Evolution of groundwater hydrochemical characteristics and formation mechanism during groundwater recharge: A case study in the Hutuo River alluvial-pluvial fan, North China Plain.

A pilot project for groundwater recharge from rivers is currently being carried out in North China Plain. To investigate the influence of river recharge on groundwater hydrochemical characteristics, dynamic monitoring and analysis of groundwater samples were conducted at a typical recharge site in the Hutuo River alluvial-pluvial fan in the North China Plain from 2019 to 2021. Hydrochemical, isotopic, and multivariate statistical analyses were used to systematically reveal the spatiotemporal variation of groundwater chemistry and its driving factors during groundwater recharge process. The results showed that the groundwater hydrochemical types and characteristics in different recharge areas and recharge periods exhibited obvious spatiotemporal differences. The groundwater type varied from HCO3·SO4-Na·Mg to HCO3·SO4-Ca·Mg in an upstream ecological area, while the groundwater type changed from SO4·HCO3-Mg·Ca to HCO3·SO4-Ca·Mg in the downstream impacted by reclaimed water. Changes in the contents of Ca2+, Mg2+ and HCO3- were mostly controlled by the water-rock interactions and mixing-dilution of recharge water, while the increases in Na+, NO3-, Cl-, SO42- and NO3- contents were mainly due to the infiltration of reclaimed water. Nitrogen and oxygen isotope (δ15N and δ18O) tests and the Bayesian isotope mixing model results further demonstrated that nitrate pollution mainly originated from anthropogenic sources, and the major contribution came from manure and sewage, with an average proportion of 64.6 %. Principal component analysis indicated that water-rock interactions, river-groundwater mixing and redox environment alternation were dominant factors controlling groundwater chemical evolution in groundwater recharge process.

Natural and anthropogenic factors regulating fluoride enrichment in groundwater of the Nansi Lake Basin, Northern China.

Excess fluoride (F-) in groundwater can be hazardous to human health of local residents who rely upon it. Beside natural sources, anthropogenic input may be an additional source to be considered. Twenty surface water and 396 groundwater samples were collected from the Nansi Lake Basin, with hydrogeochemical and isotope techniques employed to clarify the spatial variability, source, and the natural and anthropogenic factors regulating the occurrence of high F- groundwater. The factors responsible for elevated F- levels in surface water and deep confined aquifers are discussed based on their hydraulic relationship. Also a conceptual model of F- enrichment with different aquifer systems is put forward based on the geomorphic units of the basin. The results show that F- concentration is between 0.1 and 6.9 mg/L in the west of Lake, while ranged from 0.03 to 1.74 mg/L in the east of Lake. The hydrogeological setting and lithology are the primary factor determining the provenance of high-fluoride groundwater in the basin. Fluoride mainly originated from the dissolution of fluorine-bearing minerals, and is affected by the alkaline groundwater environment, cation exchange, adsorption, and evaporation. The landforms on the east side of Nansi Lake are low hills and piedmont sedimentary plains, where the aquifers consist of karst fissure water and overlying porewater. High F- groundwater is not observed in this area due to its rapid flow and Ca2+-enriched hydrochemical characteristics. The anthropogenic input (such as fertilizer application on farms and illegal industrial pollutant discharge), contribute F- to groundwater in varying degrees, especially in the shallow aquifers east of the lake and in some parts west of the lake. This work is a clear example of how natural processes together with human activities can affect the chemical quality of groundwater, which is essential to safeguard the sustainable management of water resources in semi-arid areas.

Degradation of rhodamine B by persulfate activated with green tea iron nanoparticles.

Green iron tea nanoparticles (GT-Fe NPs) were used as persulfate(PS) activators to oxidize rhodamine B (RhB) in this study. Optimized oxidative degradation condition was 0.033 mM Fe, 5 mM PS at pH 3.0 and 298 K with an initial RhB content of 50 mg/L. After 120 min of RhB degradation utilizing GT-Fe NPs activated PS, 99% of RhB reduction was achieved, while 98% RhB reduction with PS activated by citric acid-Fe2+(CA-Fe) with the same amount of Fe2+. This RhB reduction was due to the delayed release of Fe(II) in the GT-Fe NPs. The addition of GT-Fe NPs enhanced the synthesis of OH· and SO4-· while inhibiting the formation of O2-·. A possible RhB degradation pathway was the chromophore destruction and ring-opening processes using GT-Fe NPs/PS, which produced a range of low molecular weight carboxylic acids (oxalic acid, lactic acid, acetic acid, and formic acid). GT-Fe NPs seem to be a promising persulfate activator in comparison to common activators such as CA-Fe.

[Characteristics and Causes of High-manganese Groundwater in Pearl River Delta During Urbanization].

The high concentration of iron and manganese in groundwater is harmful to human health, and the sources of manganese in rapidly urbanization areas are complex. Based on more than 2500 sets of hydrochemical data in different historical periods, the spatial distribution characteristics, sources, and genesis of groundwater manganese in different aquifers and areas with different urbanization levels in the Pearl River Delta were studied by using mathematical statistics and principal component analysis. The results showed that the concentration of manganese in groundwater in the pore aquifer was obviously higher than that in the fissure and karst aquifer. The proportion of high-manganese groundwater in the pore aquifer was twice that in the fissure and karst aquifer. The proportion of high-manganese groundwater in urbanized and suburban areas was significantly higher than that in non-urbanized areas. On a regional scale, the decomposition of organic matter and the reductive dissolution of Fe-Mn (oxygen) hydroxide in sedimentary strata under reductive conditions may have been the main factors controlling the increase in manganese concentration in pore aquifers. High-manganese groundwater in fissured aquifers may have been affected by low-oxygen domestic sewage leakage accompanying urbanization and industrial wastewater leakage and infiltration accompanying industrialization. The pore high-manganese groundwater was controlled by reduction conditions, and the weakly acidic environment of fissure and karst high-manganese groundwater was the important influencing factor. In the past 10 years, the groundwater environment in the study area has been improving, and the increase in groundwater redox potential and pH was not conducive to the formation of high-manganese groundwater, which was also the main cause of the overall decrease in Mn2+ concentration in groundwater of different types of aquifers in the process of urbanization.

An ecological remediation model combining optimal substrate amelioration and native hyperaccumulator colonization in non-ferrous metal tailings pond.

The vegetation deterioration and pollution expansion from non-ferrous metal tailings pond have been found in many countries leading to water soil erosion and human health risk. Conventional ecological remediation technologies of mine tailings such as capping were costly and elusive. This study provided an economic and effective model as an alternative by substrate amelioration and vegetation restoration. A field experiment was carried out on a silver tailings pond in southwest China. Tailings substrate was ameliorated by adding organic matter (decomposed chicken manure, DCM), structural conditioner (polyacrylamide, PAM), water-retaining agent (acrylic acid-bentonite water-retaining agent, AAB), and heavy metal immobilizer (biofuel ash, BFA), which were optimized by laboratory experiment. Native heavy metal hyperaccumulator, Bidens pilosa, was colonized. Vegetation coverage and plant height of Bidens pilosa reached about 80% and over 30 cm respectively after 3 months, and the turbidity of tailings leaching solution decreased by 60%. The practice showed that the proportion of available heavy metals in tailings substrate was significantly lower than that in the soil surrounding mining area. Immobilization didn't have stabilization effect on Cd, Zn, and Pb, and As was only 0.002%, phytoremediation had stabilization effect of Cd, Zn, As, and Pb were 2.5-3.5%, 1-2%, 0.25-0.5%, and 0.25-0.75%. Phytoremediation was more effective significantly in controlling heavy metal pollution risk of tailings than immobilization. These results provided a new ecological remediation OSA-NHC model, meaning a combination of optimal substrate amelioration and native hyperaccumulator colonization, which could achieve vegetation restoration and augment heavy metal pollution control in non-ferrous metal tailings pond.

Metal(loid)s removal by zeolite-supported iron particles from mine contaminated groundwater: Performance and mechanistic insights.

Iron-based materials have been widely investigated because of their high surface reactivity, which has shown potential for the remediation of metal(loid)s in groundwater. However, the disadvantages of structural stability and economic feasibility always limit their application in permeable reactive barrier (PRB) technology. In this study, zeolite-supported iron particles (Zeo-Fe) were synthesized by an innovative low-cost physical preparation method that is suitable for mass production. The removal efficiency and mechanism of typical metal(loid)s (Pb2+, Cd2+, Cr6+ and As3+) were subsequently investigated using various kinetic and equilibrium models and characterization methods. The results of scanning electron microscopy and energy dispersive spectrometry (SEM-EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) confirmed that zero valent iron (Fe0) and oxidation product (Fe3O4) were successfully loaded and efficiently dispersed on zeolite. The synthesized Zeo-Fe exhibited excellent adsorption and redox capacities for the cations Pb2+, Cd2+ and anions Cr6+, As3+. The increase in the pH resulting from Fe0 corrosion also enhanced the precipitation of Fe-metal(loid)s. The maximum removal capacity for Pb2+, Cd2+, Cr6+ and As3+ was up to 70.00, 9.12, 2.35 and 0.36 mg/g, respectively. The removal processes were well described by the pseudo-second-order kinetic model for Pb2+ and Cd2+, Lagergren pseudo first-order kinetics model for As3+ and double phase first order kinetics model l for Cr6+. Cr6+ was rapidly reduced to Cr3+ by the Fe0 stabilized on Zeo-Fe, and the oxidation of As3+ to As5+ was attributed to the Fe0/Fe2+ oxidation process at the interface over time, which was further demonstrated by the mineral phase and element valence analyses of reacted Zeo-Fe. The removal mechanism for metal(loid)s was a combination of physical and chemical processes, including adsorption, co-precipitation and reduction-oxidation. Conclusively, Zeo-Fe has been shown to have potential as an effective and economical material for removing various metal(loid)s used in PRB.

Impact of δ-MnO2 on the chemical speciation and fractionation of Cr(III) in contaminated soils.

Oxidation of Cr(III) by birnessite (δ-MnO2) was an important geochemical reaction determining the toxicity and mobility of dissolved Cr(III) in soils. Herein, changes of Cr speciation and fractionation were systematically studied in Cr(III)-contaminated soils with δ-MnO2 in soil aging process. The results showed that Cr(III) could be rapidly oxidized to Cr (VI) by δ-MnO2, and the coating of Fe and Al oxides on δ-MnO2 had a strong hindering effect on the oxidation of Cr(III). The Cr(III) oxidation process by δ-MnO2 followed a two-phase model of pseudo first-order kinetics. The rapid decrease of oxidation rate constant in second phase was due to the coverage of adsorbed Cr(III) and newly generated Cr(VI) and Mn(II) on the active sites of δ-MnO2. X-ray photoelectron spectroscopy analysis further confirmed that the diffusion and adsorption of Cr(III) on the electron-accepting sites were important factors affecting the Cr(III) oxidation by δ-MnO2. Compared with the soils without δ-MnO2, high contents of Cr(VI) were generated in silt (22.30 mg/kg) and sandy soil (70.95 mg/kg) with 2 wt% δ-MnO2 after the addition of Cr(III) wastewater within 2 days, and the Cr(VI) contents were above 1 mg/kg in these two soils during the whole incubation process. Moreover, the total Cr proportion of the exchangeable fraction increased by 12.8% in silt and 5.2% in sandy soil with 2 wt% δ-MnO2 after soil aging for 120 days. The presence of δ-MnO2 markedly increased the oxidation potential and mobility of exogenous Cr(III) in soils.

[Geochemical Characteristics and Driving Factors of High-Iodine Groundwater in Rapidly Urbanized Delta Areas: A Case Study of the Pearl River Delta].

The source of iodine in the groundwater of coastal urbanization areas is complex, and high-iodine groundwater is a potential threat to the safety of drinking water. Based on this, this study took the Pearl River Delta, which is developing rapidly in urbanization, as the research area. Additionally, the occurrence characteristics and driving factors of iodide in shallow groundwater of different aquifers and different urbanization levels in the Pearl River Delta were studied using mathematical statistics, principal component analysis, and other methods. The results showed that the concentration of iodide in the shallow groundwater was 2.34 mg·L-1 and undetected in the form of I-. Among 1567 groundwater samples in the study area, there were 120 groups of groundwater with high iodine content greater than 0.1 mg·L-1, accounting for 7.7%. Among them, 84 and 36 groups were detected in shallow porous and shallow fissure high-iodine groundwater, respectively, whereas no high-iodine groundwater was detected in the karst aquifer. The proportion of high-iodine groundwater was 8.0% in the shallow porous aquifer and 7.5% in the shallow fissure aquifer. Both the porous aquifer and the fissured aquifer with high iodine content were mainly distributed in the urbanized areas, the proportion of which was more than three times that of the non-urbanized areas. The chemical types of the high-iodine groundwater were mainly HCO3·Cl-Ca·Na and Cl-Na type water, which have the characteristics of high pH and low redox potential. The reduction and dissolution of iodine-containing Fe/Mn (oxygen) hydroxides and the decomposition of iodine-rich organics in sediments may be the main sources of high-iodine groundwater in the shallow porous aquifers of the Pearl River Delta Plain. The degradation and urbanization of organic matter in carbonate-rich rocks is accompanied by the leakage of reducing sewage, which may be the main source of high-iodine groundwater in shallow fissured aquifers. The neutral to weakly alkaline reduction environment with rich organic matter was the main cause of high-iodine groundwater in the Delta Plain area. Weathering, leaching, cation exchange, and sea-land interactions are the main hydrogeochemical processes in the evolution of high-iodine groundwater in the Pearl River Delta.

[Geochemical Characteristics and Driving Factors of NO3-Type Groundwater in the Rapidly Urbanizing Pearl River Delta].

In response to rapid economic development, nitrate pollution of groundwater is becoming a serious issue in many parts of China. Urbanization and industrialization are the main drivers of NO3-type groundwater expansion. Focusing on the Pearl River Delta, the occurrence and driving factors of shallow nitrate groundwater are discussed. Overall, groundwater nitrate concentrations are generally high in this region. Of 1538 groundwater samples, 5.7% had nitrate concentrations higher than the groundwater quality standard(88.6 mg·L-1) and 18.5% were classified as NO3-type waters, which are mainly distributed in the hilly and piedmont areas. Guangzhou, Dongguan, Foshan, Zhuhai and other areas show high total dissolved solid(TDS)-concentration NO3-type waters, which are affected by urbanization and industrialization. In comparison, low-TDS NO3-type waters are distributed in the hilly and valley areas. In the Xijiang and Dongjiang plains, the TDS concentrations on groundwater increased significantly due to inputs of industrial wastewater and saline seawater. The NO3- concentration in the groundwater in this area exceeded the class III water standard but did not change the hydrochemical type classification. However, industrialization has led to the frequent appearance of SO4-type water in this area. The NO3-type water occurs in acidic or weakly acidic environments, typically characterized by low TDS and total hardness concentrations, and high Cl-, SO42-, and K+ concentrations. The formation of NO3-type water is mainly affected by domestic sewage, industrial wastewater, agricultural nitrogen fertilizer, septic tank outflows, and landfill leachate leakage. Generally, the pollution loads of high-TDS NO3-type waters are higher than low-TDS NO3-type waters. The delineation of NO3-type waters, especially the low-TDS type, is helpful for identifying groundwaters posing greater risks for human activities, and those with low nitrate concentrations but potential pollution risk, which is of great significance in the prevention and control of groundwater pollution.

Leaching Behaviors of Chromium(III) and Ammonium-Nitrogen from a Tannery Sludge in North China: Comparison of Batch and Column Investigations.

Tannery sludge usually has high content of trivalent chromium (Cr(III)) and ammonium-nitrogen (NH4+-N). It is important to make a critical evaluation of the releasing behaviors of Cr(III) and NH4+-N from tannery sludge before its use on improving soil fertility in agricultural applications. For this purpose, static batch and dynamic leaching experiments with different mathematical models were carried out to simulate the Cr(III) and NH4+-N releasing kinetics from tannery sludge sampled in a typical tannery disposal site in North China, and their influencing factors were also discussed. The results showed that a larger solid-liquid ratio, a higher temperature, and a lower pH value of the leaching solution were beneficial for the release of Cr(III) and NH4+-N from the tannery sludge. The release kinetics of Cr(III) and NH4+-N followed parabolic diffusion and simple Elovich models both in the static and dynamic leaching conditions, indicating that the release was a complex heterogeneous diffusion process. The NH4+-N was easy to be leached out and its released amount reached 3.14 mg/g under the dynamic leaching condition (pH 7), whereas the released amount of the Cr(III) was only 0.27 µg/g from the tannery sludge. There was a positive correlation coefficient between dissolved Fe and Cr(III) in the leachate under different leaching conditions, and the calculated average ratio of Fe/Cr(III) concentration was 3.56, indicating that the small amount of the released Cr(III) came from the dissolution of Cr0.25Fe0.75(OH)3 minerals in tannery sludge.

[Chemical Evolution of Groundwater in the Tacheng Basin of Xinjiang in the Process of Urbanization].

With the development of the local economy, the volume of groundwater production has increased continuously in the past decades in the Tacheng Basin of the Xinjiang Uygur Automous Region. Previous studies have not provided a clear pattern of the chemical composition evolution of groundwater and its driving force in this basin, which makes the future development and utilization of groundwater riskier. This study carried out systematic sampling and analysis of groundwater chemistry in this basin, and the chemical evolution of groundwater in the basin was analyzed by comparison with historical hydrochemical data. The results show that Ca2+ and Na+ are the main cations in the groundwater, HCO3-, SO42- are the main anions in the groundwater, and freshwater is widely distributed. The chemical types of groundwater changed from HCO3-Ca and HCO3·SO4-Ca·Mg in the source zone in front of the mountains to SO4·HCO3-Na·Ca type in the plain area. In comparison with the hydrochemical data of 1979, HCO3 and SO4·HCO3 type groundwater increased significantly. SO4 and Cl type groundwater with high total dissolved solids decreased significantly. However, the Cl- and SO42- concentration and total hardness in the groundwater around the cities and towns increased. Aquifer material and the change of flowing field are the two controlling factors of groundwater chemical change, but the leakage of waste water from city drainage channels also affects the groundwater chemistry drastically.

In Situ Persulfate Oxidation of 1,2,3-Trichloropropane in Groundwater of North China Plain.

In situ injection of Fe(II)-activated persulfate was carried out to oxidize chlorinated hydrocarbons and benzene, toluene, ethylbenzene, and xylene (BTEX) in groundwater in a contaminated site in North China Plain. To confirm the degradation of contaminants, an oxidant mixture of persulfate, ferrous sulfate, and citric acid was mixed with the main contaminants including 1,2,3-trichloropropane (TCP) and benzene before field demonstration. Then the mixed oxidant solution of 6 m3 was injected into an aquifer with two different depths of 8 and 15 m to oxidize a high concentration of TCP, other kinds of chlorinated hydrocarbons, and BTEX. In laboratory tests, the removal efficiency of TCP reached 61.4% in 24 h without other contaminants but the removal rate was decreased by the presence of benzene. Organic matter also reduced the TCP degradation rate and the removal efficiency was only 8.3% in 24 h. In the field test, as the solution was injected, the oxidation reaction occurred immediately, accompanied by a sharp increase of oxidation-reduction potential (ORP) and a decrease in pH. Though the concentration of pollutants increased due to the dissolution of non-aqueous phase liquid (NAPL) at the initial stage, BTEX could still be effectively degraded in subsequent time by persulfate in both aquifers, and their removal efficiency approached 100%. However, chlorinated hydrocarbon was relatively difficult to degrade, especially TCP, which had a relatively higher initial concentration, only had a removal efficiency of 30%-45% at different aquifers and monitoring wells. These finding are important for the development of injection technology for chlorinated hydrocarbon and BTEX contaminated site remediation.

Soil Pollution Characteristics and Microbial Responses in a Vertical Profile with Long-Term Tannery Sludge Contamination in Hebei, China.

An investigation was made into the effects of tannery sludge on soil chemical properties and microbial communities in a typical soil profile with long-term tannery sludge contamination, North China. The results showed that trivalent chromium (Cr(III)), ammonium, organic nitrogen, salinity and sulfide were the predominant contaminants in tannery sludge. Although the tannery sludge contained high chromium (Cr, 3,0970 mg/kg), the proportion of mobile Cr forms (exchangeable plus carbonate-bound fraction) only accounted for 1.32%. The X-ray diffraction and X-ray photoelectron spectroscopy results further demonstrated that the Cr existed in a stable state of oxides and iron oxides. The alkaline loam soil had a significant retardation effect on the migration of salinity, ammonium, Cr(III) and sulfide, and the accumulation of these contaminants occurred in soils (0⁻40 cm). A good correlation (R² = 0.959) was observed between total organic carbon (TOC) and Cr(III) in the soil profile, indicating that the dissolved organic matter from sludge leachate promoted the vertical mobility of Cr(III) via forming Cr(III)-organic complexes. The halotolerant bacteria (Halomonas and Tepidimicrobium) and organic degrading bacteria (Flavobacteriaceae, Tepidimicrobium and Balneola) became the dominant microflora in the soil profile. High contents of salinity, Cr and nitrogen were the main environmental factors affecting the abundance of indigenous microorganisms in soils.

Screening of groundwater remedial alternatives for brownfield sites: a comprehensive method integrated MCDA with numerical simulation.

Brownfield sites pollution and remediation is an urgent environmental issue worldwide. The screening and assessment of remedial alternatives is especially complex owing to its multiple criteria that involves technique, economy, and policy. To help the decision-makers selecting the remedial alternatives efficiently, the criteria framework conducted by the U.S. EPA is improved and a comprehensive method that integrates multiple criteria decision analysis (MCDA) with numerical simulation is conducted in this paper. The criteria framework is modified and classified into three categories: qualitative, semi-quantitative, and quantitative criteria, MCDA method, AHP-PROMETHEE (analytical hierarchy process-preference ranking organization method for enrichment evaluation) is used to determine the priority ranking of the remedial alternatives and the solute transport simulation is conducted to assess the remedial efficiency. A case study was present to demonstrate the screening method in a brownfield site in Cangzhou, northern China. The results show that the systematic method provides a reliable way to quantify the priority of the remedial alternatives.

Evaluation of strategies to minimize ecotoxic side-effects of sorbent-based sediment remediation.

BACKGROUND: In situ sorbent amendment for persistent organic pollutant sequestration in sediment has over the past 15 years steadily progressed from bench-scale trials to full-scale remediation applications. Hindering a wider technology uptake are, however, concerns about ecotoxic side-effects of the most commonly used sorbent, activated carbon, on sensitive, sediment dwelling organisms like Lumbriculus variegatus. Using River Tyne sediment polluted with polycyclic aromatic hydrocarbons (PAHs) and L. variegatus as a case study, sorbent alternatives and magnetic sorbent-recovery were investigated as potential engineering strategies to mitigate such ecotoxic side-effects. The potential benefits of contacting the treated sediment with fresh River Tyne water, as would naturally occur over time in the intended applications, were studied. RESULTS: Magnetic biochar was identified as an effective PAH sorbent with less ecotoxic side-effects than magnetic activated carbon. After 85.1-100% magnetic recovery of this biochar, no ecotoxic side-effects on L. variegatus were measurable in the treated sediment. Results show that ecotoxic effects of magnetic activated carbon can be alleviated through sorbent recovery. In contrast, contacting treated sediment repeatedly with River Tyne water had no measurable benefits. CONCLUSIONS: Magnetic biochar is a promising sorbent material for the remediation of PAH polluted sediment. © 2017 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Evaluation of zeolite-supported microscale zero-valent iron as a potential adsorbent for Cd2+ and Pb2+ removal in permeable reactive barriers.

A new composite adsorbent, zeolite-supported microscale zero-valent iron (Z-mZVI) was evaluated as a potential adsorbent for the removal of Cd2+ and Pb2+ from aqueous solution using batch and column experiments. Adsorption isotherms were well fitted by Langmuir model, and the maximum adsorption capacity was 63.14 mg/g for Cd2+ and 154.61 mg/g for Pb2+, respectively. Both adsorption processes followed the pseudo-second-order model which indicated that the rate-limiting step for different initial concentration was dominated by chemical adsorption process. The coexistence of Cd2+ and Pb2+ caused the reduction of Cd2+ removal efficiency, but not for Pb2+. Z-mZVI has a high removal capacity for Cd2+ and Pb2+ over a wide pH range (3.0-6.8) as well as in the presence of competitive Ca2+ or Mg2+ ions (<2 mmol/L). Moreover, Z-mZVI shows a high immobilization capacity for the adsorbed Cd2+ and Pb2+ products, even at the acid solution (pH = 3.95). Column experiment confirmed that Z-mZVI could simultaneously remove Cd2+ and Pb2+ from solution efficiently. Thomas model can simulate the equilibrium adsorption capacity of Cd2+ and Pb2+ of the Z-mZVI column well. This study demonstrates that Z-mZVI is an efficient and promising reactive material in permeable reactive barriers for Cd2+ and Pb2+ removal from aqueous solution.

Synthesis of zeolite-supported microscale zero-valent iron for the removal of Cr(6+) and Cd(2+) from aqueous solution.

Zeolite-supported microscale zero-valent iron (Z-mZVI) was synthesized and used to remove heavy metal cation (Cd(2+)) and anion (Cr(6+)) from aqueous solution. Transmission electron microscope (TEM) confirmed that mZVI (100-200 nm) has been successfully loaded and efficiently dispersed on zeolite. Atomic absorption Spectroscopy (AAS) revealed the amount of stabilized mZVI was about 1.3 wt.%. The synthesized Z-mZVI has much higher reduction ability and adsorption capacity for Cr(6+) and Cd(2+) compared to bare nanoscale zero-valent iron (nZVI) and zeolite. Above 77% Cr(6+) and 99% Cd(2+) were removed by Z-mZVI, while only 45% Cr(6+) and 9% Cd(2+) were removed by the same amount iron of nZVI, and 1% Cr(6+) and 39% Cd(2+) were removed by zeolite alone with an initial concentration of 20 mg/L Cr(6+) and 200 mg/L Cd(2+). The removal of Cr(6+) by Z-mZVI follows the pseudo first-order kinetics model, and X-ray photoelectron spectroscopy (XPS) analysis confirmed that Cr(6+) was reduced to Cr(3+) and immobilized on the surface of Z-mZVI. The removal mechanisms for Cr(6+) include reduction, adsorption of Cr(3+) hydroxides and/or mixed Fe(3+)/Cr(3+) (oxy)hydroxides. The pseudo-second-order kinetic model indicated that chemical sorption might be rate-limiting in the sorption of Cd(2+) by Z-mZVI. This synthesized Z-mZVI has shown the potential as an efficient and promising reactive material for removing various heavy metals from wastewater or polluted groundwater.

Transport of sucrose-modified nanoscale zero-valent iron in saturated porous media: role of media size, injection rate and input concentration.

The growing use of nanoscale zero-valent iron (NZVI) in the remediation of contaminated groundwater raises concerns regarding its transport in aquifers. Laboratory-scale sand-packed column experiments were conducted with bare and sucrose-modified NZVI (SM-NZVI) to improve our understanding of the transport of the nanoparticles in saturated porous media, as well as the role of media size, suspension injection rate and concentration on the nanoparticle behavior. As the main indicative parameters, the normalized effluent concentration was measured and the deposition rate coefficient (k) was calculated for different simulated conditions. Overall, compared to the high retention of bare NZVI in the saturated silica column, SM-NZVI suspension could travel through the coarse sand column easily. However, the transport of SM-NZVI particles was not very satisfactory in a smaller size granular matrix especially in fine silica sand. Furthermore, the value of k regularly decreased with the increasing injection rate of suspension but increased with suspension concentration, which could reflect the role of these factors in the SM-NZVI travel process. The calculation of k-value at the tests condition adequately described the experimental results from the point of deposition dynamics, which meant the assumption of first-order deposition kinetics for the transport of NZVI particles was reasonable and feasible.

Hydrochemistry indicating groundwater contamination and the potential fate of chlorohydrocarbons in combined polluted groundwater: a case study at a contamination site in North China.

Groundwater contamination characteristics and the potential fate of chlorohydrocarbons were investigated at a combined polluted groundwater site in North China. Groundwater chemistry and (2)D and (18)O isotope compositions indicated that high salination of groundwater was related with chemical pollution. The elevated salinity plume was consistent with the domain where typical chlorohydrocarbon contaminants occurred. The concentrations of heavy metals, oxidation-reduction potential, and pH in organic polluted areas significantly differed from those in peripheral (background) areas, indicating modified hydrochemistry possibly resulting from organic pollution. Under the presented redox conditions of groundwater, monochlorobenzene oxidation may have occurred when the trichlorohydrocarbons underwent reductive dechlorination. These findings suggested that inorganic hydrochemistry effectively indicated the occurrence of chemical contamination in groundwater and the potential fate of chlorohydrocarbons.

A critical evaluation of magnetic activated carbon's potential for the remediation of sediment impacted by polycyclic aromatic hydrocarbons.

Addition of activated carbon (AC) or biochar (BC) to sediment to reduce the chemical and biological availability of organic contaminants is a promising in-situ remediation technology. But concerns about leaving the adsorbed pollutants in place motivate research into sorbent recovery methods. This study explores the use of magnetic sorbents. A coal-based magnetic activated carbon (MAC) was identified as the strongest of four AC and BC derived magnetic sorbents for polycyclic aromatic hydrocarbons (PAHs) remediation. An 8.1% MAC amendment (w/w, equal to 5% AC content) was found to be as effective as 5% (w/w) pristine AC in reducing aqueous PAHs within three months by 98%. MAC recovery from sediment after three months was 77%, and incomplete MAC recovery had both, positive and negative effects. A slight rebound of aqueous PAH concentrations was observed following the MAC recovery, but aqueous PAH concentrations then dropped again after six months, likely due to the presence of the 23% unrecovered MAC. On the other hand, the 77% recovery of the 8.1% MAC dose was insufficient to reduce ecotoxic effects of fine grained AC or MAC amendment on the egestion rate, growth and reproduction of the AC sensitive species Lumbriculus variegatus.