Effects of arsenic on the transport and attachment of microplastics in porous media.

Understanding the impact of arsenic (As(III), inorganic pollutant widely present in natural environments) on microplastics (MPs, one type of emerging contaminants) mobility is essential to predict MPs fate and distribution in soil-groundwater systems, yet relevant research is lacking. This study explored the effects of As(III) copresent in suspensions (0.05, 0.5, and 5 mg/L) on MPs transport/attachment behaviors in porous media containing varied water contents (θ = 100 %, 90 %, and 60 %) under different ionic strengths (5, 10, and 50 mM NaCl) and flow rates (2, 4, and 8 m/day). Despite solution ionic strengths, flow rates, porous media water contents, sizes, and surface charges of MPs, with coexisting humic acid, and in actual water samples, As(III) of three concentrations increased MPs transport in quartz sand and natural sandy soil. The increased electrostatic repulsion between MPs and sand caused by the altered MPs surface charge via the adsorption of As(III) together with steric repulsion from As(III) in solution contributed to the promoted MPs mobility in porous media. The occupying attachment sites by As(III) partially contributed to the increased mobility of MPs with negative surface charge in porous media. Clearly, As(III) coexisting in suspensions would enhance MPs transport in porous media, increasing MPs environment risks.

Response of microbial taxonomic and nitrogen functional attributes to elevated nitrate in suburban groundwater.

Anthropogenic nitrogen (N) input has led to elevated levels of nitrate nitrogen (NO3--N) in the groundwater. However, insights into the responses of the microbial community and its N metabolic functionality to elevated NO3--N in suburban groundwater are still limited. Here, we explored the microbial taxonomy, N metabolic attributes, and their responses to NO3--N pollution in groundwaters from Chaobai River catchment (CR) and Huai River catchment (HR) in Beijing, China. Results showed that average NO3--N and NH4+-N concentrations in CR groundwater were 1.7 and 3.0 folds of those in HR. NO3--N was the dominant nitrogen specie both in HR and CR groundwater (over 80 %). Significantly different structures and compositions of the microbial communities and N cycling gene profiles were found between CR groundwater and HR groundwater (p < 0.05), with CR groundwater harboring significantly lower microbial richness and abundance of N metabolic genes. However, denitrification was the dominant microbial N cycling process in both CR and HR groundwater. Strong associations among NO3--N, NH4+-N, microbial taxonomic, and N functional attributes were found (p < 0.05), suggesting denitrifiers and Candidatus_Brocadia might serve as potential featured biomarkers for the elevated NO3--N and NH4+-N concentration in groundwater. Path analysis further revealed the significant effect of NO3--N on the overall microbial N functionality and microbial denitrification (p < 0.05). Collectively, our results provide field evidence that elevated levels of NO3--N and NH4+-N under different hydrogeologic conditions had a significant effect on the microbial taxonomic and N functional attributes in groundwater, with potential implications for improving sustainable N management and risk assessment of groundwater.

Solution, exchangeable and fixed ammonium in natural diatomite as a simulated PRB material: effects of adsorption and bioregeneration processes.

Ammonia nitrogen (NH4+-N) is widely found in aquifers with strong reducibility or poor adsorptivity as a dissolved inorganic nitrogen pollutant. The application of adsorbents with effective long-term in situ bioregeneration as permeable reactive barrier (PRB) media for nitrogen removal has raised concern. In this study, the advantage of natural diatomite as a PRB material was investigated by exploring its NH4+-N adsorption and desorption characteristics, and the ability of diatomite and zeolite to be loaded nitrifying bacteria was also compared. The results showed that the exchangeable ammonium from chemical-monolayer adsorption was the main form of NH4+-N and was adsorbed by diatomite. Moreover, the adsorption process was limited with a maximum adsorption capacity of 0.677 mg g-1. However, diatomite demonstrated an excellent loading of aerobic-heterotrophic microorganisms, even stronger than zeolite. Compared with zeolite reactors, a higher OD600 value of nitrifiers, a faster NH4+-N degradation rate and more abundant functional genes were observed during the bioregeneration process of diatomite. Both the solution and exchangeable ammonium forms were bioavailable, and the regeneration of diatomite was more than 80.0% after two days. Moreover, desorption-biodegradation was systematically analysed to determine the bioregeneration mechanism of diatomite. Diatomite with good regeneration ability can be used as a competitive alternative to address sudden nitrogen pollution.

EMMTE: An Excel VBA tool for source apportionment of nitrate based on the stable isotope mixing model.

Dual nitrate stable isotopes combined with end-member mixing models are typically used to identify nitrate sources in fields of geochemistry and environmental science, which helps to quantitively depict the geochemical behaviors of nitrate and accurately control the sources of nitrate pollution in waters. Recently, various models with different computation principles, working efficiency, and operation difficulty have been developed and applied in the source apportionment of nitrate. In this paper, an end-member mixing model tool on Excel™, namely EMMTE, has been written with Visual Basic for Application (VBA) and built into a macro-enabled Excel™ spreadsheet. Monte Carlo simulation and constraint relative deviation between the observed and the predicted values were included in the working algorithm to solve the mass balance equation. After comparison with the internationally recognized Bayesian framework (mixing stable isotope analysis in R, MixSIAR) in different cases (three practical cases and one virtual case), the preliminary results showed that the contribution of various sources to groundwater nitrate calculated by EMMTE was highly consistent with that by MixSIAR and the performance of EMMTE seemed to be as good as that of MixSIAR as indicated by the higher goodness-of-prediction, lower root-mean-square error, and lower relative deviation. Therefore, EMMTE is applicable in the source apportionment of groundwater nitrate, and might also be extended to other water bodies and mixtures. It provides a simple, feasible, and user-friendly for front-line workers without experience with MixSIAR to quantitively source apportionment of nitrate in waters.

Novel insights into source apportionment of dissolved organic matter in aquifer affected by anthropogenic groundwater recharge: Applicability of end-member mixing analysis based optical indices.

The composition and main sources of dissolved organic matter (DOM) in groundwater may change significantly under long-term anthropogenic groundwater recharge (AGR); however, the impact of AGR on quantitative sources of groundwater DOM has seldom been reported. This study evaluated the applicability of optical indices combined with mixing stable isotope analysis in R (MixSIAR) in end-member mixing analysis (EMMA) of groundwater DOM. Fluorescent indices, including C1%, C2%, and C3%, were more sensitive to AGR than other absorbance indices, as indicated by the significant difference between the dominant area of artificial groundwater recharged by surface water and the dominant area of natural groundwater recharged by atmospheric precipitation (NGRP). BIX-C1% was selected as the optimal dual index after the screening protocol of groundwater DOM for EMMA. Our results showed that DOM in the aquifer was mainly subject to autochthonous DOM and the contribution of background groundwater to AGRSW and NGRP groundwater accounted for 36.15% ± 32.41% and 55.46% ± 37.17% (p < 0.05), respectively. Therefore, AGR significantly changed the native DOM in the groundwater. In allochthonous sources of DOM, sewage and surface water contributed 29.54% ± 24.87% and 21.32% ± 28.08%, and 24.79% ± 15.56% and 15.21% ± 14.20% to AGRSW and NGRP groundwater, respectively. The contribution of surface water to AGRSW groundwater was significantly higher than that to NGRP groundwater (p < 0.05), indicating that AGR introduced significantly more DOM from surface water to groundwater. This study provides novel insights into the quantitative source apportionment of DOM in groundwater under long-term AGR, which will facilitate the environmental risk assessment of present AGR measures and the sustainable management of clean water.

Heterotrophic Bioleaching of Vanadium from Low-Grade Stone Coal by Aerobic Microbial Consortium.

Bioleaching is a viable method that assists in increasing the vanadium output in an economical and environmentally friendly manner. Most bioleaching is conducted by pure cultures under autotrophic conditions, which frequently require strong acidity and produce acid wastewater. However, little is known about heterotrophic bioleaching of vanadium by mixed culture. This study investigated the bioleaching of vanadium from low-grade stone coal by heterotrophic microbial consortium. According to the results, vanadium was efficiently extracted by the employed culture, with the vanadium recovery percentage in the biosystem being 7.24 times greater than that in the control group without inoculum. The average vanadium leaching concentration reached 680.7 µg/L in the first three cycles. The kinetic equation indicated that the main leaching process of vanadium was modulated by a diffusion process. Scanning electron microscopy revealed traces of bacterial erosion with fluffy structures on the surface of the treated stone coal. X-ray photoelectron spectroscopy confirmed the reduction of the vanadium content in the stone coal after leaching. Analysis of high-throughput 16S rRNA gene sequencing revealed that the metal-oxidizing bacteria, Acidovorax and Delftia, and the heterotrophic-metal-resistant Pseudomonas, were significantly enriched in the bioleaching system. Our findings advance the understanding of bioleaching by aerobic heterotrophic microbial consortium and offer a promising technique for vanadium extraction from low-grade stone coals.

Impacts of anthropogenic groundwater recharge (AGR) on nitrate dynamics in a phreatic aquifer revealed by hydrochemical and isotopic technologies.

Although anthropogenic groundwater recharge (AGR) can either elevate or decline the concentration of nitrate in the phreatic aquifer with high hydraulic conductivity, the long-term impact of AGR on nitrate dynamics in the phreatic aquifer and its reason is seldom disclosed. In this study, the hydrogen and oxygen stable isotopes (δ2H-H2O and δ18O-H2O) combined with mixing stable isotope analysis in R (MixSIAR) were used to group the study area into the dominant area of AGR by surface water (AGRSW) and the dominant area of natural groundwater recharged by precipitation (NGRP). Hydrochemical parameters and multiple stable isotopes, including δ2H-H2O, δ18O-H2O, δ15N-NO3-, δ18O-NO3-, and δ13C-DIC, were applied to explore the impacts of AGR on the concentration, biogeochemical processes, and main sources of nitrate. The results showed that AGR by surface water with low nitrate content can reduce nitrate pollution in groundwater. The characteristic of δ18O-NO3- value revealed that nitrification was the primary biogeochemical process of nitrogen in groundwater. AGR may enhance nitrification as indicated by the δ18O-NO3- value closer to the nitrification theoretical line. Dual nitrate stable isotopes and MixSIAR revealed that chemical fertilizer (CF), soil nitrogen (SN), and surface water (SW) contributed 10.88%, 49.92%, and 27.64% to nitrate in AGRSW groundwater, respectively, which was significantly different from their contributions to NGRP groundwater (p < 0.05). Notably, AGR significantly increased the contribution of SW but decreased the contribution of CF and SN in groundwater. This study provided a basis and guidance for groundwater quality assessment and pollution control in the phreatic aquifer with high hydraulic conductivity.

Dynamics of vertical vanadium migration in soil and interactions with indigenous microorganisms adjacent to tailing reservoir.

Severe vanadium pollution in deep soil through surface infiltration during mining activities has been particularly concerned, but little is known about vanadium migration dynamics in vertical soil profile. Indigenous microorganisms widely exist in soil, however, their functions and suffered impacts during vertical vanadium migration have rarely been investigated. In this study, 100 cm height columns were constructed with undisturbed soil around vanadium tailing reservoir were constructed to describe vertical vanadium transport process and corresponding interactions between vanadium and indigenous microorganisms. 91 d continuous leaching with pentavalent vanadium [V(V)] showed that V(V) gradually downward migrated. Soil microorganisms slowed down vertical V(V) migration rate by transferring V(V) to insoluble tetravalent vanadium. Enriched Gemmatimonadaceae and Actinobacteria were identified to contribute to microbial V(V) transformation. Co-existing nitrate weakened the soil's ability to intercept V(V) via electron competition. Microbial communities were reshaped by vanadium during leaching, while enzyme activities increased slightly due to vanadium stimulation. This work advances the understanding of vertical vanadium migration characteristics in soil, which is essential to risk management and effective remediation of vanadium-polluted sites.

[Difference in soil water holding capacity and the influencing factors under different land use types in the alpine region of Tibet, China]. / è¥¿è—é«˜å¯’åŒºä¸åŒåœŸåœ°åˆ©ç”¨æ–¹å¼ä¸‹åœŸå£¤æŒæ°´èƒ½åŠ›å·®å¼‚åŠå ¶å½±å“å› ç´ .

To investigate the variation of soil water holding capacity under different land use types can provide scientific basis for evaluating the change characteristics and regulation mechanism of water conservation capacity in alpine ecosystems. We collected soil samples at different depth intervals (0-10, 10-20 and 20-30 cm) under three land use types (farmland, forest, and grassland) in Tibet alpine region to measure the maximum water holding capacity, capillary water holding capacity, field capacity, and basic soil physicochemical properties. The associated environmental factors (mean annual precipitation, normalized difference vegetation index, altitude, slope gradient and surface roughness) were extracted to analyze the change characteristics and influencing factors of soil water holding capacity under different land use types. The results showed that soil water holding capacity (the maximum water holding capacity, capillary water holding capacity, and field capacity) of farmland, forest, and grassland all decreased with increasing soil depth. The mean values of the maximum water holding capacity, capillary water holding capacity, and field capacity in the 0-30 cm soil layer of grassland were 379.79, 329.57 and 194.39 g·kg-1, respectively, which were significantly higher than that of farmland (301.15, 259.67, and 154.91 g·kg-1) and forest (293.09, 251.49, and 117.01 g·kg-1). Results of the redundancy analysis showed that soil properties significantly influenced soil water holding capacity, with explanation rate of 44.6%, 42.7%, 37.6% and 35.8% for total porosity, soil organic matter, capillary porosity and soil bulk density, respectively. Results of the principal component analysis showed that mean annual precipitation, normalized difference vegetation index, altitude, slope gradient, and surface roughness were the main environmental factors affecting the spatial variation of soil water holding capacity, with a cumulative contribution of 72.4%. The grassland in the alpine region of Tibet had the highest water holding capacity and could effectively prevent soil erosion. Therefore, the implementation of returning farmland to grassland and the enclosure management of degraded grassland would be conducive to improve soil water conservation capacity in the alpine regions.

[Simulation of Water Quality Response of Guishui River Wetland Plants and Water Diversion].

A two-dimensional model MIKE21 coupled with a modified EcoLab module was applied to model the water quality of surface flow wetlands. In the model, vegetation effects, oxygen production, nutrient consumption by microorganisms and vegetation were set in the solutions of hydrodynamic, chemical, and biological processes. Based on the field investigation and measurements in the Guishui River wetland, the model was established for the downstream reaches of the Guishui River and the Sanli River. The model calculated the hydrodynamics and water quality changes by vegetation type and distribution. The model parameters were calibrated and results were validated using the measurements. The concentrations of ammonia nitrogen, phosphate, and total nitrogen at outflow decreased by 14.29%, 33.33%, and 20.00% in the presence of wetland vegetation compared to no wetland vegetation. During water circulation, the flow rate increased by 0.4 m3 ·s-1 at the inlet of Guishui and Sanli rivers, increasing the water level and velocity in some parts of the rivers. The water areas with vegetation in Sanli and Guishui rivers increased by 144.44% and 13.16%, respectively. The concentrations of ammonia nitrogen, phosphate, and total nitrogen at outflow decreased by 35.71%, 50.00%, and 46.67% compared to no wetlands and no circulation. The circulation strengthened the wetland purification function. The wetland vegetation distribution was organically integrated into the model for water quality calculation, which provides the technical support for the water quality response research under comprehensive measures such as river and lake wetland ecological restoration and water conservancy regulation.

Re-evaluation of sulfate radical based-advanced oxidation processes (SR-AOPs) for treatment of raw municipal landfill leachate.

Sulfate radical (SO4-) -based advanced oxidation processes (SR-AOPs) have proven effective for simultaneously removing refractory dissolved organic matter (DOM) and ammonia in municipal landfill leachates. However, the knowledge on the competition of leachate DOM and ammonia for SO4-, the utilization efficiency of persulfate, as well as the reaction pathways and final products of ammonia oxidation during the SR-AOP treatment remains little known, thereby leading to a lack of a comprehensive evaluation of the emerging leachate treatment technology. The objective of this study was to further investigate the performance of a thermally activated persulfate system for treatment of a mature landfill leachate and re-evaluate the benefits and restrictions of SR-AOPs for leachate treatment. The laboratory experimental results showed that removal patterns of chemical oxygen demand (COD) and ammonia relied heavily upon the dose of persulfate that could be thermally activated to produce reactive sulfate radicals, reflecting the competition of leachate DOM, ammonia, and non-target leachate constituents for SO4-. The utilization efficiency of the added persulfate could be more efficiently utilized for removing the two target leachate pollutants at a lower persulfate dose, whereas more persulfate was wasted due to the reactions with non-target leachate constituents (e.g. Cl- and CO32-) and/or self-decomposition with the increasing persulfate dose. During the treatment, ammonia was oxidized, via the direct attack of SO4- and/or by molecular chlorine produced from the reactions of chloride and sulfate radicals, into nitrate and nitrogen gas, while nitrite was not detected. Of importance, this study highlighted three potentially negative impacts of SR-AOPs on the quality of treated leachate, including accumulation of total dissolved solids, the production of undesirable nitrate, and the pH decrease due to the continuous formation of hydrochloric acid. Therefore, the three issues should be carefully evaluated when a SR-AOP is selected for leachate treatment. Because these impacts become less pronounced with a decreasing persulfate dose, SR-AOPs as a pre-treatment, which is achieved at a relatively low persulfate dose, may be an appropriate option for the SR-AOP application to leachate treatment.

Improved decolorization of dye wastewater in an electrochemical system powered by microbial fuel cells and intensified by micro-electrolysis.

Electrochemical decolorization is of particular importance for the efficient treatment of dye wastewater. A promising electrochemical system powered by microbial fuel cells (MFCs) and intensified by Fe-C micro-electrolysis is proposed and enhanced decolorization of methyl orange (MO) is realized in this study. The decolorization efficiency reached as high as 97.1 ±â€¯1.8% after 180 min of operation with initial MO concentration of 50 mg/L and applied voltage of 700 mV. Decolorization efficiency initially increased and then decreased with rising Fe-to-C ratio. In addition, efficiency was enhanced with the increase of aeration rate up to 6.0 L/min. Lower initial MO concentration and pH were also shown to facilitate MO decolorization. A study of mechanisms, with results from control tests and scavenger experiments indicated that MO decolorization was contributed by the indirect oxidation by various oxidizing substances, especially O2-, that were generated during the process. MO molecule was decomposed and low molecular weight compounds such as indolizine, hydrazide and thione were generated. This study advances the performance of MFC in dye wastewater treatment by combining with a standard technique.

Melem-based derivatives as metal-free photocatalysts for simultaneous reduction of Cr(VI) and degradation of 5-Sulfosalicylic acid.

Carbon nitride has been considered as promising metal-free polymers for low-cost photocatalysis. Most prevailing concern about this fantastic material focuses on g-C3N4, while the potential of other derivatives have been overlooked. Herein, in order to determine the desired derivatives for environmental pollutant treatment, the impact of degree of thermal polymerization on the microstructure of carbon nitride was investigated. Interestingly, melem-based derivatives exhibit 4- and 6-fold enhanced activities than g-C3N4, when used as synergetic photocatalysts for the simultaneous treatment of heavy metal ions and organic contaminants. According to the fundamental study of reactive species formation, a microstructure-dependent photocatalytic mechanism was established. Hydrogen bond-facilitated trapping of photogenerated holes and superior ability for oxygen molecular activation contributed to the high-performance of melem-based derivatives. In contrast, g-C3N4 shows inferior performance during superoxide radical-dominated photodegradation reactions, as its microstructure is favorable for the generation of . Our research not only sheds new insights into the microstructure design of metal-free carbon nitride photocatalysts, but also has immense scientific and technological values for high-efficiency and synergetic environmental applications.

[Simultaneous Photocatalytic Reduction of Cr(â ¥) and Oxidation of SSA by Carbon Nitride].

Carbon nitride is a novel nonmetal semiconductor photocatalyst, which has developed into an ideal environmental treatment material in recent years. Graphite carbon nitride(g-C3N4) was prepared through pyrolysis melamine, and the structure, morphology and optical properties of samples were characterized by X-ray diffraction(XRD), transmission electron microscopy(TEM) and UV-Vis diffuse reflectance spectra(UV-Vis DRS). The potential application of g-C3N4 in the simultaneous photocatalysis reduction of Cr(Ⅵ) and oxidation of sulfosalicylic acid(SSA) was further explored. And the effects of different conditions such as catalyst dosage, pH and initial concentration ratio of Cr(Ⅵ) with SSA on the simultaneous photocatalysis were also investigated. The results showed that when the catalyst dosage was 0.5 g·L-1, pH=2, the initial concentration ratio of Cr (VI) and SSA was 1:4(10 mg·L-1:40 mg·L-1), optimal simultaneous photocatalysis efficiency was achieved, which was more than 3 times higher than that of the separated photoreduction or photooxidation reactions. Within 3 hours, the reduction ratio of Cr(Ⅵ) and oxidation ratio of SSA could reach 98.9% and 93.4%, respectively. The mechanism of simultaneous photocatalysis was discussed. Cr(Ⅵ) was reduced by electrons and SSA was oxidized by the combined function of hole, O2·- and·OH under visible light.