Thiocyanate Biodegradation Research Articles

Effective thiocyanate biodegradation mediated by bacteria associated to Argentinean mining areas potentially applicable to wastewater biotreatment

Effective thiocyanate biodegradation mediated by bacteria associated to Argentinean mining areas potentially applicable to wastewater biotreatment

Enhanced biodegradation of thiocyanate by immobilized Bacillusbrevis

Biodegradation of Thiocyanate by Free and Immobilized Bacillus brevis was explored. Lignite carbon and Alginate beads have been used as immobilization matrices to study the degradation of thiocyanate with immobilized cells. The rate of thiocyanate degradation is found to be higher by immobilized cells. Cells on lignite carbon matrix are more efficient than cells on alginate beads. The tolerance of the bacteria to the toxic chemical increases by immobilization. Degradation of 100 ppm of thiocyanate was achieved in 20 h by immobilized Bacillus brevis onto lignite carbon. Reduced cost and simplicity make this technique very useful for wastewater treatment.

Metabolic engineering of Oryza sativa for complete biodegradation of thiocyanate

Industrial thiocyanate (SCN−) waste streams from gold mining and coal coking have caused serious environmental pollution worldwide. Phytoremediation is an efficient technology in treating hazardous wastes from the environment. However, the phytoremediation efficiency of thiocyanate is very low due to the fact that plants lack thiocyanate degradation enzymes. In this study, the thiocyanate hydrolase module was assembled correctly in rice seedlings and showed thiocyanate hydrolase activity. Rice seedlings engineered to express thiocyanate degrading activity were able to completely remove thiocyanate from coking wastewater. Our findings suggest that transforming the thiocyanate hydrolase module into plants is an efficient strategy for rapid phytoremediation of thiocyanate in the environment. Moreover, the rice seedlings expressing apoplastic or cytoplasmic targeted thiocyanate hydrolase module were constructed to compare the phytoremediation efficiency of secretory/intracellular recombinant thiocyanate hydrolase. The most obvious finding from this study is that the apoplastic expression system is more efficient than the cytoplasm expression system in the phytoremediation of thiocyanate. At last, this research also shows that the secreted thiocyanate hydrolase from engineered rice plants does not influence rhizosphere bacterial community composition.

The effect of heavy metals on thiocyanate biodegradation by an autotrophic microbial consortium enriched from mine tailings

Bioremediation systems represent an environmentally sustainable approach to degrading industrially generated thiocyanate (SCN−), with low energy demand and operational costs and high efficiency and substrate specificity. However, heavy metals present in mine tailings effluent may hamper process efficiency by poisoning thiocyanate-degrading microbial consortia. Here, we experimentally tested the tolerance of an autotrophic SCN−-degrading bacterial consortium enriched from gold mine tailings for Zn, Cu, Ni, Cr, and As. All of the selected metals inhibited SCN− biodegradation to different extents, depending on concentration. At pH of 7.8 and 30 °C, complete inhibition of SCN− biodegradation by Zn, Cu, Ni, and Cr occurred at 20, 5, 10, and 6 mg L−1, respectively. Lower concentrations of these metals decreased the rate of SCN− biodegradation, with relatively long lag times. Interestingly, the microbial consortium tolerated As even at 500 mg L−1, although both the rate and extent of SCN− biodegradation were affected. Potentially, the observed As tolerance could be explained by the origin of our microbial consortium in tailings derived from As-enriched gold ore (arsenopyrite). This study highlights the importance of considering metal co-contamination in bioreactor design and operation for SCN− bioremediation at mine sites.Key points• Both the efficiency and rate of SCN−biodegradation were inhibited by heavy metals, to different degrees depending on type and concentration of metal.• The autotrophic microbial consortium was capable of tolerating high concentrations of As, potential having adapted to higher As levels derived from the tailings source.

Development and characterization of an aerobic bacterial consortium for autotrophic biodegradation of thiocyanate

During the SCN− bioremediation, the use of microbial consortia seems to have higher removal rate and steadier removal efficiency than the use of single bacterium, especially in the continuous bioreactor. However, little explanation has been given towards this phenomenon. Here we obtained an aerobic autotrophic bacterial consortium from river sediment after one month of enrichment. It was able to tolerate and degrade up to 70 mM SCN− in batch culture and had a maximum removal rate of 1.4 mmol L−1h−1 in a continuous biofilm reactor. High-throughput sequencing and metagenomic analysis revealed that the genus Thiobacillus was the predominant member in the bacterial consortium, which accounted for 43% and 58% of the total communities, respectively. Along with the identification of SCNase encoding genes only in Thiobacillus, this bacterial group was recognized as the main contributor responsible for the SCN− removal. Seven bacterial strains were isolated from the bacterial consortium; only the isolate belonging to Thiobacillus was determined to be able to degrade SCN−. In particular, in the presence of other sulfide-oxidizing bacterium (Hydrogenophaga), the Thiobacillus strain could achieve higher removal efficiency than it alone. According to the genome-based analysis, a cross-feeding pattern between the SCN− -degrading autotrophs and sulfide-oxidizing heterotrophs was proposed, which makes the cooperation between individuals more effective than the single bacterial group for the SCN− removal. This study provides a new insight into the SCN− degradation and gives a potential explanation as to why consortium would be more suitable for the SCN− removal.

Continuous removals of phenol, organics, thiocyanate and nitrogen in horizontal subsurface flow constructed wetland

The objective of the present study was to achieve treatment of phenol, thiocyanate and ammonia containing wastewater in a horizontal subsurface flow constructed wetland. Influent wastewater contained acetate of 850 mg/L, phenol of 92 mg/L, thiocyanate of 45 mg/L, ammonium nitrogen of 88 mg/L with chemical oxygen demand of 624 mg/L. The system was operated under aerial organic loading of 24.5 g COD/m2 d and volumetric organic loading of 65.4 g COD/m3 d. The CW was divided into four zones (zones I to IV) and operated in continuous flow mode at hydraulic retention time (HRT) of 3 days. Typha angustifolia was planted in zone I, II and IV. Increase in ambient temperature improved pollutant removal in CW. Intermittent aeration and feed sodium acetate (carbon source) had a negligible effect on the performance of the CW. Phenol and COD removals were 99 % and 93 %, respectively and zone 1 was highly efficient for removal of organics. Feed alkalinity addition improved thiocyanate removal to 91 % and sulphate concentration increased in the effluent. Thiocyanate biodegradation followed both aerobic and anaerobic pathways. Ammonia nitrogen and total nitrogen removal efficiencies varied between 17–30 % and 7–28 %, respectively, and the removal might be mainly due to plant uptake. Typha angustifolia grew well in the wetland without showing any toxicity effects.

Biodegradation of thiocyanate by a native groundwater microbial consortium.

Gold ore processing typically generates large amounts of thiocyanate (SCN−)-contaminated effluent. When this effluent is stored in unlined tailings dams, contamination of the underlying aquifer can occur. The potential for bioremediation of SCN−-contaminated groundwater, either in situ or ex situ, remains largely unexplored. This study aimed to enrich and characterise SCN−-degrading microorganisms from mining-contaminated groundwater under a range of culturing conditions. Mildly acidic and suboxic groundwater, containing ∼135 mg L−1 SCN−, was collected from an aquifer below an unlined tailings dam. An SCN−-degrading consortium was enriched from contaminated groundwater using combinatory amendments of air, glucose and phosphate. Biodegradation occurred in all oxic cultures, except with the sole addition of glucose, but was inhibited by NH4+ and did not occur under anoxic conditions. The SCN−-degrading consortium was characterised using 16S and 18S rRNA gene sequencing, identifying a variety of heterotrophic taxa in addition to sulphur-oxidising bacteria. Interestingly, few recognised SCN−-degrading taxa were identified in significant abundance. These results provide both proof-of-concept and the required conditions for biostimulation of SCN− degradation in groundwater by native aquifer microorganisms.

Thiocyanate biodegradation: harnessing microbial metabolism for mine remediation

Thiocyanate (SCN–) forms in the reaction between cyanide (CN–) and reduced sulfur species, e.g. in gold ore processing and coal-coking wastewater streams, where it is present at millimolar (mM) concentrations1. Thiocyanate is also present naturally at nM to µM concentrations in uncontaminated aquatic environments2. Although less toxic than its precursor CN–, SCN– can harm plants and animals at higher concentrations3, and thus needs to be removed from wastewater streams prior to disposal or reuse. Fortunately, SCN– can be biodegraded by microorganisms as a supply of reduced sulfur and nitrogen for energy sources, in addition to nutrients for growth4. Research into how we can best harness the ability of microbes to degrade SCN– may offer newer, more cost-effective and environmentally sustainable treatment solutions5. By studying biodegradation pathways of SCN– in laboratory and field treatment bioreactor systems, we can also gain fundamental insights into connections across the natural biogeochemical cycles of carbon, sulfur and nitrogen6.

In Situ Stimulation of Thiocyanate Biodegradation through Phosphate Amendment in Gold Mine Tailings Water.

Thiocyanate (SCN-) is a contaminant requiring remediation in gold mine tailings and wastewaters globally. Seepage of SCN--contaminated waters into aquifers can occur from unlined or structurally compromised mine tailings storage facilities. A wide variety of microorganisms are known to be capable of biodegrading SCN-; however, little is known regarding the potential of native microbes for in situ SCN- biodegradation, a remediation option that is less costly than engineered approaches. Here we experimentally characterize the principal biogeochemical barrier to SCN- biodegradation for an autotrophic microbial consortium enriched from mine tailings, to arrive at an environmentally realistic assessment of in situ SCN- biodegradation potential. Upon amendment with phosphate, the consortium completely degraded up to ∼10 mM SCN- to ammonium and sulfate, with some evidence of nitrification of the ammonium to nitrate. Although similarly enriched in known SCN--degrading strains of thiobacilli, this consortium differed in its source (mine tailings) and metabolism (autotrophy) from those of previous studies. Our results provide a proof of concept that phosphate limitation may be the principal barrier to in situ SCN- biodegradation in mine tailing waters and also yield new insights into the microbial ecology of in situ SCN- bioremediation involving autotrophic sulfur-oxidizing bacteria.

Biodegradation of Thiocyanate and Cyanide in CIL Leaching Waste’s Liquid Phase

The ability of neutrophilic bacterium association to destruct thiocyanates and cyanides was found when working with oxidation of elemental and sulphide sulfur in biocake [1]. It was used for microorganisms association selection, which will oxidize thiocyanates and cyanides in liquid CIL tails of Olimpiada gold recovery plant. Originally selection occurred in laboratory reactors in periodical and later in continuous operation with thiocyanate content of 400-500 ml/l. Molasses in concentration of 0,5 g/l used as a source of carbons. After thiocyanates and cyanides stable oxidation in laboratory conditions the process was transferred to larger reactors (capacity of 2,2 m3). As a result of the research, rhodanides concentration reached 1800 mg/l. During the research rhodanides concentration was reduced from 1800 mg/l to 0,02 mg/l and cyanides concentration was reduced from 20 mg/l to 0,01 mg/l. Oxidation took 24 hours. Microbiological researches with application of molecular genetic analysis have shown that in the selected thiocyanate destructive association prevail the following strains: Pseudomonasaeruginosa, Stenotrophomonasmaltophilia and Enterobacter.

Performance of a continuously stirred tank bioreactor system connected in series for the biodegradation of thiocyanate and free cyanide

A microbial consortium which was largely dominated by Thiobacillus sp. and Serratia sp. was evaluated for the biodegradation of thiocyanate (SCN−) and free cyanide (CN−) under neutral to alkaline conditions, in a two-staged stirred tank bioreactor system operated in series. The bioreactors were operated across a range of residence times (7 d to 24h), SCN− (100–1000mg SCN−/L) and CN− (200–450mg CN−/L) concentrations at room temperature (21–25°C). The bioreactors were characterised by high SCN− degradation efficiencies (>99.9%) throughout the experimental run except when the microorganisms were temporarily shocked by a pH increase and the introduction of CN− within the system. Similarly, high CN− biodegradation efficiencies (>99.9%) were observed subsequent to its introduction to the system. Planktonic microbial activity tests by organisms within the bioreactor system revealed high SCN− and CN− degradation efficiencies (>80%); a direct indication of high planktonic microbial activity within the bioreactor system. Furthermore, there was an observed total nitrogen removal by the organisms within the system, which demonstrated the nitrification and denitrification capacity of the organisms while the sulphate concentration increased as a result of SCN− biodegradation, over a period of approximately 300days. This is the first report on the simultaneous biodegradation of high CN− and SCN− concentrations, coupled with nitrogen removal under alkaline conditions. The results demonstrated the potential of the process to treat CN− and SCN− laden wastewaters.

Understanding the simultaneous biodegradation of thiocyanate and salicylic acid by Paracoccus thiocyanatus and Pseudomonas putida

Phenolic and cyanide compounds, which frequently appear mixed in several industrial effluents, are difficult to be biodegraded under certain conditions. In this work, salicylic acid (SA) and thiocyanate (SCN−) were selected as model pollutants of these two families and experiments of biodegradation with specific microorganisms were developed. It was found that the best well-known bacteria able to biodegrade each one of these pollutants, Pseudomonas putida for SA and Paracoccus thiocyanatus for SCN−, do not biodegrade the other one. Therefore, the co-culture was required, producing interesting interaction phenomena. When both pollutants were simultaneously biodegraded, a commensalism effect was observed improving SCN− removal. Experimental data for SCN− and SA removals were successfully fitted to zero reaction kinetic orders, with induction time in the case of SCN−, and substrate dependences were fitted to Tessier models. A flow cytometry method was developed and employed to obtain the evolution of the viable, damaged and dead cells for different substrate concentration and the degree of agglomeration in the co-culture experiments.

Characterisation of the complex microbial community associated with the ASTER™ thiocyanate biodegradation system

The ASTER™ process is used to bioremediate cyanide- (CN−) and thiocyanate- (SCN−) containing waste water. This aerobic process is able to reduce the CN− and SCN− concentrations to below 1mg/L efficiently in a continuous system, facilitating reuse of process water or safe discharge. Such remediation systems, which completely eliminate risk associated with the pollutants, are essential for sustainable mineral processing and the long term minimisation of environmental burden through both pollutant destruction and exploiting opportunities for nutrient recycle. Process robustness of these bioremediation options can be enhanced by good understanding of the microbial community involved in the process. To date, the microbial consortia associated with the ASTER™ bioprocess have been poorly characterised using isolation approaches only. As a result, the relative abundance and diversity of the community has been significantly under-represented. In this study, both planktonic and biofilm-associated biomass have been observed. Microscopy has revealed the diversity of these communities, including bacteria, motile eukaryotes, filamentous fungi and algae, with the biofilm densely packed with microorganisms. The results of the molecular characterisation study reported here, using a clone library approach, demonstrate that the microbial community associated with the ASTER™ bioprocess system is far more complex than previously suggested, with over 30 bacterial species identified thus far. On-going investigations focus on identification of key microbial community members associated with SCN− biodegradation and other critical metabolic functions, as well as the expected dynamic response of this complex microbial community to shifts in the operating window of the process.

Conditions and Mechanisms in Thiocyanate Biodegradation

Presence of thiocyanate (SCN–) is a problem of considerable interest in many industrial wastewaters, where this contaminant often appears accompanied by secondary sources of carbon, nitrogen and/or sulphur. In order to understand the effect of these compounds on the biodegradability of SCN–, this work investigates how the bacterium Pararacoccus thiocyanatus utilises the three elements that form the molecule of thiocyanate and compare this behaviour with those obtained in presence of other sources of N, S and C. Result showed that the bacterium was capable of utilizing thiocyanate as the sole substrate, achieving specific biodegradation rates of approximate 1.20 mg SCN– (mg cell·h)–1 and eliminating initial thiocyanate concentrations up to 5,000 mg L–1. Experimental data were successfully fitted to a Teisser model, assuming the existence of substrate inhibition obtaining values of μmax of 0.059 h–1, Ks of 790 mg L–1 and Ki of 6,520 mg L–1 for free mineral medium. Presence of additional carbon and nitrogen sources implied catabolic repression of the biodegradation of thiocyanate. In this case, only concentrations lower than 3,500 mg L–1 could be treated, obtaining specific degradation rates of around 0.70 mg SCN–·(h·mg cell)–1. Tessier model values showed a higher maximum specific growth rate (0.344 h–1), changing also the values for affinity and inhibition constants (1,150 mg L–1 and 1,730 mg L–1, respectively).

Biodegradation of thiocyanate by a novel strain of Burkholderia phytofirmans from soil contaminated by gold mine tailings

A novel B.phytofirmans strain with the capacity to degrade thiocyanate was isolated from pH approximately 6·5 soil contaminated by effluent from gold mine tailings. This Burkholderia strain uses thiocyanate as its sole nitrogen source and can grow on acetate as a sole carbon source in a minimal medium. While biodegradation of thiocyanate has been reported to occur within alkaline environments (e.g. soda lakes and wastewater from coking plants), this work presents the first observation of thiocyanate degradation by Burkholderia at pH <9·0. Our findings therefore inform remediation strategies for thiocyanate contamination in nonalkaline soils and waters impacted by gold-mining activities. This work describes thiocyanate biodegradation by a novel Burkholderia phytofirmans strain isolated from circumneutral pH gold mining-contaminated soils. Previous reports of bacterial thiocyanate degradation have mainly focused on alkaline environments or culturing conditions (pH≥9). Because cyanidation is used globally in gold mining, with thiocyanate as the major contaminant, our results will interest those working on biotechnological approaches to gold mine waste remediation.

Thiocyanate Oxidation by Coculture from a Coke Wastewater Treatment Plant

Bacterial strains in an activated sludge aerobic reactor from a coke wastewater were found to be able to utilize thiocyanate as carbon source when the thiocyanate-containing wastewater was deprived of carbon source. This study showed that three thiocyanate-oxidizing bacterial strains, Burkholderia sp., Chryseobacterium sp., and Ralstonia sp. were isolated from the activated sludge of a coke wastewater treatment plant as evidenced by the fact that complete decomposition of thiocyanate was achieved either by coculture or individual pure culture. The thiocyanate biodegradation by the coculture occurred with an optimal pH range between 6.5 and 8.5 and an optimal temperature range between 30°C and 40°C. The biodegradation kinetics of thiocyanate was well fitted with the Andrew-Haldane model, which demonstrated a distinct substrate concentration-inhibited bacterial growth pattern. The effects of different types of additional carbon, nitrogen or sulfur sources on thiocyanate biodegradation were also investigated. Analysis of the end-products indicated that thiocyanate degradation by these strains should proceed via two pathways.

Effects of temperature and pH on the biokinetic properties of thiocyanate biodegradation under autotrophic conditions

The simultaneous effects of temperature and pH on the biokinetic properties of thiocyanate biodegradation under mixed-culture, autotrophic conditions were investigated using response surface analysis (RSA) combined with biokinetic modeling. A partial cubic model, based on substrate inhibition biokinetics, was constructed for each kinetic coefficient in Andrew model (i.e., maximum specific growth rate (μm), saturation coefficient (KS), and substrate inhibition coefficient (KSI)). Each model proved statistically reliable to approximate the responses of the kinetic coefficients to temperature and pH changes (r2 > 0.8, p < 0.05). The response surface plots demonstrated that the biokinetic coefficients change with respect to temperature and pH significantly and in different ways. The model response surfaces were substantially different to each other, indicating distinct correlations between the independent (temperature and pH) and dependent (model response) variables in the models. Based on the estimated response surface models, temperature was shown to have significant effects on all biokinetic coefficients tested. A dominant influence of temperature on μm response was observed while the interdependence of temperature and pH was apparent in the KS and KSI models. Specific growth rate (μ) versus substrate (i.e., thiocyanate) concentration plots simulating using the obtained response surface models confirmed the significant effects of temperature and pH on the microbial growth rate and therefore on the thiocyanate degradation rate. Overall, the response surface models able to describe the biokinetic effects of temperature and pH on thiocyanate biodegradation within the explored region (20–30 °C and pH 6.0–9.0) were successfully constructed and validated, providing fundamental information for better process control in thiocyanate treatment.

Polyphasic bacterial community analysis of an aerobic activated sludge removing phenols and thiocyanate from coke plant effluent

Biological purification processes are effective tools in the treatment of hazardous wastes such as toxic compounds produced in coal coking. In this study, the microbial community of a lab-scale activated sludge system treating coking effluent was assessed by cultivation-based (strain isolation and identification, biodegradation tests) and culture-independent techniques (sequence-aided T-RFLP, taxon-specific PCR). The results of the applied polyphasic approach showed a simple microbial community dominated by easily culturable heterotrophic bacteria. Comamonas badia was identified as the key microbe of the system, since it was the predominant member of the bacterial community, and its phenol degradation capacity was also proved. Metabolism of phenol, even at elevated concentrations (up to 1500 mg/L), was also presented for many other dominant ( Pseudomonas, Rhodanobacter, Oligella) and minor ( Alcaligenes, Castellaniella, Microbacterium) groups, while some activated sludge bacteria ( Sphingomonas, Rhodopseudomonas) did not tolerate it even in lower concentrations (250 mg/L). In some cases, closely related strains showed different tolerance and degradation properties. Members of the genus Thiobacillus were detected in the activated sludge, and were supposedly responsible for the intensive thiocyanate biodegradation observed in the system. Additionally, some identified bacteria (e.g. C. badia and the Ottowia-related strains) might also have had a significant impact on the structure of the activated sludge due to their floc-forming abilities.

Biodegradation of thiocyanate using co-culture of Klebsiella pneumoniae and Ralstonia sp.

Thiocyanate-degrading microbial co-culture was isolated from thiocyanate-contaminated site and tested for thiocyanate degradation potential and thiocyanate-toxicity tolerance and identified as Klebsiella pneumoniae and Ralstonia sp. by 16S rDNA sequencing. The co-culture was able to degrade thiocyanate with degradation rate of 500 mg L(-1)d(-1) at 2,500 mg L(-1) thiocyanate concentration at pH 6.0 and 37 degrees C following thiocyanate hydrolase pathway. The Haldane kinetic model elucidates the growth and thiocyanate biodegradation kinetics of the co-culture with Ki value of 1,876 mg L(-1). The thiocyanate biodegradation kinetics was not affected by the additional supply of glucose. The very high activities of thiocyanate hydrolase, cyanide oxygenase, and cytochrome P-450 content during growth on thiocyanate were observed, showing the induction mechanism.

Biochemical indication of microbial mass changes using ATP and DNA measurement in biological treatment of thiocyanate

This study was designed to monitor changes in the levels of adenosine 5'-triphosphate (ATP) and deoxyribonucleic acid (DNA) per unit of microbial mass during the autotrophic biodegradation of thiocyanate (SCN(-)). An artificial medium containing trace minerals and 500 mg SCN(-)/L was used as a substrate for bacterial growth. An SCN(-)-degrading bioreactor with a working volume of 6 L, equipped with temperature, pH, and dissolved oxygen controls, was operated in batch mode. During the exponential phase of SCN(-) biodegradation, the ratios of ATP and DNA to microbial dry weight varied from 0.6 to 1.1 microg ATP/mg of volatile suspended solid (VSS), and from 3.5 to 8.8 microg DNA/mg of VSS, respectively. The ATP and DNA concentrations correlated linearly with microbial mass (r (2) > 0.9) within the exponential phase. The linear regression equations were as follows: (1) microbial mass concentration (mg/L) = 0.663 x ATP concentration (microg/L) + 11.1 and (2) microbial concentration (mg/L) = 0.081 x DNA concentration (microg/L) + 10.9. The applicable ranges were 6.8 to 47.4 microg/L for ATP concentration and 41.5 to 395 microg/L for DNA concentration, respectively.