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Batch adsorption and column tests were conducted to explore characteristics of transports of TNT and aniline and their interactions in saturated Chinese loess sampled from Xi’an, China. Batch tests show that the performances of TNT and aniline adsorptions on Chinese loess are not same when they exist alone. When they coexist, their adsorptions inhibit each other and their inhibitions potentials were different. TNT inhibition on aniline adsorption is in linear and increases with TNT concentration increasing, while aniline inhibition on TNT adsorption also depends on its concentration but in two stages, where the inhibition is few when aniline concentration is lower than 5 mg/L, and then also gets linear increasing with aniline concentration increasing over 5 mg/L. Even though, the inhibition of aniline on TNT adsorption is generally greater than that of TNT on aniline adsorption. Column tests show that, compared with the transport behavior when they exist alone, theier coexistence can promote each other to transport in the saturated loess, importantly, aniline promotes more obviously TNT transport than TNT promotes aniline transport. Kinetics, isotherms and thermodynamics studies indicat that, TNT adsorption is primarily through the surface adsorption while aniline adsorption is mainly via electrostatic adsorption and inner pore diffusion adsorption as well as surface adsorption. There is a certain competitive relationship in their adsorptions on Chinese loess because they have same adsorption sites, meanwhile, they have different adsorption sites, especially, electrostatic force is greater than surface force, when they coexist. So, these inhibitions on adsorption are conducive to the existences of TNT and aniline in the water solution rather than being fixed on Chinese loess, thus enhancing their transports in the saturated loess and aniline has a great effect on TNT migration, while TNT has a small effect on aniline transport, indicating their coexistence can increase the risk of deep soil and even groundwater pollution.

Fluorine (F) in water has a negative effect on the environment and human health. Schwertmannite has potential remediation to contamination in solution. In this study, the adsorption mechanism and influencing factors of synthetic schwertmannite for low-concentration F were studied through batch experiments. The results suggested that the adsorption of F by schwertmannite reached equilibrium after about 60 min, and the adsorption efficiency exceeded 94%. The experimental data can be best-fit by the pseudo-second-order kinetic and Langmuir models well. Schwertmannite showed effective adsorption at pH 4, dosage 1.5 g L−1, low temperature, and low concentration of co-existing anion. The adsorption process was a spontaneous and exothermic reaction, which was dominated by chemical adsorption. FT-IR and XPS spectra analysis revealed that F adsorption on schwertmannite through the surface complexation and anion exchange reaction between SO42− and OH− with F−, especially the primary role of OH−. The results can provide theoretical support for the schwertmannite application in the treatment of F-containing wastewater.

Contrary to the fact that NO3--N can serve as electron acceptor to promote organics degradation, it was also found NO3--N reduction does not necessarily promote organics degradation. We speculate nitrogen (N) species may control the interaction between NO3--N reduction and organics degradation via shifting related microbial community structure. To prove the hypothesis, oxic-anoxic transition zone (OATZ) microcosms simulated by lake water and sediment were conducted with the addition of N species (NO3--N, NO2--N, and NH4+-N) and aniline as typical organics. High-throughput sequencing was used to analyze the microbial community structure and functional enzyme in the microcosms. Results show that, NO2--N inhibited NO3--N reduction while enhanced aniline degradation. For NH4+-N, it promoted NO3--N reduction when NH4+-N/NO3--N concentration ratio ≤ 2 and inhibited aniline degradation when NH4+-N/aniline concentration ratio ≥ 0.5. The presence of NO2--N or NH4+-N weakened the interaction between NO3--N reduction and aniline degradation, which might be caused by significant changes in the diversity and abundance of microbial communities controlled by N species. The microbial mechanism indicates that NO2--N weakened the interaction by affecting both denitrification enzyme activity and electron transfer capability, while NH4+-N weakened the interaction mainly by affecting electron transfer capability. These results imply that N species, as well as other electron acceptors and donors, in the contaminated OATZ should be fully considered, when performing in situ remediation technology of NO3--N reduction.

To explore the adsorption removal mechanism of Mg–Al layered double oxides (LDOs) for low-concentration (≤ 5 mg L−1) Cr(VI), the adsorption kinetics, adsorption isotherms and its influencing factors were studied by batch experiments. Cr(VI) adsorption reached equilibrium after 6, 11 and 15 h for initial Cr(VI) concentrations of 1, 3 and 5 mg L−1, respectively, and the final adsorption efficiency exceeded 99.0%. The residual concentration of Cr(VI) was within the allowable limit of Drinking Water Quality Standard of World Health Organization (0.05 mg L−1). The experimental data fitted the pseudo-second-order and Freundlich models well. Mg–Al LDOs showed effective adsorption efficiency in the range of pH 3–9, and the adsorption efficiency was influenced by anions competition (HPO42− > SO42− > CO32− > NO3− > Cl−). The analyses of XRD, SEM and FT-IR spectra suggested adsorption Cr(VI) on Mg–Al LDOs was caused by capturing dichromate ions to reconstruct its structure. Therefore, Mg–Al LDOs is promising adsorbents for the low-concentration Cr(VI) treatment in polluted surface water and groundwater.

Herein, xylan-g-PMMA was synthesized by grafting poly(methyl methacrylate) (PMMA) onto xylan and characterized by FT-IR and HSQC NMR spectroscopies, and the xylan-g-PMMA/TiO2 solution was used to electrospun nanofibers at the voltage of 15 Kv, which was the first time employing xylan to electrospun nanofibers. Moreover, the electrospinning operating parameters were optimized by assessing the electrospinning process and the morphology of electrospun fibers, as follows: the mixed solvent of DMF and chloroform in a volume ratio of 5:1, an anhydroxylose unit (AXU)/MMA molar ratio lower than 1:2, the flow speed of 0.00565–0.02260 mL/min, and a receiving distance of 10–15 cm. Diameters of the electrospun fibers increased with increasing DMF content in the used solvent mixture, MMA dosage, and receiving distance. TiO2 nanoparticles were successfully dispersed in electrospun xylan-g-PMMA nanofibers and characterized by scanning electron microscopy, energy dispersive X-ray diffraction spectrum, and X-ray photoelectron spectroscopy, and their application for methylene blue (MB) degradation presented above 80% photocatalytic efficiency, showing the good potential in water treatment.

The lack of information on the origin and behavior of iodine in deep groundwater restricts the development and use of groundwater resources. To address this issue, the Cangzhou region in the eastern North China Plain (NCP) was selected for a case study. In total, 296 deep groundwater samples were collected, their iodine concentrations were determined, and the distribution characteristics of iodine concentrations were analyzed. Iodine concentrations ranged from < 0.002 to 1.22 mg/L, with a mean of 0.19 mg/L; 42% of the samples had high iodine concentrations. The levels were higher in the east than in the west, and most of the samples with high iodine concentrations were obtained from sites east of the boundary between the Cangxian uplift and the Huanghua depression. The weathering and dissolution of iodine-bearing minerals and the leaching of marine sediments can facilitate iodine enrichment. In the Cangxian uplift, iodine was mainly a result of the conversion of organic iodine, while in the Huanghua depression, iodine enrichment was a factor of the conversion of IO3-. Overall, the main factors for the enrichment of iodine are the sedimentary environmental and the hydrodynamic conditions. Our results provide a theoretical basis to understand the occurrence of high iodine concentrations in deep groundwater.

Through batch adsorption and column leaching experiments, this study aimed to investigate the adsorption and transport behavior of aniline in loess and related mechanism under different hydrochemical conditions. Batch experiments results indicated that aniline adsorption reached equilibrium after about 120 min, and the adsorption fitted the pseudo-second-order kinetic and Freundlich models well. The adsorption was spontaneous and exothermic process, indicating the aniline adsorbed by inherent colloidal particles (ICPs) tended to transport. Low pH value, ionic strength and temperature benefitted the adsorption. Column experiments results under different ionic strengths (100, 10 and 1 mM) confirmed the potential transport of aniline. The FT-IR spectra have further suggested that aniline was adsorbed by the ICPs through hydrogen-bond, hydrophobic effect and cation exchange interactions. Low ionic strength was advantageous for the adsorption of aniline in loess and the stabilities of ICPs in solution, but enhanced the co-transport probability of ICPs with aniline in loess.

Based on matched data from the Chinese industrial enterprise database and General Administration of Customs (GAC) database for 2000–2013, this paper examines export manufacturers in the context of ...

Soil columns packed by Chinese loess were tested under stimulated wetting–drying cycles. The results of leaching tests showed that ACPs concentration, although changed with initial peak concentrati...

No consensus has been achieved among researchers on the effect of dissolved oxygen (DO) on nitrate (NO3--N) transformation and the microbial community, especially during aerobic-anoxic transition. To supplement this knowledge, NO3--N transformation, microbial communities, co-occurrence networks, and functional genes were investigated during aerobic-anoxic transition via microcosm simulation. NO3--N transformation rate in the early stage (DO ≥2 mg/L) was always significantly higher than that in the later stage (DO

The sources and primary mechanisms of high iodine concentration in deep groundwater are rarely reported, thereby restricting the development and utilization of the related groundwater resources. To address these issues, 194 deep groundwater samples were collected from the Zhangwei watershed in the North China Plain, China, to analyze their constituents including iodine. Statistics, principal component analysis and hydrological methods were employed to determine the distribution of iodine concentrations and their controlling hydrogeochemical processes. The results show that the iodine concentration ranged from 2 to 446 μg/L and generally increased along the groundwater flow direction. Three zones with high iodine concentration (> 20 μg/L) were delineated as the alluvial–proluvial plain (Zone A, average 70 μg/L), alluvial–lake plain (Zone B, average 83 μg/L) and coastal plain (Zone C, average 199 μg/L), respectively. In Zone A, aquifer minerals weathering probably releases iodate ions into groundwater. The iodate is reduced with nitrate as the electron acceptor of iodine and transported with the precipitation infiltrating through the vadose zone to recharge groundwater, resulting in increasing the groundwater iodine concentration. In Zone B, the iodine concentrations depend on the contents of the organic matter, clay minerals, and iron aluminum oxide in the alluvial–lake sediments, due to that the deeply buried organic matter is rich in iodine which is released into groundwater through the biodegradation of organic matter, In Zone C, the iodine is probably derived from the sediments which were deposited in Quaternary marine transgression events, and its enrichment was controlled by the strong reduction condition of the deep aquifers. In one word, the iodine sources and hydrogeological conditions determined the high iodine concentrations of deep groundwater in the studied watershed. These findings can provide foundation for further insight into the high iodine concentration of deep groundwater in other hydrogeological units of the North China Plain and other similar units over the world, thereby ensuring drinking groundwater safety.

Mixed cultures were established by a sediment to investigate the changes in organic carbon (C) in a combined ammonium and phenanthrene biotransformation process in aquatic ecosystems. The microorganisms in the sediment demonstrated significant ammonium-N and phenanthrene biotransformation capacity with removal efficiencies of 99.96% and 99.99%, respectively. The changes in the organic C characteristics were evaluated by the fluorescence intensity, degradability (humification index (HIX) and UV absorbance at 254 nm (A254)), aromaticity (specific UV absorbance at 254 nm (SUVA254) and fluorescence index (FI)). Compared with C2 (the second control), the lower values of fluorescence intensity (after the 15th d), HIX (after the 8th d), A254 (after the 11th d), and SUVA254 (after the 8th d) and the higher FI value (after the 8th d) in ammonium and phenanthrene-fed mixed cultures (N_PHE) suggest that aromatic structures and some condensed molecules were easier to break down in N_PHE. Similar results were obtained from Fourier transformation infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H NMR) spectra. Changes in organic C characteristics may be due to two key organisms Massilia and Azohydromonas. The biodiversity also suggested that the selective pressure of ammonium and phenanthrene is the decisive factor for changes in organic C characteristics. This study will shed light on theoretical insights into the interaction of N and aromatic compounds in aquatic ecosystems.

Contrary to the fact that NO

To explore the adsorption removal mechanism of Mg-Al layered double oxides (LDOs) for low-concentration (≤ 5 mg L

Although nitrogen (N) transformations have been widely studied under oxic or anoxic condition, few studies have been carried out to analyze the transformation accompanied with NO

A heterotrophic nitrification-aerobic denitrification (HN-AD) mixed culture was established as a simulated aquatic ecosystem to investigate the simultaneous removal of aniline and ammonium, as well as the succession of bacterial community. Aniline and ammonium were found to be simultaneously transformed, with maximum removal efficiencies of 99.98% and 89.87%, respectively. The presence of aniline at lower concentrations (0 to 100 mg/L) slightly inhibited ammonium oxidation, whereas further increasing the aniline concentration (from 100 to 500 mg/L) yielded an apparent enhancement effect, increasing the ammonium-N removal rate from 0.33 to 1.26 mg/L/day. In contrast, ammonium-N concentrations of 100 mg/L were able to facilitate aniline removal. Ammonium was the preferred nitrogen source for aniline removal when compared with nitrification metabolites such as nitrate or nitrite. The analysis of microbial community succession using high-throughput sequencing revealed that the microbial diversity generally decreased throughout the aniline and ammonium removal process. Proteobacteria is observed to increase at the climax stage, and the average relative abundances of Pseudomonas, Massilia, and Bacillus were highest at the climax stage and were positively related to the removal rate of aniline and ammonium-N. Surprisingly, the abundance of these microbes at the end stage was almost equal to that observed at the initial stage. This study demonstrated that polluted aquatic ecosystems hold potential for simultaneous removal of pollutants (hazardous organic carbon and ammonium), and have excellent self-rehabilitation abilities.

Aromatic compounds (ACs) releases aroused by sediment resuspension would certainly change the concentrations of suspended sediment (SPS) and organic carbon, which may alter nitrate-N transformation during aerobic-anoxic transition. To prove this, three typical ACs (aniline, nitrobenzene, and methylbenzene) with different octanol-water partition coefficients (Kow) were selected to investigate the effects of ACs releases aroused by sediment resuspension on nitrate-N transformation during aerobic-anoxic transition. ACs releases aroused by sediment resuspension accelerated nitrate-N transformation and enhanced the potential for dissimilatory nitrate reduction to ammonium (DNRA), compared to that without sediment resuspension. With sediment resuspension, methylbenzene releases affected nitrate-N transformation rates and pathways more significantly than aniline and nitrobenzene releases. Microbial analysis indicated that sediment resuspension created complicated microbial co-occurrence networks and changed the associations among bacteria; dominant bacteria abundance varied with different ACs releases. Further analysis revealed that ACs distributed in SPS, which increased with logKow, indirectly affected nitrate-N transformation rates and pathways via altering dominant bacteria abundance and electron transport system activity (ETSA). Especially, ETSA, which was positively associated with ACs distributed in SPS, affected nitrate-N transformation most directly. Overall, ACs release fate played important roles in nitrate-N transformation, causing ammonia-N retention and alterations in nitrogen cycle during aerobic-anoxic transition.

To exploit the advantages of less electron donor consumptions in partial-denitrification (denitratation, NO3− → NO2−) as well as less sludge production in autotrophic denitrification (AD) and anammox, a novel biological nitrogen removal (BNR) process through combined anammox and thiosulfate-driven denitratation was proposed here. In this study, the ratio of S2O32−-S/NO3−-N and pH are confirmed to be two key factors affecting the thiosulfate-driven denitratation activity and nitrite accumulation. Simultaneous high denitratation activity and substantial nitrite accumulation were observed at initial S2O32−-S/NO3−-N ratio of 1.5:1 and pH of 8.0. The optimal pH for the anammox reaction is determined to be 8.0. A sequential batch reactor (SBR) and an up-flow anaerobic sludge blanket (UASB) reactor were established to proceed the anammox and the high-rate thiosulfate-driven denitratation, respectively. Under the ambient temperature of 35 °C, the total nitrogen removal efficiency and capacity are 73% and 0.35 kg N/day/m3 in the anammox-SBR. At HRT of 30 min, the NO3− removal efficiency could achieve above 90% with the nitrate-to-nitrite transformation ratio of 0.8, implying the great potential to apply the thiosulfate-driven denitratation & anammox system for BNR with minimal sludge production. Without the occurrence of denitritation (NO2− → N2O → N2), theoretically no N2O could be emitted from this BNR system. This study could shed light on how to operate a high rate BNR system targeting to electron donor and energy savings as well as biowastes minimization and greenhouse gas reductions.

A series of silica with diverse channel structures or pore diameters were synthesized via the hydrothermal method. Corresponding amine/nitro-modified materials were obtained by grafting, nitrating reaction, respectively. Textural and chemical properties were analyzed by Scanning electron micrograph (SEM), Small angle powder X-ray diffraction (SAXRD), Nitrogen adsorption-desorption measurement, Fourier transform infrared spectroscopy (FTIR), Thermogravimetric (TG) analysis and Zeta potential. Batch adsorption results revealed that distinct uptake capacities of Cu2+ and methylene blue occurred at the solid-liquid interface of prepared adsorbents. Especially, pure SBA-12-OH displayed the highest removal behavior toward methylene blue, mainly owing to its larger pore diameter. Amine-grafted SBA-12 (SBA-12-NH2) presented higher affinity to Cu2+ than others, originating from the complexation function of amine groups and its superior framework structure. Moreover, their adsorption isotherms and kinetics were further investigated to explore the application in industrial operation system.

In this study, the Mg-Fe-LDH@biochar composite was firstly fabricated and applied for effectively activation peroxymonosulfate (PMS) for aqueous doxycycline (DOX) degradation. The physiochemical properties of the as-synthesized composite were thoroughly characterized. In the developed Mg-Fe-LDH@biochar/PMS system, the catalytic DOX degradations were evaluated under different conditions. Under the optimal condition (0.75 g/L catalyst loading, 0.75 g/L PMS dosage, pH = 7.0), about 88.76% DOX (35 mg/L) was removed within 120 mins. The results of quenching test and electron paramagnetic resonance (EPR) illustrated that the •OH, SO4•- and •O2– radicals all contributed to the DOX degradation in the Mg-Fe-LDH@biochar/PMS system, whereas the 1O2-based non-radical degradation played the dominant role in DOX removal. The developed system was almost not adversely affected by the high-strength anions and exhibited high DOX decomposition rates in a wide pH range from 3.0 to 9.0, indicating the great potential in the practical application. The satisfactory reusability of the composite catalyst was demonstrated in the recycling test, with the DOX removal efficiency slightly declined from 90.08 to 84.42% after five runs. Based on the generation of reactive oxidative species and the transformation intermediates identified by HPLC-MS, the possible degradation pathways and reaction mechanism of DOX degradation in Mg-Fe-LDH@biochar/PMS system were proposed.

A comparative study on denitrifying sludge granulation with different electron donors (sulfide, thiosulfate and organics) was carried out. Longer time was spent on sulfide-denitrifying granular sludge (DGS) cultivation (88 days) than thiosulfate- and organics-DGS cultivations (57 days). All the three DGS were characterized in terms of particle size distribution, sludge settling ability (indicated by sludge volume index and settling velocity), permeability (indicated by fractal dimension) and extracellular polymeric substances (EPS, including polysaccharide and protein) secretion. Sludge productions in the three DGS-reactors were also monitored. The key functional microorganisms in three granular reactors were revealed via high through-put pyrosequencing analysis. Batch tests were performed to measure the denitrification activities of each DGS, including both denitratation (NO3- → NO2-) and denitritation (NO2- → N2). We found that thiosulfate-driven denitrifying sludge granulation (TDDSG) should be the most efficient and compact technology for effective BNR in municipal wastewater treatment. The findings of this study suggests the TDDSG could further increase the nitrogen removal potential in an enhanced sulfur cycle-driven bioprocess for co-treatment of wet flue gas desulfurization wastes with fresh sewage depending on three short-cut biological reactions, including: 1) short-cut biological sulfur reduction (SO42-/SO32- → S2O32-); 2) thiosulfate-driven denitritation (S2O32- + NO2- → SO42- + N2↑); and 3) nitritation (NH4+ + O2 → NO2-).

Dissolved organic matter (DOM), as the most active organic carbon in the soil, has a coherent affinity with heavy metals from inherent and exogenous sources. Although the important roles of DOM in the adsorption of heavy metals in soil have previously been demonstrated, the heterogeneity and variability of the chemical constitution of DOM impede the investigation of its effects on heavy metal adsorption onto soil under natural conditions. Fresh DOM (FDOM) and degraded DOM (DDOM) from sugarcane rind were prepared, and their chemical properties were measured by Fourier-transform infrared spectrometry (FTIR), excitation-emission matrix (EEM) fluorescence spectroscopes, nuclear magnetic resonance (NMR), and molecular weight distribution (MWD). They were also used in batch experiments to evaluate their effects on the adsorption of Cu(II) onto farmland red soil. Based on our results, the chemical structure and composition of DDOM greatly varied; compared with FDOM, the C/O ratio (from 24.0 to 9.6%) and fluorescence index (FI) (from 1.4 to 1.0) decreased, and high molecular weight (>10 kDa) compounds increased from 23.18 to 70.51%, while low molecular weight (

Using Chinese Industrial Enterprise Database and Foreign Investment Enterprises database (2003–2007), this article studies the impact of institutional environment and outward foreign direct investm...

A sulfur cycle-based bioprocess for co-treatment of wet flue gas desulfurization (WFGD) wastes with freshwater sewage has been developed. In this process the removal of organic carbon is mainly associated with biological sulfate or sulfite reduction. Thiosulfate is a major intermediate during biological sulfate/sulfite reduction, and its reduction to sulfide is the rate-limiting step. In this study, the impacts of saline sulfite (the ionized form: HSO3− + SO32−) and free sulfurous acid (FSA, the unionized form: H2SO3) sourced from WGFD wastes on the biological thiosulfate reduction (BTR) activities were thoroughly investigated. The BTR activity and sulfate/sulfite-reducing bacteria (SRB) populations in the thiosulfate-reducing up-flow anaerobic sludge bed (UASB) reactor decreased when the FSA was added to the UASB influent. Batch experiment results confirmed that FSA, instead of saline sulfite, was the true inhibitor of BTR. And BTR activities dropped by 50% as the FSA concentrations were increased from 8.0 × 10−8 to 2.0 × 10−4 mg H2SO3-S/L. From an engineering perspective, the findings of this study provide some hints on how to ensure effective thiosulfate accumulation in biological sulfate/sulfite reduction for the subsequent denitrification/denitritation. Such manipulation would result in higher nitrogen removal rates in this co-treatment process of WFGD wastes with municipal sewage.

Although it is known that wetting–drying (W–D) cycles can enhance the release and transport of soil colloidal particles (SCPs), the effects of cycle times and soil layer thickness on the enhancement are open questions. Artificial loess column laboratory tests were conducted for these questions. The results showed that the concentration of SCPs has one initial peak and several secondary peak concentrations in leachate, and all the peak concentrations decreased with increasing loess layer thickness. The concentrations of 30-, 20- or 10-cm-thick loess layer finally changes into stable levels at about 10, 16 and 23 mg L−1 within 48 h, respectively. Via ten W–D cycles, the initial peak concentrations of 30-, 20- or 10-cm-thick loess layer increased by 37.02%, 40.21% and 53.76%, respectively. After the same number of W–D cycles, the initial peak concentration from 10-cm-thick loess layer was about double that from 30 cm. In short, the release and transport of SCPs would increase with the increase of the times of W–D cycle and the decrease of loess layer thickness, which demonstrates a “memory effect” and a “leapfrogging mode” in time and space, respectively. The mobile SCPs have the potential to enhance the co-transport with contaminants in vadose zone, and even to groundwater. These findings can help to better understand the release and transport of SCPs and contaminants under seasonal rainfall climate conditions, and are helpful in evaluating the risk of soil and groundwater pollution.

Nitrogen (N) loss is generally caused by denitrification under anaerobic conditions and the N loss in the heterotrophic nitrification_aerobic denitrification (HN_AD) system is of recent research interest. However, previous studies are generally focused on pure cultures-based system and the information on HN_AD in the complex aquatic ecosystem is limited. In this study, HN-AD system was established in the mixed cultures of the sediments and the performances of HN-AD were evaluated under different conditions. Further, the N loss mechanism in HN_AD system was explored. The study found that the N was lost in the sediment cultures with ammonium-N (NH4+_N) (or) and nitrate-N (NO3−_N) as N source under aerobic conditions. The highest N loss rate was achieved under the TOC/TN mass ratio of 10 with citrate as the carbon source. Under this condition, the N loss percentages of NH4+_N (201.91 mg/L) and NO3−_N (130.00 mg/L) reached 99.61% and 100.00%, respectively, which were higher than those in the pure HN_AD strains reported in the literature. High NH4+_N removal efficiencies were also achieved at low C/N mass ratio and high NH4+_N concentration (493.12 mg L−1). The N loss pathway in the system was investigated by adding Na2WO4 as the nitrate reductase inhibitor. The study found that the N was not lost via partial nitrification/denitrification pathway, i.e., NH4+ → NH2OH → NO2− → N2O (N2), instead via full nitrification/denitrification pathway, i.e., NH4+ → NH2OH → NO2− → NO3− → NO2− → N2O (N2), since nitrate was a key intermediate. The variation in NH4+_N, NO3−_N, and NO2−_N concentrations in the HN_AD processes further confirmed the N transformation pathway. Therefore, HN_AD may occur and cause N loss in natural aquatic ecosystems. The results of this study demonstrate that N was lost through HN-AD and that the well-cultured HN-AD sediments could be useful biological tool to remediate eutrophic water bodies.

Residual heavy metals are commonly considered to be immobile in soils, leading to an underestimation of their environmental risk. This study investigated the distribution and transport of residual heavy metals along soil profiles, using the Xiaoqinling gold mining region in North China as a case study. Soil samples were collected at three depths from three locations near the tailing heap. The speciation of copper (Cu) and lead (Pb) (exchangeable, carbonate-bound, Fe-Mn oxide-bound, organic matter-bound, and residual fractions) was determined using a sequential extraction procedure. The residual fraction's morphology was observed using scanning electron microscopy (SEM). Results showed that metal fraction distributions along the soil profiles were influenced by each fraction's mobility. Residual fraction with high chemical stability can not be transformed from or into other fractions. This led to the conclusion that the high concentration of residual metals in soils mainly resulted from residual fraction transport. The SEM analysis showed that fine particles (submicrons) were mainly attached to large particles and were likely released and transported by water flow. The more sorptive fractions (non-residual fractions) were mainly retained in the top soil, and the more mobile fractions (residual fraction) were mainly leached to the deep soil. Cu and Pb concentrations in the residual fraction decreased slightly and those in the non-residual fractions decreased significantly with soil depth. These suggest a relatively higher residual metal mobility along the soil profiles. Therefore, residual metals can be transported in soils and their environmental risk can not be ignored in assessing soil contamination.

The release of soil organic matter (SOM) has been frequently studied, while its effects on sorption kinetics and on the capacity of phenanthrene (PHE) on sediments have seldom been studied. In this study, sodium chloride (NaCl, 0-0.1 mol/L) was introduced to adjust the release of SOM, and three sediments were prepared: a raw sediment (S1), an eluted sediment (S2), and an SOM-removed sediment (S3). The release of SOM , with dissolved organic matter (DOM) formed in solution, was confirmed in sediment 1. Sorption kinetics on sediment 1 showed atypical results as three stages: rapid sorption, pseudo sorption with partial desorption, and slow sorption. Also, a defined "sorption valley" occurred in the kinetic curve, which can be qualitatively determined by the characteristics of the release of SOM, including its amount, rate and sequence in each SOM fraction. Sorption capacity on sediments 1 and 2 was negatively correlated with aqueous DOM concentrations. By changing sediment characteristics and solution properties, the release of SOM significantly impacts polycyclic aromatic hydrocarbons (PAHs) sorption behaviors. These results help clarify the transport of PAHs in sediment-water systems.

Exposed mine tailing wastes with considerable heavy metals can release hazardous colloidal particles into soil under transient chemical and physical conditions. Two-layered packed columns with tailings above and soils below were established to investigate mobilization and transport of colloidal particles from metal-rich mine tailings into soil under transient infiltration ionic strength (IS: 100, 20, 2 mM) and flow rate (FR: 20.7, 41, and 62.3 mm h(-1)), with Cu and Pb as representatives of the heavy metals. Results show that the tailing particles within the colloidal size (below 2 μm) were released from the columns. A step-decrease in infiltration IS and FR enhanced, whereas a step-increase in the IS and FR restrained the release of tailing particles from the column. The effects of step-changing FR were unexpected due to the small size of the released tailing particles (220-342 nm, being not sensitive to hydrodynamic shear force), the diffusion-controlled particle release process and the relatively compact pore structure. The tailing particles present in the solution with tested IS were found negatively charged and more stable than soil particles, which provides favorable conditions for tailing particles to be transported over a long distance in the soil. The mobilization and transport of Cu and Pb from the tailings into soil were mediated by the tailing particles. Therefore, the inherent toxic tailing particles could be considerably introduced into soil under certain conditions (IS reduction or FR decrease), which may result in serious environmental pollution.

The present study investigated the nitrogen removal characteristics and metabolic pathway of bacteria in aquatic ecosystem, with a focus on heterotrophic nitrification and aerobic denitrification. The bacteria demonstrated significant heterotrophic nitrification and aerobic denitrification capacity. The highest ammonium-N, nitrate-N, and nitrite-N removal efficiencies were 95.31 ± 0.11%, 98.91 ± 0.05%, and 98.79 ± 0.09%, respectively. The Monod model was used to estimate the maximum rate of substrate utilization (Rmo) and the half-saturation concentration (Ks) for the two substrates, i.e., ammonium and nitrate. The kinetic coefficients were 3.34 mg/L/d (Rmo) and 30.59 mg/L (Ks) for ammonium-N, respectively, and 14.23 mg/L/d (Rmo) and 215.24 mg/L (Ks) for nitrate-N, respectively. The effects of initial nitrogen (ammonium-N or nitrate-N) concentration, temperature, and dissolved oxygen (DO) on nitrogen removal rate were investigated using response surface methodology (RSM), and the optimal conditions for nitrogen removal were determined. The principal nitrogen removal pathway of the bacteria was proposed as complete heterotrophic nitrification and aerobic denitrification, which was performed by six key genera: Arthrobacter, Pseudomonas, Rhodococcus, Bacillus, Massilia, and Rhizobium. Chryseobacterium and other denitrifying species may also reduce nitrification products (NOX−) via aerobic denitrification.

Although nitrogen (N) transformations have been widely studied under oxic or anoxic condition, few studies have been carried out to analyze the transformation accompanied with NO2−-N accumulation. Particularly, the control of mixed N species in N-transformation remains unclear in an oxic-anoxic transition zone (OATZ), a unique and ubiquitous redox environment. To bridge the gap, in this study, OATZ microcosms were simulated by surface water and sediments of a shallow lake. The N-transformation processes and rates at different NH4+-N/NO3−-N ratios, and NO2−-N accumulations in these processes were evaluated. N-transformation process exhibited a turning point. Simultaneous nitrification and denitrification occurred in its early stage (first 10 days, dissolved oxygen (DO) ≥ 2 mg/L) and then denitrification dominated (after 10 days, DO

In present study, batch and column tests were conducted to investigate the kinetic and thermodynamic characteristics of the adsorption and transport of 2,4,6-trinitrotoluene (TNT) in Chinese loess with specific focus on the role of inherent colloid particles. Batch tests showed that a lot of TNT was absorbed in suspended colloid particles, and its adsorption reached equilibrium after about 10 h, the adsorption process can be best-fit by the pseudo-second order kinetic and Freundlich model. The adsorption was spontaneous, endothermic process, implying the adsorbed TNT is likely to release from soil matrix. These portend that the adsorbed TNT has a potential to co-transport with inherent colloid particles in loess. The column tests identified the potential, and showed TNT transport had obvious retardation effect, which may be ascribed to the release and transport of inherent colloidal particles as a key carrier. These findings are helpful to evaluate the loess interception and antifouling performance.

Heterotrophic/autotrophic denitrification (HAD) is an effective approach to remove nitrate from contaminated groundwater. To improve its performance, easily degradable organics (methanol, ethanol, oxalic acid, and sodium acetate) and nano-zero valent iron (nZVI) were selected as co-electron donors for HAD, and their effectiveness in enhancing HAD to remove nitrate from simulated groundwater was evaluated. It was found that the removal efficiency of HAD to nitrate was significantly affected by the species of easily degradable organics as their different biological availability. Among the tested organics, ethanol-supported HAD system exhibited a better removal efficiency, and after 10 days reaction, it could achieve a high nitrate removal rate to 85.6% with an initial concentration of 90.94 mg/l, and at the end of the test (27 days), nitrate was almost completely removed in the interaction of heterotrophic denitrification (HD) and autotrophic denitrification (AD), and there was no nitrite and ammonium accumulation (

The efficiency of Fenton-like catalysis using nano zerovalent iron (nZVI) is limited by nZVI aggregation and activity loss due to inactive ferric oxide forming on the nZVI surface, which hinders electron transfer. A novel iron–carbon composite catalyst consisting of nZVI and granular activated carbon (GAC), which can undergo internal iron–carbon microelectrolysis spontaneously, was successfully fabricated by the adsorption–reduction method. The catalyst efficiency was evaluated in nitrobenzene (NB) removal via the Fenton-like process (H2O2-nZVI/GAC). The results showed that nZVI/GAC composite was good for dispersing nZVI on the surface of GAC, which permitted much better removal efficiency (93.0%) than nZVI (31.0%) or GAC (20.0%) alone. Moreover, iron leaching decreased from 1.28 to 0.58 mg/L after reaction of 240 min and the oxidation kinetic of the Fenton-like reaction can be described well by the second-order reaction kinetic model (R2 = 0.988). The composite catalyst showed sustainable catalytic ability and GAC performed as a medium for electron transfer in internal iron–carbon microelectrolysis to promote Fe2+ regeneration and Fe3+/Fe2+ cycles. Therefore, this study represents an important method to design a low cost and high efficiency Fenton-like catalyst in practical application.

The nature of dissolved organic matter (DOM) strongly influences heavy metal sorption onto soil. However, the constituents and structures of DOM change continuously as DOM is subjected to microbial decomposition and photodegradation at natural field scales. Thus, this study was designed to explore the effects of chemical changes of DOM on heavy metal sorption onto farmland soil in natural degradation. Fresh DOM (FDOM) and degraded DOM (DDOM) both were extracted from the straw of maize which was extensively planted in Loess Plateau, China. The characteristics of DOM were determined by Fourier transform infrared spectroscopy (FTIR), elemental analysis, excitation-emission matrix (EEM) fluorescence spectra, UV-visible spectra (UV-vis), nuclear magnetic resonance (NMR), and molecular weight analysis. Farmland loess soil in Loess Plateau and heavy metal Cu(II) which can easily form a complex with DOM in soil were employed to investigate the effects of DOM dynamic changes on Cu(II) sorption onto loess through batch tests. Compared with FDOM, DDOM changed significantly in composition including oxygen content, functional group species, aromatic properties, and molecular weight distribution. Oxygen content, aromaticity, and low-molecular-weight fraction ( 10 kDa) increased for DDOM. For these changes, the effects of FDOM and DDOM on heavy metal Cu(II) sorption onto loess were significantly different due to DOM-Cu(II) binding ability varied with FDOM degradation. FDOM promoted Cu(II) sorption onto loess at Cu(II) concentration below 400 mg l−1 while inhibited above 400 mg l−1, but DDOM always showed inhibition effects on Cu(II) sorption onto loess. Moreover, both the promotion and inhibition effects depended mainly on the initial concentrations and pH values of FDOM and DDOM. The results of the present study demonstrate that chemical characteristics of FDOM and DDOM are greatly diverse in components, functional group species, molecular weight distribution, etc. although they are from the same source. The apparent differences can explain their distinct effects on copper sorption onto loess soil. Hence, future researches are supposed to focus on the dynamic changes of DOMs when evaluating their influence on heavy metals environmental behaviors under actual conditions.

A composite combination of nano-zero valent iron (nZVI) and granular activated carbon (GAC) was introduced to achieve nitrate transformation into nitrogen with minimum byproducts via chemical reduction. The results showed that nitrate removal was significantly intensified and GAC was an excellent partner of nZVI chemical reduction. Both the dispersion and long-term reactivity of nZVI were improved, and more than 80% of nitrate was removed at 10 g/L nZVI/GAC composite within 90 min in steady state. The byproducts of nitrite and ammonium formed in reduction process were below 0.008 and 0.04 mg/L, respectively, and nitrogen was the main end product, which was confirmed by X-ray photoelectron spectroscopy analysis. Moreover, the kinetic model of nitrate reduction by nZVI/GAC composite can be described well by pseudo-first-order reaction kinetic (R2 = 0.984). The intensification is closely related to the dispersion effect of GAC matrix to nZVI and the promotion effect to electrons transfer between nZVI...

Soil/sediment organic matter (SOM) releasing with inherent dissolved organic matter (DOM) formed in solution was confirmed both in rhizosphere sediment (S) and uncultivated sediment (P) water systems, and correlations between SOM characteristics subject to sediment’s humification degree and its releasing effects on phenanthrene sorption were emphasized. The sequential SOM releasing evidenced by fluorescence and 1H-NMR profiles coupled with aqueous DOM solubilization was found to make sorption kinetics atypical and sorption capacity reduced, by comparing sorption results among sediments of different pretreatments. More importantly, the tested S was proved less humified with inherent DOM rich in microbial sources than P, and DOM affinity to phenanthrene was thus weakened (K doc values of 2.02–3.63 × 104 L kg−1), while the inhibitive effects of SOM releasing on sorption were strengthened, ascribing to the enlarged alterations of sediment characters, and particularly the amplified solubilization effects resulted from the larger proportion of soluble SOM and lower critical micelle concentration (5.66 mg L−1) of DOM. Moreover, relative contribution of DOM solubilization to the releasing effects enhanced from 0.67 for P to 0.78 for S relative to alterations of sediment characters. Consequently, mobility and exposure risk of polycyclic aromatic hydrocarbons would be enhanced in a plant-soil/sediment-water system.

In the Hebei Plain of North China, 70% of the inhabitants depend on groundwater for drinking water. Little is known regarding high-iodine concentrations in groundwater because there have been few systematic studies on high levels of iodine in groundwater in this region. To help identify the mechanisms that control the spatial distribution of iodine in groundwater, 61 samples of shallow groundwater and 161 samples of deep groundwater were collected along a sample section from Taihang Mountain to the Bo Sea. There were four pockets of high-iodine concentrations along the sample section. As the groundwater depth increased, the ratio of undetected iodine decreased, and the ratio of high-iodine concentrations increased. The high-iodine concentrations in the groundwater reflect the geological and sedimentary settings, and were mainly controlled by pH and Eh. Iodine concentrations were particularly high when the pH was between 7.3 and 8.5, and there was an inflection point at 150 μg/L in the curve of the relationship between iodine concentrations and Eh.

In this study, Fe(III)-cross-linked chitosan beads (Fe(III)-CBs) were synthesized and employed to explore the characteristics and primary mechanism of their hexavalent chromium (Cr(VI)) adsorption under low concentration Cr(VI) (less than 20.0 mg l −1 ) and a pH range from 2.0 to 8.0. Batch tests were conducted to determine the Cr(VI) adsorption capacity and kinetics, and the effects of pH and temperature on the adsorption under low concentration Cr(VI) and a pH range from 2.0 to 8.0. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy were employed to explore the characteristics of Fe(III)-CBs and their Cr(VI) adsorption mechanisms. The results show that, unlike the adsorption of other absorbents, the Cr(VI) adsorption was efficient in a wide pH range from 2.0 to 6.0, and well described by the pseudo-first-order model and the Langmuir–Freundlich isotherm model. The capacity of Cr(VI) adsorption by Fe(III)-CBs was as high as 166.3 mg g −1 under temperature 25°C and pH 6.0. The desorption test was also carried out by 0.1 mol l −1 NaOH solution for Fe(III)-CBs regeneration. It was found that Fe(III)-CBs could be re-used for five adsorption–desorption cycles without significant decrease in Cr(VI) adsorption capacity. Ion exchange was confirmed between functional groups (i.e. amino group) and Cr(VI) anions (i.e. CrO 4 2 − ). The amino-like functional groups played a key role in Cr(VI) distribution on the Fe(III)-CBs surface; Cr(VI) adsorbed on Fe(III)-CBs was partially reduced to Cr(III) with alcoholic group served as electron donor, and then formed another rate-limiting factor. So, Fe(III)-CBs has a good prospect in purifying low concentration Cr(VI) water with a pH range from 2.0 to 6.0.

The economic and effective application of surfactant enhanced remediation (SER) technology in a sediment-freshwater/saline water system was investigated by batch method using the combined effects of inorganic salt (sodium chloride, NaCl) and anionic surfactant (sodium dodecylbenzene sulfonate (SDBS)) on phenanthrene (PHE) removal via sorption by sediment. In all cases, PHE sorption followed a linear equation and partition as the main mechanism for PHE removal from aqueous solution. Separate addition of SDBS (2 mmol L−1) and NaCl (2–100 mmol L−1) moderately enhanced PHE removal, while with their combined addition the enhancement was substantial, and the removal efficiency achieved a peak of 92.8%. The combined effect expressed a synergy, and the sorption enhancement increased by factors of 2.7, 3.2 and 3.4 when compared with the sum of the separate entities at elevated salinity. This was because the sorbed SDBS, with increasing amount and a high packing conformation at elevated salinity, outcompeted aqueous SDBS for PHE partition. Moreover, a combination of 2 mmol L−1 SDBS and 2 mmol L−1 NaCl was optimal for PHE removal. Therefore, SER technology appears more effective for PHE removal in saline water than in freshwater, and preliminary water quality monitoring is essential for economic and efficient SER application.