Metabolism Of Sulfate Reducing Bacteria Research Articles

Accelerated microbiologically influenced corrosion of copper by sulfate‐reducing bacterium Desulfovibrio desulfovibrio

AbstractThe corrosion behavior and electrochemical damage mechanisms induced by sulfate‐reducing bacteria (SRB) on copper (Cu) were investigated in this study. Electrochemical impedance spectroscopy revealed that SRB accelerated the corrosion of Cu, albeit with a mitigating effect observed due to the formation of a protective and dense biofilm. However, upon the rupture of this protective film, the corrosion tendency of Cu significantly increased. Surface analysis corroborated these findings, with the predominant corrosion product identified as Cu2S, a result further supported by thermodynamic calculations. The accelerated corrosion of Cu was primarily attributed to the physiological metabolism of SRB, which generates hydrogen sulfide as the principal agent driving corrosion processes.

Desulfovibrio-induced gauzy FeS for efficient hexavalent chromium removal: The influence of SRB metabolism regulated by carbon source and electron carriers

Biosynthetic metal sulfides showed great application prospects in the environmental treatment against high-valence metal pollutants. However, the efficiency of biosynthesis, agglomeration during the reaction process, and the formation of the passivation layer during the reduction process were always the important factors restricting its development. This study explored the composition of the culture medium to promote the growth of highly corrosive sulfate-reducing bacteria (SRB) and its metabolism to produce FeS nanoparticles (NPs). The results showed that reducing the carbon source (CS) and adding electron carriers in the culture medium effectively promoted the production of small, dispersed, and loose FeS NPs in cells. At pH = 7, 24 °C and 10 min reaction time, 0.1 g/L FeS NPs produced by SRB under the conditions of 10 % CS with 10 ppm cytochrome c medium could achieve 100 % removal efficiency of 1 mM hexavalent chromium (Cr(VI)). Under this condition, FeS NPs could be produced by intracellular metabolism in SRB cells, and environmental factors such as pH, metal cations, and Cl− had little effect on the removal of Cr(VI) by this FeS NPs. The surface proteins of FeS NPs significantly enhanced their antioxidant properties. After 7 days of natural environment exposure, the Cr(VI) removal efficiency of FeS NPs was only reduced by 16 % compared with the initial sample. This work provided an in-depth understanding of Cr(VI) removal by SRB biosynthesis of FeS and contributes to the widespread application of FeS in the future.

Study on mechanism underlying the acceleration of pitting corrosion of B30 copper–nickel alloy by sulfate-reducing bacteria in seawater

In this paper, the relationship between the pitting corrosion formation of B30 copper–nickel (CuNi) alloy and the metabolism of sulfate-reducing bacteria (SRB) was investigated. Combined with the influence of temperature during the actual operation of the cooling systems, the evolution law of the alloy passivation film was analyzed, and the mechanism of SRB promoting the accelerated development of B30 CuNi alloy pitting corrosion was revealed. The results show that SRB significantly promoted the pitting formation and development of B30 CuNi alloy. The maximum pitting depth was 3.9 μm in the sterile system and 15.3 μm with SRB, which was 3.9 times higher than that of sterile system. The loose porous Cu2S film formed by SRB metabolites and copper matrix was easily penetrated by corrosive anions, which promoted copper dissolution and led to pit nucleation. The sulfide adsorbed on the surface prevented or delayed the passivation of B30 CuNi alloy by blocking the adsorption site of O atom, and the corrosion nuclei continued to grow. The non-uniformity caused by the film peeling accelerated the longitudinal development of pitting corrosion, and the expansion and coalescence of adjacent pits caused the transverse development of pitting corrosion. Temperature had a certain influence on the SRB and the formation of B30 CuNi alloy passivation film. The passivation film was formed rapidly at 50 °C with poor quality and the passivation property of Cu2O film was weakened. With the increase of temperature, the pitting potential of sterile system negative shifted from 0.447 to 0.360 V (vs. SCE), while SRB system from 0.340 to 0.198 V (vs. SCE), and the pitting resistance decreased. The passivation film with defects and the Cu2S reduced the barrier efficiency of the film and accelerated the pitting corrosion of B30 CuNi alloy.

Desulfovibrio desulfuricans induced corrosion of welded joint in X80 pipeline steel below delaminated coating

Buried pipelines are an important tool for long-distance oil and gas transportation. Welded joints are the weak components of buried pipelines. Interestingly, the biocorrosion degree of the heat affected zone (HAZ) of the welded joint is the lowest in mediums. However, there is no report on the biocorrosion of the welded joints when the protective coating is delaminated. In this paper, sulfate-reducing bacteria (SRB) corrosion of X80 steel welded joint was studied below delaminated coating. Results showed that SRB corrosion of the welded joint was selective at the opening of the delaminated coating, and such selected SRB corrosion gradually faded along the direction from the opening to the far end. At the far end below the delaminated coating, the corrosion of the welded joint was related more to its microstructural characteristics rather than to the SRB metabolism process. The concentration decrease of the SRB cells was responsible for the gradual decrease of the SRB corrosion of the welded joint below the delaminated coating.

Remediation of Acid Mine Drainage in the Haizhou Open-Pit Mine through Coal-Gangue-Loaded SRB Experiments

To address the pollution problem of acid mine drainage (AMD) characterized by high concentrations of Fe2+, Mn2+, and SO42−, a combination of coal gangue (CG) and sulfate-reducing bacteria (SRB) was employed. The effects of coal-gangue dosage, SRB inoculation concentration, and temperature on AMD treatment with coal-gangue-loaded SRB were determined through single-factor experiments and response surface methodology (RSM) experiments. By considering the principles of adsorption isotherms, adsorption kinetics, and reduction kinetics, the removal mechanisms of SO42−, Fe2+, and Mn2+ in AMD using coal gangue-loaded SRB in the the Haizhou open-pit mine was revealed. The results showed that the overall effectiveness of the four types of coal-gangue-loaded SRB in repairing AMD was as follows: 3# CG-loaded SRB > 2# CG-loaded SRB > 1# CG-loaded SRB > 4# CG-loaded SRB, with coal-gangue-loaded SRB in the the Haizhou open-pit mine showing the best performance. According to the RSM test, the optimum conditions for repairing AMD with coal-gangue-loaded SRB in the open-pit mine were a coal-gangue dosage of 52 g, SRB inoculation concentration of 11.7%, and temperature of 33.4 °C. The order of factors affecting the removal of SO42− and Fe2+ from AMD by SRB loaded on coal gangue was SRB inoculation concentration > temperature > coal-gangue dosage. For Mn2+, the order of influence was temperature > SRB inoculation concentration > coal-gangue dosage. In the process of repairing Fe2+ with coal-gangue-loaded SRB in the the Haizhou open-pit mine, the biological activity metabolism of SRB played a leading role, while the adsorption isotherm of Mn2+ followed the Freundlich model. The adsorption kinetics of coal-gangue-loaded SRB in the the Haizhou open-pit mine for Fe2+ and Mn2+ in AMD conformed to Lagergren’s second-order kinetic model, while the reduction kinetics of SO42− conformed to a first-order reaction model.

Effects of cathodic protection potential on microbiologically induced corrosion behavior of X70 steel in a near-neutral pH solution

Sulfate reducing bacteria (SRB) are considered as one of the main causes for the failures of buried metal pipes. Although many researchers reported that more negative cathodic protection potential was required in environments containing SRB, SRB would increase the concentration of hydrogen adsorbed on steel surface and thus lead to hydrogen embrittlement. In the study, the optimum cathodic protection (CP) potentials of X70 steel in bacterial and sterile media were evaluated with electrochemical impedance spectroscopy. The morphology and composition of corrosion products were characterized by a scanning electron microscope (SEM), an energy dispersion x-ray spectrometer (EDS), and an x-ray photoelectron spectrometer (XPS). The corrosion morphology of X70 steel in NS4 medium was pits and the corrosion in the bacterial medium was more serious than that in the sterile medium. The corrosion products of X70 steel were FeOOH and Fe2O3 in the sterile medium, whereas its corrosion products in the bacterial medium were FeOOH and FeS. When CP potential was −775 mV, SRB growth was promoted and the optimal protection effect on X70 steel was achieved in the bacterial NS4 medium. Pits were still observed under the biofilm and the corresponding corrosion mechanism was extracellular electron transfer (EET). When CP potential was −875 mV, X70 steel realized the optimal protection in the sterile NS4 solution. However, CO2 hydrolysis and SRB metabolism in the bacterial medium resulted in hydrogen-induced pits. When CP potential was −1025 mV, the growth of SRB was inhibited and severe hydrogen evolution corrosion occurred on X70 steel in bacterial and sterile NS4 media. The optimal CP potential for pipeline steel in the sterile medium may lead to hydrogen corrosion in the bacterial medium when H+ concentration was high.

Corrosion behaviors of 2205 duplex stainless steel in biotic and abiotic NaCl solutions

Biofilms on metal surfaces are important in microbiologically influenced corrosion processes. In this study, the corrosion behaviors of 2205 duplex stainless steel (DSS) in 3.5% biotic and abiotic NaCl solutions were explored with scanning Kelvin probe force microscope (SKPFM), electrochemical techniques, and X-ray photoelectron spectroscope (XPS). The results of SKPFM showed that the development process of sulfate-reducing bacteria (SRB) biofilms on 2205DSS was a slow and dynamic process and SRB preferentially attached to the ferrite phase. In the bacterial medium, the pittings of 2205DSS were narrower and deeper and the occlusion degree of pittings was aggravated. XPS and electrochemical measurement results showed that 2205DSS passivation film was sulfureted and that the corrosion current density was increased significantly by SRB metabolism. The voltaic potential measurement results indicated that the biofilm increased the potential difference on the steel surface. In the logarithmic and stable growth phases of SRB, the corrosion mechanism of 2205DSS was dominated by cathode depolarization. In the decline phase of SRB, starved SRB was more corrosive and the corrosion mechanism of 2205DSS was dominated by the extracellular electron transfer process, in which electrons were directly provided by ferrite.

Effect of SRB and Applied Potential on Stress Corrosion Behavior of X80 Steel in High-pH Soil Simulated Solution.

The effect of SRB and applied potential on the stress corrosion sensitivity of X80 pipeline steel was analyzed in high-pH soil simulated solution under different conditions using a slow strain rate tensile test, electrochemical test, and electronic microanalysis. The experimental results showed that X80 pipeline steel has a certain degree of SCC sensitivity in high-pH simulated solution, and the crack growth mode was trans-granular stress corrosion cracking. In a sterile environment, the SCC mechanism of X80 steel was a mixture mechanism of anode dissolution and hydrogen embrittlement at −850 mV potential, while X80 steel had the lowest SCC sensitivity due to the weak effect of AD and HE; after Sulfate Reducing Bacteria (SRB) were inoculated, the SCC mechanism of X80 steel was an AD–membrane rupture mechanism at −850 mV potential. The synergistic effect of Cl− and SRB formed an oxygen concentration cell and an acidification microenvironment in the pitting corrosion pit, and this promoted the formation of pitting corrosion which induced crack nucleation, thus significantly improving the SCC sensitivity of X80 steel. The strong cathodic polarization promoted the local corrosion caused by SRB metabolism in the presence of bacteria, whereby the SCC sensitivity in the presence of bacteria was higher than that in sterile conditions under strong cathodic potential.

The Impact of Ecological Restoration on Biogeochemical Cycling and Mercury Mobilization in Anoxic Conditions on Former Mining Sites in French Guiana.

Successive years of gold mining in French Guiana has resulted in soil degradation and deforestation leading to the pollution and erosion of mining plots. Due to erosion and topography, gold panning sites are submitted to hydromorphy during rainfall and groundwater increases. This original study focused on characterizing the impact of hydromorphic anaerobic periods on bio-geochemical cycles. We sampled soil from five rehabilitated sites in French Guiana, including sites with herbaceous vegetation and sites restored with fabaceous plants, Clitoria racemosa (Cli) mon-oculture, Acacia mangium (Aca) monoculture, Clitoria racemosa and Acacia mangium (Mix) bi-culture. We conducted mesocosm experiments where soil samples were incubated in anaerobic conditions for 35 days. To evaluate the effect of anaerobic conditions on biogeochemical cycles, we measured the following parameters related to iron-reducing bacteria and sulfate-reducing bacteria metabolism throughout the experiment: CO2 release, carbon dissolution, sulphide production and sulphate mobilization. We also monitored the solubilization of iron oxyhydroxides, manganese oxides, aluminum oxides and mercury in the culture medium. Iron-reducing bacteria (IRB) and sulfate-reducing bacteria (SRB) are described as the major players in the dynamics of iron, sulfur and metal elements including mercury in tropical environments. The results revealed two trends in these rehabilitated sites. In the Aca and Mix sites, bacterial iron-reducing activity coupled with manganese solubilization was detected with no mercury solubilization. In herbaceous sites, a low anaerobic activity coupled with sulphide production and mercury solubilization were detected. These results are the first that report the presence and activity of iron- and sulfate-reductive communities at rehabilitated mining sites and their interactions with the dynamics of metallic elements and mercury. These results report, however, the positive impact of ecological restoration of mining sites in French Guiana by reducing IRB and SRB activities, the potential mobility of mercury and its risk of transfer and methylation.

Basic Bioelement Contents in Anaerobic Intestinal Sulfate-Reducing Bacteria

The monitoring of trace metals in microbial cells is relevant for diagnosis of inflammatory bowel disease (IBD). Sulfate-reducing bacteria (SRB) represent an important factor in the IBD development. The content of trace metals in bacterial cells may reflect the functioning of the enzyme systems and the environmental impact on the occurrence of SRB. The aim of our research was to compare the content of trace elements in the cells of SRB cultures isolated from fecal samples of patients with IBD and healthy people. The contents of 11 chemical elements in the bacterial cells of SRB were analyzed by the inductively coupled plasma-mass-spectrometry (ICP-MS) method. Significant changes in the content of calcium, zinc, magnesium, potassium, and iron were observed in patients with IBD compared to healthy individuals. Through a principal component analysis (PCA), a total variability of 67.3% in the difference between the samples was explained. The main factors influencing the total variability in the bacterial cells of SRB isolated from patients suffering from IBD were the content of the micro- and trace elements, such as manganese (with power 0.87), magnesium and cobalt (0.86), calcium (0.84), molybdenum (0.81), and iron (0.78). Such changes in the elemental composition of SRB under different conditions of existence in the host may indicate adaptive responses of the microorganisms, including the inclusion of oxidative stress systems, which can lead to changes in SRB metabolism and the manifestation of parameters of IBD in humans. The use of PCA might make it possible in the future to predict the development and ratio of SRB in patients with various diseases.

Genotypic, physiological and biochemical features of Desulfovibrio strains in a sulfidogenic microbial community isolated from the soil of ferrosphere

The purpose of this work was the isolation of the predominant representatives of sulfate-reducing bacteria (SRB) of the sulfidogenic microbial community separated from the soil ferrosphere and the examination of their morphological, physiological, biochemical and genotypic peculiarities, the evaluation of some physiological processes under co-culturing with their satellite species Anaerotignum propionicum. During the study two isolates of sulfatereducing bacteria NUChC SRB1 and NUChC SRB2 were obtained from sulfidogenic microbial community isolated from soil ferrosphere on Postgate’s “B” medium and their belonging to different strains (using ISSR-PCR method) was proved. As a result of molecular-genetic analysis of the strains, a 16S rRNA gene fragments of 613 bp and 522 bp were amplified and sequenced. The strains were identified as Desulfovibrio oryzae by the complex of microbiological, physiological and biochemical features and on the basis of 16S rRNA gene sequences (phylogenetic analysis). The 16S rRNA gene sequences were submitted in GenBank as MT102713 (NUChC SRB1) and MT102714 (NUChC SRB2). The co-cultivation of isolated SRB strains with A. propionicum NUChC Sat1 strain (in the absence of electron donors, the presence of sulfates and yeast extract) showed the formation of sulfur-reducing bacteria of hydrogen sulfide, which was not observed during their mono-cultivation. In this case, the phenomenon of syntrophy probably takes place- co-growth on the nutrient substrate, and the electron donor appears due to the use of the yeast extract compounds by the NUChC Sat1 strain. Therefore, in the sulfidogenic community isolated from the soil ferrosphere, there is a mutual growth of the association of bacteria D. oryzae and A. propionicum, which is caused by trophic interaction. Possibly the contribution of these associated bacteria to the corrosion process lies in the utilization of hydrogen (D. oryzae) and the formation of substrate products of SRB metabolism (hydrogen and organic acids), which are both corrosive compounds (A. propionicum). Without a doubt the corrosion process involving this association needs further investigation.

A Mathematical Model to Facilitate Study of Hydrogen Cross-feeding by the Human Colonic Microbiota (P13-036-19)

ObjectivesThe role of hydrogen cross-feeding microbes in digestive function is unclear, but several such organisms have been implicated in functional gastrointestinal disorders. In order to study the dynamics of hydrogen cross-feeders, we require a computational model that provides realistic predictions of food metabolism and metabolite cross-feeding by the human intestinal microbiota. The goal is to produce a model that captures the relationships between the concentrations of all major metabolites in the colon and the microbial population. MethodsWe adapted the existing model microPop [Kettle et al., Methods in Ecology and Evolution, 9, 399–409, (2017)] to the human colonic environment. The model divides the microbiota into functional groups, determined by the metabolites that they feed upon and produce. We introduced alterations to the bacterial functional groups in the original model, including the addition of sulphate-reducing bacteria (SRB), which have an important role in hydrogen cross-feeding. Further adaptions included running the model through three sequentially connected compartments representing the proximal, transverse and distal colon. To enhance the applicability of the model to the colon, the production of sulphated colonic mucins by the host was included. ResultsThe model predicts comparable conditions to those found in experimental work. The sulphated mucins were degraded by saccharolytic members of the microbiota to smaller molecules, including hydrogen, short-chain sugars and free sulphate. These metabolites formed a food source for hydrogen cross-feeders, including SRB, as has been seen in rodent models. Cross-feeding for sulphate released from mucins may be more significant in the metabolism of SRB than dietary sulphate. ConclusionsThe model may be used to make predictions about the consequences of certain diets on the production of microbial-derived metabolites and the composition of the microbiota. It also provides predictions about the availability of nutrients in the colon to the host. Finally, the model allows us to perform theoretical studies on the role of hydrogen cross-feeders and the metabolites they secrete in digestive function. Funding SourcesThis work was funded by the Riddet Institute, a New Zealand Centre of Research Excellence.

电子供体对硫酸盐还原菌生长代谢的影响

电子供体对硫酸盐还原菌生长代谢的影响

Study of the Fe(II-III) hydroxysalts transformation according to the pH and the concentration of the ions present

Sulphated green rust, GR (SO4 2- ), is one of the main corrosion products of carbon steel in marine environments. It is Fe (II)-Fe(III) hydroxylsalt in sheets, consisting of alternating layers of iron-hydroxide type Fe(OH)2 , loaded positively due to the presence of the cations Fe(III) and negative interlayers consisting of anions and water molecules. This compound is strongly associated with the metabolism of sulphate-reducing bacteria, and can also evolve under cathodic protection. Thus, recently, GR (CO3 2- ) has been detected in place of GR (SO4 2- ) on already corroded ordinary steel, newly subjected to cathodic protection. This presence is due to the pH and[SO4 2−] [HCO3 − ⁄ ] conditions imposed by the cathodic protection. In this paper, we chemically synthesize sulfated and carbonate green rust in a chlorinated medium; we then study their respective transformation according to the concentration [SO4 2- ] / [HCO3 - ] ratio and pH. Our results show that from a GR (SO4 2- ), GR (CO3 2- ) is formed from a pH ≥8.2 for [SO4 2- ] / [HCO3 - ] = 12 and without any change in pH for [SO4 2- ] / [HCO3 - ] <12. Whereas from GR (CO3 2- ), GR (SO4 2- ) is formed for [SO4 2- ] / [HCO3 - ] > 1 without any change in pH.

Field-scale bioremediation of arsenic-contaminated groundwater using sulfate-reducing bacteria and biogenic pyrite

This research demonstrates that biogenic pyrite formed by stimulation of indigenous sulfate-reducing bacteria (SRB) in a natural aquifer can remove dissolved arsenic from contaminated groundwater under strongly reducing conditions. SRB metabolism led to the precipitation of biogenic pyrite nanoparticles capable of sorbing and co-precipitating arsenic. The field site is an industrial site where shallow groundwater in an unconfined sandy aquifer is contaminated by arsenic. Therefore, biodegradable organic carbon, ferrous iron, sulfate, and fertilizer were injected into groundwater and SRB metabolism began about 1 week later. Microscopic, X-ray diffraction, X-ray fluorescence, and electron microprobe analyses confirm the bio-mineralization of pyrite and over time, pyrite nanoparticles grew to form well-formed crystals (1–10 µm in diameter) or spherical aggregates that contain 0.05–0.4 wt. % arsenic, indicative of their capacity to sequester arsenic. Consequently, dissolved arsenic decreased from its initial concentration of 0.3–0.5 mg/L to below the regulatory clean-up standard for the site of 0.05 mg/L in three downgradient wells in a matter of weeks after injection. The main sequestration stage, with total arsenic removal rates greater than 90%, lasted for at least 6 months until the arrival and mixing of untreated groundwater from upgradient. Treated groundwater with most active bacterial sulfate reduction became enriched in heavy 34S (range from 2.02 to 4.00 ‰) compared to unaffected well water (0.40–0.61 ‰). One to three orders of magnitude increases in SRB cells were observed in treated wells for at least 2 months after injection. For a full-scale remediation, the injection of solution should start at positions hydrologically upgradient from the major plume and proceed downgradient. If needed, aquifers may be repeatedly amended with biodegradable organic carbon to reestablish the reducing conditions that favor arsenic sequestration.

Influence of thermophilic sulfate-reducing bacteria and deposited CaCO3 on the corrosion of water injection system

Abstract Herein, a schematic model was established to assess the combined effect of deposited CaCO3 and thermophilic sulfate-reducing bacteria (SRB), at high CO2 and low O2 dissolution levels on the corrosion behavior and growth of corrosion scale on X65 pipeline carbon steel. Field emission scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction, confocal laser scanning microscopy, open circuit potential, and electrochemical impedance spectroscopy were used to characterize the corrosion pattern of water injection pipe. The results showed that a synergistic effect exists between CaCO3 and thermophilic SRB, both uniform and localized corrosion of CaCO3-coated X65 steel were promoted when inoculated with SRB. The corrosion process was comprised of three stages depending on the metabolism of SRB.

Corrosion behavior of the chitosan‑zinc composite films in sulfate-reducing bacteria

Sulfate-reducing bacteria (SRB) are one of the chief inducers of microbiologically influenced corrosion in marine environment. In our previous work, a novel chitosan‑zinc film was electrodeposited and found to be effectively antibacterial, so research on the corrosion behavior of chitosan‑zinc films in SRB medium is highly significant for estimating the films to be applied in real-sea environment. In this paper, detection of SRB metabolism, electrochemical methods and surface analyses were performed to clarify the corrosion behavior. During 6 d exposure in SRB, obvious inhibition on SRB growth and metabolism were found by monitoring the environment corrosive factors. By calculating the corrosion rate and analyzing surface morphologies, chitosan‑zinc films showed relatively high corrosion resistance. After exposure, biofilm together with corrosion products formed on zinc film, while corrosion product layer with little bacteria attached on chitosan‑zinc composite film. Further electrochemical results showed that the addition of chitosan did not change the anodic and cathodic behavior of the films, but enhanced the corrosion resistance by reducing the corrosive ability SRB medium, inhibiting bacteria attachment and raising the films' electric conductibility to a certain extent.

Effect of strain rate on stress corrosion cracking of X100 pipeline steel in environments with sulfate-reducing bacteria

Abstract Pipelines installed in the seabed for long periods suffer from high stress levels, and the sea mud environment is complex because it contains various microorganisms that make pipelines prone to stress corrosion cracking (SCC). In this study, a self-designed stress electrochemical corrosion test device was adopted to ensure the normal growth and metabolism of sulfate-reducing bacteria (SRB). The effects of strain rate on the SCC behavior of X100 pipeline steel with SRB in a simulation solution of sea mud from the South China Sea were studied using the slow strain rate test, electrochemical impedance spectroscopy, and scanning electron microscopy fractography. Results show that SRB can promote the stress corrosion susceptibility of X100 pipeline steel. As strain rate increases, the stress corrosion susceptibility decreases in general. When the strain rate is 5 × 10−7 × s−1, the stress corrosion susceptibility is largest and SCC occurs. Under the impact of SRB and strain rate, the stress corrosion fracture mechanism is hydrogen embrittlement mechanism. With the increase in strain rate, the effect of SRB becomes weak and the stress corrosion susceptibility shows a decreasing trend in general. Consequently, SCC does not occur in the specimen and the fracture is dominated by mechanical factors.

Experiment on the treatment of acid mine drainage with optimized biomedical stone particles by response surface methodology.

The immobilized particles were used to treat acid mine drainage (AMD) in the study, which owns the characteristics of serious pollution and high managing cost. The immobilized particles were prepared with sulfate reducing bacteria (SRB) and medical stones. In order to investigate the interactive influence of medical stones on the particle properties, the salt modification condition, content, and size of the medical stone were taken as the influential factors. At the same time, the removal rate of SO42- and Mn2+, the release of total irons (TFe) and chemical oxygen demand (COD) and pH value were taken as the response values in the experiment. On the basis of the orthogonal experimental research, a response surface model was established. The experimental analysis showed that the particles can get the best treatment effect, when using the salt-modified medical stone with the content of 15% and particle size of 200~300 mesh. At this time, the removal rates of Mn2+ and SO42- in wastewater were 83.10 and 96.22%, respectively. The release contents of TFe and COD were 2.99mgL-1 and 1828.54mgL-1, respectively, and the pH value was 7.05. Then, biological medical stone particles were prepared according to the optimal ratio in the response surface experiment. The adaptability of biomedical stone particles was studied at different concentrations of SO42-, Mn2+ and pH value. The results showed that the high concentration of SO42- inhibited the metabolism of SRB, while Mn2+ had a less effect. The biomedical stone particles could regulate pH value very well.

Coupled physicochemical and bacterial reduction mechanisms for passive remediation of sulfate- and metal-rich acid mine drainage

Treatment of acid mine drainage (AMD) highly rich in sulfate and multiple metal elements has been investigated in a continuous flow column experiment using organic and inorganic reactive media. Treatment substrates that composed of spent mushroom compost (SMC), limestone, activated sludge and woodchips were incorporated into bacterial sulfate reduction (BSR) treatment for AMD. SMC greatly assisted the removals of sulfate and metals and acted as essential carbon source for sulfate-reducing bacteria (SRB). Alkalinity produced by dissolution of limestone and metabolism of SRB has provided acidity neutralization capacity for AMD where pH was maintained at neutral state, thus aiding the removal of sulfate. Fe, Pb, Cu, Zn and Al were effectively removed (87–100%); however, Mn was not successfully removed despite initial Mn reduction during early phase due to interference with Fe. The first half of the treatment was an essential phase for removal of most metals where contaminants were primarily removed by the BSR in addition to carbonate dissolution function. The importance of BSR in the presence of organic materials was also supported by metal fraction analysis that primary metal accumulation occurs mainly through metal adsorption onto the organic matter, e.g., as sulfides and onto Fe/Mn oxides surfaces.