Study of microbial perchlorate reduction: considering of multiple pH, electron acceptors and donors

Comparative effects of ammonium nitrogen on perchlorate degradation performance under heterotrophic condition with different carbon sources

Perchlorate (ClO4-) mainly exists in the form of ammonium perchlorate in industrial production. However, the degradation mechanisms of different concentrations of ammonium nitrogen (NH4+-N) and ClO4- mixed pollutants in the environment are not well understood. This study aims to explore the potential of different types of carbon sources for ClO4- and NH4+-N biodegradation. Experimental results showed that the concentration and type of carbon sources are decisive to simultaneous removal of NH4+-N and ClO4-. Under condition of C(COD)/C(ClO4-) ratio of 21.15 ± 4.40, the simultaneously removal efficiency of ClO4- and NH4+-N in acetate (Ace) was relatively higher than that in methanol (Met). C(NH4+-N)/C(ClO4-) ratio of 9.66 ± 0.51 and C(COD)/C(ClO4-) ratio of 2.51 ± 0.87 promoted ClO4- reduction in glucose-C (Glu-C). However, high concentration of Glu could cause pH decrease (from 7.57 to 4.59), thereby inhibiting ClO4- reduction. High-throughput sequencing results indicated that Proteobacteria and Bacteroidetes have made a major contribution to the simultaneous removal of NH4+-N and ClO4-. They are two representative bacterial phyla for participating in both ClO4- reduction and denitrification. Notably, the abundance of main ClO4- degrading bacteria (such as Proteobacteria, Chloroflexi, and Firmicutes) significantly increased by 528.57 % in Glu-C. It can be inferred that the concentration of carbon source and NH4+-N were the most important factors determining the removal efficiency of ClO4- by influencing changes in the core microbial community. This study will provide new techniques and mechanistic insights for the simultaneous removal of mixed ClO4- and nitrogen pollutants, which can also provide theoretical support for innovation in future biological treatment processes.

Occurrence and removal technologies of perchlorate in water: A systematic review and bibliometric analysis

The pollution resulting from the emergence of the contaminant perchlorate is anticipated to have a substantial effect on the water environment in the foreseeable future. Considerable research efforts have been devoted to investigating treatment technologies for addressing perchlorate contamination, garnering widespread international interest in recent decades. A systematic review was conducted utilizing the Web of Science, Scopus, and Science Direct databases to identify pertinent articles published from 2000 to 2024. A total of 551 articles were chosen for in-depth examination utilizing VOS viewer. Bibliometric analysis indicated that countries such as China, the United States, Chile, India, Japan, and Korea have been prominent contributors to the research on this topic. The order of ClO4- occurrence was as follows: surface water > groundwater > drinking water. Various remediation methods for perchlorate contamination, such as adsorption, ion-exchange, membrane filtration, chemical reduction, and biological reduction, have been suggested. Furthermore, the research critically evaluated the strengths and weaknesses of each approach and offered recommendations for addressing their limitations. Advanced technologies have shown the potential to achieve notably enhanced removal of perchlorate and co-contaminants from water sources. However, the low concentration of perchlorate in natural water sources and the high energy consumption related to these technologies need to be solved in order to effectively remove perchlorate from water.

Developing a microbial community structure index (MCSI) as an approach to evaluate and optimize bioremediation performance

Much attention is placed on organohalide-respiring bacteria (OHRB), such as Dehalococcoides, during the design and performance monitoring of chlorinated solvent bioremediation systems. However, many OHRB cannot function effectively without the support of a diverse group of other microbial community members (MCMs), who play key roles fermenting organic matter into more readily useable electron donors, producing corrinoids such as vitamin B12, or facilitating other important metabolic processes or biochemical reactions. While it is known that certain MCMs support dechlorination, a metric considering their contribution to bioremediation performance has yet to be proposed. Advances in molecular biology tools offer an opportunity to better understand the presence and activity of specific microbes, and their relation to bioremediation performance. In this paper, we test the hypothesis that a specific microbial consortium identified within 16S ribosomal ribonucleic acid (rRNA) gene next generation sequencing (NGS) data can be predictive of contaminant degradation rates. Field-based data from multiple contaminated sites indicate that increasing relative abundance of specific MCMs correlates with increasing first-order degradation rates. Based on these results, we present a framework for computing a simplified metric using NGS data, the Microbial Community Structure Index, to evaluate the adequacy of the microbial ecosystem during assessment of bioremediation performance.

Impacts of co-contaminants and dilution on perchlorate biodegradation using various carbon sources

This research investigates the biodegradation of perchlorate in the presence of the co-contaminants nitrate and chlorate using soluble and slow-release carbon sources. In addition, the impact of bio-augmentation and dilution, which results in lower total dissolved salts (TDS) and contaminant levels, is examined. Laboratory microcosms were conducted using actual groundwater and soils from a contaminated aquifer. The results revealed that both soluble and slow-release carbon sources support biodegradation of contaminants in the sequence nitrate > chlorate > perchlorate. Degradation rates, including and excluding lag times, revealed that the overall impact of the presence of co-contaminants depends on degradation kinetics and the relative concentrations of the contaminants. When the lag time caused by the presence of the co-contaminants is considered, the degradation rates for chlorate and perchlorate were two to three times slower. The results also show that dilution causes lower initial contaminant concentrations, and consequently, slower degradation rates, which is not desirable. On the other hand, the dilution resulting from the injection of amendments to support remediation promotes desirably lower salinity levels. However, the salinity associated with the presence of sulfate does not inhibit biodegradation. The naturally occurring bacteria were able to support the degradation of all contaminants. Bio-augmentation was effective only in diluted microcosms. Proteobacteria and Firmicutes were the dominant phyla identified in the microcosms.

Fermentation broth of food waste: A sustainable electron donor for perchlorate biodegradation

Microbial reduction has been considered an effective way to remove perchlorate (ClO₄^-), during which, additional electron donors and carbon sources are required. This work aims to study the potential of fermentation broth of food waste (FBFW) serving as an electron donor for ClO₄^- biodegradation, and further investigates the variance of the microbial community. The results showed that FBFW without anaerobic inoculum at 96 h (F-96) exhibited the highest ClO₄^- removal rate of 127.09 mg/L/d, attributed to higher acetate and lower ammonium contents in the F-96 system. In a 5 L continuous stirred-tank reactor (CSTR), with a 217.39 g/m³·d ClO₄^- loading rate, 100% removal efficiency of ClO₄^- was achieved, indicating that the application of FBFW in the CSTR showed satisfactory performance for ClO₄^- degradation. Moreover, the microbial community analysis revealed that Proteobacteria and Dechloromonas contributed positively to ClO₄^- degradation. Therefore, this study provided a novel approach for the recovery and utilization of food waste, by employing it as a cost-effective electron donor for ClO₄^- biodegradation.

Molecular Mechanisms Determining the Role of Bacteria from the Genus Azospirillum in Plant Adaptation to Damaging Environmental Factors

Agricultural plants are continuously exposed to environmental stressors, which can lead to a significant reduction in yield and even the death of plants. One of the ways to mitigate stress impacts is the inoculation of plant growth-promoting rhizobacteria (PGPR), including bacteria from the genus Azospirillum, into the rhizosphere of plants. Different representatives of this genus have different sensitivities or resistances to osmotic stress, pesticides, heavy metals, hydrocarbons, and perchlorate and also have the ability to mitigate the consequences of such stresses for plants. Bacteria from the genus Azospirillum contribute to the bioremediation of polluted soils and induce systemic resistance and have a positive effect on plants under stress by synthesizing siderophores and polysaccharides and modulating the levels of phytohormones, osmolytes, and volatile organic compounds in plants, as well as altering the efficiency of photosynthesis and the antioxidant defense system. In this review, we focus on molecular genetic features that provide bacterial resistance to various stress factors as well as on Azospirillum-related pathways for increasing plant resistance to unfavorable anthropogenic and natural factors.

Perchlorate reduction kinetics and genome-resolved metagenomics identify metabolic interactions in acclimated saline lake perchlorate-reducing consortia

Perchlorate is a widely detected environmental contaminant in surface and underground water, that seriously impacts human health by inhibiting the uptake of thyroidal radioiodine. Perchlorate reduction due to saline lake microorganisms is not as well understood as that in marine environments. In this study, we enriched a perchlorate-reducing microbial consortium collected from saline lake sediments and found that the perchlorate reduction kinetics of the enriched consortium fit the Michaelis-Menten kinetics well, with a maximum specific substrate reduction rate (q_max) of 0.596 ± 0.001 mg ClO₄^-/mg DW/h and half-saturation constant (K_s) of 16.549 ± 0.488 mg ClO₄^-/L. Furthermore, we used improved metagenome binning to reconstruct high-quality metagenome-assembled genomes from the metagenomes of the microbial consortia, including the perchlorate-reducing bacteria (PRB) Dechloromonas agitata and Wolinella succinogenes, with the genome of W. succinogenes harboring complete functional genes for perchlorate reduction being the first recovered. Given that the electrons were directly transferred to the electronic carrier cytochrome c-553 from the quinone pool, the electron transfer pathway of W. succinogenes was shorter and more efficient than the canonical pattern. This finding provides a theoretical basis for microbial remediation of sites contaminated by high concentrations of perchlorate. Metagenomic binning and metatranscriptomic analyses revealed the gene transcription variation of perchlorate reductase pcr and chlorite dismutase cld by PRB and the synergistic metabolic mechanism.

Perchlorate bioreduction in UASB reactor: S2--autotrophic granular sludge formation and sulphate generation control

Perchlorate (ClO4-) industrial wastewater requires efficient removal to prevent adverse environmental impacts, however, high concentration and low biodegradability give rise to poor ClO4- bioreduction performance. S2--autotrophic granular sludge (S2--AuGS) was firstly cultivated for high concentration perchlorate (ClO4-) removal in the upflow anaerobic sludge blanket (UASB) reactor (ClO4-: 150 mg L^-1). Simultaneously, the S2- was utilized to control the SO42- generation as electron donor, the effluent SO42- concentration (190 mg L^-1) was satisfied with drinking water standard (250 mg L^-1). Under the optimized condition of hydraulic retention time (HRT) (6 h) and S2-/ClO4- molar ratio (2.2), more EPS was secreted, which promoted the S2--AuGS formation and stability. Though acclimation of 146 d, the S2--AuGS was formed with a large average granular sludge size (612 μm) and an excellent settleability (sludge volume index: SVI₅/SVI₃₀= 1). With the mature S2--AuGS formation, the highest ClO4- and S2- loading was increased to 1.06 and 0.75 kg m^-3 d^-1. Interestingly, Georgfuchsia, Methyloversatilis, Sulfurisoma, and Exiguobacterium were the main microbial community in the S2--AuGS. This study proposed to form a novel S2--AuGS for developing the high ClO4- concentration removal performance and to utilize the S2- as an electron donor for controlling the excessive SO42- generation.

Catalytic enhancement of hydrogenation reduction and oxygen transfer reaction for perchlorate removal: A review

Perchlorate is the main contaminant in surface water and groundwater, and it is of current urgency to remove due to its high water solubility, mobility, and endocrine-disrupting properties. The conversion of perchlorate into harmless chloride ions by using appropriate catalysts is the most promising and effective route to overcome its high activation energy and kinetic stability. Perchlorate is usually reduced in two ways: (1) indirect reduction via oxygen atom transfer (OAT) reaction or (2) hydrodeoxygenation through highly active reducing H atoms. This paper discusses the mechanisms underlying both the OAT reaction catalyzed by homogenous rhenium-oxo complexes or biological Mo-based enzymes and the heterogeneous hydrogenation for perchlorate reduction. Particular emphasis is placed on the factors affecting the catalytic process and the synergy between the (1) and (2) reactions. For completeness, the applicability of different electrolysis devices, electrodes, and bioreactors is also illustrated. Finally, this article gives prospects for the synthesis and application of catalysts in different pathways.

Inhibition of perchlorate biodegradation by ferric and ferrous iron

Previous observations from in-situ biological treatments in the subsurface of a perchlorate-contaminated site revealed multiple reduction processes occurring parallel to perchlorate degradation. Iron reduction was accelerated and correlated with a decline in the efficiency of the in-situ perchlorate reduction. In the current study, we examined the influence of iron forms on perchlorate reduction. A series of kinetic laboratory experiments were conducted, using an indigenous mixed perchlorate-reducing culture, enriched from the polluted soil that was undergoing bioremediation. The results show that ferrous iron was a non-competitive inhibitor with a 41% decrease in µ_max for perchlorate reduction. Moreover, chlorate was accumulated in all samples treated with ferrous iron, indicating a disruption to the chlorate reduction step. Ferric iron, however, had less impact on perchlorate degradation with non-competitive inhibition reaching a 23% decrease in µ_max. Scanning electron microscopy (SEM) revealed that the presence of ferrous iron in the perchlorate degradation enrichment culture initiated cell encrustation. We propose that during perchlorate reduction and the emission of oxygen from chlorite dismutation, the chemical oxidation of ferrous iron occurred near the bacteria's surface where the enzyme is located, forming an oxidized iron crust layer that can directly affect the perchlorate reduction enzymatic system.

Electro-assisted autohydrogenotrophic reduction of perchlorate and microbial community in a dual-chamber biofilm-electrode reactor

The electro-assisted autohydrogenotrophic reduction of perchlorate (ClO₄^-) was investigated in a dual-chamber biofilm-electrode reactor (BER), in which the microbial community was inoculated from natural sediments. To avoid the effect of extreme pH and direct electron transfer on perchlorate reduction, a novel cathode configuration was designed. The pH of the cathode compartment was successfully controlled in the range of 7.2-8.4 during whole experiment. The effective biological autohydrogenotrophic reduction of perchlorate was achieved using hydrogen generated in-situ on the electrode surface, and the removal rate of 10 mg L^-1 perchlorate reached 98.16% at HRT of 48 h. The highest perchlorate removal flux reached to 1498.420 mg m^-2·d^-1 with a 0.410 kW·h g-perchlorate^-1 energy consumption. The microbial community evolution in the BER was determined by high-throughput sequencing and the results indicated that the Firmicutes and Bacteroidetes were dominant at phylum level when perchlorate concentration was 10 mg L^-1 or lower. And the Proteobacteria became ascendant at the perchlorate concentration of 20 mg L^-1. The functional populations for perchlorate reduction were successfully enriched including Nitrosomonas (30%), Thermomonas (9%), Comamonas (8%) and Hydrogenophaga (3%). Meanwhile, the proportion of functional population in biofilm linked to perchlorate concentration. With the increase of influent perchlorate concentration, the perchlorate-reducing bacteria (PRB) were enriched successfully and became ascendant.

Perchlorate Contamination: Sources, Effects, and Technologies for Remediation

Perchlorate is a persistent pollutant, generated via natural and anthropogenic processes, that possesses a high potential for endocrine disruption in humans and biota. It inhibits iodine fixation, a major reason for eliminating this pollutant from ecosystems. Remediation of perchlorate can be achieved with various physicochemical treatments, especially at low concentrations. However, microbiological approaches using microorganisms, such as those from the genera Dechloromonas, Serratia, Propionivibrio, Wolinella, and Azospirillum, are promising when perchlorate pollution is extensive. Perchlorate-reducing bacteria, isolated from harsh environments, for example saline soils, mine sediments, thermal waters, wastewater treatment plants, underground gas storage facilities, and remote areas, including the Antarctica, can provide removal yields from 20 to 100%. Perchlorate reduction, carried out by a series of enzymes, such as perchlorate reductase and superoxide chlorite, depends on pH, temperature, salt concentration, metabolic inhibitors, nutritional conditions, time of contact, and cellular concentration. Microbial degradation is cost-effective, simple to implement, and environmentally friendly, rendering it a viable method for alleviating perchlorate pollution in the environment.

Perchlorate bioreduction by anaerobic granular sludge immobilised with Fe-HA complex: Performance, extracellular polymeric substances and microbial community structure

An iron-humic acid (Fe-HA) complex was used as a redox mediator in perchlorate (ClO₄^-) bioreduction. Bioreduction performance, extracellular polymeric substances (EPS), and microbial community structure were comprehensively explored using different types of anaerobic granular sludge (AnGS) immobilised without the Fe-HA complex (AnGS_CON) and with the Fe-HA complex (AnGS_FH). The ClO₄^- was completely removed by AnGS_CON by day 20, while the ClO₄^- was completely removed by AnGS_FH by day 6. The AnGS immobilised with the Fe-HA complex significantly increased the ClO₄^- bioreduction. The acceleration of ClO₄^- bioreduction was also explained by the mixed liquor volatile suspended solids (MLVSS), MLVSS/mixed liquor suspended solids (MLSS), EPS composition, and microbial community structure. Compared with AnGS_CON, the MLVSS and MLVSS/MLSS of the AnGS_FH increased 1.4- and 1.2-fold, respectively. Humic substances in the EPS were stimulated by the Fe-HA complex. The microbial community structure analysis indicated that perchlorate and quinone reducing bacteria were enriched by the Fe-HA complex. Based on the analysis, the ClO₄^- bioreduction mechanism of the AnGS_FH was revealed because the Fe-HA complex in the AnGS increased the biomass concentration, biological activity, and redox-active mediator and shifted the microbial community structure.

Isolation and characterization of a chlorate-reducing bacterium Ochrobactrum anthropi XM-1

A Gram-negative chlorate-reducing bacterial strain XM-1 was isolated. The 16S rRNA gene sequence identified the isolate as Ochrobactrum anthropi XM-1, which was the first strain of genus Ochrobactrum reported having the ability to reduce chlorate. The optimum growth temperature and pH for strain XM-1 to reduce chlorate was found to be 30 °C and 5.0-7.5, respectively, under anaerobic condition. Strain XM-1 could tolerate high chlorate concentration (200 mM), and utilize a variety of carbohydrates (glucose, L-arabinose, D-fructose, sucrose), glycerin and sodium citrate as electron donors. In addition, oxygen and nitrate could be used as electron acceptors, but perchlorate could not be reduced. Enzyme activities related to chlorate reducing were characterized in cell extracts. Activities of chlorate reductase and chlorite dismutase could be detected in XM-1 cells grown under both aerobic and anaerobic conditions, implying the two enzymes were constitutively expressed. This work suggests a high potential of applying Ochrobactrum anthropi XM-1 for remediation of chlorate contamination.

Biological perchlorate reduction: which electron donor we can choose?

Biological reduction is an effective method for removal of perchlorate (ClO₄^-), where perchlorate is transformed into chloride by perchlorate-reducing bacteria (PRB). An external electron donor is required for autotrophic and heterotrophic reduction of perchlorate. Therefore, plenty of suitable electron donors including organic (e.g., acetate, ethanol, carbohydrate, glycerol, methane) and inorganic (e.g., hydrogen, zero-valent iron, element sulfur, anthrahydroquinone) as well as the cathode have been used in biological reduction of perchlorate. This paper reviews the application of various electron donors in biological perchlorate reduction and their influences on treatment efficiency of perchlorate and biological activity of PRB. We discussed the criteria for selection of appropriate electron donor to provide a flexible strategy of electron donor choice for the bioremediation of perchlorate-contaminated water.

A combined heterotrophic and sulfur-based autotrophic process to reduce high concentration perchlorate via anaerobic baffled reactors: Performance advantages of a step-feeding strategy

The combined anaerobic baffled reactors (ABRs) of heterotrophic and sulfur-based autotrophic processes were first investigated for the removal of high perchlorate concentration under different feeding strategies. The removal efficiency of the step-feeding ABR (SF-ABR) reached 97.56% at 800 mg/L perchlorate, which was significantly superior to the normal-feeding ABR (NF-ABR). In three components of the extracellular polymeric substances (EPS), the fluorescence intensity of the tryptophan-like component were identified by fluorescence excitation-emission matrix (EEM) spectra with parallel factor (PARAFAC) analysis, and exhibited a positive relationship with the perchlorate removal rate in the heterotrophic perchlorate reduction unit (HPR unit) of the SF-ABR (R² = 0.9791) and NF-ABR (R² = 0.9860). Bacterial community analysis suggested the dominating perchlorate reducing bacteria and the diversity in two ABRs. Principal component analysis indicated that the electron donor affected the microbial community structures. The study confirms that the SF-ABR is a powerful bioreactor for the combined heterotrophic and sulfur-based autotrophic process.

Worldwide occurrence and origin of perchlorate ion in waters: A review

Perchlorate (ClO₄^-) is a persistent water soluble oxyanion of growing environmental interest. Perchlorate contamination can be a health concern due to its ability to disrupt the use of iodine by the thyroid gland and the production of metabolic hormones. Its widespread presence in surface water and groundwater makes the aquatic environment a potential source of perchlorate exposure. However, the amount of published data on perchlorate origins and water contamination worldwide remains spatially limited. Here, we present an overview of research on perchlorate origins and occurrences in water, and the methodology to distinguish the different perchlorate sources based on isotope analysis. All published ranges of isotopic content in perchlorate from different sources are presented, including naturally occurring and man-made perchlorate source types, as well as the effects of isotope fractionation that accompanies biodegradation processes. An example of a case study in France is presented to emphasize the need for further research on this topic.

Bio-mixotrophic perchlorate reduction to control sulfate production in a step-feed sulfur-based reactor: A study of kinetics, ORP and bacterial community structure

Excess sulfate production and low concentration of perchlorate removal are the main problems for sulfur-based perchlorate reduction reactor. In this study, the problems were firstly solved by step-feeding under mixotrophic conditions. The performances of step-feed sulfur-based reactor (SFSBR) and up-flow sulfur-based reactor (UFSBR) are compared. At perchlorate of 194 mg/L, acetate of 28.8 mg/L and hydraulic retention time of 0.9 h, the Half-order reaction rate constant and the sulfate production of SFSBR were 29.7 mg^1/2/L^1/2·h and 171 mg/L, respectively, which were superior to those of UFSBR. The oxidation-reduction potential values of SFSBR were lower than that of UFSBR. Meanwhile, the biodiversity along the height of the reactor was decreased by step-feeding. Principal component analysis showed significant interrelations existed among the bacterial community composition and the operational/environmental conditions in each treatment zone. Consequently, the SFSBR provides an effectively alteration for the removal of high perchlorate concentration and control sulfate.

Bio-reduction of free and laden perchlorate by the pure and mixed perchlorate reducing bacteria: Considering the pH and coexisting nitrate

Pure bacteria cell (Azospira sp. KJ) and mixed perchlorate reducing bacteria (MPRB) were employed for decomposing the free perchlorate in water as well as the laden perchlorate on surface of quaternary ammonium wheat residuals (QAWR). Results indicated that perchlorate was decomposed by the Azospira sp. KJ prior to nitrate while MPRB was just the reverse. Bio-reduction of laden perchlorate by Azospira sp. KJ was optimal at pH 8.0. In contrast, bio-reduction of laden perchlorate by MPRB was optimal at pH 7.0. Generally, the rate of perchlorate reduction was controlled by the enzyme activity of PRB. In addition, perchlorate recovery (26.0 mg/g) onto bio-regenerated QAWR by MPRB was observed with a small decrease as compared with that (31.1 mg/g) by Azospira sp. KJ at first 48 h. Basically, this study is expected to offer some different ideas on bio-regeneration of perchlorate-saturated adsorbents using biological process, which may provide the economically alternative to conventional methods.

Perchlorate contamination in Chile: Legacy, challenges, and potential solutions

This paper reviews the unique situation of perchlorate contamination in Chile, including its sources, presence in environmental media and in the human population, and possible steps to mitigate its health impacts. Perchlorate is a ubiquitous water contaminant that inhibits thyroid function. Standards for drinking water range from 2 to 18 µg L^-1 in United States and Europe. A major natural source of perchlorate contamination is Chile saltpeter, found in the Atacama Desert. High concentrations of perchlorate have presumably existed in this region, in soils, sediments, surface waters and groundwaters, for millions of years. As a result of this presence, and the use of Chile saltpeter as a nitrogen fertilizer, perchlorate in Chile has been found at concentrations as high as 1480 µg L^-1 in drinking water, 140 µg/kg^-1 in fruits, and 30 µg L^-1 in wine. Health studies in Chile have shown concentrations of 100 µg L^-1 in breast milk and 20 µg L^-1 in neonatal serum. It is important to acknowledge perchlorate as a potential health concern in Chile, and assess mitigation strategies. A more thorough survey of perchlorate in Chilean soils, sediments, surface waters, groundwaters, and food products can help better assess the risks and potentially develop standards. Also, perchlorate treatment technologies should be more closely assessed for relevance to Chile. The Atacama Desert is a unique biogeochemical environment, with millions of years of perchlorate exposure, which can be mined for novel perchlorate-reducing microorganisms, potentially leading to new biological treatment processes for perchlorate-containing waters, brines, and fertilizers.

Draft Genome Sequence of Azospira sp. Strain I13, a Nitrous Oxide-Reducing Bacterium Harboring Clade II Type nosZ

We report here a draft genome sequence of Azospira sp. strain I13 in the class Betaproteobacteria, a facultative anaerobic bacterium responsible for nitrous oxide (N₂O) reduction. Deciphering this genome would pave the way for the use of Azospira sp. strain I13 to facilitate N₂O consumption in a nitrogen-removing bioreactor emitting N₂O.

Bioelectroremediation of perchlorate and nitrate contaminated water: A review

Fresh water is a fundamental source for humans, hence the recent shrinkage in freshwater and increase in water pollution are imperative problems that vigorously affect the people and the environment worldwide. The breakneck industrialization contributes to the procreation of substantial abundance of wastewater and its treatment becomes highly indispensable. Perchlorate and nitrate containing wastewaters poses a serious threat to human health and environment. Conventional biological treatment methods are expensive and also not effective for treating wastewater effectively and incapable of in situ bioremediation. Bioelectrochemical systems are emerging as a new technology platform for a sustainable removal of such contaminants from wastewater streams. This article reviews the state of art of bioelectroremediation of contaminated waters with perchlorate and nitrate. Different aspects of this technology such as configuration and design, mode of operation and type of substrate are considered in detail.

Chlorate origin and fate in shallow groundwater below agricultural landscapes

In agricultural lowland landscapes, intensive agricultural is accompanied by a wide use of agrochemical application, like pesticides and fertilizers. The latter often causes serious environmental threats such as N compounds leaching and surface water eutrophication; additionally, since perchlorate can be present as impurities in many fertilizers, the potential presence of perchlorates and their by-products like chlorates and chlorites in shallow groundwater could be a reason of concern. In this light, the present manuscript reports the first temporal and spatial variation of chlorates, chlorites and major anions concentrations in the shallow unconfined aquifer belonging to Ferrara province (in the Po River plain). The study was made in 56 different locations to obtain insight on groundwater chemical composition and its sediment matrix interactions. During the monitoring period from 2010 to 2011, in June 2011 a nonpoint pollution of chlorates was found in the shallow unconfined aquifer belonging to Ferrara province. Detected chlorates concentrations ranged between 0.01 and 38 mg/l with an average value of 2.9 mg/l. Chlorates were found in 49 wells out of 56 and in all types of lithology constituting the shallow aquifer. Chlorates concentrations appeared to be linked to NO₃^-, volatile fatty acids (VFA) and oxygen reduction potential (ORP) variations. Chlorates behaviour was related to the biodegradation of perchlorates, since perchlorates are favourable electron acceptors for the oxidation of labile dissolved organic carbon (DOC) in groundwater. Further studies must take into consideration to monitor ClO₄^- in pore waters and groundwater to better elucidate the mass flux of ClO₄^- in shallow aquifers belonging to agricultural landscapes.

Effect of thiosulfate on rapid start-up of sulfur-based reduction of high concentrated perchlorate: A study of kinetics, extracellular polymeric substances (EPS) and bacterial community structure

Perchlorate (ClO₄^-) contamination is more and more concerned due to the hazards to humans. Based on the common primary bacterium (Helicobacteraceae) of both thiosulfate-acclimated sludge (T-Acc) and sulfur-acclimated sludge (S-Acc) for perchlorate reduction, the rapid start-up of sulfur-based perchlorate reduction reactor (SBPRR) was hypothesized by inoculating T-Acc. Furthermore, the performance of SBPRR, the SO₄^2- yield, kinetics of ClO₄^- reduction and the extracellular polymeric substances (EPS) of biofilm confirmed the hypothesis. The start-up time of R3 (reactor inoculating T-Acc) was 0.18 and 0.21 times that of R1 (control) and R2 (reactor with the influent containing thiosulfate), respectively. The SO₄^2- yield of R3 was lower than that of R2 and R1 with perchlorate removal rate 166.7mg/(Lh). The kinetic study and EPS demonstrated that inoculating T-Acc was beneficial for the development of biofilm. Consequently, the present study indicated that SBPRR can be rapidly and successfully started-up via inoculation of T-Acc.

Characteristics of electron transport chain and affecting factors for thiosulfate-driven perchlorate reduction

The mechanism for perchlorate reduction was investigated using thiosulfate-driven (T-driven) perchlorate reduction bacteria. The influences of various environmental conditions on perchlorate reduction, including pH, temperature and electron acceptors were examined. The maximum perchlorate removal rate was observed at pH 7.5 and 40 °C. Perchlorate reduction was delayed due to the coexistence of perchlorate-chlorate and perchlorate-nitrate. The mechanism of the T-driven perchlorate reduction electron transport chain (ETC) was also investigated by utilizing different inhibitors. The results were as follows: firstly, the NADH dehydrogenase was not involved in the ETC; secondly, the FAD dehydrogenase and quinone loop participated in the ETC; and thirdly, cytochrome oxidase was the main pathway in the ETC. Meanwhile, microbial consortium structure analysis indicated that Sulfurovum which can oxidize sulfur compounds coupled to the reduction of nitrate or perchlorate was the primary bacterium in the T-driven and sulfur-driven consortium. This study generates a better understanding of the mechanism of T-driven perchlorate reduction.

Bacterial reduction of highly concentrated perchlorate: Kinetics and influence of co-existing electron acceptors, temperature, pH and electron donors

Perchlorate reduction kinetics and effects of various environmental conditions on removal of perchlorate from synthetic water were investigated to seek high-strength perchlorate removal using mixed perchlorate reducing bacteria. Results demonstrated that perchlorate (50-1500 mg L(-1)) could be degraded rapidly within 28 h under the optimal conditions. The maximum specific perchlorate reduction rate (qmax) and half saturation constant (Ks) were 0.92 mg-perchlorate (mg-dry weight)(-1) h(-1) and 157.7 mg L(-1), respectively. In the ClO4(-)-NO3(-) systems obvious but recoverable lags were caused in perchlorate reduction and the lag time increased with the ratio of nitrate to perchlorate concentration increasing from 0.5 to 3. While in the ClO4(-)-SO4(2-) systems inhibitions didn't occur until the ratio of sulfate to perchlorate concentration exceeded 10. The optimum temperature and pH value were 35 °C and 6.85, respectively. The optimal acetate-to-perchlorate ratio that could consume all perchlorate and acetate simultaneously was about 2. Dechloromonas, one of the most prominent perchlorate reducing bacteria, was identified as the dominant bacterium in the acclimated culture (69.33% of the whole clones). The study demonstrated that the perchlorate-acclimated mixed microorganisms can readily and efficiently realize reduction of highly concentrated perchlorate in wastewater.

Perchlorate in Lake Water from an Operating Diamond Mine

Mining-related perchlorate [ClO4(-)] in the receiving environment was investigated at the operating open-pit and underground Diavik diamond mine, Northwest Territories, Canada. Samples were collected over four years and ClO4(-) was measured in various mine waters, the 560 km(2) ultraoligotrophic receiving lake, background lake water and snow distal from the mine. Groundwaters from the underground mine had variable ClO4(-) concentrations, up to 157 μg L(-1), and were typically an order of magnitude higher than concentrations in combined mine waters prior to treatment and discharge to the lake. Snow core samples had a mean ClO4(-) concentration of 0.021 μg L(-1) (n=16). Snow and lake water Cl(-)/ClO4(-) ratios suggest evapoconcentration was not an important process affecting lake ClO4(-) concentrations. The multiyear mean ClO4(-) concentrations in the lake were 0.30 μg L(-1) (n = 114) in open water and 0.24 μg L(-1) (n = 107) under ice, much below the Canadian drinking water guideline of 6 μg L(-1). Receiving lake concentrations of ClO4(-) generally decreased year over year and ClO4(-) was not likely [biogeo]chemically attenuated within the receiving lake. The discharge of treated mine water was shown to contribute mining-related ClO4(-) to the lake and the low concentrations after 12 years of mining were attributed to the large volume of the receiving lake.

Chitosan derivatives as important biorefinery intermediates. Quaternary tetraalkylammonium chitosan derivatives utilized in anion exchange chromatography for perchlorate removal

There has recently been great interest in the valorization of biomass waste in the context of the biorefinery. The biopolymer chitosan, derived from chitin, is present in large quantities of crustacean waste. This biomass can be converted into value-added products with applications in energy, fuel, chemicals and materials manufacturing. The many reported applications of this polymer can be attributed to its unique properties, such as biocompatibility, chemical versatility, biodegradability and low toxicity. Cost effective water filters which decontaminate water by removal of specific impurities and microbes are in great demand. To address this need, the development of ion exchange resins using environmentally friendly, renewable materials such as biopolymers as solid supports was evaluated. The identification and remediation of perchlorate contaminated water using an easy, inexpensive method has come under the spotlight recently. Similarly, the use of a low cost perchlorate selective solid phase extraction (SPE) cartridge that can be rapidly employed in the field is desirable. Chitosan based SPE coupled with colorimetric analytical methods showed promise as a renewable anion exchange support for perchlorate analysis or removal. The polymers displayed perchlorate retention comparable to the commercial standard whereby the quaternized iron loaded polymer TMC-Fe(III) displayed the best activity.