Adsorptive Removal of Low-Concentration Cr(VI) in Aqueous Solution by Mg-Al Layered Double Oxides.

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.

Adsorption Performance and Mechanism of Synthetic Schwertmannite to Remove Low-Concentration Fluorine in Water.

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.

Characteristics and metabolic pathway of the bacteria for heterotrophic nitrification and aerobic denitrification in aquatic ecosystems.

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.

NH4+-N/NO3--N ratio controlling nitrogen transformation accompanied with NO2--N accumulation in the oxic-anoxic transition zone.

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 < 2 mg/L), which were not greatly affected by the NH4+-N/NO3--N ratio, on the contrary, the transformation rates of NH4+-N and NO3--N were distinctly affected. The NH4+-N transformation rates were positively correlated with the NH4+-N/NO3--N ratio. The highest NO3--N transformation rate was observed at an NH4+-N/NO3--N ratio of 1:1 with organic carbon/NO3--N of 3.09. The NO2--N accumulation, which increased with the decrease in NH4+-N/NO3--N ratio, was also controlled by organic carbon concentration and type. The peak concentration of NO2--N accumulation occurred only when the NO3--N transformation rate was particularly low. Thus, NO2--N accumulation may be reduced by adjusting the control parameters related to N and organic carbon sources, which enhances the theoretical insights for N-polluted aquatic ecosystem bioremediation.

Batch Adsorption and Column Leaching Studies of Aniline in Chinese Loess Under Different Hydrochemical Conditions.

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.

Batch Adsorption and Column Transport Studies of 2,4,6-Trinitrotoluene in Chinese Loess.

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.

Effects of the Release of Soil Organic Matter on Phenanthrene Sorption by Sediments.

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.

Enhanced Fenton-like removal of nitrobenzene via internal microelectrolysis in nano zerovalent iron/activated carbon composite.

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.

Synergistic effects of inorganic salt and surfactant on phenanthrene removal from aqueous solution by sediment.

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.

Recent advances and future perspective on lignocellulose-based materials as adsorbents in diverse water treatment applications.

The growing shortage of non-renewable resources and the burden of toxic pollutants in water have gradually become stumbling blocks in the path of sustainable human development. To this end, there has been great interest in finding renewable and environmentally friendly materials to promote environmental sustainability and combat harmful pollutants in wastewater. Of the many options, lignocellulose, as an abundant, biocompatible and renewable material, is the most attractive candidate for water remediation due to the unique physical and chemical properties of its constituents. Herein, we review the latest research advances in lignocellulose-based adsorbents, focusing on lignocellulosic composition, material modification, application of adsorbents. The modification and preparation methods of lignin, cellulose and hemicellulose and their applications in the treatment of diverse contaminated water are systematically and comprehensively presented. Also, the detailed description of the adsorption model, the adsorption mechanism and the adsorbent regeneration technique provides an excellent reference for understanding the underlying adsorption mechanism and the adsorbent recycling. Finally, the challenges and limitations of lignocellulosic adsorbents are evaluated from a practical application perspective, and future developments in the related field are discussed. In summary, this review offers rational insights to develop lignocellulose-based environmentally-friendly reactive materials for the removal of hazardous aquatic contaminants.

Aromatic compounds releases aroused by sediment resuspension alter nitrate transformation rates and pathways during aerobic-anoxic transition.

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.

Fabrication of Electrospun Xylan-g-PMMA/TiO2 Nanofibers and Photocatalytic Degradation of Methylene Blue.

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.

Nitrogen species control the interaction between NO3--N reduction and aniline degradation and microbial community structure in the oxic-anoxic transition zone.

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.

Iodine enrichment and the underlying mechanism in deep groundwater in the Cangzhou Region, North China.

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.

Dissolved oxygen disturbs nitrate transformation by modifying microbial community, co-occurrence networks, and functional genes during aerobic-anoxic transition.

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 <2 mg/L) during aerobic-anoxic transition, and NO2--N accumulation was more significant during the anoxic stage, consistent with the result obtained under constant DO conditions. These NO3--N transformation characteristics were not affected by other environmental factors, indicating the important role of DO in NO3--N transformation during aerobic-anoxic transition. Changes in DO provoked significant alterations in microbial diversity and abundance of functional bacteria dominated by Massilia, Bacillus, and Pseudomonas, leading to the variation in NO3--N transformation. Co-occurrence network analysis revealed that NO3--N transformation was performed by the interactions between functional bacteria including symbiotic and competitive relationship. In the presence of oxygen, these interactions accelerated the NO3--N transformation rate, and bacterial metabolization proceeded via increasingly varied pathways including aerobic and anoxic respiration, which was demonstrated through predicted genes. The higher relative abundance of genes narG, narH, and napA suggested the occurrence of coupled aerobic-anoxic denitrification in the early stage. NO3--N transformation rate decreased accompanied by a significant NO2--N accumulation with the weakening of coupled aerobic-anoxic denitrification during aerobic-anoxic transition. Structural equation modeling further demonstrated the relationship between DO and NO3--N transformation. DO affects NO3--N transformation by modifying microbial community, bacterial co-occurrence, and functional genes during aerobic-anoxic transition.

Changes in the fluorescence intensity, degradability, and aromaticity of organic carbon in ammonium and phenanthrene-polluted aquatic ecosystems.

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 (A 254)), 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), A 254 (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.

The correlation analyses of bacterial community composition and spatial factors between freshwater and sediment in Poyang Lake wetland by using artificial neural network (ANN) modeling.

As one of the most important components of the lake ecosystem, microorganisms from the freshwater and sediment play an important role in many ecological processes. However, the difference and correlation of bacterial community between these two niches were not clear. This study investigated the diversity of microbial community of freshwater and sediment samples from fifteen locations in Poyang Lake wetland. The correlation between the bacterial community and physicochemical property of Poyang Lake wetland was analyzed by artificial neural network (ANN). Our results demonstrated that the freshwater and sediment bacterial community were dominated by groups of the Bacteroidetes (23.33%) and ß-Proteobacteria (22.54%) separately, whereas, Canalipalpata, Bacillariophyta, Gemmatimonadetes, and Verrucomicrobia were detected in freshwater niches only. Phylogenetic analysis further indicated that bacterial composition in freshwater significantly differed with the sediment niches. There are 34 unique species accounted for 85% in fresh water samples and 28 unique species accounted for 82% in sediment samples. Cluster analysis further proved that all the samples from freshwater niches clustered closely together, far from the rest sediment samples. ANN analysis revealed that the freshwater with high N and P nutrients will greatly increase the diversity of the bacterial communities. In general, both environmental physicochemical properties, not each factor independently, contributed to the shift in the bacterial community structure. The five tributaries (Gan, Fu, Xin, Rao, Xiu Rivers) play a vital role in shaping the bacterial communities of Poyang Lake. This study provides new insights for understanding of microbial community compositions and structures of Poyang Lake wetland.

A lab-scale study on heterotrophic nitrification-aerobic denitrification for nitrogen control in aquatic ecosystem.

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.

Effects of ethanol on benzene degradation under denitrifying conditions.

As a popular fuel oxygenate, ethanol frequently co-occurs with petroleum hydrocarbons, including benzene, in groundwater that is contaminated by gasoline. Anaerobic pathways have been identified in benzene biodegradation. Limited reports focus on denitrifying degradation of benzene; however, the role of ethanol in this pathway is unknown. This study investigated the effects of ethanol on benzene degradation under denitrifying condition by using groundwater and sediment samples collected from locations with known history of benzene contamination. Results indicate that benzene can be biodegraded under denitrifying conditions. When concentrations of nitrate were in the range of 480-920 mg/L, there is a critical value in ethanol concentration:Ethanol at concentration less than the critical value enhanced the denitrifying degradation of benzene over a period of time; in contrast, ethanol at concentration higher than the critical value, which was degraded before benzene, demonstrated an inhibitory effect. And the critical value varied with nitrate concentration. It appears that the role of ethanol may be closely associated with its own and nitrate concentrations. Two mathematical equations were established based on the data and may be used to determine if ethanol presents an enhancing or inhibitory effect on denitrification of benzene. The roles of ethanol in COD/NO(3) (-)-N and the subsequent denitrification of benzene were also studied. An optimal COD/NO(3) (-)-N ratio of 1.32 was obtained for this testing system, in which the highest rate of benzene degradation can be achieved under denitrifying conditions.

Classification of groundwater contamination in Yuxi River Valley, Shaanxi Province, China.

This study investigated groundwater contamination in the Yuxi River Valley in northern Shaanxi Province, one of largest energy resource centers in China. Groundwater samples collected from 129 locations in the Yuxi River Valley area were analyzed and evaluated to establish the local groundwater quality zonings. Results indicate that groundwater in the Yuxi River Valley is contaminated, and the dominant contaminants in the groundwater are ammonium (NH(4)(+)) and nitrite (NO(2)(-)). Maximal concentration of NH(4)(+) was detected at 0.019 and 3.50 mg/L in the samples collected up-gradient and down-gradient, respectively, of the segment of Yuxi River that flows through Yulin City. Concentration of NO(2)(-) was detected at 0.0015 and 1.522 mg/L, respectively from the same samples. Zones I through IV, from non-polluted to seriously polluted, were identified for groundwater quality in the Yuxi River Valley. We attribute the groundwater contamination in the Yuxi River valley to sources in the Yulin township, presumably its wastewater discharge.