Reduction of perchlorate by salt tolerant bacterial consortia

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.

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.

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.

The rapid adsorption-microbial reduction of perchlorate from aqueous solution by novel amine-crosslinked magnetic biopolymer resin

The aim of this work was to study the adsorption characters of resin, microbial reduction of perchlorate and combined process of perchlorate removal in aqueous solution. Study demonstrated the adsorption equilibrium was achieved in 120min, which based on ion exchange reaction. Dissolved perchlorate (100mg/L) can be completely removed by acclimated anaerobic sludge in 15h, and the concentrated perchlorate (∼200mg/g) on the surface of resin would be effectively microbial reduced after 3days. Neutral environment (pH=7.4), higher biomass and additional electron donor can apparently improve the biological reduction efficiency of concentrated perchlorate. Addition of many co-anions showed the competition adsorption towards perchlorate, especially in the presence of NO₃^-. This study provides an effective method for perchlorate reduction by the adsorption-microbial process.

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.

Removal of perchlorate from water using a biofilm magnetic ion exchange resin: feasibility and effects of dissolved oxygen, pH and competing ions

A biofilm magnetic ion exchange (BMIEX) resin was obtained by mixing a magnetic ion exchange (MIEX) resin with perchlorate-acclimated cultures and was first proposed to remove perchlorate from water.

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

Bioremediation of perchlorate-cotaminated water by a heterotrophic perchlorate reducing bacterium creates a multiple electron acceptor-donor system. We experimentally determined the perchlorate reduction by Azospira sp. KJ at multiple pH, electron acceptors and donors systems; this was the aim of this study. Perchlorate reduction was drastically inhibited at the pH 6.0, and the maximum reduction of perchlorate by Azospira sp. KJ was observed at pH value of 8.0. Perchlorate reduction was retarded in ClO4(-)-ClO3(-), ClO4(-)-ClO3(-)-NO3(-),and ClO4(-)-NO3(-) acceptor systems, while being completely inhibited by the additional O2 in the ClO4(-)-O2 acceptor system. The reduction proceeded as an order of ClO3(-), ClO4(-), and NO3(-) in the ClO4(-)-ClO3(-)-NO3(-) system. K(S), v(max), and q(max) obtained at different e(-) acceptor and donor conditions are calculated as 140.5-190.6 mg/L, 8.7-13.2 mg-perchlorate/L-h, and 0.094-0.16 mg-perchlorate/mg-DW-h, respectively.

Perchlorate reduction in microbial electrolysis cell with polyaniline modified cathode

Excellent perchlorate reduction was obtained under various initial concentrations in a non-membrane microbial electrolysis cell with polyaniline (PANI) modified graphite cathode as sole electron donor. PANI modification is conducive to the formation of biofilm due to its porous structure and good electrocatalytic performance. Compared with cathode without biofilm, over 12% higher reduction rates were acquired in the presence of biocathode. The study demonstrates that, instead of perchlorate reduction, the main contribution of biofilm is involved in facilitate electron transfer from cathode to electrolyte. Interestingly, hairlike structure, referred as to pili-like, was observed in the biofilm as well as in the electrolyte. Additionally, the results show that pili were prone to formation under the condition of external electron field as sole electron donor. Analysis of microbial community suggests that perchlorate reduction bacteria community was most consistent with Azospiraoryzae strain DSM 13638 in the subdivision of the class Proteobacteria.