Complete Perchlorate Reduction Research Articles

Methane-Driven Perchlorate Reduction by a Microbial Consortium.

The phenomenon of methane oxidation linked to perchlorate reduction has been reported in multiple studies; yet, the underlying microbial mechanisms remain unclear. Here, we enriched suspended cultures by performing methane-driven perchlorate reduction under oxygen-limiting conditions in a membrane bioreactor (MBR). Batch test results proved that perchlorate reduction was coupled to methane oxidation, in which acetate was predicted as the potential intermediate and oxygen played an essential role in activating methane. By combining DNA-based stable isotope probing incubation and high-throughput sequencing analyses of 16S rRNA gene and functional genes (pmoA, pcrA, and narG), we found that synergistic interactions between aerobic methanotrophs (Methylococcus and Methylocystis) and perchlorate-reducing bacteria (PRB; Denitratisoma and Dechloromonas) played active roles in mediating methane-driven perchlorate reduction. This partnership was further demonstrated by coculture experiments in which the aerobic methanotroph could produce acetate to support PRB to complete perchlorate reduction. Our findings advance the understanding of the methane-driven perchlorate reduction process and have implications for similar microbial consortia linking methane and chlorine biogeochemical cycles in natural environments.

Perchlorate reduction in a thiosulfate-based denitrifying membrane bioreactor

Reductive removals of perchlorate and nitrate, which can be present simultaneously in groundwater, were investigated in a novel thiosulfate-based denitrifying lab-scale membrane bioreactor (MBR) equipped with a polyethersulfone membrane module. Complete denitrification at a hydraulic retention time (HRT) as low as 3 h and a rate of 800 mg NO3--N/(L.d) was accomplished. Simultaneous with nitrate, complete perchlorate reduction was also detected at the feed concentration of 3000 µg/L and at 12 h HRT. Although further rise in perchlorate loading caused its incomplete reduction, the reduction rate reached up to 38 mg/(L.d). Hence, the developed process is promising for simultaneous perchlorate and nitrate reduction from contaminated groundwater. Sustainable filtration performance was observed up to a flux of 12.5 L/(m2.h) (LMH) at which the fouling rate was 85.32 ± 19.65 mbar/d. However, when the flux was raised further to 25 L/(m2.h), the TMP drastically increased to a rate of 393 ± 40 mbar/d.

Simultaneous nitrate and perchlorate reduction in an elemental sulfur-based denitrifying membrane bioreactor

Perchlorate is a man-made and naturally occurring anion that causes hypothyroidism and is often present in groundwater together with nitrate. In this study, a novel elemental sulfur-based denitrifying membrane bioreactor was tested for simultaneous nitrate and perchlorate reduction. A bench scale 4 L bioreactor equipped with polyethersulfone (PES) ultrafiltration membranes (0.04 μm of pore size) was used. Influent nitrate was varied between 25 and 100 mg NO3−-N/L. Complete denitrification of 100 mg NO3−-N/L was achieved at HRT as low as 6 h corresponding to 400 mg NO3−-N/(L.d) denitrification rate. Complete reduction of perchlorate was also achieved when the influent concentration was 3000 μg/L and HRT of 12 h. Further increase in perchlorate load resulted in elevated effluent perchlorate concentration and maximum perchlorate reduction rate was 15.1 mg/(L.d). Sulfate was produced as a result of sulfur based denitrification. Influent was supplemented with NaHCO3 (1000 mg CaCO3/L) to meet the alkalinity requirement of the process. Membrane fouling was not significant at 12.5 L/(m2.h) membrane flux.

Evolution of the microbial community of the biofilm in a methane-based membrane biofilm reactor reducing multiple electron acceptors.

Previous work documented complete perchlorate reduction in a membrane biofilm reactor (MBfR) using methane as the sole electron donor and carbon source. This work explores how the biofilm's microbial community evolved as the biofilm stage-wise reduced different combinations of perchlorate, nitrate, and nitrite. The initial inoculum, carrying out anaerobic methane oxidation coupled to denitrification (ANMO-D), was dominated by uncultured Anaerolineaceae and Ferruginibacter sp. The microbial community significantly changed after it was inoculated into the CH4-based MBfR and fed with a medium containing perchlorate and nitrite. Archaea were lost within the first 40days, and the uncultured Anaerolineaceae and Ferruginibacter sp. also had significant losses. Replacing them were anoxic methanotrophs, especially Methylocystis, which accounted for more than 25% of total bacteria. Once the methanotrophs became important, methanol-oxidizing denitrifying bacteria, namely, Methloversatilis and Methylophilus, became important in the biofilm, probably by utilizing organic matter generated by the metabolism of methanotrophs. When methane consumption was equal to the maximum-possible electron-donor supply, Methylomonas, also an anoxic methanotroph, accounted for >10% of total bacteria and remained a major part of the community until the end of the experiments. We propose that aerobic methane oxidation coupled to denitrification and perchlorate reduction (AMO-D and AMO-PR) directly oxidized methane and reduced NO3 (-) to NO2 (-) or N2O under anoxic condition, producing organic matter for methanol-assimilating denitrification and perchlorate reduction (MA-D and MA-PR) to reduce NO3 (-). Simultaneously, bacteria capable of anaerobic methane oxidation coupled to denitrification and perchlorate reduction (ANMO-D and ANMO-PR) used methane as the electron donor to respire NO3 (-) or ClO4 (-) directly. Graphical Abstract ᅟ.

Simultaneous nitrate and perchlorate reduction using sulfur-based autotrophic and heterotrophic denitrifying processes

BACKGROUND This study aims at comparing the performances of sulfur-based autotrophic and methanol-based heterotrophic denitrification processes for simultaneous removal of perchlorate and nitrate. Influent nitrate concentration was kept at 25 mg L−1 NO3−-N throughout the study and perchlorate concentration was varied between 50 and 1000 µg L−1. RESULTS The heterotrophic process reduced nitrate and perchlorate completely in all tested conditions (i.e. various nitrate and perchlorate loadings). As for the autotrophic process, although high perchlorate removals were attained, perchlorate was always detected in the effluent with varying concentrations from 21.88–85 µg L−1 depending on the perchlorate and nitrate loadings. Perchlorate was reduced from 1000 µg L−1 to 53 ± 21.36 µg L−1, corresponding to around 95% reduction in the autotrophic process at HRT of 2 h. The presence of perchlorate did not adversely affect the denitrification performance of autotrophic and heterotrophic processes under the conditions studied. The presence of nitrate inhibited autotrophic perchlorate reduction and prevented complete perchlorate reduction. CONCLUSION An autotrophic process may be preferred over a heterotrophic one due to the elimination of organic supplementation and the risk of effluent contamination with organic substrate, but further polishing steps may also be required. © 2015 Society of Chemical Industry

Complete perchlorate reduction using methane as the sole electron donor and carbon source.

Using a CH4-based membrane biofilm reactor (MBfR), we studied perchlorate (ClO4(-)) reduction by a biofilm performing anaerobic methane oxidation coupled to denitrification (ANMO-D). We focused on the effects of nitrate (NO3(-)) and nitrite (NO2(-)) surface loadings on ClO4(-) reduction and on the biofilm community's mechanism for ClO4(-) reduction. The ANMO-D biofilm reduced up to 5 mg/L of ClO4(-) to a nondetectable level using CH4 as the only electron donor and carbon source when CH4 delivery was not limiting; NO3(-) was completely reduced as well when its surface loading was ≤ 0.32 g N/m(2)-d. When CH4 delivery was limiting, NO3(-) inhibited ClO4(-) reduction by competing for the scarce electron donor. NO2(-) inhibited ClO4(-) reduction when its surface loading was ≥ 0.10 g N/m(2)-d, probably because of cellular toxicity. Although Archaea were present through all stages, Bacteria dominated the ClO4(-)-reducing ANMO-D biofilm, and gene copies of the particulate methane mono-oxygenase (pMMO) correlated to the increase of respiratory gene copies. These pieces of evidence support that ClO4(-) reduction by the MBfR biofilm involved chlorite (ClO2(-)) dismutation to generate the O2 needed as a cosubstrate for the mono-oxygenation of CH4.

Characterisation of chlorate reduction in the haloarchaeon Haloferax mediterranei

BackgroundHaloferax mediterranei is a denitrifying haloarchaeon using nitrate as a respiratory electron acceptor under anaerobic conditions in a reaction catalysed by pNarGH. Other ions such as bromate, perchlorate and chlorate can also be reduced. MethodsHfx. mediterranei cells were grown anaerobically with nitrate as electron acceptor and chlorate reductase activity measured in whole cells and purified nitrate reductase. ResultsNo genes encoding (per)chlorate reductases have been detected either in the Hfx. mediterranei genome or in other haloarchaea. However, a gene encoding a chlorite dismutase that is predicted to be exported across the cytoplasmic membrane has been identified in Hfx. mediterranei genome. Cells did not grow anaerobically in presence of chlorate as the unique electron acceptor. However, cells anaerobically grown with nitrate and then transferred to chlorate-containing growth medium can grow a few generations. Chlorate reduction by the whole cells, as well as by pure pNarGH, has been characterised. No clear chlorite dismutase activity could be detected. ConclusionsHfx. mediterranei pNarGH has its active site on the outer-face of the cytoplasmic membrane and reacts with chlorate and perchlorate. Biochemical characterisation of this enzymatic activity suggests that Hfx. mediterranei or its pure pNarGH could be of great interest for waste water treatments or to better understand biological chlorate reduction in early Earth or Martian environments. General significanceSome archaea species reduce (per)chlorate. However, results here presented as well as those recently reported by Liebensteiner and co-workers [1] suggest that complete perchlorate reduction in archaea follows different rules in terms of biological reactions.

Using a Two-Stage Hydrogen-Based Membrane Biofilm Reactor (MBfR) to Achieve Complete Perchlorate Reduction in the Presence of Nitrate and Sulfate

We evaluated a strategy for achieving complete reduction of perchlorate (ClO(4)(-)) in the presence of much higher concentrations of sulfate (SO(4)(2-)) and nitrate (NO(3)(-)) in a hydrogen-based membrane biofilm reactor (MBfR). Full ClO(4)(-) reduction was achieved by using a two-stage MBfR with controlled NO(3)(-) surface loadings to each stage. With an equivalent NO(3)(-) surface loading larger than 0.65 ± 0.04 g N/m(2)-day, the lead MBfR removed about 87 ± 4% of NO(3)(-) and 30 ± 8% of ClO(4)(-). This decreased the equivalent surface loading of NO(3)(-) to 0.34 ± 0.04-0.53 ± 0.03 g N/m(2)-day for the lag MBfR, in which ClO(4)(-) was reduced to nondetectable. SO(4)(2-) reduction was eliminated without compromising full ClO(4)(-) reduction using a higher flow rate that gave an equivalent NO(3)(-) surface loading of 0.94 ± 0.05 g N/m(2)-day in the lead MBfR and 0.53 ± 0.03 g N/m(2)-day in the lag MBfR. Results from qPCR and pyrosequencing showed that the lead and lag MBfRs had distinctly different microbial communities when SO(4)(2-) reduction took place. Denitrifying bacteria (DB), quantified using the nirS and nirK genes, dominated the biofilm in the lead MBfR, but perchlorate-reducing bacteria (PRB), quantified using the pcrA gene, became more important in the lag MBfR. The facultative anaerobic bacteria Dechloromonas, Rubrivivax, and Enterobacter were dominant genera in the lead MBfR, where their main function was to reduce NO(3)(-). With a small NO(3)(-) surface loading and full ClO(4)(-) reduction, the dominant genera shifted to ClO(4)(-)-reducing bacteria Sphaerotilus, Rhodocyclaceae, and Rhodobacter in the lag MBfR.

Heterogeneous Catalytic Reduction of Perchlorate in Water with Re−Pd/C Catalysts Derived from an Oxorhenium(V) Molecular Precursor

The molecular Re(V) complex, chlorobis(2-(2'-hydroxyphenyl)-2-oxazoline)-oxorhenium(V), Re(O)(hoz)(2)Cl, has been investigated as a suitable precursor, when combined with activated carbon powder containing 5 wt % Pd, to provide a heterogeneous catalyst for the reduction of aqueous perchlorate by hydrogen. Two general methods for catalyst preparation have been adopted: first, by a standard "incipient wetness" impregnation of the carbon powder with handling under largely aerobic conditions for convenience and, second, by a completely anaerobic procedure maintaining a hydrogen atmosphere during adsorption of the complex in water onto the powder. Both types of catalyst were efficient for the complete reduction of perchlorate to chloride within a few hours at room temperature over a range of initial concentrations (2-200 ppm) under 1 atm of H(2) and acidic conditions (pH 2.7-3.7). The perchlorate reduction profiles displayed pseudo-first-order kinetics, and the rates were insensitive to excess chloride. Complete reduction of perchlorate was observed even at pH 5.9 in a phosphate buffer over the course of two weeks. Under comparable conditions, chlorate reduction proceeded ca. 10 times more quickly than perchlorate reduction. The impregnated catalyst was examined by STEM/EDS, which revealed a wide distribution in Pd nanoparticle sizes and also suggested that the Re complex did not aggregate preferentially on or near the Pd particles. XPS of this material provided evidence for reduced Pd after the reaction, but only a +7 oxidation state was seen for the Re sites both pre- and postreduction. Elemental analyses of the catalyst materials taken pre- and postreduction showed variable amounts of Re loss (0-50%) but relatively unchanged amounts of nitrogen. These results show the need to maintain a reducing atmosphere during the preparation and operation of the catalyst in order to achieve optimum activity and stability.

THE EFFECT OF OXYGEN ON PERCHLORATE REDUCTION IN A BIOFILM REACTOR

The purpose of this research was to investigate the effects of low concentration of oxygen on reduction of perchlorate, especially low perchlorate influent concentrations in a biofilm reactor, as well as the effect of flow pattern in a biofilm reactor. Dissolved oxygen averaging 1 mg/L did not inhibit reduction of influent perchlorate from 23 to 426 μg/L in the biofilm reactors when sufficient acetate was added, probably due to limitation of oxygen diffusion into the biofilm. Influent perchlorate ranging from 23 to 426 μg/L was reduced to below detection level (4 μg/L) in the presence of 1 mg/L dissolved oxygen (DO). Chloride was produced in a ratio of 0.37gCl-/gClO₄- and 0.35gCl-/gClO₄- in plug flow and recirculation biofilm reactor which is similar to stoichiometric amount (0.36gCl-/gClO₄-) indicating complete perchlorate reduction at 426 μg/L of ClO₄- feeding. At 23 μg/L influent perchlorate, total biomass solids were 3.18 g and 2.81 g in the plug flow and recirculation biofilm reactors. The most probable number (MPN) analysis for perchlorate-reducing bacteria showed 104 to 105 cells/cm2 in both biofilm reactors throughout the experiments. The effluent perchlorate concentrations were not significantly different in the two different flow regimes, plug flow and recirculation biofilm reactors.

Effluent recirculation to improve perchlorate reduction in a fixed biofilm reactor

The effect of effluent recirculation on perchlorate reduction in a nominally plug-flow fixed biofilm reactor was studied in two cases: influent concentrations of 10 and 400 microg/L at low hydraulic loading rates (1.9 and 37.5 m(3)/m(2)/day without and with recirculation, respectively) and after a step increase in perchlorate concentration to 1,000 microg/L at the higher hydraulic loading rate (5 and 100 m(3)/m(2)/day without and with recirculation, respectively). Complete perchlorate reduction was sustained for influent concentrations of 400 and 10 microg/L in both flow regimes at the lower hydraulic loading rates. Reactor tracer profiles showed that biofilm diffusion had a more significant effect on mass transfer in the plug flow reactor compared with recirculation. The recirculation bioreactor acclimated more rapidly to increased hydraulic and perchlorate mass loading rates with significantly lower effluent perchlorate compared to the plug flow reactor: 16 microg/L versus 46 microg/L, respectively, although complete perchlorate removal was not achieved in either flow regime after 21 days acclimation to the higher loading. Total biofilm mass was more uniformly distributed in the recirculation reactor which may have contributed to better performance under increased perchlorate loading.

Microbial reduction of perchlorate with zero-valent iron

Microbial reduction of perchlorate in the presence of zero-valent iron was examined in both batch and column reactors to assess the potential of iron as the electron donor for biological perchlorate reduction process. Iron-supported mixed cultures completely removed 65 mg/L of perchlorate in batch reactors in 8 days. The removal rate was similar to that observed with hydrogen gas (5%) and acetate (173 mg/L) as electron donors. Repeated spiking of perchlorate to batch reactors containing iron granules and microorganisms showed that complete perchlorate reduction by the iron-supported culture was sustained over a long period. Complete removal of perchlorate by iron-supported anaerobic culture was also achieved in a bench-scale iron column with a hydraulic residence time of 2 days. This study demonstrated the potential applicability of zero-valent iron as a source of electrons for biological perchlorate reduction. Use of zero-valent iron may eliminate the need to continually supply electron donors such as organic substrates or explosive hydrogen gas. In addition, iron is inexpensive, safe to handle, and does not leave organic residuals in the treated water.

Enhanced reduction of perchlorate by elemental iron at elevated temperatures

Kinetics of perchlorate reduction by elemental iron was examined at elevated temperatures using microwave heating and conventional block heating. It was hypothesized that increasing the solution temperature may accelerate the reduction of perchlorate by overcoming the high activation energy barrier. Results from microwave heating study showed that 98% of aqueous perchlorate was removed in 1 h at 200 °C. Similar results observed in control experiments with a block heater indicated that the enhancement in the extent and rate of perchlorate removal by elemental iron was mostly due to heat energy at high temperature. The rapid and complete reduction of perchlorate by elemental iron at elevated temperatures suggests that iron reduction process at elevated temperature may be an option to consider for complete removal of perchlorate from industrial discharges.

Perchlorate Reduction by Nanoscale Iron Particles

We report herein the near complete reduction of perchlorate (ClO $$_{4}^{-}$$ ) to chloride by nanoscale iron particles. The nanoparticles also reduce chlorate (ClO $$_{3}^-$$ ), chlorite (ClO $$_{2}^-$$ ) and hypochlorite (ClO $$^{-}$$ ) to chloride. No reaction was observed with microscale iron powder under identical conditions. The temperature sensitivity of the perchlorate-nanoparticle reaction is evidenced by progressively increasing rate constant values of 0.013, 0.10, 0.64 and 1.52 mg perchlorate per g nanoparticles per hour (mg-g-1-hr-1), respectively, at temperatures of 25, 40, 60 and 75°C. The activation energy of perchlorate-iron reaction was calculated to be 79.02 ± 7.75 kJ/mole. Despite favorable thermodynamics, the relatively large activation energy for this reaction suggests that perchlorate reduction is limited by the slow kinetics. The nanoscale iron particles may represent a potential treatment method for perchlorate-contaminated water.

Perchlorate reduction by a novel chemolithoautotrophic, hydrogen-oxidizing bacterium.

Water treatment technologies are needed that can remove perchlorate from drinking water without introducing organic chemicals that stimulate bacterial growth in water distribution systems. Hydrogen is an ideal energy source for bacterial degradation of perchlorate as it leaves no organic residue and is sparingly soluble. We describe here the isolation of a perchlorate-respiring, hydrogen-oxidizing bacterium (Dechloromonas sp. strain HZ) that grows with carbon dioxide as sole carbon source. Strain HZ is a Gram-negative, rod-shaped facultative anaerobe that was isolated from a gas-phase anaerobic packed-bed biofilm reactor treating perchlorate-contaminated groundwater. The ability of strain HZ to grow autotrophically with carbon dioxide as the sole carbon source was confirmed by demonstrating that biomass carbon (100.9%) was derived from CO2. Chemolithotrophic growth with hydrogen was coupled with complete reduction of perchlorate (10 mM) to chloride with a maximum doubling time of 8.9 h. Strain HZ also grew using acetate as the electron donor and chlorate, nitrate, or oxygen (but not sulphate) as an electron acceptor. Phylogenetic analysis of the 16S rRNA sequence placed strain HZ in the genus Dechloromonas within the beta subgroup of the Proteobacteria. The study of this and other novel perchlorate-reducing bacteria may lead to new, safe technologies for removing perchlorate and other chemical pollutants from drinking water.

Persistence of Perchlorate and the Relative Numbers of Perchlorate- and Chlorate-Respiring Microorganisms in Natural Waters, Soils, and Wastewater

Cell numbers of perchlorate (PRM)- and chlorate (CRM)-reducing microorganisms and the persistence of perchlorate were determined in samples of soils, natural waters, and wastewater incubated under laboratory conditions. Complete perchlorate reduction in raw wastewater and creek water was achieved in 4 to 7 days and 8 to 29 days, respectively, depending on the individual growth substrate (acetate, lactate, citric acid, or molasses) employed. Perchlorate persisted in most mixed cultures developed with 2 g of “pristine” soil, but declined in mixed cultures developed with 100 g of soil. Less than seven days were required to completely reduce perchlorate in cultures started with 10 g of a perchlorate-contaminated soil obtained from a site in Texas. The concentration of PRM was estimated using a 5-tube most probable number (MPN) procedure. To account for discrepancies due to differences in the total number of bacteria (per mass of sample) in the samples, difficulty in removing bacteria from soil samples, and the lack of an unequivocal method to measure total viable cells in these different systems, we normalized our MPN results on the basis of 106 or 109 total bacteria counted using acridine orange direct counts (AODC). There were more PRM in wastewater samples on a per-cell basis (15 to 350 PRM/106-AODC) than in water samples (0.02 to 0.4 PRM/106-AODC). There were also more PRM in soils from sites exhibiting direct evidence of perchlorate contamination (100 to 200 PRM/109-AODC) than from other sites (nondetectable to 0.77 PRM/109-AODC). These results demonstrate that perchlorate-reducing bacteria are present at perchlorate-contaminated sites, and that perchlorate can be degraded by these microorganisms through the addition of different electron donors, such as acetate and lactate.