Mechanisms of well iron clogging in groundwater heat pump systems: Insights from video imaging, hydrogeochemical analysis, and geochemical modeling.

Groundwater heat pump (GWHP) systems are increasingly popular as low-carbon and environmentally friendly technologies, but well clogging induced by iron remains a significant issue. This study investigated the clogging characteristics and biogeochemistry of three typical wells (pumping, injection, and observation wells) in an operating GWHP system using video imaging, sampling, and analysis of hydrogeochemical and microbial data. The results revealed that iron-induced well clogging is a complex process involving physical, chemical, and microbial factors. Pumping wells experience clogging due to water mixing with varying redox conditions, resulting in hematite-based iron oxide deposits. Injection wells exhibit higher clogging severity, with transformed oxidation and accumulation of reduced iron minerals at the solid-liquid interface, resulting in darker colored clogs with magnetite. Clogging in both extraction and injection wells is closely related to iron-rich aquifer sections, where severe clogging occurs. Shallow clogging due to iron oxide is limited and attributed to the oxidation of zero-valent iron in well casing material. Iron-oxidizing bacteria and iron-reducing bacteria were detected in the consolidated deposits of clogged wells, indicating their involvement in the clogging formation process. Moreover, a strong correlation was observed between the presence of nitrate-reducing bacteria in the water phase and the severity of clogging, suggesting a possible link between iron oxidation and nitrate reduction in the system. Geochemical modeling results further supported the observed clogging severity in GWHP systems and confirmed varying clogging mechanisms in different wells and depths. These findings contribute to the understanding of clogging in GWHP operations, aiding in robust water utilization and energy-saving efforts, and supporting global carbon reduction initiatives.

Facilitating New Chromium Reducing Microbes to Enhance Hexavalent Chromium Reduction by In Situ Sonoporation-Mediated Gene Transfer in Soils.

Chromium (Cr) is a heavy metal with a high toxicity and pathogenicity. Microbial reduction is an effective strategy to remove Cr(VI) at contaminated sites but suffers from the low populations and activities of Cr-reducing microorganisms in soils. This study proposed an in situ sonoporation-mediated gene transfer approach, which improved soil Cr(VI) reduction performance by delivering exogenous Cr-transporter chrA genes and Cr-reducing yieF genes into soil microorganisms with the aid of ultrasound. Besides the increasing populations of Cr-resistant bacteria and elevated copy numbers of chrA and yieF genes after sonoporation-mediated gene transfer, three new Cr-reducing strains were isolated, among which Comamonas aquatica was confirmed to obtain Cr-resistant capability. In addition, sonoporation-mediated gene transfer was the main driving force significantly shaping soil microbial communities owing to the predominance of Cr-resistant microbes. This study pioneered and evidenced that in situ soil sonoporation-mediated gene transfer could effectively deliver functional genes into soil indigenous microbes to facilitate microbial functions for enhanced bioremediation, e.g., Cr-reduction in this study, showing its feasibility as a chemically green and sustainable remediation strategy for heavy metal contaminated sites.

Oxygen micro-nanobubbles for mitigating eutrophication induced sediment pollution in freshwater bodies.

Sediment hypoxia is a growing problem and has negative ecological impacts on the aquatic ecosystem. Hypoxia can disturb the biodiversity and biogeochemical cycles of both phosphorus (P) and nitrogen (N) in water columns and sediments. Anthropogenic eutrophication and internal nutrient release from lakebed sediment accelerate hypoxia to form a dead zone. Thus, sediment hypoxia mitigation is necessary for ecological restoration and sustainable development. Conventional aeration practices to control sediment hypoxia, are not effective due to high cost, sediment disturbance and less sustainability. Owing to high solubility and stability, micro-nanobubbles (MNBs) offer several advantages over conventional water and wastewater treatment practices. Clay loaded oxygen micro-nanobubbles (OMNBs) can be delivered into deep water sediment by gravity and settling. Nanobubble technology provides a promising route for cost-effective oxygen delivery in large natural water systems. OMNBs also have the immense potential to manipulate biochemical pathways and microbial processes for remediating sediment pollution in natural waters. This review article aims to analyze recent trends employing OMNBs loaded materials to mitigate sediment hypoxia and subsequent pollution. The first part of the review highlights various minerals/materials used for the delivery of OMNBs into benthic sediments of freshwater bodies. Release of OMNBs at hypoxic sediment water interphase (SWI) can provide significant dissolved oxygen (DO) to remediate hypoxia induced sediment pollution Second part of the manuscript unveils the impacts of OMNBs on sediment pollutants (e.g., methylmercury, arsenic, and greenhouse gases) remediation and microbial processes for improved biogeochemical cycles. The review article will facilitate environmental engineers and ecologists to control sediment pollution along with ecological restoration.

Influence of calcium and magnesium elimination on plant biomass and secondary metabolites of Stevia rebaudiana Bertoni.

This study reports the increment in the secondary metabolites in Stevia rebaudiana plant after exposure to the elimination of Ca and Mg from Murashige and Skoog culture medium. The effect of nutrient stress on regenerants of S. rebaudiana is measured, which reveals significantly enhanced growth parameters, steviol glycosides (SGs) content, and nonenzymatic antioxidants; total phenolic content, total flavonoid content, total antioxidant capacity, total reducing power, and DPPH-free radical scavenging activity as compared with the control treatment. However, significantly highest amounts are obtained in a medium with only Ca deficiency. The amount of rebaudioside A (Reb A) and stevioside (ST) obtained in the case of Ca-deficient medium is 4.08 and 0.69%, respectively. It is followed by the results obtained from both Ca- and Mg-deprived medium [Reb A (3.23%) and ST (0.52%)] and the lowest values are obtained from medium lacking Mg only [Reb A (2.60%) and ST (0.40%)]. The most probable adaptation mechanism might be the production of reactive oxygen species by nutrients' stress, which results in secondary metabolites production as defensive moieties to overcome stress situation. This effective protocol needs to be refined to apply on an industrial scale in bioreactors for increasing quantities of commercially important pharmaceutical compounds.

Isolation of functional bacterial strains from chromium-contaminated site and bioremediation potentials.

In this study, two Cr(VI)-reducing functional bacterial strains (TJ-1 and TJ-5) were successfully isolated and screened from the chromium-contaminated soil from a real site. The 16S rRNA gene sequences were analysed, which showed high similarity (>99%) with Stenotrophomonas maltophilia (TJ-1) and Brucella intermedius (TJ-5) species. The optimum growth for the two bacteria to reduce Cr(VI) were achieved at pH 7.0 and initial inoculation amount of 5%. The two strains were applied to real contaminated soil samples and showed better Cr removal when external carbon sources were added. Using sawdust as a solid-phase carbon source supplement, both TJ-1 and TJ-5 showed higher remediation efficiency (99.77% and 93.86%) than using glucose as the carbon source (68.56% and 70.87%). Results of the stability of soil Cr(VI) bioremediation revealed that the water-soluble Cr(VI) content of bioremediated sample remained unchanged, indicating that Cr(VI) is not easily released after death of the strains. Solid-phase carbon source supplements may help the cells to attach and grow into biofilms, creating a better growth condition which improved the remediation efficiency. Column experiments showed that the total remediation efficiencies by the two strains were 34.23% and 20.63%, respectively, within a short time period (76 h). Therefore, the two strains showed great bioremediation potentials for chromium-contaminated sites and can be used in future application of in-situ bioremediation.

Stable Carbon Isotope Analysis of Hexachlorocyclohexanes by Liquid-Liquid Extraction Gas Chromatography Isotope Ratio Mass Spectrometry: Method Evaluation and Applications.

Compound specific isotope analysis (CSIA) and enantiomer specific isotope analysis (ESIA) are powerful tools for assessing the fate of hexachlorocyclohexanes (HCHs) in the environment. However, there is no systematic study on the CSIA and ESIA analysis test methods of the carbon isotopes of HCHs in water and soil environments, in particular the isotope fractionation in the pre-concentration process. We endeavored to test the compatibility of CSIA and ESIA with the liquid-liquid extraction method of HCHs in water. The results showed that there were negligible changes in the δ13C of HCHs after extraction, indicating that liquid-liquid extraction can be used as a pre-concentration method for the determination of δ13C of HCHs in water. The optimized method was validated and then applied to differentiate three HCHs from different manufacturers, to identify in situ degradation of HCHs of groundwater from a contaminated site and to resolve the carbon isotope fractionation occurring in the α-HCH oxidation by CaO2/Fe(II) Fenton system. The results showed that the same reagents from different manufacturers have different carbon isotope compositions, and different isomers from the same manufacturer also have different isotope compositions, showing useful evidence in identifying the source of HCHs. The more enriched δ13C in the down-gradient wells indicated that HCHs have undergone biodegradation or/and chemical reactions in the groundwater system of the site. Carbon isotopic enrichment factors (εC) of -1.90 ± 0.10‱ were obtained in the oxidation process. Hence, the method validated in this study has great potential as a method for identifying the degradation of HCHs in a water environment.

Potential risk assessment of groundwater to address the agricultural and domestic challenges in Ordos Basin.

The safety of groundwater has been a great concern for irrigation and drinking purposes in recent decades due to the increasing impacts of anthropogenic activities. There are several standards to evaluate the groundwater quality for different utilization purposes. In this paper, 804 samples covering the entire Ordos Basin across five provinces were used to evaluate the irrigation suitability and human health risks. The results showed that the sequence of cationic concentration was Na+ > Ca2+ > Mg2+ > K+ > NH4 +, and the anion concentration was HCO3 - > SO4 2- > Cl- > NO3 - > F- > NO2 -. For drinking purposes, TDS, Na+, SO4 2-, F-, TH and NO3 - exceed seriously the regulated standard in the study area. For irrigating purposes, 80% of the water in the study area belongs to "good water" according to the evaluation of salinity and alkalinity. Saline water which is not suitable for irrigation accounts for about 9%. High health risks of fluoride ions are mainly observed to the samples representing the western part of the study area, while the health risks of nitrates spread throughout the study area. Health risk is not only related to location, but also varies with age, and it is found that children suffer more threats than adults.

Biodegradation of Phenol by Rhodococcus sp. Strain SKC: Characterization and Kinetics Study.

This study focuses on the kinetics of a pure strain of bacterium Rhodococcus sp. SKC, isolated from phenol-contaminated soil, for the biodegradation of phenol as its sole carbon and energy source in aqueous medium. The kinetics of phenol biodegradation including the lag phase, the maximum phenol degradation rate, maximum growth rate (Rm) and maximum yield coefficient (Y) for each Si (initial phenol concentration, mg/L) were fitted using the Gompertz and Haldane models of substrate inhibition (R2 > 0.9904, RMSE < 0.00925). The values of these parameters at optimum conditions were µmax = 0.30 h-1, Ks = 36.40 mg/L, and Ki = 418.79 mg/L, and that means the inhibition concentration of phenol was 418.79 mg/L. By comparing with other strains of bacteria, Rhodococcus sp. SKC exhibited a high yield factor and tolerance towards phenol. This study demonstrates the potential application of Rhodococcus sp. SKC for the bioremediation of phenol contaminate.

Engineered ZnO and CuO Nanoparticles Ameliorate Morphological and Biochemical Response in Tissue Culture Regenerants of Candyleaf (Stevia rebaudiana).

Sustainable production of secondary metabolites in medicinal plants by artificial culturing on the industrial scale has gained worldwide importance. Engineered nanoparticles (ENPs) play a pivotal role in the elicitation of compounds of medicinal value. This investigation explores the influence of ZnO and CuO ENPs on in vitro roots formation, non-enzymatic antioxidant activities, and production of steviol glycosides (SGs) in regenerants of Candyleaf, Stevia rebaudiana. ENPs were applied in 0, 2, 20, 200, and 2000 mg/L of concentration in the MS medium containing plant shoots. The percentage of rooting induced was 91% and 94% by applying ZnO ENPs (2 mg/L) and CuO ENPs (20 mg/L), respectively. Moreover, at 2 mg/L of ZnO and 20 mg/L of CuO ENPs, the high performance liquid chromatography studies determined the significantly greatest content of SGs; rebaudioside A (4.42 and 4.44) and stevioside (1.28 and 1.96). Phytochemical studies including total flavonoid content, total phenolic content, and 2,2-diphenyl-1-picryl hydrazyl-free radical scavenging activity were calculated highest by the regenerants grown in 2 mg/L of ZnO and 20 mg/L of CuO ENPs dosage. Both ZnO and CuO ENPs at 200 mg/L and 2000 mg/L of concentration induced adverse effects on plant biomass, antioxidant activities, and SGs content up to 1.22 and 1.77 for rebaudioside A and 0.21 and 0.25 for stevioside. Hence, the biochemical and morphophysiological responses of Candyleaf were elicited as a defense against ZnO and CuO ENPs applied under threshold limit. This artificial biotechnological technique holds great promise for continued production of natural antioxidants on commercial scale and our study has further strengthened this impact.

Sustainable Chromium (VI) Removal from Contaminated Groundwater Using Nano-Magnetite-Modified Biochar via Rapid Microwave Synthesis.

This study developed a nano-magnetite-modified biochar material (m-biochar) using a simple and rapid in situ synthesis method via microwave treatment, and systematically investigated the removal capability and mechanism of chromium (VI) by this m-biochar from contaminated groundwater. The m-biochar was fabricated from reed residues and magnetically modified by nano-Fe3O4. The results from scanning electron microscopy (SEM) and X-ray diffraction (XRD) characterisations confirmed the successful doping of nano-Fe3O4 on the biochar with an improved porous structure. The synthesised m-biochar exhibited significantly higher maximum adsorption capacity of 9.92 mg/g compared with that (8.03 mg/g) of the pristine biochar. The adsorption kinetics followed the pseudo-second-order model and the intraparticle diffusion model, which indicated that the overall adsorption rate of Cr(VI) was governed by the processes of chemical adsorption, liquid film diffusion and intramolecular diffusion. The increasing of the pH from 3 to 11 significantly affected the Cr(VI) adsorption, where the capabilities decreased from 9.92 mg/g to 0.435 mg/g and 8.03 mg/g to 0.095 mg/g for the m-biochar and pristine biochar, respectively. Moreover, the adsorption mechanisms of Cr(VI) by m-biochar were evaluated and confirmed to include the pathways of electrostatic adsorption, reduction and complexation. This study highlighted an effective synthesis method to prepare a superior Cr(VI) adsorbent, which could contribute to the effective remediation of heavy metal contaminations in the groundwater.

Graphite nanoparticle as nanoquencher for 17ß-estradiol detection using shortened aptamer sequence.

A graphite nanoparticle (GN) with a spherical shape and stacked by a few layered graphene sheets is an ideal fluorescent nanoquencher for the fluorophore. We developed a novel aptasensor based on fluorescence resonance energy transfer for the sensitive and specific detection of 17ß-estradiol (E2) by using the GN as a fluorescent nanoquencher and the shorter E2 specific aptamer as the sensing probe. The physiological and chemical properties of the aptasensor in response to the E2 capture were investigated with an atomic force microscopic analysis and an E2 detection principle was clarified accordingly. Also, it was demonstrated that the sensitivity of the aptasensor was affected by the length of aptamer and the particle size of the nanoquencher, and the highest sensitivity for E2 detection was achieved with a shorter aptamer of 35 base sequences and a smaller GN with a particle size of around 5 nm. And the detection limit was 1.02 ng mL-1. Moreover, this presented no cross reaction with E2 analogs and was successfully utilized for the real environmental water monitoring.

Cell cycle arrest mediated by Cd-induced DNA damage in Arabidopsis root tips.

Accumulating evidence demonstrates that the aberrant expression of cell cycle regulation and DNA repair genes can result in abnormal cell proliferation and genomic instability in eukaryotic cells under different stresses. Herein, Arabidopsis thaliana (Arabidopsis) seedlings were grown hydroponically on 0.5 × MS media containing cadmium (Cd) at 0-2.5mgL-1 for 5d of treatment. Real time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis revealed that expression of DNA damage repair and cell cycle regulation genes, including BRCA1, MRE11, WEE1, CDKA;1 and PCNA1, showed an inverted U-shaped dose-response. In contrast, notably reduced expression was observed for G1-to-S transition-related genes, Histone H4, E2Fa and PCNA2; DSB end processing, GR1; G2-to-M transition-related gene, CYCB1;1; and DNA mismatch repair, MSH2, MSH6 and MLH1 genes in root tips exposed to 0.125-2.5mg/L Cd for 5d. Flow cytometry (FCM) analysis revealed significant increases of cells with a 2C nuclear content and with a 4C and 8C nuclear content under Cd stresses of 0.125 and 1-2.5mgL-1, respectively. Our results suggest that 0.125mgL-1 Cd-induced DNA damage induced the marked G1/S arrest, leading to accelerated growth in root tips, while 1.0-2.5mgL-1 Cd-induced DNA damage caused a notable G2/M arrest in root tips, leading to reduced growth in root tips. This may be a protective mechanism that prevents cells with damaged DNA from dividing under Cd stress.

Direct Electrochemical Detection of Bisphenol A Using a Highly Conductive Graphite Nanoparticle Film Electrode.

We developed an accurate and sensitive sensor for electrochemical detection of bisphenol A (BPA) with a high-conductivity graphite nanoparticle (GN) film electrode. The GNs consisted of several stacked graphene sheets and showed a homogenous spherical shape, high conductivity, large surface area and good adsorption properties to BPA. The constructed GN film electrode exhibited improved amperometric current responses such as decreased impedance and lowered BPA oxidation potential compared with those of a pristine electrode, and also possessed a large surface area to allow fast electron transfer and BPA accumulation. A pre-accumulation process with BPA adsorption resulted in considerable current signal enhancement during BPA detection. The loading amount of GNs on the film electrode and the time for target BPA enrichment were optimized. The GN film electrode-based sensor showed high reproducibility and high selectivity for BPA over other reagents. Differential pulse voltammetry experiments revealed that the concentrations of BPA were linearly correlated with the current changes, and the lowest limit of detection of the sensor was 35 nM. Furthermore, the sensor showed great accuracy and reliability, as confirmed by high-performance liquid chromatography measurements. The sensor was also successfully used for BPA determination in groundwater samples, demonstrating its potential for real environmental analysis.

Interplay of Natural Organic Matter with Flow Rate and Particle Size on Colloid Transport: Experimentation, Visualization, and Modeling.

The investigation on factors that affect the impact of natural organic matter (NOM) on colloid transport in complex hydraulic flow systems remains incomplete. Using our previously established approach, the interplay of flow rate and particle size on the NOM effect was quantified, using flow rates of 1 and 2 mL/min and particle sizes of 50 and 200 nm to represent small nanoparticles (1-100 nm) and large non-nano-microspheres (100-1000 nm) in the low-flow groundwater environment. Latex particles, Suwannee River humic acid (SRHA), and iron oxide-coated sand were used as model particles, NOM, and the aquifer medium, respectively. The quantitative results show NOM blocked more sites for large particles at a high flow rate: 1 µg of SRHA blocked 5.95 × 10(9) microsphere deposition sites at 2 mL/min but only 7.38 × 10(8) nanoparticle deposition sites at 1 mL/min. The particle size effect dominated over the flow rate, and the overall effect of the two is antagonistic. Granule-scale visualization of the particle packing on the NOM-presented sand surface corroborates the quantification results, revealing a more dispersed status of large particles at a high flow rate. We interpret this phenomenon as a polydispersivity effect resulting from the differential size of the particles and NOM: high flow and a high particle size enlarge the ratio of particle-blocked to NOM-blocked areas and thus the NOM blockage. To our knowledge, this is the first model-assisted quantification on the interplay of NOM, flow rate, and particle size on colloid transport. These findings are significant for nanorisk assessment and nanoremediation practices.

Processes and mechanisms in remediation of aqueous chromium contamination by sulfidated nano-scale zerovalent iron (S-nZVI): Experimental and computational investigations.

Sulfidated nano-scale zerovalent iron (S-nZVI) has emerged as an advanced functional nanomaterial for efficiently remediating Cr(VI) contamination in aqueous environments. However, there is an insufficient understanding of its coherent process, removal pathway, and hydrochemical reactive mechanisms, presenting potential challenges for its future environmental applications. To address this gap, this study successfully synthesized S-nZVI through a chemical precipitation method and effectively applied it for the removal of Cr(VI). Additional characterization revealed that the removal of Cr(VI) followed a sequence of rapid chemisorption and intraparticle diffusion processes, concomitant with an increase in pH and a decrease in oxidation-reduction potential. The remediation mechanism encompassed a synergistic reduction of Cr(VI) to Cr(III) and simultaneous immobilization via Cr2FeO4 coprecipitation. The highest Cr(VI) removal capacity of 75 mg/g was attained during dynamic removal experiments in the sand column packed with S-nZVI. Further computational analysis, employing density functional theory calculations based on the experimental data, revealed the involvement of multiple molecular orbitals of Cr(VI) in the removal process. It also elucidated a step-by-step reduction pathway for Cr(VI) characterized by decreasing free energy. These findings provide evidence-based insights into Cr(VI) remediation using S-nZVI and can serve as valuable technical support for future environmental management of heavy metals.

E. coli cotransport with composite colloid in unsaturated porous media: Multi-risk on migration and biomolecular response.

The diversity of colloidal types and the differences in the composite ratios in porous media are important factors governing the migration and biological risk of pathogenic microorganisms in the subsurface environment. In this study, E. coli O157:H7 was subjected to co-migration experiments with different compositions of the composite colloid montmorillonite (MMT)-Fe2O3, and the biomolecular response of E. coli under the action of colloids was analyzed by Raman spectroscopy to quantify the risk of E. coli under the action of composite colloids based on both. The results showed that Fe2O3 colloids inhibited E. coli migration mainly by electrostatic adsorption and reduced E. coli metabolism. MMT colloid inhibited E. coli migration mainly by blockage, and E. coli metabolism increased, and surface macromolecules decreased to reduce E. coli adhesion. MMT-Fe2O3 complex colloids inhibited migration through electrostatic attraction between the two and formation of cohesive colloids, with reduced E. coli metabolism and insignificant biomolecular response. It was briefly assessed that the composite colloids reduced E. coli risk less strongly than single colloids, stemming from the difference in the mechanism of influence and the actual need to consider colloid interactions. This conclusion can inform the management and control of pathogen risk in porous media environments.

Enhanced bioelectroremediation of heavy metal contaminated groundwater through advancing a self-standing cathode.

Hexavalent chromium (Cr(VI)) contamination in groundwater poses a substantial global challenge due to its high toxicity and extensive industrial applications. While the bioelectroremediation of Cr(VI) has attracted huge attention for its eco-friendly attributes, its practical application remains constrained by the hydrogeochemical conditions of groundwater (mainly pH), low electron transfer efficiency, limitations in electrocatalyst synthesis and electrode fabrication. In this study, we developed and investigated the use of N, S co-doped carbon nanofibers (CNFs) integrated on a graphite felt (GF) as a self-standing cathode (NS/CNF-GF) for the comprehensive reduction of Cr(VI) from real contaminated groundwater. The binder free cathode, prepared through electro-polymerization, was employed in a dual-chamber microbial fuel cell (MFC) for the treatment of Cr (VI)-laden real groundwater (40 mg/L) with a pH of 7.4. The electrochemical characterization of the prepared cathode revealed a distinct electroactive surface area, more wettability, facilitating enhanced adsorption and rapid electron transfer, resulting in a commendable Cr(VI) reduction rate of 0.83 mg/L/h. The MFC equipped with NS/CNF-GF demonstrated the lowest charge transfer resistance (Rct) and generated the highest power density (155 ± 0.3 mW/m2) compared to control systems. The favorable electrokinetics for modified cathode led to swift substrate consumption in the anode, releasing more electrons and protons, thereby accelerating Cr(VI) reduction to achieve the highest cathodic coulombic efficiency (C.Eca)of80 ± 1.3 %. A similar temporal trend observed between Cr(VI) removal efficiency, COD removal efficiency, and C.Eca, underscores the effective performance of the modified electrode. The reusability of the binder free cathode, exemption from catholyte preparation and the absence of pH regulation requirements highlighted the potential scalability and applicability of our findings on a larger scale.

Migration risk of Escherichia coli O157:H7 in unsaturated porous media in response to different colloid types and compositions.

The vadose zone is a critical zone for microbial entry into the subsurface environment, and various types of inorganic and organic colloids can affect the migration of pathogenic bacteria. In the study, we explored the migration behavior of Escherichia coli O157:H7 with humic acids (HA), iron oxides (Fe2O3) or their mixture, uncovering their migration mechanisms in the vadose zone. The effect of complex colloids on the physiological properties of E. coli O157:H7 was analyzed based on the measured particle size, zeta potential and contact angle. HA colloids significantly promoted the migration of E. coli O157:H7, where Fe2O3 was opposite. The migration mechanism of E. coli O157:H7 with HA and Fe2O3 is obviously different. Multiple colloids dominated by organic colloid will further highlight its promoting effect on E. coli O157:H7 under the guidance of electrostatic repulsion due to the influence of colloidal stability. Multiple colloids dominated by metallic colloid will inhibit the migration of E. coli O157:H7 under the control of capillary force due to the restriction of contact angle. The risk of secondary release of E. coli O157:H7 can be effectively reduced when the ratio of HA/Fe2O3 is ≥ 1. Combining this conclusion with the distribution characteristics of soil in China, an attempt was made to analyse the migration risk of E. coli O157:H7 on a national scale. In China, from north to south, the migration capacity of E. coli O157:H7 gradually decreased, and the risk of secondary release gradually increased. These results provide ideas for the subsequent study of the effect of other factors on the migration of pathogenic bacteria on a national scale and provide risk information about soil colloids for the construction of pathogen risk assessment model under comprehensive conditions in the future.

Surface clogging process modeling of suspended solids during urban stormwater aquifer recharge.

Aquifer recharge, which uses urban stormwater, is an effective technique to control the negative effects of groundwater over-exploitation, while clogging problems in infiltration systems remain the key restricting factor in broadening its practice. Quantitative understanding of the clogging process is still very poor. A laboratory study was conducted to understand surface physical clogging processes, with the primary aim of developing a model for predicting suspended solid clogging processes before aquifer recharge projects start. The experiments investigated the clogging characteristics of different suspended solid sizes in recharge water by using a series of one-dimensional fine quartz sand columns. The results showed that the smaller the suspended particles in recharge water, the farther the distance of movement and the larger the scope of clogging in porous media. Clogging extents in fine sand were 1 cm, for suspended particle size ranging from 0.075 to 0.0385 mm, and 2 cm, for particles less than 0.0385 mm. In addition, clogging development occurred more rapidly for smaller suspended solid particles. It took 48, 42, and 36 hr respectively, for large-, medium-, and small-sized particles to reach pre-determined clogging standards. An empirical formula and iteration model for the surface clogging evolution process were derived. The verification results obtained from stormwater recharge into fine sand demonstrated that the model could reflect the real laws of the surface clogging process.

Natural colloids facilitated transport of steroidal estrogens in saturated porous media: Mechanism and processes.

Steroid estrogens (SEs) as typical endocrine disrupting compounds (EDCs) are widely detected in terrestrial environment, whilst the transport of SEs in groundwater remains unwell understood. Specifically, the effects of ubiquitous natural colloids on the SEs transport are unclear in subsurface environment, especially in aquifer systems. Here, the influence of inorganic colloids (i.e. silica and illite) and organic colloids, i.e. Humic acid (HA), on the transport of estrone (E1) and estradiol (E2) in saturated porous media was studied utilizing laboratory scale column experiments. Characterization on the colloids and porous aquifer material was conducted to provide a basis for interpretation of the experimental findings. Results showed that the transport of SEs was clearly affected by the natural colloids migrating through the saturated porous media. About 38.5% of E1 and 24.6% of E2 were retained in the column when colloids were absent in the system. When transporting with silica colloids, illite colloids, and HA colloids, the transport of E1 was enhanced by 15.64%, 11.17% and 25.60%, respectively; whilst the transport of E2 was improved by 19.56%, 23.06% and 36.40%, respectively. The SEs transport enhancement by colloids depended upon not only the mobility of the colloids but also their geochemical characteristics. The organic colloids showed 1.5-2.5 times greater ability on promoting the transport of SEs than the inorganic ones tested in this study. The proposed mechanisms of nature colloids facilitated transport of SEs including competing for adsorption sites on the sand surfaces by the colloids resulting mobilization of adsorbed SEs from solid matrix, and transport of colloids as carriers for SEs.