene (2,4-DNT) was achieved 91.5 % within 3 h, while 78.6 % and 66.9 % degradation efficiency were shown in PGSR and G-PGSR, respectively. The PGSR and G-PGSR both could create persistent oxidation degradation of 2,4-DNT. Results suggested that colloidal silica and gelatin could be used to create PGSR and G-PGSR for persistent oxidation in groundwater remediation.

Insights into the synergistic removal mechanisms of thallium(I) by biogenic manganese oxides in a wide pH range.

The behavior and mechanism of thallium (Tl) adsorption by biogenic manganese oxides (BMnOx) are poorly understood. In this study, BMnOx was applied for Tl(I) removal from aqueous solution, and the adsorption interactions were systematically revealed for the first time. BMnOx was successfully prepared with high productivity by effectively oxidizing Mn(II) with a manganese oxide bacterium in an optimal Mn(II) concentration range of 4.0-28 mg/L. Compared with other adsorbents, the prepared BMnOx achieved high Tl(I) adsorption capacity over a wide pH range from 3.0 to 9.0 and high humic acid (HA) concentration (40 mg/L) interference. The experimental results were well depicted by pseudo-second-order kinetics and the Langmuir isotherm model, indicating that chemisorption played the dominant role during the adsorption process. The adsorption mechanisms were verified as synergetic interactions of oxidation-precipitation, electrostatic attraction, ion exchange and surface complexation. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) results suggested that 19.46% of the highly toxic Tl(I) was transformed into the much less toxic product Tl2O3 after adsorption onto BMnOx. This study provides theoretical guidance for high-concentration Tl(I) decontamination from groundwater by biogenic manganese oxides.

Ferrous oxalate covered ZVI through ball-milling for enhanced catalytic oxidation of organic contaminants with persulfate.

Zero-valent iron (ZVI), with high reduction capacity and cost effectiveness, has been widely used as an activator for persulfate in remediation of organic pollutants. However, the existence of inherent iron oxide shell blocked the transfer of proton and further reduced its reactivity. In present study, a novel persulfate (PS) activator BZVI@OA was synthesized via ball milling ZVI with oxalic acid dihydrate. Scanning electron microscope, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectrometry and Time-of-flight secondary ion mass spectroscopy confirmed the original low proton conductive oxidation shell was replaced by a high proton conductive FeC2O4 shell. The generated shell significantly improved persulfate activated capacity, through which degradation rates of various contaminants were enhanced for 1.64 to 2.33 times. Dissolved oxalate was proved to form complexes with iron ions, dramatically reduced the potential difference and relieved the blocked cyclic conversion. Electron paramagnetic resonance and quenching experiments confirmed an inner sphere adsorption of PS on FeC2O4·2H2O shell which facilitated the peroxide bonds cleavage, leading high efficiency of ROS generation. The accelerated proton transition was confirmed with AC impedance method, resulting in fast and elevated surface bound Fe2+ for persulfate decomposition into active species. Furthermore, BZVI@OA/PS system demonstrated high tolerance over wide initial pH range and promising reusability within 6 cycles. This work clarifies an effective strategy for developing efficient modified ZVI as a PS activator for organic pollutant degradation in water.

Nitrogen addition increases the ecological and human health risks of PAHs in different fractions of soil in sewage-irrigated area.

Nitrogen (N) is one of the most important nutrients required by soil and crops. N addition improves soil quality and fertility. However, long-term N addition changes the soil environment, which may affect the adsorption and accumulation of organic pollutants in soil. The adsorption of pollutants by the light fractions (LF) and heavy fractions (HF) of soil, and their resulting risks, might differ. In addition, several organic pollutants, especially PAHs, accumulate in farmland soil under long-term sewage irrigation. However, few studies have examined the response of PAHs to N addition in soil in sewage-irrigated areas, including whether there is a difference in the response of the LF and HF of soil. Here, a long-term experiment was carried out in farmland soils in typical sewage-irrigated areas to reveal the adsorption and accumulation of PAHs in bulk soil, LF, and HF, and the human health and ecological environment risks posed by PAHs under different levels of N addition. Under long-term N addition, the concentration of PAHs in soil increased and fluctuated from 7598 µg kg-1 to 10,414 µg kg-1. Significant differences in the PAHs concentration in the LF (5048 µg kg-1 to 1889 µg kg-1) and HF (2536 µg kg-1 to 8521 µg kg-1) and the human health and ecological risks of soil with N addition in typical sewage-irrigated areas were observed. The HF of soil was characterized by low carcinogenic and ecological risks. The results of our research provide insight into possible management actions that could be taken to enhance the environmental protection and safety of agricultural production activities, such as sustainability fertilization.

Microwave-assisted functionalization of PAN fiber by 2-amino-5-mercapto-1,3,4-thiadiazol with high efficacy for improved and selective removal of Hg2+ from water.

Mercury (Hg2+) contamination in water is associated with potential toxicity to human health and ecosystems. Many research studies have been ongoing to develop new materials for the remediation of Hg2+ pollution in water. In this study, a novel thiol- and amino-containing fibrous adsorbent was prepared by grafting 2-amino-5-mercapto-1,3,4-thiadiazol (AMTD) onto PAN fiber through a microwave-assisted method. The synthesized functional fiber was characterized by FTIR, SEM, and elemental analysis. Adsorption tests depicted that for mercury uptake, PANMW-AMTD fiber exhibited enhanced adsorption capacity compared with other fibrous adsorbents and selective adsorption feature under the interference of other metal ions, including Pb2+, Cu2+, Cd2+, and Zn2+. The influence of pH on the adsorption process was investigated and the effect of temperature revealed that the adsorption sorption process was endothermic and the adsorption performance of PANMW-AMTD was elevated with the increase of temperature. Kinetic studies of PANMW-AMTD fiber followed the pseudo-second-order and the adsorption isotherm of Hg2+ was well fitted by Sips and Langmuir equations, given the maximum adsorption amount of 332.9 mg/g. XPS results suggested that a synergetic coordination effect of sulfur and nitrogen in functional fiber with mercury took responsibility for the adsorption mechanism in the uptake process. In addition, the prepared PANMW-AMTD fiber could easily be regenerated with 0.1 M HCl for five times without significant reduction of mercury removal efficiency. Thus, this study will facilitate the research on novel functional material for the removal of mercury from water.

[Different Responses of Soil Microbial Community Structure to Irrigation with Treated Wastewater from Domestic and Industrial Sources].

To investigate the long-term effects of irrigation with treated domestic and industrial wastewater on the microbial community structure of the soil, Illumina MiSeq high-throughput sequencing technology was applied. Groundwater irrigated soil was used as a control. The effects of soil environmental factors and their interactions on the microbial community structure were investigated. Compared with the groundwater irrigation, irrigation with treated domestic wastewater can significantly increase the contents of TOC, DOC, Eh, NH4+-N, and TP, whereas irrigation with treated industrial wastewater can increase the contents of Cd, Cr, Cu, Pb, and Zn in the soil. Irrigation with treated wastewater also increases the relative abundance of Acidobacteria and Planctomycetes, and reduces the relative abundance of Firmicutes and Tectomicrobia. The effects of treated wastewater from different sources on functional microorganisms in soil are also different; irrigation with treated domestic wastewater can increase the relative abundance of Chloroflexi and Nitrospirae, whereas irrigation with treated industrial wastewater has negative effects on the abundance of Actinobacteria. The results of db-RDA analysis show that TN, TP, DOC, and Eh are the main factors that impact the microbial communities in soils irrigated with treated domestic wastewater (P<0.05), and heavy metals are the main factors that impact the microbial communities in soils irrigated with treated industrial wastewater (P<0.05). Compared with groundwater irrigation, treated wastewater irrigation can change the correlations between soil environmental factors, which in turn affect the microbial community structure. The growth of microorganisms in soils irrigated with treated domestic wastewater is mainly controlled by the increase in the nutrients such as DOC, TN, and TP and changes in soil redox conditions. The abundance of microorganisms in soil irrigated with treated industrial wastewater is significantly correlated with the accumulation of heavy metals.

Hydrogeochemical and statistical analysis of high fluoride groundwater in northern China.

Understanding the formation of high fluoride (F-) groundwater in water-scarce northern China is critical for the sustainable development of the region. This study investigates the effects of F- enrichment in groundwater from seven typical regions of northern China, including Datong, Guide, Junggar, Yinchuan, Taiyuan, and Tarim basins and the North China Plain. A literature survey of 534 samples of selected regions showed that 45.13% of groundwater F- exceeded the 1.0 mg/L of Chinese drinking water guideline. Based on the geological background and hydrogeochemical analysis, in Datong and Yinchuan basins and part of the North China Plain, the main types of groundwater are soda water and controlling processes of F- enrichment are salinization, mineral dissolution, and desorption. In Taiyuan and Guide basins with Cl-Na water type, F- enrichment is mainly affected by salinization, cation exchange, and evaporation. The hydrogeochemical characteristics of high F- groundwater in Tarim and Junggar basins reflect the extent of salinization and weathering dissolution of minerals in groundwater. According to PCA, the contribution of salinization and mineral dissolution to F- enrichment is relatively high. Under the alkaline condition, groundwater with high Cl-, HCO3-, and Na+ concentration favors F- enrichment. Based on HCA, index clustering category I explains the influence of pH and buried depth on F- enrichment, and category II explains the effect of different ions. It is concluded that F- enrichment in groundwater is related to hydrogeochemical processes and hydrogeological conditions. The hydrogeochemical and alkaline conditions of groundwater are regulated by mineral dissolution, ion exchange, and evaporation, resulting in different degrees of F- enrichment.

A comparative study on the treatment of 2,4-dinitrotoluene contaminated groundwater in the combined system: efficiencies, intermediates and mechanisms.

In this study, scrap irons (SI)/granular activated carbons (GAC) micro-electrolysis treatment and persulfate-releasing materials (PRM) treatment were employed to construct the combination reduction and oxidation system to treat 2,4-dinitrotoluene (2,4-DNT) contaminated groundwater. The 2,4-DNT treatment efficiencies in the PRM pre-treatment before SI/GAC micro-electrolysis treatment (FM-1 = PRM + SI/GAC) and SI/GAC micro-electrolysis pre-treatment before the PRM treatment (FM-3 = SI/GAC + PRM) were investigated in two separated columns. As control groups, the separated SI and GAC instead of the SI/GAC mixture were used in another two separated columns (FM-2 = PRM + SI + GAC; FM-4 = SI + GAC + PRM). The highest treatment efficiencies of 2,4-DNT in the FM-1 and FM-3 systems reached 79% and 93% during 5 PV, respectively. We found that the filling position of SI, GAC and PRM significantly affected the variations of pH, oxidation-reduction potential, Fe2+ and S2O82- concentrations in the combined systems. These results indicated that the SI/GAC micro-electrolysis pre-treatment of 2,4-DNT before the PRM treatment (FM-3) is more beneficial. The fifteen main intermediates in the combined system were identified by the detection of liquid chromatograph mass spectrometer. Furthermore, the possible treatment pathways of 2.4-DNT were proposed on the basis of identified intermediates. The treatment mechanisms in the FM-1 and FM-3 systems were proposed with the reduction mechanism in the SI/GAC micro-electrolysis system and the oxidation mechanism in the PRM treatment. Therefore, the combination of the reduction pre-treatment with the SI/GAC micro-electrolysis system and the oxidation post-treatment with persulfate can effectively treat the nitroaromatic compounds contaminated groundwater.

Groundwater pollution early warning based on QTR model for regional risk management: A case study in Luoyang city, China.

Groundwater pollution early warning has been regarded as an effective tool for regional groundwater pollution prevention, especially in China. In this study, the systemic model was established to assess the groundwater pollution early warning by integrating the present situation of groundwater quality (Q), groundwater quality trend (T) and groundwater pollution risk (R). The model integrated spatial and temporal variation of groundwater quality, and combined the state and process of the groundwater pollution. Q, T and R were assessed by the methods of fuzzy comprehensive assessment, Spearman or nonparametric Mann-Kendall trend test, and overlay index, respectively. Taking the Luoyang City as an example, the groundwater pollution early warning mapping was generated, and verified by corresponding the groundwater quality classes and the early warning degrees. The results showed that the groundwater was dominated by the levels of no warning and light warning, which accounted for 77% of the study area. The serious and tremendous warning areas were affected by the worse trend and relatively bad/bad present situations of groundwater quality with the typical contaminants of total hardness, nitrate, Hg and COD. In summary, the present situation of groundwater quality was the most important factor of groundwater pollution early warning mapping in the study area. The worse trend of groundwater quality played equally a key role in the local regions, as well as the high pollution risk, which was mainly affected by the pollution source loading. Targeted measures for groundwater pollution prevention were proposed in the corresponding degrees of groundwater pollution early warning. The QTR model was proved to be effective for assessing the regional groundwater pollution early warning. The accuracy of the model could be improved if there is further data acquisition of groundwater quality in longer time series and in larger number, and further investigation of pollution sources. The QTR model is proposed and proved to be effective for assessing regional groundwater pollution early warning.

Groundwater nitrate pollution risk assessment of the groundwater source field based on the integrated numerical simulations in the unsaturated zone and saturated aquifer.

Groundwater pollution risk assessment in the groundwater source field (GSF) is crucial to ensure groundwater quality safety. A systematic method of assessing groundwater pollution in the GSF was established by combining the numerical models of groundwater flow and solute transport in the vadose zone and aquifer. It is featured by revealing the paramount fate of contaminant from the surface to receptor "well (wells)" via the pathway of vadose zone and aquifers. The method was verified in the phreatic and semi-confined aquifers of a vital GSF, Beijing-Tianjin-Hebei region (BTHR) in China. Nitrate was selected as the model pollutant. The results indicated that the groundwater pollution risk of the phreatic aquifer was dominated by the mediate level (45.27%), and that the second semi-confined aquifer was mainly ranked as relatively low (30.29%) and mediate (38.17%) levels. The groundwater pollution risk maps of the two aquifers were similar. The high and relatively high risk areas were affected by the high intensities of groundwater pollution sources (GPSIs) or short distances from the pollution sources to the pumping well. The low and relatively low risk areas were controlled by low GPSIs and adequate attenuation and denitrification of nitrate in the aquifer. The groundwater pollution risk in the semi-confined aquifer was lower than that in the phreatic aquifer. The groundwater pollution risk mapping provides a valuable scientific reference for the groundwater pollution prevention and control with the focus on the "pollution source" and "groundwater source field". The proposed method can be further applied to the protections of the GSFs in the BTHR.