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

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

A New Type of Ecological Floating Bed Based on Ornamental Plants Experimented in an Artificially Made Eutrophic Water Body in the Laboratory for Nutrient Removal.

In this study, a new type of ecological floating bed (NT-EFB) employing ornamental plants (either Spathiphyllum floribundum, Hydrocotyle sibthorpioids, Chlorophytum comosum or Peperomia obtusifolia) was designed to purify confected eutrophic water for 39 days. The growth characteristics of the plants and the effect of water treatment were analyzed and compared. The results showed that: (1) all the four ornamental plants examined survived well in the eutrophic water and an increase of plant biomass was observed; (2) the degradation efficiency of TOC by adding plants was about 85.0%; (3) the removal rate of NH4+-N was about 97.0%; (4) all the four plants can be used as floating bed plants to treat eutrophic water and Hydrocotyle sibthorpioids had the best growth characteristics and treatment efficiency. The study provides an adequate reference for the treatment of eutrophication using ecological floating beds.

Temporal-Spatial Evolution of Groundwater Nitrogen Pollution Over Seven Years in a Highly Urbanized City in the Southern China.

Understanding the temporospatial variation in nitrogen pollution in groundwater and the associated controlling factors is important to establish management practices that ensure sustainable use of groundwater. In this study, we analyzed inorganic nitrogen content (nitrate, nitrite, and ammonium) in 1164 groundwater samples from shallow, middle-deep, and deep aquifers in Zhanjiang, a highly urbanized city in the southern China. Our data span a range of 7 years from 2005 to 2011. Results show that shallow aquifers had been heavily contaminated by nitrate and ammonium. Temporal patterns show that N contamination levels remained high and relatively stable over time in urban areas. This stability and high concentration is hypothesized as a result of uncontrolled, illicit sewer discharges from nearby business facilities. Groundwater in urban land and farmland displays systematic differences in geochemical characteristics. Collectively, our findings demonstrate the importance of continuously monitoring groundwater quality and strictly regulating sewage discharges in Zhanjiang.

Distribution of Nitrate in Different Aquifers in the Urban District of Zhanjiang, China.

The study of NO3 (-) contamination in groundwater is becoming increasingly significant as high concentrations of NO3 (-) in groundwater can do damage to public health. Nitrate pollution in the shallow, middle-deep and deep aquifers in the urban district of Zhanjiang was studied using the ordinary Kriging interpolation method combined with hydrochemical and correlation analyses in 2011. The results showed NO3 (-) pollution was present in the shallow groundwater, with average concentrations of 47.43 mg/L and standard deviation of 50.92. Nitrate concentrations were lower in middle-deep and deep aquifers, with average concentrations of 2.36, 0.80 mg/L, and standard deviation of 6.23, 0.93, respectively. Nitrate was correlated with Na(+) + K(+), Mg(2+), Cl(-) and SO4 (2-) in the shallow aquifer, and the spatial distributions of NO3 (-) exhibited a same pattern with TDS in the shallow aquifer, the NO3 (-) pollution in the middle-deep and deep aquifers is less serious.

Algicidal effects of four Chinese herb extracts on bloom-forming Microcystis aeruginosa and Chlorella pyrenoidosa.

Extracts from four Chinese herbs, Phellodendri chinensis cortex, Artemisia annua L., Scutellaria baicalensis G. and Citrus reticulate peel were tested for their algicidal effects on Microcystis aeruginosa and Chlorella pyrenoidosa. The results showed that M. aeruginosa was more susceptible than C. pyrenoidosa. The growth of M. aeruginosa was significantly inhibited (p < 0.05) by the four herb extracts. Among the four herbs, P. chinensis cortex and S. baicalensis had the greatest inhibitory effects on M. aeruginosa, followed by C reticulate peel and A. annua. The 50% effective concentrations (EC50) of S. baicalensis, P chinensis cortex, C. reticulate peel and A. annua were 0.87, 0.88, 5.27 and 1 1.16 gherb L-1, respectively. The growth of C. pyrenoidosa was moderately inhibited by the herb extracts individually. The EC5o concentrations for S. baicalensis, P. chinensis cortex, C. reticulate peel andA. annua were 8.67, 11.67, 12.81 and 12.44 g herb L-1', respectively. Extract from S. baicalensis displayed stronger algicidal effects on C. pyrenoidosa than the other three herbs, although no lethal effect on C. pyrenoidosa was observed during the cultivation period. Compared with corresponding individual extract at the same dosage, the binary mixtures of the four herb extracts enhanced the algicidal effects on M. aeruginosa. The maximum inhibitory rates of all binary mixtures of the four herb extracts were all above 92% during the 10-day incubation. The results demonstrate that Chinese herbs, such as P. chinensis cortex or S. baicalensis and their combinations, could offer an effective alternative for mitigating outbreaks of harmful algal blooms in water bodies.

Influence of Geometric Characteristics on Water Flow and Solute Transport at Fracture Intersections.

Laboratory experiments and numerical simulations were performed to explore the influence of intersection geometry on fluid flow and solute transport in fractures. Fractures were engraved and sealed into an acrylic plate and two orthogonal intersections with different geometry were constructed. The effects of curvature and relative shear displacement at intersections on preferential flow and solute transport were investigated. By solving the Navier-Stokes (NS) equation, the fluid mixing and solute distribution were predicted. The results showed that the geometric characteristics at the intersection have a significant effect on the preferential flow and solute distribution. The results agreed well with the experimental results, in terms of flow direction, preferential flow rate, and heterogeneous solute distribution. With an increase in curvature, the flow difference between the two outlets increases gradually. Increasing curvature can reduce the preferential flow and weaken the inhomogeneity of solute distribution. An increase of relative shear displacement decreases the pressure gradient and flow rate at the entrance of the two branch fractures, and thereby increases preferential flow and inhomogeneity of solute distribution. The results provide a basis and reference for further exploring the relationship between the geometric characteristics of fracture intersections and flow behaviors.

The bimolecular reactive transport in heterogeneous porous media: Sub-diffusion in interpretation of laboratory experiment.

This present work consists of investigating the effects of particle size heterogeneity and flow rates on transport-reaction kinetics of CuSO4 and Na2EDTA2- in porous media, via the combination of a bimolecular reaction experiment and model simulations. In the early stages of transport, a peak is observed in the concentration breakthrough curve of the reactant CuSO4, related to the delayed mixing and reaction of the reactants. The numerical results show that an increase in flow rate promotes the mixing processes between the reactants, resulting in a larger peak concentration and a slighter tail of breakthrough curves, while an increase in medium heterogeneity leads to a more significant heavy tail. The apparent anomalous diffusion and heavy-tailing behavior can be effectively quantified by a novel truncated fractional derivative bimolecular reaction model. The truncated fractional-order model, taking into account the incomplete mixing, offers a satisfactory reproduction of the experimental data.

Behavior characteristics of bimolecular reactive transport in heterogeneous porous media.

In order to study the mechanism of bimolecular reactive solute transport in heterogeneous porous media, the chemical reaction (CuSO4 + Na2EDTA2-→CuEDTA2) was carried out by laboratory experiments and numerical simulation in heterogeneous porous media. Three different kinds of heterogeneous porous media (Sd2 = 1.72, 1.67 and 0.80 mm2) and flow rates (1.5, 2.5 and 5.0 mL/s) were considered. The increase of flow rate would promote the mixing between reactants, resulting in a greater peak value and a slighter "tailing" of product concentration, while the increase of medium heterogeneity would result in a more significant "tailing". It was found that the concentration breakthrough curves of reactant CuSO4 had a peak in the early stage of the transport, and the peak value increased with the increase of flow rate and medium heterogeneity. The concentration peak of CuSO4 was caused by the delayed mixing and reaction of reactants. The IM-ADRE (The advection-dispersion-reaction equation considering incomplete mixing) model could well simulate the experimental results. The simulation error of IM-ADRE model for the concentration peak of product was less than 6.15%, and the fitting accuracy for "tailing" increased with the increase of flow. The dispersion coefficient increased logarithmically with the increase of flow, and was negatively correlated to the heterogeneity of the medium. In addition, the dispersion coefficient of CuSO4 simulated by IM-ADRE model was one order of magnitude larger than that simulated by ADE model, indicating that the reaction promoted dispersion.

Prediction of post-Darcy flow based on the spatial non-local distribution of hydraulic gradient: Preliminary assessment of wastewater management.

Understanding high-velocity pollutant transport dependent on the large hydraulic gradient and/or heterogeneity of the aquifer and criteria for the onset of post-Darcy flow have attracted considerable attention in water resources and environmental engineering applications. In this study, a parameterized model is established based on the equivalent hydraulic gradient (EHG) which affected by spatial nonlocality of nonlinear head distribution due to the inhomogeneity at a wide range of scales. Two parameters relevant to the spatially non-local effect were selected to predict the development of post-Darcy flow. Over 510 sets of laboratory one-dimensional (1-D) steady hydraulic experimental data were used to validate the performance of this parameterized EHG model. The results show that (1) the spatial nonlocal effect of the whole upstream is related to the mean grain size of the medium, and the anomalous variation due to the small grain size implies the existence of the particle size threshold. (2) The parameterized EHG model can effectively capture the nonlinear trend that fails to be described by the traditional local form of nonlinear models, even if the specific discharge stabilizes at the later stages. (3) The Sub-Darcy flow distinguished by the parameterized EHG model can be equated to the post-Darcy flow, and then the criteria for the post-Darcy flow will be strictly distinguished under the premise of determining the hydraulic conductivity. The results of this study facilitate the identification and prediction of high-velocity non-Darcian flow in wastewater management and provide insight into mass transport by advection at the fine-scale.

A fractional derivative model for nuclides transport in heterogeneous fractured media.

Nuclide transport in fractured media involves the advection, dispersion, adsorption, etc. The dispersion and adsorption properties of the rock matrix have spatial variability, which results in an anomalous transport of nuclides. In this study, a time-fractional advection-diffusion equation (t-FADE) model is utilized to capture the sub-diffusion transport behavior with heavy-tail property, including the breakthrough curves (BTCs) of uranium and thorium transport in granite plates. Moreover, hydrodynamic dispersion of tritiated water, strontium and cesium in granite fractures are also studied. The results indicate that BTCs of nuclides transport in the granite fractures are unimodal and asymmetric. The decrease of the fractional order α reflects the stronger sub-diffusion. Furthermore, small initial velocity enhances sub-diffusion effect of nuclides and lengthens the breakout time of BTCs, which results in obvious heavy-tail phenomena. The analysis results demonstrate that the t-FADE model can accurately describe sub-diffusion behavior of nuclides transport. At last, the advantages of the t-FADE model in prediction and remediation of nuclides contamination are put forward.

Influence of aquifer heterogeneity on Cr(VI) diffusion and removal from groundwater.

Previous studies have indicated aquifer heterogeneity has an important influence on the removal of Cr(VI) in groundwater, but little attention is paid to the effects of aquifer heterogeneity during the process especially under conditions like actual groundwater temperature and hydraulic gradient in the field. Thus, in this study, in situ remediation of Cr(VI)-contaminated shallow groundwater in a sandbox was conducted, and the influences of the heterogeneous aquifer composed of coarse, medium, and fine sand on Cr(VI) diffusion and removal before and after emulsified vegetable oil (EVO) injection were investigated, under the conditions of 19±0.5 °C and hydraulic gradient 3‰. The results show that Cr(VI) diffused consistently with groundwater from top left to bottom right; Cr(VI) spread faster in the horizontal direction than in vertical direction, and the horizontal diffusion of Cr(VI) in coarse, medium, and fine sand was 0.054 m/day, 0.036 m/day, and 0.018 m/day, respectively; a high performance of EVO toward Cr(VI) removal by over 95% was mainly because different concentrations of microorganisms migrated among heterogeneous aquifers vertically and horizontally; compared with coarse and medium sand, fine sand, with a better adsorption capacity and a lower permeability, retained relatively more microorganisms, providing favorable conditions during the remediation; a stable and unified effective removal zone, similar to the shape of Æ© (approximately 1357.87 cm2), was ultimately formed downstream of the injection well.

Sensitivity analysis of factors influencing pollutant removal from shallow groundwater by the PRB method based on numerical simulation.

Permeable reactive barrier (PRB) is one of the most promising in situ treatment methods for shallow groundwater pollution. However, optimal design of PRB is very difficult due to a lack of comprehensive understanding of various complex influencing factors of PRB remediation. In this study, eight of the main factors of PRB, including hydraulic gradient I, permeability coefficient KPRB of PRB material, PRB length L, PRB width W, PRB distance from pollution source Dist., the ratio of the maximum adsorption capacity to Langmuir constant of PRB material Qmax/KL, the discharge rate of pollution source DR, and recharge concentration RC were investigated, to carry out the sensitivity analysis of PRB removal efficiency. The simulation experiments for Morris analysis were designed, and pollutant removal efficiency was numerically simulated by coupling MODFLOW and MT3DMS under two scenarios of high and low permeability and dispersivity. For a typical low permeability with low dispersity medium, the sensitivity ranking of factors from high to low is DR, RC, I, W, L, Dist., Qmax/KL, and KPRB, and for a typical high permeability with a high dispersity medium, the sensitivity ranking of factors from high to low is I, W, DR, Qmax/KL, L, RC, Dist., and KPRB. When considering multiple factors in PRB design, the greater the KPRB, L, W, Qmax/KL is, the higher the removal efficiency is; the greater the RC, I is, the lower the removal efficiency is. The rest factors remain ambiguous enhancement to removal efficiency.

Nitrate removal from groundwater in columns packed with reed and rice stalks.

Nitrate leaching contaminates groundwater. The objective of this study was to determine if reed and rice stalks could enhance denitrification and reduce nitrate leaching into groundwater. Artificial groundwater spiked with nitrate and field groundwater samples were tested in the columns in sand reactors packed with either reed or rice stalks. The maximum nitrate removal rates were determined to be 1.93 and 1.97 mg nitrate-N l(-1) h(-1), respectively, in the reed and rice stalk-packed columns. The maximum nitrate-nitrogen removal rate in reactors packed with reed stalk was 1.33 mg nitrate-N l(-1) h(-1) when experimented with natural groundwater. Chemical oxygen demand consumption was higher when rice stalk (176.1 mg l(-1)) was used as the substrate, compared to reed stalk (35.2 mg l(-1)) at the same substrate dosage. No nitrite accumulation was detected during the test. The results demonstrate that agricultural byproducts, such as reed and rice stalks, may be used as substrate amendments for enhanced denitrification in natural settings, such as lakeside lagoons, ditches or wetlands.

Keystone taxa shared between earthworm gut and soil indigenous microbial communities collaboratively resist chlordane stress.

Chlordane is an organochlorine pesticide that is applied extensively. Residual concentrations that remain in soils after application are highly toxic to soil organisms, particularly affecting the earthworm gut and indigenous soil microorganisms. However, response mechanisms of the earthworm gut and indigenous soil microorganism communities to chlordane exposure are not well known. In this study, earthworms (Metaphire guillelmi) were exposed to chlordane-contaminated soils to investigate their response mechanisms over a gradient of chlordane toxicity. Results from high-throughput sequencing and network analysis showed that the bacterial composition in the earthworm gut varied more significantly than that in indigenous soil microbial communities under different concentrations of chlordane stress (2.3-60.8 mg kg-1; p < 0.05). However, keystone species of Flavobacterium, Candidatus Nitrososphaera, and Acinetobacter remained stable in both the earthworm gut and bacterial communities despite varying degrees of chlordane exposure, and their relative abundance was slightly higher in the low-concentration treatment group (T1, T2) than in the high-concentration treatment group (T3, T4). Additionally, network analysis demonstrated that the average value of the mean degree of centrality, closeness centrality, and eigenvector centrality of all keystone species screened by four methods (MetagenomeSeq, LEfSe, OPLS-DA, Random Forest) were 161.3, 0.5, and 0.63, respectively, and that these were significantly higher (p < 0.05) than values for non-keystone species (84.9, 0.4, and 0.2, respectively). Keystone species had greater network connectivity and a stronger capacity to degrade pesticides and transform carbon and nitrogen than non-keystone species. The keystone species, which were closely related to the microbial community in soil indigenous flora and earthworm intestinal flora, could resist chlordane stress and undertake pesticide degradation. These results have increased understanding of the role of the earthworm gut and indigenous soil bacteria in resisting chlordane stress and sustaining microbial equilibrium in soil.

Application of spectral induced polarization for characterizing surfactant-enhanced DNAPL remediation in laboratory column experiments.

The widespread presence of entrapped dense non-aqueous phase liquid (DNAPL) in the subsurface poses a continuing challenge to groundwater remediation. Cost-effective and high-resolution subsurface characterization is a critical issue for further DNAPL recovery due to the complexity of DNAPL source zone architecture (SZA). Geophysical techniques provide a noninvasive, spatially continuous and cost-effective way for monitoring the DNAPL remediation process. In particular, the spectral induced polarization (SIP) method has shown great potential in environmental problems. In this study, we performed real-time SIP measurements on DNAPL contaminated soil in columns to quantitatively assess the ability of SIP method for monitoring surfactant-enhanced DNAPL remediation process. Chemical data was simultaneously collected during the remediation process to verify the results obtained by SIP method. Taking account into the variations of subsurface environment, we conducted a series of column flushing experiments under different flow rate, surfactant concentrations and fluid salinities. The results highlight that SIP method is able to effectively monitor the DNAPL remediation process, as well as to evaluate the remediation efficiency under different conditions. The variations in the flow rate, the concentration of surfactant and the salinity of pore water not only affect remediation effectiveness, but also have an impact on the SIP signatures. This study shows that SIP performs better for monitoring DNAPL remediation at a relatively low flow rate of ~ 0.4 m/d, low surfactant concentration of 5000 mg/L and high salinity of 1.0 S/m, with an error of saturation estimation (RMSES) <0.1.

Influence of recurrent rainfall and oxalic acid on phosphorus releasing from rocks phosphate in the Chaohu watershed, China.

In order to understand the spatial distribution characteristics, loss risk and leaching behaviors of phosphorous from exposed rocks in typical small-area of Chaohu watershed, phosphorus-rich rock was selected for conducting a series of column leaching experiments to investigate the phosphorus leaching. By simulating the intermittent cycle of acid rainfall, effects of oxalic acid on the weathering of phosphate rocks were studied. Total phosphorus contents, pH and phosphate leaching capacity from phosphorus rocks were tested in the presence of oxalic acid at different dry-wet intervals. The results indicated that the cumulative release of phosphorus increased first and then decreased with the duration of dry-wet intervals increasing. Four typical kinetic equations can describe phosphorus release from phosphate rocks with the action of oxalic acid. The best fitting models were the weight function and parabolic equation, with a mean correlation coefficient R2 of 0.9727 and 0.9941, respectively, which reached significance level. Total phosphorus (TP) leaching distribution in each column showed a tendency of gradually decreasing from top to bottom except for time interval of 5 d and 7 d. Occluded-bound P (Oc-P) is the dominant form in rocks. The change point value of rocks phosphorus is 4.11  mg kg-1 after intermittent leaching, and the phosphorus loss risk is relatively large in some rocks formations.

Can a Time Fractional-Derivative Model Capture Scale-Dependent Dispersion in Saturated Soils?

Time nonlocal transport models such as the time fractional advection-dispersion equation (t-fADE) were proposed to capture well-documented non-Fickian dynamics for conservative solutes transport in heterogeneous media, with the underlying assumption that the time nonlocality (which means that the current concentration change is affected by previous concentration load) embedded in the physical models can release the effective dispersion coefficient from scale dependency. This assumption, however, has never been systematically examined using real data. This study fills this historical knowledge gap by capturing non-Fickian transport (likely due to solute retention) documented in the literature (Huang et al. 1995) and observed in our laboratory from small to intermediate spatial scale using the promising, tempered t-fADE model. Fitting exercises show that the effective dispersion coefficient in the t-fADE, although differing subtly from the dispersion coefficient in the standard advection-dispersion equation, increases nonlinearly with the travel distance (varying from 0.5 to 12 m) for both heterogeneous and macroscopically homogeneous sand columns. Further analysis reveals that, while solute retention in relatively immobile zones can be efficiently captured by the time nonlocal parameters in the t-fADE, the motion-independent solute movement in the mobile zone is affected by the spatial evolution of local velocities in the host medium, resulting in a scale-dependent dispersion coefficient. The same result may be found for the other standard time nonlocal transport models that separate solute retention and jumps (i.e., displacement). Therefore, the t-fADE with a constant dispersion coefficient cannot capture scale-dependent dispersion in saturated porous media, challenging the application for stochastic hydrogeology methods in quantifying real-world, preasymptotic transport. Hence improvements on time nonlocal models using, for example, the novel subordination approach are necessary to incorporate the spatial evolution of local velocities without adding cumbersome parameters.

Increased lead and cadmium tolerance of Typha angustifolia from Huaihe River is associated with enhanced phytochelatin synthesis and improved antioxidative capacity.

Heavy metal contamination of water is an increasing environmental problem worldwide, and the use of aquatic plants for phytoremediation of heavy metal pollution has become an important subject of research. One key to successful phytoremediation is the identification of plants that are efficient at sequestering heavy metals. In this study, we examined the growth and heavy metal accumulation of Typha angustifolia and compared growth characteristics and tolerance mechanisms in plants from the Huaihe and Chaohu Rivers irrigated with different concentrations of lead (Pb) and cadmium (Cd). T. angustifolia from Huaihe River showed enhanced tolerance and accumulation of Pb and Cd and had greater biomass and more vigorous growth than the ecotype from Chaohu River. In addition, higher phytochelatin (PC) content and significantly higher superoxide dismutase and catalase activities were detected in T. angustifolia from Huaihe River than in T. angustifolia from Chaohu River. These findings suggest that high Pb and Cd accumulation and tolerance in T. angustifolia from Chaohu River is associated with its higher PC synthesis and better antioxidative capacity, and that the Huaihe ecotype of T. angustifolia might also be an efficient species for phytoremediation of Pb and Cd in water contaminated by heavy metals.

[Distribution and bioavailability of nitrogen and phosphorus species in the urban dusts from Hefei City].

To find out the distribution and bioavailability of nitrogen (N) and phosphorus (P) species in the urban dusts of Hefei City, 52 samples were collected from impervious areas with six different urban land-use types. The contents of ammonia nitrogen (NH4(+) -N), nitrate nitrogen (NO3(-) -N), exchangeable P (Ex-P), Al-bound P (Al-P), Fe-bound P (Fe-P), occluded P (Oc-P), Ca-bound P (Ca-P), detrital apatite P (De-P), organic P (Or-P) as well as total nitrogen (TN) and total phosphorus (TP) were measured by sequential extraction methods. The studies on spatial distribution, correlation and bioavailability of nitrogen and phosphorus species were made according to the analyzed data. The results show that the TN is composed mainly of organic nitrogen (Or-N) while the TP consists chiefly of inorganic phosphorus (IP) in the urban dusts of Hefei City, and the spatial variability of nitrogen and phosphorus species contents are greatly affected by the mode of urban land-use type. In addition, there are significant correlations among partial nitrogen and phosphorus forms in dusts. Corresponding to different urban land-use types such as industrial area, commercial area, residential area, educational area, traffic area and public landscapes and city squares, the average ratios of bioavailable nitrogen content (the sum of NH4(+) -N and NO3(-) -N) to TN are 8.87%, 9.60%, 6.68%, 9.37%, 8.20% and 8.17%, respectively, while the mean ratios of bioavailable phosphorus content (the sum of Ex-P, Al-P and Fe-P) to TP, are equal to 6.70%, 18.19%, 10.10%, 9.69%, 10.64% and 14.03%, respectively.

Acid tolerance of an acid mine drainage bioremediation system based on biological sulfate reduction.

The acid tolerance response of an AMD bioremediation system based on sulfate reduction was investigated. Efficient sulfate reduction was observed with a maximum sulfate reduction rate of 12.3±0.8 mg L(-1) d(-1) and easily available organic carbon was released during high acid treatment with an initial pH of 2.0. The rapid increase in sulfate reduction was observed when the extreme acid treatment with an initial pH of 1.0 was stopped. Column experiment on acid shock showed that efficient sulfate reduction was maintained while precipitation of Cu or Zn still occurred during extreme or high acid shock. More than 98% of Cu and 85% of Zn were removed in the high acid column experiment with influent pH of 2.0. The majority bacteria in the remediation system used for high acid drainage belonged to genera Clostridiaceae, Eubacterium, Pseudobutyrivibrio, and Clostridium. These findings showed high acid tolerance of the straw remediation system.