ArticleLiterature Review

# Microbial destruction of cyanide wastes in gold mining: Process review

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## Abstract

Microbial destruction of cyanide and its related compounds is one of the most important biotechnologies to emerge in the last two decades for treating process and tailings solutions at precious metals mining operations. Hundreds of plant and microbial species (bacteria, fungi and algae) can detoxify cyanide quickly to environmentally acceptable levels and into less harmful by-products. Full-scale bacterial processes have been used effectively for many years in commercial applications in North America. Several species of bacteria can convert cyanide under both aerobic and anaerobic conditions using it as a primary source of nitrogen and carbon. Other organisms are capable of oxidizing the cyanide related compounds of thiocyanate and ammonia under varying conditions of pH, temperature, nutrient levels, oxygen, and metal concentrations. This paper presents an overview of the destruction of cyanide in mining related solutions by microbial processes.

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... Hundreds of plant and microbial species (bacteria, fungi and algae) can detoxify cyanide quickly to environmentally acceptable levels and into less harmful by-products. Fullscale bacterial processes have been used effectively for many years in commercial applications in North America (Akcil & Mudder, 2003). ...
... Several species of bacteria can convert cyanide, under both aerobic and anaerobic conditions, using it as a primary source of nitrogen and carbon. It is known that other organisms are capable of oxidizing the cyanide related compounds of thiocyanate and ammonia under varying conditions of pH, temperature, nutrient levels, oxygen, and metal concentrations (Akcil & Mudder, 2003). Iron and sulfide can be microbially oxidized to produce ferric iron and sulfuric acid, and these chemicals convert the insoluble sulfides of metals such as copper, nickel and zinc to soluble metal sulfates that can be readily recovered from a solution. ...
... Biological treatment of cyanide has been shown to be a viable and robust process for destroying cyanide in the mine process water. The classic aerobic biological process involves two separate bacterial oxidation steps to facilitate complete assimilation of the wastewater (Akcil and Mudder 2003). SCN -+ 2H 2 O + 5/2O 2 = SO 2-4 + HCO -3 + NH 3 ; (1) ...
... Related to lignin degradation, white-rot fungi face three major challenges associated with lignin structure, i.e. (1) the lignin polymer is large; therefore ligninolytic systems must be extracellular, (2) lignin structure is comprised of interunit carbon-carbon and ether bonds, therefore the degradation mechanism must be oxidative rather than hydrolytic, and (3) lignin polymer is stereo-irregular, therefore the ligninolytic agents must be much less specific than degradative enzymes (Kirk and Cullen, 1998). ...
... Cyanide is often removed from industrial effluents by alkaline chlorination or by using H2O2 or ozone. However, biotechnological treatment of cyanide is considered as most cost-effective and environmentally acceptable than chemical methods (Akcil and Mudder, 2003). The biotechnological processes still being used in this field are mainly based on the results of the studies of the hydrolytic, oxidative, reductive and substitution/transfer pathways for biodegradation of cyanides. ...
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The growing concern over the pollution issues by the rapid industrialization has posed a serious problem forcing researchers around the world to seek alternative eco-friendly technologies. Textile, pulp and paper industries discharge a huge quantity of waste in the environment, and the disposal of this waste is an immense problem. To solve this problem, work has done to discover biotechnological applications such a biological process, which can detoxify wastes and is not damaging the environment. Examples of white-rot fungi that possess selective decay at least under certain condition are C. subvermispora, Dichomitus squalens, P. chrysosporium, and Phlebia radiata. Examples of white-rot fungi that possess non-selective decay are Trametes versicolor and Fomes fomentarius. These enzymatic complexes mainly consist of lignin peroxidases (LiPs), manganese peroxidases (MnPs) and laccases. They also have capability to detoxify a range of environmental pollutants. The present work explores the potential of WRF in more recent areas of their applications such as, textile industries, food industries, bio remediation, pulp and paper industries and animal feed digestibility.
... The first description of an anaerobic cyanide biodegradation process was reported by Fedorak and Hrudey (1989) in methanogenic semicontinuous batch cultures. Since then, various applications based on anaerobic reactors or combining both aerobic and anaerobic processes have been developed for the treatment of different cyanide-containing wastewaters (Gijzen et al. 2000;Akcil and Mudder 2003;Chakraborti and Veeramani 2006;Novak et al. 2013;Joshi et al. 2016), although in general the anaerobic cyanide degradation process is not well understood and there is little knowledge about the microbial communities involved. In addition, abiotic anaerobic cyanide degradation may also occur when cyanide spontaneously hydrolyzes generating formic acid. ...
... The cyanidation process used for extraction of gold and other metals from ores in mining activities generates large amounts of cyanide-containing wastes that require treatment before they can be released to the environment (Luque-Almagro et al. 2016;Mekuto et al. 2016). Different approaches have been applied to remove cyanide from cyanidation and electroplating wastewater, but they operate basically under aerobic conditions (Akcil and Mudder 2003;Sirianuntapiboon et al. 2008;Kuyucak and Akcil 2013;Mekuto et al. 2016). However, laboratory and engineered wetland experiments based on aerobic and anaerobic processes have been used for the construction of a pilot field-scale passive system at a gold mine in northern Spain (Álvarez et al. 2013). ...
Article
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Cyanide is one of the most toxic chemicals for living organisms described so far. Its toxicity is mainly based on the high affinity that cyanide presents toward metals, provoking inhibition of essential metalloenzymes. Cyanide and its cyano-derivatives are produced in a large scale by many industrial activities related to recovering of precious metals in mining and jewelry, coke production, steel hardening, synthesis of organic chemicals, and food processing industries. As consequence, cyanide-containing wastes are accumulated in the environment becoming a risk to human health and ecosystems. Cyanide and related compounds, like nitriles and thiocyanate, are degraded aerobically by numerous bacteria, and therefore, biodegradation has been offered as a clean and cheap strategy to deal with these industrial wastes. Anaerobic biological treatments are often preferred options for wastewater biodegradation. However, at present very little is known about anaerobic degradation of these hazardous compounds. This review is focused on microbial degradation of cyanide and related compounds under anaerobiosis, exploring their potential application in bioremediation of industrial cyanide-containing wastes.
... Owing to their potential environmental toxicity, different cyanide detoxification strategies were adopted and modified during the last few decades. Many chemical and physical methods have been found useful in this detoxification process but numerous factors such as the chemical composition of the waste, its volume, the effluent quality, reagents availability are negatively affecting the feasibility of these methods (Akcil and Mudder 2003;Botz et al. 2015). In the last two decades, many conventional methods including natural, physical, chemical and biological methods (phytoremediation and microbial remediation) have been followed to remove cyanide containing waste from different environmental compartments. ...
... It was found that among all the degradative pathways, only reductive/hydrolytic pathways are feasible under anaerobic conditions (Fallon 1992). Enzymatic cyanide detoxification and cyanide assimilation by different microorganisms have been reviewed extensively and documented well in a number of reviews (Akcil and Mudder 2003;Samiotakis and Ebbs 2004;Baxter and Cummings 2006;Huertas et al. 2006;Dash et al. 2009;Gupta et al. 2010;Kumar et al. 2017;Luque-Almagro et al. 2016;Mekuto et al. 2016;Park et al. 2017). The following section has elaborately described the enzymatic degradation pathways of cyanide bioremediation. ...
Article
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Cyanide is a nitrile which is used extensively in many industries like jewelry, mining, electroplating, plastics, dyes, paints, pharmaceuticals, food processing, and coal coking. Cyanides pose a serious health hazard due to their high affinity towards metals and cause malfunction of cellular respiration by inhibition of cytochrome c oxidase. This inhibition ultimately leads to histotoxic hypoxia, increased acidosis, reduced the functioning of the central nervous system and myocardial activity. Different physicochemical processes including oxidation by hydrogen peroxide, alkaline chlorination, and ozonization have been used to reduce cyanide waste from the environment. Microbial Cyanide Degradation which is considered as one the most successful techniques is used to take place through different biochemical/metabolic pathways involving reductive, oxidative, hydrolytic or substitution/transfer reactions. Groups of enzymes involved in microbial degradation are cyanidase, cyanide hydratase, formamidase, nitrilase, nitrile hydratase, cyanide dioxygenase, cyanide monooxygenase, cyanase and nitrogenase. In the future, more advancement of omics technologies and protein engineering will help us to recoup the environment from cyanide effluent. In this review, we have discussed the origin and environmental distribution of cyanide waste along with different bioremediation pathways and enzymes involved therein.
... To this end, several approaches have been designed to remove cyanide from water bodies and this technique falls into two broad categories namely physical/chemical and biological methods. [5] The current physical/chemical approach mostly involves ozonization, chlorination, etc. [6] In summary, these chemical techniques are often relatively expensive and it also leads to the release of further toxic reaction by-products into the water-bodies. The biological approach to the treatment of cyanide-contaminated wastewater is regarded as the best approach since it is inexpensive, eco-friendly, highly efficient and no release of toxic by-products is observed. ...
... The biological approach to the treatment of cyanide-contaminated wastewater is regarded as the best approach since it is inexpensive, eco-friendly, highly efficient and no release of toxic by-products is observed. [5] Hence the use of biological agents such as microorganisms (bacteria/fungi) and enzymes offer an easily adaptable and environmentally friendly approach to cyanide detoxification in these cyanidecontaminated water-bodies. However, the use of microorganisms in the biodegradation of cyanide albeit comes with some known operational problems like the cassava wastewater (cww) being low in nitrogen and high in chemical oxygen demand. ...
Article
Extracellular rhodanese obtained from Aureobasidium pullulans was employed in both free and immobilized forms for the biodegradation of cyanide present in cassava processing mill effluent (CPME). Crosslinking with glutaraldehyde (at an optimum concentration of 5% v/v) before entrap-ment in alginate beads resulted in the highest immobilization yield of 94.5% and reduced enzyme leakage of 1.8%. Rhodanese immobilized by cross-linking before entrapment (cbe) retained about 46% of its initial activity after eight cycles of catalysis compared to the entrapment in alginate alone (eaa) which lost more than 79% after the fifth catalytic cycle. A cross-examination of thermodynamic (DG Ã d , DS Ã d , DH Ã d) kinetic (k d , t 1=2 , D and z À values) parameters at 30-70
... Cyanide from mining tailings is degraded by natural attenuation, physical, chemical and biological treatments, including phytoremediation and microbial remediation (Mekuto et al. 2016). Particularly, microbial treatment of cyanide is preferred for being more economical and faster Akcil and Mudder 2003), although it depends on several environmental factors such as pH, temperature, concentration, and chemical forms of cyanide, among others. There are four enzymatic pathways for cyanide biodegradation: hydrolytic, oxidative, reductive, and substitution/transfer (Ebbs 2004;Gupta et al. 2010). ...
... Pseudomonas pseudoalcaligenes can use cyanate, cyanoacetamide, and several cyanide-metal complexes as nitrogen sources (Luque-Almagro et al. 2005). Cyanide bioremediation with Pseudomonas sp. is used in the biological treatment process in the Homestake mine (Akcil and Mudder 2003). ...
Article
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Mine tailings and wastewater generate man-made environments with several selective pressures, including the presence of heavy metals, arsenic and high cyanide concentrations, but severe nutritional limitations. Some oligotrophic and pioneer bacteria can colonise and grow in mine wastes containing a low concentration of organic matter and combined nitrogen sources. In this study, Pseudomonas mendocina P6115 was isolated from mine tailings in Durango, Mexico, and identified through a phylogenetic approach of 16S rRNA, gyrB, rpoB, and rpoD genes. Cell growth, cyanide consumption, and ammonia production kinetics in a medium with cyanide as sole nitrogen source showed that at the beginning, the strain grew assimilating cyanide, when cyanide was removed, ammonium was produced and accumulated in the culture medium. However, no clear stoichiometric relationship between both nitrogen sources was observed. Also, cyanide complexes were assimilated as nitrogen sources. Other phenotypic tasks that contribute to the strain’s adaptation to a mine tailing environment included siderophores production in media with moderate amounts of heavy metals, arsenite and arsenate tolerance, and the capacity of oxidizing arsenite. P. mendocina P6115 harbours cioA/cioB and aoxB genes encoding for a cyanide-insensitive oxidase and an arsenite oxidase, respectively. This is the first report where P. mendocina is described as a cyanotrophic and arsenic oxidizing species. Genotypic and phenotypic tasks of P. mendocina P6115 autochthonous from mine wastes are potentially relevant for biological treatment of residues contaminated with cyanide and arsenic.
... Liquid waste containing cyanide and derivatives is generated at a large scale by different industrial activities, such as mining and metal processing, electroplating, coal coking, and nitrile polymer synthesis [5,8,[13][14][15][16][17]. These cyanide-containing wastes often present heavy metals and metalloids, increasing their toxicity and becoming hazardous effluents that are difficult to remove from the environment due to the very high stability of the metal-cyanide complexes. ...
... However, these methods are expensive, require special equipment and maintenance, and are usually inappropriate to degrade metal-cyanide complexes. Therefore, cyanide biodegradation may be an interesting alternative to these treatments [5,[13][14][15][16][17]19]. In this context, the strain P. pseudoalcaligenes CECT5344 was able to grow in a batch reactor at pH 9.5 in the presence of sodium cyanide as the sole nitrogen source, removing cyanide at an optimal rate of 2.3 mg/L × A 600 × h [10]. ...
Article
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The alkaliphilic bacterium Pseudomonas pseudoalcaligenes CECT5344 can grow with cyanate, cyanide, or cyanide-containing industrial residues as the sole nitrogen source, but the assimilation of cyanide and cyanate takes place through independent pathways. Therefore, cyanide degradation involves a chemical reaction between cyanide and oxaloacetate to form a nitrile that is hydrolyzed to ammonium by the nitrilase NitC, whereas cyanate assimilation requires a cyanase that catalyzes cyanate decomposition to ammonium and carbon dioxide. The P. pseudoalcaligenes CECT5344 cynFABDS gene cluster codes for the putative transcriptional regulator CynF, the ABC-type cyanate transporter CynABD, and the cyanase CynS. In this study, transcriptional analysis revealed that the structural cynABDS genes constitute a single transcriptional unit, which was induced by cyanate and repressed by ammonium. Mutational characterization of the cyn genes indicated that CynF was essential for cynABDS gene expression and that nitrate/nitrite transporters may be involved in cyanate uptake, in addition to the CynABD transport system. Biodegradation of hazardous jewelry wastewater containing high amounts of cyanide and metals was achieved in a batch reactor operating at an alkaline pH after chemical treatment with hydrogen peroxide to oxidize cyanide to cyanate.
... carbon dioxide under low oxygen levels at early stationary phase of growth (Laville et al. 1998;Zdor 2014). However, environmental and health problems related to cyanide and its derivatives are caused by human activities, such as nitrile polymers production, plastics, paints, dyes and drugs synthesis, food processing, and particularly coal coking, steel handling, electroplating, jewellery industry and mining, which produce the largest amounts of liquid wastes containing cyanide (Akcil and Mudder 2003;Dash, Gaur and Balomajumder 2009; Luque-Almagro, Moreno-Vivián and Roldán 2016). These industrial wastes often contain metals, which increase the toxicity of the effluents that can be potentially released to the environment. ...
... However, these conventional physical-chemical methods are expensive, require special equipment and maintenance, and are not effective to remove metal-cyanide complexes. Some microorganisms are capable of enzymatic cyanide detoxification, or even cyanide assimilation using this compound as a nitrogen source, so that the biodegradation technology may constitute a potential alternative for the treatment of cyanide-containing liquid industrial wastes (Raybuck 1992;Akcil and Mudder 2003;Ebbs 2004;Baxter and Cummings 2006;Huertas et al. 2006;Dash, Gaur and Balomajumder 2009;Gupta, Balomajumder and Agarwal 2010;Kumar et al. 2016;Luque-Almagro, Moreno-Vivián and Roldán 2016;Park, Sewell and Benedik 2017). Microbial cyanide degradation leads to the formation of non-toxic products, like ammonia and carbon dioxide, and takes place by different biochemical routes involving oxidative, reductive, hydrolytic or substitution/transfer reactions (Table 1). ...
Article
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Mining, jewellery and metal-processing industries use cyanide for extracting gold and other valuable metals, generating large amounts of highly toxic wastewater. Biological treatments may be a clean alternative under the environmental point of view to the conventional physical or chemical processes used to remove cyanide and related compounds from these industrial effluents. Pseudomonas pseudoalcaligenes CECT5344 can grow under alkaline conditions using cyanide, cyanate or different nitriles as the sole nitrogen source, and is able to remove up to 12 mM total cyanide from a jewellery industry wastewater that contains cyanide free and complexed to metals. Complete genome sequencing of this bacterium has allowed the application of transcriptomic and proteomic techniques, providing a holistic view of the cyanide biodegradation process. The complex response to cyanide by the cyanotrophic bacterium Pseudomonas pseudoalcaligenes CECT5344 and the potential biotechnological applications of this model organism in the bioremediation of cyanide-containing industrial residues are reviewed.
... These toxic compounds are discharged in relatively high concentrations and therefore have to be handled promptly to minimize their direct potential risk on the aquatic organisms, as well as indirectly on terrestrial organisms, including humans, through drinking water or contaminated food-chain sources. Traditionally, the chemical oxidation and chlorination reaction processes were the common chemical methods for the detoxification of cyanate and cyanide compounds (Akcil and Mudder 2003;di Biase et al. 2020). However, these chemically-dependent techniques may have a lot of disadvantages including the potential output of toxic byproducts in addition to the high cost (Srivastava and Muni 2010). ...
... Considerable attention has been given to the application of biological treatments especially when chemical treatments have been used. Microbial treatment processes (either aerobic or anaerobic) have been successfully utilized for the aim of removal or extermination of hazardous as organic compounds, inorganic, and metal (Akcil and Mudder 2003). Biological treatments can be applied in many conditions in situ including aerobic, anaerobic, active, passive, and suspended, or attached with growth. ...
Article
Two strains of the chlorophyte Chlamydomonas reinhardtii, a wild type (WT) and a transgenic strain (C.CYN) contained an exogenous cyanase gene (CYN), were used to investigate the growth and cyanate biosorption capability through the analysis of the adsorption equilibrium isotherm. The potential antioxidants activity of the algal strains was also investigated under cyanate concentration. The antioxidants activity of both C.CYN and WT were enhanced by the application of cyanate. Two adsorption isotherm models and the sorption kinetics were used to check the efficiency of the cyanate removal process. The results showed the biosorbent efficiency of Chlamydomonas in the removal of KCNO from aqueous solution. The C.CYN strain has great efficiency to remove cyanate as compared to the WT. The maximum percentage of cyanate removal was 83.75% for the C.CYN and 50% for the WT as treated with 0.8 mg.ml⁻¹ KCNO. The data were adapted to the nonlinear Langmuir model on the basis of the coefficient of determination. The calculated qmax was 0.54 and 0.42 µg.mg⁻¹ for C.CYN and WT which correlated to the experimental one (0.67 and 0.4 µg.mg⁻¹, respectively). Our data highlight the application of the transgenic algal strain toward the removal of highly toxic materials as cyanate. Novelty statement The main objective of this work is to find out an efficient genetically-modified Chlamydomonas strain to remove the highly toxic cyanate compound from contaminated area. Moreover, to evaluate the biosorption ability of this transgenic strain with its wild one via two adsorption isotherm (the Langmuir and Freundlich) models. Also, to estimate the antioxidants activity of these strains under the cyanate toxicity through four different assays.
... To this end, several approaches have been designed to remove cyanide from water bodies and this technique falls into two broad categories namely physical/chemical and biological methods. [5] The current physical/chemical approach mostly involves ozonization, chlorination, etc. [6] In summary, these chemical techniques are often relatively expensive and it also leads to the release of further toxic reaction by-products into the water-bodies. The biological approach to the treatment of cyanide-contaminated wastewater is regarded as the best approach since it is inexpensive, eco-friendly, highly efficient and no release of toxic by-products is observed. ...
... The biological approach to the treatment of cyanide-contaminated wastewater is regarded as the best approach since it is inexpensive, eco-friendly, highly efficient and no release of toxic by-products is observed. [5] Hence the use of biological agents such as microorganisms (bacteria/fungi) and enzymes offer an easily adaptable and environmentally friendly approach to cyanide detoxification in these cyanidecontaminated water-bodies. However, the use of microorganisms in the biodegradation of cyanide albeit comes with some known operational problems like the cassava wastewater (cww) being low in nitrogen and high in chemical oxygen demand. ...
Article
A purified thermostable intracellular laccase obtained from the mycelia of Aureobasidium pullulans (iLAp) was deployed in the biodegradation of bisphenol A (BPA), an endocrine-disrupting compound. iLAp, a 61 kDa monomeric protein, has an of optimal pH and temperature of 3.0, and 50°C respectively with 2, 2-azino-bis [3-ethylbenzothiazoline-6-sulfonic acid] (ABTS) as substrate. iLAp was stable at these optimum pH and temperature for 6 and 8 h respectively retaining about 79 and 80% activity respectively. Thekm(90.7μM),kcat(35.7s−1) and kcatkm(0.39μM−1s−1) values obtained for iLAp, indicated it was more specific for ABTS than pyrogallol, guaiacol, and catechol. iLAp was stable in 10%v/v DMSO, methanol, and DMF. Metals such as Cu²⁺, Ca²⁺, and Mg²⁺ enhanced laccase activity. Thioglycolic acid, dithiothreitol, sodium azide, and SDS strongly inhibited the laccase activity. The values of the kinetic/thermodynamic parameters obtained for iLAp such as: D-value (7302 and 2865 min), t1/2(2198and862min) ΔHd(67.5and67.4kJmol), ΔSd(−[89.4and89.1]J/mol/K) and ΔGd(94.6and95.3kJmol) indicated resistance to thermal inactivation at 40 to 50°C respectively. iLAp was able to biodegrade BPA and the biodegradation efficiency significantly increased (p<0.05) in the presence of ABTS as a mediator. From the GI values, the iLAp-treated BPA showed mild/no phytotoxicity towards Sorghum bicolor.
... Moreover, Tarras-Wahlberg et al. (2001) found that in the Puyango River, which was contaminated by small scale gold mining in southern Ecuador, the concentration of total CN was as high as 110 μg L − 1 , even at 30 km downstream of the mining area. However, CN is still widely used in industrial products, including acrylic plastics, adhesives, and pharmaceuticals (Akcil 2003;Akcil and Mudder 2003). As a result, efficient removal of CN is required. ...
... However, these treatments are expensive and require sophisticated techniques (Akcil 2003). It has been demonstrated that several bacteria and fungi Akcil and Mudder 2003) can break and transform CN into simple non-toxic substances. While bacteria and fungi have been extensively utilized for the biological treatment of CN, only a few studies have reported CN treatment by algae (Gurbuz et al. 2004). ...
Article
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To evaluate the removal of potassium cyanide (KCN) and its toxicity in algae, an initial comprehensive analysis was performed with Chlorella vulgaris. The algae showed potential removal capability for KCN, with the maximal removal rate of 61%. Moreover, effects of KCN on growth, cellular morphology and antioxidant defense system of C. vulgaris were evaluated. Cell number and chlorophyll a content decreased in most cases, with the maximal inhibition rates of 48% and 99%, respectively. The 100 mg L− 1 KCN seriously damaged the algal cell membrane. Additionally, activity of superoxide dismutase (SOD) was promoted by KCN exposure among 0.1–50 mg L− 1 and inhibited by 100 mg L− 1 KCN, while the malondialdehyde (MDA) content gradually decreased in C. vulgaris with increasing exposure concentration compared to the control. The present study reveals that C. vulgaris is useful in bio-treatment of cyanide-contaminated aquatic ecosystem, except in high concentrations which would cause overwhelming effects.
... Several methods of cyanogen reduction have been proposed and include physical, chemical and biological methods [6,21]. However, it has been reported that some of these methods require high input costs and sophisticated knowledge and/or training to implement successful strategies for their reduction [4]. ...
... The focus of this review is that cassava can be toxic when consumed in large quantities owing to its cyanogen content [49]. The prolonged consumption of cassava in different forms can be harmful for humans in particular, owing to inadequacies in post-harvest treatment techniques [8,21]. For instance, studies on cassava-cyanide effects in humans revealed that a permanent consumption of low-level concentrations of cyanide from poorly processed cassava could result in goitres and Tropical Ataxic Neuropathy (TAN) [24,59], whereas a high consumption of the produce could result in neurological disorders, such as konzo [23,50]. ...
Chapter
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Cyanogens and mycotoxins are vital in protecting flora against predation. Nevertheless, their increased concentrations and by-products in agricultural soil could result in produce contamination and decreased crop yield and soil productivity. When exposed to unsuitable weather conditions, agricultural produce such as cassava is susceptible to bacterial and fungal attack, culminating in spoilage, particularly in arid and semi-arid regions, and contributing to cyanogen and mycotoxins loading of the arable land. The movement of cyanogen including mycotoxins in such soil can result in sub-surface and/ or groundwater contamination, thus deteriorating the soil’s environmental health and negatively affecting wildlife and humans. Persistent cyanogen and mycotoxins loading into agricultural soil changes its physico-chemical characteristics and biotic parameters. These contaminants and their biodegradation by-products can be dispersed from soil’s surface and sub-surface to groundwater systems by permeation and percolation through the upper soil layer into underground water reservoirs, which can result in their exposure to humans and wildlife. Thus, an assessment and monitoring of cyanogen and mycotoxins loading impacts on arable land and groundwater in communities with minimal resources should be done. Overall, these toxicants impacts on agricultural soil’s biotic community, affect soil’s aggregates, functionality and lead to the soil’s low productivity, cross-contamination of fresh agricultural produce.
... Moreover, cyanate is released into the environment through the biological breakdown of various metabolites such as urea and carbamoylphosphate (Guillotonm and Karst 1987). Chemical treatment methods such as oxidation or chlorination reactions are commonly applied for the detoxification of cyanate-containing compounds (Akcil and Mudder 2003). However, These chemical methods have some limitations such as high costs and production of hazardous byproducts (Srivastava and Muni 2010). ...
... However, These chemical methods have some limitations such as high costs and production of hazardous byproducts (Srivastava and Muni 2010). Bioremediation systems based on the usage of plants or microorganisms are eco-friendly and more affordable alternatives (Akcil and Mudder 2003). In this regard, microbial degradation systems are probably inconvenient because of the accumulation of toxic metabolites and/or overloading the system with high amounts of the pollutant. ...
Article
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Cyanate and its derivatives are considered as highly dangerous materials that threaten human health and environment. Cyanate arises from both natural resources and anthropogenic activities including various chemical industries, herbicide production, and mining wastewater. Despite its toxicity, cyanate is considered as an important nitrogen (N) source in marine ecosystems. Cyanase (CYN) catalyzes the decomposition of cyanate into CO2 and NH3 in a bicarbonate-dependent reaction. In marine cyanobacteria, endogenous cyanases participate in detoxification of low concentrations of cyanate. However, this cyanate biodegradation system is seemingly inconvenient especially at contaminated sites due to high cyanate concentrations. In the current study, we have transferred the activity of the cyanobacterial enzyme cyanase into the micro-alga, Chlamydomonas reinhardtii, via Agrobacterium tumefaciens–mediated transformation method. The recombinant cyanase enzyme was shown to be active in transgenic C. reinhardtii lines. When variable concentrations of cyanate (up to 30 mM) is applied to growth medium, transgenic lines showed higher rate of NH3 release, reduced loss of pigmentation symptoms, decreased levels of induced antioxidant enzymes, and low percentage of growth retardation compared to wild-type controls. Results of this study provide an effective eco-friendly phytoremediation system for cyanate detoxification using micro-algae compared to previously reported plant systems.
... Sulfate, the by-product, was observed for 30 days, and it stabilized in the range of 30-50 mg/L during days 3-24 and then increased to 61-100 mg/L during days 25-30 of the study, which was consistent with the degradation of thiocyanate (Fig. 4). This is consistent with other studies which reported that sulfate is the endproduct of thiocyanate degradation by microbes as shown in the following equation (Akcil and Mudder 2003;Lim et al. 2008;Grigor'eva et al. 2009;Huddy et al. 2015): ...
... Moreover, ammonia in this Suspended growth of mixed culture bacteria in the bio-column system study was not detected, except on days 19-21, when it reached a concentration of 0.14 mg/L. This may be due to the ammonia oxidizing and transforming into its nitrate form (Eqs. 6, 7) (Akcil and Mudder 2003): ...
Article
The degradation capacity of a mixed culture of Agrobacterium tumefaciens SUTS 1 and Pseudomonas monteilii SUTS 2 for thiocyanate and metal cyanide, in the form of zinc and cadmium, has been determined. The growth of a mixed culture of SUTS 1 and SUTS 2 in cyanide complexes and the cyanide removal efficiency of a fixed-film bio-column system were studied. The results showed that the mixed culture of bacteria can survive and grow in broth media containing thiocyanate and metal cyanide complexes with a maximum cell of 1.03 × 10⁸ CFU/mL on day 3. In addition, the optimal conditions of the fixed-film bio-column system were continuously tested for 24 h, and it was found that this system had the highest removal efficiency at a flow rate of 10 mL/min and 21 min of empty bed retention time, with decreasing thiocyanate, zinc, and cadmium from 85, 0.44, and 0.044 to 65, 0.21, and 0.038 mg/L, respectively; this is in contrast to cyanide, which was not found within 12 h. Next, the conditions were maintained for 30 days, and it was found that the system had removed more than 50% of cyanide complexes, except cadmium. The complex residues were 29.96, 0.16, 0.204, and 0.085 mg/L of thiocyanate, cyanide, zinc, and cadmium, respectively. In addition, the growth of the SUTS 1 and SUTS 2 mixed culture increased. The by-product compounds sulfate and nitrate were found throughout the experiment, whereas bicarbonate and ammonia were found only on certain days.
... Considering this fact, alkalophilic microorganisms should be required to remove cyanide efficiently from contaminated areas and wastewaters. These cyanide-containing residues need to be treated to reduce their toxicity, but physical-chemical treatments have not been demonstrated to be very efficient and, therefore bioremediation processes constitute a potent alternative to decontaminate industrial cyanide-containing residues [14,15,16]. ...
Article
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The alkaliphilic bacterium Pseudomonas pseudoalcaligenes CECT5344 uses free cyanide and several metal−cyanide complexes as the sole nitrogen source and tolerates high concentrations of metals like copper, zinc and iron, which are present in the jewelry wastewaters. To understand deeply the regulatory mechanisms involved in the transcriptional regulation of cyanide-containing wastewaters detoxification by P. pseudoalcaligenes CECT5344, RNA-Seq has been performed from cells cultured with a cyanide-containing jewelry wastewater, sodium cyanide or ammonium chloride as the sole nitrogen source. Small RNAs (sRNAs) that may have potential regulatory functions under cyanotrophic conditions were identified. In total 20 sRNAs were identified to be differentially expressed when compared the jewelry residue versus ammonium as nitrogen source, 16 of which could be amplified successfully by RT-PCR. As predicted targets of these 16 sRNAs were several components of the nit1C gene cluster encoding the nitrilase NitC essential for cyanide assimilation, the cioAB gene cluster that codes for the cyanide-insensitive cytochrome bd-type terminal oxidase, the medium length-polyhydroxyalkanoates (ml-PHAs) gene cluster, and gene clusters related with a global nitrogen limitation response like those coding for glutamine synthase and urease. Other targets were non-clustered genes (or their products) involved in metal resistance and iron acquisition, such as metal extrusion systems and the ferric uptake regulatory (Fur) protein, and a GntR-like regulatory family member probably involved in the regulation of the cyanide assimilation process in the strain CECT5344. Induction of genes targeted by sRNAs in the jewelry residue was demonstrated by qRT-PCR.
... Concerning biological processes, many researchers reported in the past the application of different microorganisms for the removal of cyanide from wastewaters (specially, from gold mining) (Evangelho et al. 2001, Akcil and Mudder 2003, Ebel et al. 2007, Mekuto et al. 2015, Mekuto et al. 2016. Although biological systems have interesting advantages, as described by Akcil (2003), there are also limitations related to operational conditions. ...
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Cyanidation is widely used by several gold mining companies worldwide. Since its wastewaters contain cyanide, appropriate treatments must be applied to remove this pollutant. Combinations of ozone (O3), hydrogen peroxide (H2O2) and activated carbon (AC) can be used for this purpose. In this work, synthetic cyanide solutions ([CN¯]o = 15.37 mM) were treated using O3 and the combinations O3/H2O2, O3/AC and O3/H2O2/AC under alkaline conditions. O3 was produced from dry oxygen at a rate of 2.51 g O3/h([O3] gas-phase = 6.9x10–2 g/L). The concentration of cyanide (CN¯) and O3 consumption were measured and the performance of the treatments evaluated. The highest cyanide removal was reached at pH 11.0 for all cases and with 10 mg H2O2/mg O3 upon adding H2O2. In contrast, the addition of AC did not improve the cyanide removal in comparison with O3 alone. The best cyanide removal was achieved with the combination O3/H2O2 followed by the combination O3/H2O2/AC. Moreover, cyanidation effluents were treated using the combination O3/H2O2. In this case, almost a total removal of free cyanide was achieved after 3 min of treatment.
... En concentraciones altas, el cianuro es tóxico a estos microorganismos ya que permanece sin ser cambiado a otras formas y atraviesa el suelo llegando hasta el agua subterránea [3]. Las distintas formas de exposición a este compuesto para algunos animales y humanos son: Al respirar aire cerca de sitios de desechos peligrosos que contienen cianuro; al beber agua, tocar tierra o comer alimentos que contienen cianuro de manera natural como algunos tipos de frijoles y almendras; el humo de cigarrillos y el humo proveniente de incendios, son fuentes importantes de cianuro [1,4]. En la actualidad, grandes cantidades de cianuro en sus distintas formas son descargados a diario en suelos, aguas y aire procedente de diferentes actividades industriales tales como la minería, en el proceso de recuperación de oro [5]. ...
Article
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Combination of hydrogen peroxide and caustic soda in solution, denominated by the authors "Perso method", results in the formation of a strong oxidant, which is effective in the detoxification of total cyanide and precipitation of complex metals that are found in solutions. The present work shows the technical feasibility of reusing water from the gold tailings instead of fresh water (as in agriculture or in the mining process) avoiding the saturation of cyanicide metals in the operation circuit. After a chemical treatment at an optimum pH, follows the obtaining of a solution with a lesser amount of cyanicide metals, impacting favorably in the production of better quality doré bars. The hexagonal experimental design was applied which involves a series of tests of different molar ratios of hydrogen peroxide and caustic soda, time (min) vs concentration of total cyanide, and concentration of copper and silver. The process was fast and efficient. With an initial concentration of 200 mg/l of free cyanide, 2.2 mg/L of silver, 200 mg/l of copper and a molar ratio of (H2O2 NaOH)/(CN-) = 8, it was possible to achieve a final concentration of 1.5 ppm of cyanide, 1 ppm Ag, 5 ppm Cu. In contrast, a molar ratio of (H2O2 NaOH)/(CN-) = 12, afforded a final concentration of 0.8 ppm of cyanide, 0.8 ppm Ag and 2 ppm Cu, in the same time of reaction (45 min). The precipitate of metals such as silver and copper characterized as economically usable sludge, has an economic interest in the market.
... Despite the toxicity of cyanide, cyanotrophic microorganisms such as Pseudomonas sp. (Akcil and Mudder 2003;Oyedeji et al. 2013), Bacillus pumilus (Kandasamy et al. 2015), and Bacillus cereus (Itakorode et al. 2019) has been reported to survive in the presence of cyanide due to their ability to synthesize cyanide metabolizing enzyme such as rhodanese. Rhodanese catalyzes cyanide detoxification by transferring sulfur from a suitable substrate such as thiosulfate to cyanide. ...
Article
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Microorganisms are increasingly being used in cyanide bioremediation. Several organisms have been reported to thrive in cyanide contaminated wastewater due to their ability to produce cyanide detoxifying enzymes. However, to improve the production efficiency of these enzymes combinations of process variables need to be optimized. In this study, Klebsiella oxytoca JCM 1665 was isolated from industrial wastewater, identified by sequencing its 16S rRNA gene and subjected to rhodanese production using submerged fermentation. The conditions for production were optimized using response surface methodology (RSM). Central composite design was employed to evaluate the effects of three production parameters-peptone (1-5 %), KCN (0.1-0.5 %), and time of incubation (1-24 h). Second-order polynomial model was used to predict the response. Rhodanese activity in the experiments varied from 0.05 to 7.5 RU.mg-1. Under the optimum conditions of 4.35 % peptone, 0.4 % KCN and incubation time of 13 hr., the value for rhodanese yield was 7.810 U.mL-1. The R 2 value for the model was 0.9925 (R 2 = 0.9925). Also, the experimental values are in accordance with those predicted, indicating the suitability of the employed model and the success of RSM in optimizing the production conditions.
... Humans are in close contact with cyanide in their daily life through food, drink, and medicines. Other routes of cyanide exposure include smoking tobacco (0.5mg/cigarette), respiring exhaust from vehicles, handling certain type of pesticides and insecticides (Akcil and Mudder, 2003). Cyanide is widely distributed in the environment and this causes severe environmental problems when produced in high amounts by anthropogenic activities, such as the electroplating industry (Parga et al., 2003), metal finishing or mining industries/processes (Mansfeldt et al., 2004), iron and steel mill, publicly owned wastewater treatment facilities and organic chemical industries As cyanides are produced regularly by industries in large quantity in waste water streams, it is a potent health hazard for human and ecosystem (Rodrigo et al., 2005). ...
... Por outro lado, os microorganismos na natureza têm o potencial de reduzir a toxicidade dos poluentes e degradar os componentes perigosos que são liberados no ambiente nas atividades industriais (Samantaray et al, 2014). Em particular, o biotratamento de cianeto tem sido amplamente estudado na indústria da mineração (Akcil, 2003;Kuyucak e Akcil, 2013). Porém, o tratamento de cianeto nos efluentes de galvanoplastia apresenta novos desafios devido à presencia de metais e as baixas concentrações de fontes de carbono nas águas residuais (Sirianuntapiboon et al, 2008). ...
... The pH of the media was set at 9.9 and at a temperature of 30 ºC for both nitrification and denitrification studies. These conditions were based on (i) the fact that cyanide containing wastewaters are mostly alkaline [13,14] and (ii) previous optimization studies on cyanide degrading organisms observed these conditions as being most suitable for successful CNbiodegradability [15]; hence these conditions were chosen on a pragmatic basis. ...
Article
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The impact of free cyanide (CN-) and thiocyanate (SCN-) on the CN- (CDO) and SCN- degraders (TDO) to nitrify and denitrify aerobically was evaluated under alkaline conditions. The CDO’s were able to nitrify under cyanogenic conditions, achieving NH4+-N removal rates above 1.66 mg NH4+-N.L-1.h-1, except when CN- and SCN- loading was 15 mg CN-/L and 50 mg SCN-.L-1 respectively, which slightly inhibitednitrification. The TDO’s were able to achieve a nitrification rate of 1.59 mg NH4+-N.L-1.h-1 in the absence of both CN- and SCN-, while the presence of CN- and SCN- was inhibitory, with a nitrification rates of 1.14 mg NH4+-N.L-1.h-1. The CDO’s and TDO’s were able to denitrify aerobically, with the CDO’s obtaining NO3--N removal rates above 0.67 mg NO3--N.L-1.h-1, irrespective of the tested CN- and SCN- concentration range. Denitrification by the TDO’s was inhibited by CN-, achieving a removal rate of 0.46 mg NO3--N.L-1.h-1 and 0.22 mg NO3--N.L-1.h-1 when CN- concentration was 10 and 15 mg CN-.L-1, respectively. However, when the CDO’s and TDO’s were co-cultured, the nitrification and aerobic denitrification removal rateswere 1.78 mg NH4+-N.L-1.h-1 and 0.63 mg NO3--N.L-1.h-1 irrespective of CN- and SCN- concentrations.
... Cyanide biodegradation produces nitrogenous compounds such as ammonium and nitrates, and these compounds are environmental contaminants and therefore need to be treated (Akcil & Mudder, 2003). Biological nitrogen removal (BNR) is commonly utilized for the effective removal of nitrogenous compounds in wastewater (Kim et al., 2011). ...
Conference Paper
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CN- (≥10 mg CN- .L-1 ) inhibited nitrification and denitrification in media inoculated with SCN degrading organisms (TDOs), while the CN degrading organisms (CDOs) were not inhibited by SCN nor CN- , irrespective of the concentration load. A mixed culture containing both SCN and CN degraders was able to nitrify and aerobically denitrify without being inhibited by the presence of both SCN and CN- , irrespective of the toxicant concentration load. Therefore, the CDO’s and TDO’s can be categorized as CN- and SCN degraders, nitrifiers and denitrifiers.
... After cyanidation, the solid and liquid fractions are separated and stored in storage ponds for the natural attenuation of cyanide and related complexes. The liquid fraction generated from the cyanidation process normally contains elevated concentrations of free cyanide (CN − ), thiocyanate (SCN − ) and metal-complexed cyanides in the form of weak acid dissociable (CN WAD ) and strong acid dissociable cyanides (CN SAD ) (Akcil 2002;Akcil and Mudder 2003). In most cases, SCN − and CN − are normally observed to be the major contaminants found in cyanidation wastewaters. ...
Article
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This study focused on the identification of free cyanide (CDO) and thiocyanate (TDO) degrading microbial communities using a culture-dependent and independent approach. Culturable microbial species were isolated from the CDOs (n = 13) and TDOs (n = 18). The CDOs were largely dominated by Bacillus sp. while the TDOs were dominated by Bacillus sp., Klebsiella oxytoca, Providencia sp. and Pseudomonas sp. However, 16S rRNA amplicon gene sequencing revealed the complexity and diversity of the microbial communities in contrast to the organisms that were detected using culture-dependent technique. Overall, the organisms were mainly dominated by Myroides odoratimimus and Proteus sp. at 37.82% and 30.5% for CDOs, and 35.26% and 17.58% for TDOs, respectively. The co-culturing of the CDOs and TDOs resulted in biochemical changes of key metabolic enzymes, and this resulted in the complete degradation of CN- and SCN- simultaneously; a phenomenon which has not been witnessed, especially under alkaline conditions. Current ongoing studies are focused on the application of these organisms for the biodegradation of CN- and SCN- in a continuous system, under changing operational parameters, to assess their effectiveness in the biodegradation of CN- and SCN-.
... Second, microorganisms can be applied to destroy or degrade toxic compounds (e.g. cyanide) (Akcil and Mudder, 2003), or perform bioprocesses that are more environmentally friendly as no or less toxic chemicals are employed (Zinke and Gabor, 2009). Third, bioprocessing can efficiently recover valuable metals concomitantly to detoxifying the processed wastes (Natarajan, 2013). ...
Article
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As there is a high potential for microbe-based technologies to bring the recovery of metals from waste streams to an ecologically friendly and financially reasonable level, it is worth to invest efforts into the advancement of these biotechnologies in the future.
... Cyanide can be present in wastewaters in different forms like: free cyanide (CN -), weak acid dissociable, strong cyanide complexes, among others [3,4]. Free cyanide is highly toxic to living organisms because it inhibits cellular respiration and is considered a significant pollutant of water bodies and soils [2][3][4][5][6][7][8][9][10]. ...
Article
In this study we modeled and simulated biofilm growth and free cyanide biological removal from gold mine wastewater using a bench-scale rotating biological contactor (RBC). Eight batch cultures were run in three independent compartments (1.7 L, each) of the RBC. The system worked under the following conditions: [CN-] = 0.3 g/L, pH = 10.5 ± 0.5, T = 20 ± 5 °C, ω = 5 rpm, and 40.5% of disc submersion. During each culture, biofilm thickness, biomass, and free cyanide concentration in the liquid were quantified. Subsequently, umax, KCN-, Y' x/CN-, qmax, b', Df, k, and JCN-, were determined using experimental data to later model and simulate the biofilm thickness and free cyanide biological removal with Wolfram Mathematica software. After the experiments, free cyanide biological removal was 96.33% after three days, and maximum biofilm thickness was 0.0292 cm in the 16th day. Moreover, biofilm growth and free cyanide consumption models adjusted to the experimental data with r2 = 0.90 and r2 = 0.99. Also, there was an equivalent error of 7.89 and 7.38 and a standard deviation of 10.89% and 10.17%, between the models and their experimental data, respectively. Finally, the proposed models will allow to improve reactor operation and its design.
... Figure 2 show the bioremediation applied on the entity polluted by cyanide in the World. Most of them were observed in America such as United States (Akcil and Mudder, 2003;Fernandez et al., 2004;Kunz et al., 1992;Kunz et al., 1998;Pinedo-Rivilla et al., 2009;Silvaavalos et al., 1990;Singleton et al., 1988;Wang et al., 1996), Mexico (Meehan et al., 1999), Ecuador (Diaz and Caizaguano, 1999); Europa such as France (Dumestre et al., 1997;Ferret, 2012), Germany (Ingvorsen en Godtfredsen, 1991), Switzerland (Brandl et al., 2003), Italy (Cipollone et al., 2007), Spain (Luque-Almagro et al., 2005;Luque-Almagro et al., 2008;Quesada et al., 2007), United Kingdom (Baxter and Cummings, 2006;Ezzi and Lynch, 2005), Ukraine (Podolska et al., 2003); Asia such as China (Zhou et al., 2007), India (Bipinraj et al., 2003;Shete and Kapdnis, 2012), Japan (Yamasaki et al., 2002), Iran (Mirizadeh et al., 2014;Naghavi et al., 2012), Malaysia (Maniyam et al., 2011), Taiwan , Thailand (Potivichayanon and Kitleartpornpairoat, 2010) and Oceania such as Australia (Markwiese and White 1991). Few Africans countries as Ghana (Adii, 2011), Nigeria (Oyedeji et al., 2013), South Africa (Akinpelu et al., 2015;Dent et al., 2009;Jandhyala et al., 2003;Mekuto et al., 2013;Ntwampe and Santos, 2013;Santos et al., 2014;Van Zyl et al., 2011) and Burkina Faso (Razanamahandry et al., 2016) have been applied bioremediation in laboratory scale. ...
Article
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Cyanide is a chemical that is widely distributed in the environment, mainly as a result of anthropogenic activities. Only small quantities are naturally produced. Most industrial activities use this chemical compound for manufacturing a product as electroplating or for extracting gold. Exposure to cyanide results in negative health impacts to the wildlife and humans. In nature, cyanide occurs in several species and fates, of which the free cyanide forms are the most toxic ones. Cyanide can be removed by chemical or biological processes. Biological treatment called bioremediation, which is cost-effective and eco-friendly, is the most applied process to remove cyanide from contaminated environments. This technology focused on the use of microorganisms to remove pollutants. Many microorganisms have been reported to transform the cyanide in another less toxic compound, or to consume cyanide for their growth. The reactions are influenced by environmental parameters such as pH and temperature and by the nutriment availability. Bioremediation technologies were few applied in most of African Countries. Future works should focus on how to adapt the bioremediation technologies that already applied in other parts of the World in African context.
... Pseudomonas pseudoalcaligenes CECT 5344 was isolated from sludge of Guadalquivir River, and it is able to use cyanide as the only source of nitrogen [4]. Cyanide is an extremely toxic compound used in the synthesis of organic compounds such as nitriles, plastics, paints, adhesives, cosmetics, etc., while mining activities and the jewellery industry are the main source of cyanurated wastes [5][6][7][8]. This strain tolerates an unusually high concentration of cyanide (up to 30 mM) [4], but it requires a suitable carbon source for growing. ...
Article
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Pseudomonas pseudoalcaligenes CECT 5344 is a bacterium able to assimilate cyanide as a nitrogen source at alkaline pH. Genome sequencing of this strain allowed the detection of genes related to the utilization of furfurals as a carbon and energy source. Furfural and 5-(hydroxymethyl) furfural (HMF) are byproducts of sugars production during the hydrolysis of lignocellulosic biomass. Since they inhibit the yeast fermentation to obtain bioethanol from sugars, the biodegradation of these compounds has attracted certain scientific interest. P. pseudoalcaligenes was able to use furfuryl alcohol, furfural and furoic acid as carbon sources, but after a lag period of several days. Once adapted, the evolved strain (R1D) did not show any more prolonged lag phases. The transcriptomic analysis (RNA-seq) of R1D revealed a non-conservative punctual mutation (L261R) in BN5_2307, a member of the AraC family of activators, modifying the charge of the HTH region of the protein. The inactivation of the mutated gene in the evolved strain by double recombination reverted to the original phenotype. Although the bacterium did not assimilate HMF, it transformed it into value-added building blocks for the chemical industry. These results could be used to improve the production of cost-effective second-generation biofuels from agricultural wastes.
... Numerous processes have been proposed for the treatment of cyanide in wastewater including electrolytic oxidation (Dutra et al. 2008), distillation (Han et al. 2005), iron precipitation (Yu et al. 2016), ion exchange (Simsek et al. 2015), acidification-volatilization-reneutralization (AVR) (Vapur and Bayat 2007), reverse osmosis (Bodalo-Santoyo et al. 2003), the patented process marketed by INCO Ltd. that uses a mixture of sulfur dioxide (SO 2 ) and air (Akcil and Mudder 2003), biological degradation (Guamán Guadalima and Nieto Monteros 2018;Mekuto et al. 2018), adsorption (Dash et al. 2009a), and oxidation by Caro's acid (Teixeira et al. 2013), hydrogen peroxide, ozone (Kepa et al. 2008), and chlorine (Parga et al. 2003). Among these treatments, chemical oxidation techniques (e.g., caustic chlorination) have been most commonly used in practice to treat cyanide-containing industrial effluents (e.g., metal plating wastewater) (Dash et al. 2009b). ...
Article
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Cyanide is highly toxic and must be destroyed or removed before discharge into the environment. This study examined the ability of commercial anion-exchange resins to remove residual cyanide complexes from industrial plating wastewater as a complement to conventional treatment. Cyanide removal experiments were conducted with various initial concentrations, reaction times, and temperatures, and the presence of co-existing anions. The maximum cyanide removal capacity (Qm) of the Bonlite BAMB140 resin is 31.82 mg/g and effectively removes cyanide from aqueous solution within 30 min. The cyanide removal by the resin is an endothermic process and is affected by the presence of anions in industrial plating wastewater. The relative competitiveness observed in this study was sulfate > nitrate > chloride. A mixture of 0.05 M NaCl and NaOH regenerates resin for continuous reuse for 5 cycles. The Bonlite BAMB140 resin was able to remove residual cyanide complexes from industrial plating wastewater, but the removal capacity of the resin was reduced by more than three times in batch (9.94 mg/g) and column (6349.12 mg/L) systems. Based on the results, the anion-exchange resins are expected to be used as a complementary technique to remove residual cyanide complexes in industrial plating wastewater after conventional treatment.
... However, it is not known to what extent and at which rates microorganisms degrade thiocyanate in natural seawater. Studies to date have dealt with the artificial reduction of thiocyanate from mining wastewaters only (Akcil and Mudder 2003;Boucabeille et al. 1994;Chaudhari and Kodam 2010;Vu et al. 2013). ...
Article
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Solutions for the ornamental marine fish trade in the Philippines.
... However, it is not known to what extent and at which rates microorganisms degrade thiocyanate in natural seawater. Studies to date have dealt with the artificial reduction of thiocyanate from mining wastewaters only (Akcil and Mudder 2003;Boucabeille et al. 1994;Chaudhari and Kodam 2010;Vu et al. 2013). ...
Article
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Full-cycle mariculture roadblocks and opportunities for red grouper species in the Philippines.
... The extensive used of nitriles in various industries has sparked a great interest in finding new nitriledegrading microorganisms as well as their involved enzymes (nitrile hydratase and amidase) to be used both as biocatalyst in commercially chemicals synthesis and also as agents for detoxification of nitrile/cyanide containing waste [6,7,8]. Although there are several chemical methods could be used for handling this kind of toxic waste [9,10], these methods are expensive and hazardous chemicals are used as the reagents and some of them create additional toxic and biological persistent chemicals. In general, biological treatments are eco-friendly, cost effective and sometimes more efficient and thus considered as a feasible alternative to the chemical methods [11,12,13]. ...
Article
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Nitriles are toxic organo-cyanide compounds, but extensively used in various industries as solvents, plastics, synthetic rubber, pharmaceuticals, herbicides, and starting materials for other industrially important chemicals. The wider use of these toxic compounds could lead to an environmental pollution, which have a negative impact on health. Some microbes are reported to be able to utilize both aliphatic and aromatic nitrile s as growth substrates and convert them into non-toxic compounds, some of which also have economic value as well. An indigenous bacterial isolate I-benzo, capable of growing on and utilizing of a high concentration of acetonitrile (CH 3 CN) and benzonitrile (C 6 H 5 CN), could be isolated from leather tanning waste by the enrichment-culture technique. Based on 16S rDNA sequence, the strain was identified as Rhodococcus pyridinivorans . These bacterium was shown to able to grow on acetonitrile (0.2-2.0 M) and on benzonitrile (5-25 mM), as a sole source of energy, carbon and nitrogen, respectively. The best growth of R. pyridinivorans strain I-benzo was on 500 mM acetonitrile and on 15 mM benzonitrile. During the degradation of both nitriles using whole cells of the bacterium, amide and carboxilic acid were detected in the reaction media, indicating that nitrile hydratase and amidase involved in the metabolism of the substrate. The involvement of both enzymes on the conversion of acetonitrile and benzonitrile was also proved by the ability of R. Pyridinivorans I-benzo to grow on their intermediate degradation products, acetamide (CH 3 CONH 2 ) and benzamide (C 6 H 5 ONH 2 ), respectively. Based on these results, R. pyridinivorans strain I-benzo could be expected as a potential candidate for biological treatment for nitriles-containing wastes, although further research is still needed before being applied on a field scale.
... In general, fish and other aquatic life are killed by cyanide concentrations in the microgram per litre (part per billion) range, whereas bird and mammal deaths result from cyanide concentrations in the milligram per litre (part per million) range. Chronic cyanide exposure may affect physiology, and levels of activity of many fish species, and may render the fishery resource non-viable [12]. ...
Conference Paper
Cyanide is any chemical compound that contains monovalent combining group of carbon and nitrogen (CN). It breaks down some group of heavy metals resulting in the formation of complexes with such metals. The complexes that are formed are usually very stable even under mildly acidic conditions.Cyanide has been preferred in gold and silver mining worldwide, but its potential toxicity and environmental impact has been of health concern.Although cyanide can be recovered or degraded by several processes, it is still widely discussed and examined. Biological treatment of cyanide is a well-established environmental friendly alternative and has been commercially used at gold mining operations to complement the existing physical and chemical processes. Biological treatment techniques facilitate growth of microorganisms that are essential for the treatment procedures. The present study describes the environmental challenges of cyanide in the mining industry and provided an alternative use of biological processes to treat the chemical.
... Because of high cyanide toxicity, it has the ability to kill the respiratory system by preventing the last step of electrons to oxygen from cytochrome C oxidase thereby preventing ATP production. Small quantity of cyanide exposure can be fatal regardless of the way of exposure [4]. More so, Cyanide waste is gradually becoming a rampant problem in today's society. ...
Article
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Gold mining companies have been known to use cyanide to extract gold from minerals. The indiscriminate use of cyanide presents a major issue in the environment. The used of linearisation methods using natural logarithm transformation is inaccurate, even though is standard and can just give an estimated value for the sole parameter measured; the specific growth rate. In this study, various cyanide concentrations ranging from 0 - 350 mg/L was used. Seven different mathematical models such as such as modified Logistics, modified Gompertz, modified Richards, modified Schnute, Baranyi-Roberts, Von Bertalanffy and most recent Huang were used to get values for the above constants or parameters from bacterial growth Pseudomonas putida on cyanide. The best model was found to be modified Logistics with the lowest AICc and RMSE value. The modified Logistics parameters such as Ymax (bacterial growth upper asymptote), Î» (lag time), Âµmax (maximum specific bacterial growth rate) and A or Y0 (bacterial growth lower asymptote) were found to be 2.41 (95% confidence interval of 2.37 - 2.45), -3.16 (95% confidence interval of -4.64 to -1.68) and 0.12 (95% confidence interval of 0.11 to 0.13). This is the first report of growth mathematical modelling of the effect of cyanide on Pseudomonas Putida (Naun-16).
... Comprehensive reviews have summarized current chemical and biological treatment methods for either CN − degradation (Gould et al. 2012) or concomitant degradation of CN − and SCN − (Akcil 2003;Botz et al. 2016;Mudder et al. 2001). Compared to physical or chemical approaches, bioremediation systems are considered to be more environmentally friendly, efficient (Akcil 2003), cost-effective (Akcil and Mudder 2003;Nelson et al. 1998), and substrate specific (Das and Dash 2014). Accordingly, they constitute a preferred treatment approach in the mining industry, especially when cleaner effluents are targeted (Akcil 2003). ...
Article
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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.
... These microorganisms were able to degrade 131 (65.5%) and 177 (44.3%) mg CN − /L in cultures containing 200 and 400 mg CN − /L over a period of 8 days, respectively. Furthermore, cyanide was degraded by many microbes under aerobic conditions and transformed into less toxic forms by extracellular enzymes found on the cell wall of cyanide-oxidizing bacteria into byproducts such as ammonia (NH 3 -N), nitrite (NO 2 − -N), nitrate (NO 3 − -N), and bicarbonate (HCO 3 − ) (Akcil and Mudder 2003;Sirianuntapiboon and Chuamkaew 2007;White and Schnabel 1998;Watanabe et al. 1998). Thus, this study investigated the byproducts ammonia (NH 3 -N), nitrite (NO 2 − -N) and nitrate ...
Article
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The fixed-film sequencing batch reactor, or F-SBR, was developed to treat high organic compound levels and toxic cyanide concentrations in cassava wastewater. The performance of the F-SBR was compared with that of a conventional sequencing batch reactor, or SBR, that was operated with organic compound contents of 16,266.67–26,666 mg COD/L and 132.92–252.66 mg CN−/L. The cyanide and chemical oxygen demand removal efficiencies of the conventional SBR system were 42.61% and 36.83%, respectively, while those of the F-SBR were 77.95% and 74.43%, respectively; the cyanide removal efficiency reached 95.45% when the hydraulic retention time was increased to 5 days, and the F-SBR was very effective for the complete removal of cyanide when the hydraulic retention time was increased to 10 days. This effectiveness was similar to the effectiveness of chemical oxygen demand removal, which reached 40–78% efficiency with the F-SBR system. These results showed that the immobilization of cyanide-degrading bacteria such as Agrobacterium tumefaciens SUTS 1 and Pseudomonas monteilii SUTS 2 carried out with a polypropylene ring in a fixed-film aerobic system enhanced the performance of the reactor and can be successfully applied for cyanide and chemical oxygen demand removal from industrial wastewater with high cyanide and chemical oxygen demand concentrations. This study may provide a promising alternative technique that reduces economic operation costs in solving wastewater contamination problems.
... Many industrial applications such as plastics, electroplating, organic chemicals production, photographic development, and drugs are important sources of cyanide wastes. In gold and silver mines, cyanide is used to recover the precious metal through the washing process [6]. Cyanide is the most preferred solvent in the extraction of gold and silver ore over a century because of strong complexing ability, availability of existing, relatively low cost and famous chemical [7]. ...
Article
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Abstract: In this study, the elimination of cyanide by the addition of hydrogen peroxide and calcium hypochlorite was investigated. This study was conducted to determine the optimum conditions of H2O2 and Ca(OCl)2: concentration, pH and contact time, and the combined ratio of concentration H2O2 with Ca(OCl)2 to remove cyanide in gold mining wastewater. Cyanide obtained by steam distillation of wastewater by steam distillation and Barnstead electromantel and assay using 0.02N silver nitrate. The results showed that the cyanide level was 50.22% w/v. The optimum conditions were obtained when the concentration of H2O2 at 500 ppm, pH 8 within 60 minutes contact time and Ca(OCl)2 concentration was at 500 ppm, pH 8 within 60 minutes contact time. The best cyanide removal was obtained at the concentration ratio of 5:5 amounting to 45.76% w/v. Keywords: Cyanide, Hydrogen Peroxide, Calcium Hypoclorite, Steam Distillation, Silver Nitrate
... Several destructive and/or recovery processes have been developed to treat cyanide-containing solutions or slurries. Treatment methods include, but are not limited to: (i) physical (reverse osmosis [9], acidification, volatilization and reneutralization-AVR- [2], adsorption [10,11], sulfurization, recycle and thickening-SART- [9,12]) and (ii) chemical processes (alkaline chlorination [13], INCO process [2], hydrogen peroxide [14], Caro's acid [8], oxonization [15], biological treatment [16,17], photochemical processes [18], and electrochemical methods [19]). Note that each technology presents limitations and drawbacks (e.g., effectiveness depending on cyanide concentration, the formation of toxic substances, high costs, generation of sludge, and additional byproducts). ...
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This study examines the electro-oxidation (EO) of cyanide originating from an industrial plant´s gold leaching effluent. Experiments were carried out in a laboratory-scale batch cell reactor. Monopolar configuration of electrodes consisting of graphite (anode) and aluminum (cathode) was employed, operating in galvanostatic mode. Response Surface Methodology (RSM), based on a Box–Behnken experimental Design (BBD), was used to optimize the EO operational conditions. Three independent process variables were considered: initial cyanide concentration ([CN⁻]0 = 1000–2000 mg L⁻¹), current density (J =7–107 mA cm⁻²), and stirring velocity (η = 250–750 rpm). The cyanide conversion XCN-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\left( {X_{{{\text{CN}}^{ - } }} } \right)$$\end{document}, Chemical Oxygen Demand (COD) removal percentage (%RCOD), and specific Energy Consumption per unit mass of removed cyanide (EC) were analyzed as response variables. Multi-objective optimization let to establish the most effective EO conditions ([CN⁻]0 = 1000 mg L⁻¹, J = 100 mA cm⁻² and η = 750 rpm). The experimental data (XCN-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$X_{{{\text{CN}}^{ - } }}$$\end{document}, %RCOD, and EC) were fitted to second-order polynomial models with adjusted correlation coefficients (Radj2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$R_{\text{adj}}^{2}$$\end{document}) of ca. 98, 99 and 87%, respectively. The kinetic analysis, performed at optimal EO operational conditions, allowed determination of time required to meet Colombian permissible discharge limits. The predictive capacity of kinetic expressions was verified against experimental data obtained for gold leaching effluent. Total cyanide removal and 96% of COD reduction were obtained, requiring EC of 71.33 kWh kg⁻¹ and 180 min. The BOD5 (biological oxygen demand)/COD ratio increased from 4.52 × 10⁻⁴ to 0.5573, confirming effluent biodegradability after EO treatment. Graphic Abstract The variation of cyanide (CN⁻), cyanate (CNO⁻) and ammonium (NH4⁺) ions concentrations vs. time at alkaline conditions. EO operational conditions: [CN⁻]0 = 1000 mg/L, J = 100 mA/cm² , η = 750 rpm, [NaCl] = 0.15 M and pH 11.1.
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Toxic sodium cyanate is always present in cyanide-contaminated waste. A new technology for the efficient decomposition of toxic sodium cyanate by hematite was first proposed in this study. The decomposition of sodium cyanate under various atmospheres has been studied. Studies show that sodium cyanate decomposes above 782 °C in Ar and above 627 °C in air. Sodium cyanate does not decompose even roasted at 400 °C for 120 min in air. Hematite does not promote the decomposition of sodium cyanate in Ar. However, almost all sodium cyanate decomposes efficiently at 400 °C and the mass ration of hematite to sodium cyanate of 1:1 for 30 min in air or oxygen atmosphere. The increased mass ratio of hematite to sodium cyanate and roasting temperature can both favor the efficient decomposition of sodium cyanate. The efficient decomposition of sodium cyanate occurs within 30 min, and it is almost stagnant with the prolongation of roasting time. When roasted in air or oxygen in the presence of hematite, sodium cyanate decomposes to Na2CO3, CO2 and N2 and a small amount of NaNO3 and NOx. The optimal efficient decomposition of sodium cyanate is to roast above 400 °C for 30 min in air or O2 at a mass ration of hematite to sodium cyanate greater than 1:1.
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Cyanide is a known toxic chemical compound that has an adverse effect on living organisms. Nonetheless, it is one of the active reagents in industries such as mining, pharmaceutical, cosmetics, and food processing companies worldwide. The beneficiation of gold and other precious metals from ore generates great amount of cyanide-bearing contaminants, which is released into the environment. The abundance of cyanide contaminants from these industries have created public health concern since the inception of metal extraction from ore. There are strict regulations on the production, transportation, utilization, and disposal of cyanide-bearing contaminants worldwide. The conventional treatment of cyanide waste is either chemical or physical process. The use of these treatment processes has certain pitfalls like operational challenges, an increase in capital cost, and generation of secondary waste. A number of microorganisms have the potential to utilize cyanide as nitrogen and carbon source and transform it into ammonia and carbon dioxide. Biodetoxification might be efficiently, economically and environmentally safe to detoxify cyanide in contaminants and attractive alternative to conventional detoxification method like chemical or physical. This paper reviews the principles and methods of biodetoxification of cyanide contaminants found in the ecosystem.
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Artisanal and small-scale mining are informal activities used as a source of family income in many countries, mostly in developing regions. They also represent rudimentary practices that generate environmental and health impacts. In these activities, gold is the main mineral extracted commonly using cyanide leaching as the main technique in their production process, despite its environmental impacts. Biodegradation is an alternative technology that has shown advantages over other techniques; however, most microorganisms studied in cyanide biodegradation processes do not tolerate alkaline environments. Thus, the present study assessed the cyanide biodegradation potential under alkaline conditions of a native strain isolated from an artisanal gold mine. The methodology used consisted in the following steps: isolation of bacteria, identification of the isolated strain, adaptation to alkaline environments, and cyanide degradation tests. The strain was identified using the mass spectrometry technique (MALDI-TOF) and it was subsequently compared with the 16S rDNA sequencing technique. Degradation assays were performed with adapted bacteria in an agitated flask containing a synthetic solution with 500 mg.L−1 of free-cyanide (CN−) and initial cell concentration of 2.5 × 1011 CFU.mL−1. Incubation was performed in orbital agitation at 27 °C and 190 rpm for 120 h. In conclusion, the identification techniques elucidated that the isolated strain probably belongs to the Bacillus subtilis species. Finally, cyanide degradation assays showed that the B. subtilis strain adapted to alkaline environments was able to degrade 100% of the free-cyanide in the solution in three days.
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In the current paper, the adsorption capability of gold from solution by activated carbon and functionalized graphene/carbon activated composite were studied. The results of AuCN2- adsorption on activated carbon showed that gold adsorption could reach 60 mg/g under the optimum conditions of pH = 9 and AuCN2- solution concentration = 1000 mg/l. Isotherm, kinetic and thermodynamic studies of gold adsorption on activated carbon were also examined. The effects of new adsorbent concentration (i.e. functionalized graphene/activated carbon composite), pH and AuCN2- were analyzed. SEM, FT-IR and EDX were used to evaluate and measure the quality of adsorption. The results indicated that AuCN2- adsorption of 200 mg/g could be reached under the following solution conditions: pH of 9, AuCN2- concentration of 1000 mg/l. It was concluded that functionalized graphene/carbon activated composite could be considered a stronger adsorbent rather than activated carbon for AuCN2-. The experiment results were further validated through SEM and EDX results.
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Hydrogen cyanide is an industrially important chemical, and its annual production is more than 1.5 million tons. Because of its toxicity, the cyanide‐containing effluents from industries have caused many environmental problems. Among various methods to treat the contaminated soils or water, the biological degradation is regarded to be promising. We isolated two cyanide‐degrading microorganisms, Pedobacter sp. EBE‐1 and Bacillus sp. EBE‐2, from soil contaminated with cyanide. Among these bacteria, Bacillus sp. EBE‐2 exhibited significantly a high cyanide‐degrading ability. Bacillus sp. EBE‐2 might be used for the remediation of cyanide contaminated water or soil. A nitrilase gene was cloned from Bacillus sp. EBE‐2. Bacillus nitrilase was expressed in E. coli and purified. Bacillus nitrilase exhibited cyanide‐degrading activity as a large oligomer. Since formic acid formation from cyanide was observed, Bacillus nitrilase is likely to be a cyanide hydrolase. Although there exist various homologous enzymes annotated as carbon‐nitrogen family hydrolases, this is the first report on the cyanide degrading activity. The structure and catalytic site of Bacillus nitrilase were studied by homology modeling and molecular docking simulation. This article is protected by copyright. All rights reserved
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Microorganisms actively participate in biogeochemical cycles of various elements in the environment, including gold. To explore the core microbiota associated with gold ore, this study examined the bacterial composition of mined rock from the Rozália gold mine (two subsurface samples from the gold mine and one from the heap of mined ore) using a cultivation approach. Cultivation analyses showed the occurrence of bacteria with colony forming units (CFU) ranging from 2.18 × 10⁵ to 3.16 × 10⁵ per 1 gram of dry ore material, and the data analysis indicates that the type of cultivation medium used significantly influences the observed biodiversity of cultivable bacteria. Cultivated members of the microbial community were identified using a combination of MALDI-TOF MS and 16S rRNA gene sequencing. The cultivable microbiota of gold-bearing ore samples was predominantly composed of the phylum Proteobacteria. Identification of 473 isolates revealed the presence of 4 dominant genera: Rhizobium, Microbacterium, Pseudomonas, and Acinetobacter, which together accounted for 89% of the gold ore-associated cultivated bacteria. These results are consistent with previous studies on the microbiota of gold mines and suggest that these genera constitute the core microbiota of gold ore.
Chapter
Biotechnology relevant to gold exploration, mining, recovery, and waste disposal is illustrated with respect to microbiological aspects of gold mineralization, Biooxidation of refractory sulfide ores and concentrates, cyanide-free gold dissolution, and biodegradation of cyanide containing effluents. Current industrial status of technological innovations in the bioreactor processing and heap bioleaching of refractory sulfide ores and concentrates are discussed. Biodetoxification and degradation of cyanides in waste tailings and waters are critically analyzed with examples from industrial practice. Prospects for direct biodissolution of gold are brought out. Recovery of gold from spent leach cyanide solutions and electronics wastes is examined. Bright future prospects for Biotechnology in gold exploration, mining, extraction, and waste disposal are emphasized.
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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 (TSFs). 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 less costly remediation option to 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. When amended with phosphate, the consortium completely degraded up to ~10 mM SCN- to ammonium and sulfate, with some evidence for 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 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-oxidising bacteria.
Chapter
Occurrence of huge quantity of cyanide in the environment is due to extensive use in metal-finishing and mining industries. The strong affinity of cyanide with metals makes it favorable as an agent for metal-finishing and lixivant for metal leaching. For many years, cyanide has been used as a leaching reagent for the extraction of precious metals, particularly gold and silver. As a high toxicity of the cyanide it appears on the international priority pollution list. Considering the lethal impact of cyanide on the environment as well as human health, environmental authorities have taken a more stringent attitude toward the presence of cyanide in water. The researchers are trying to investigate best removal techniques for treating hazardous materials like cyanide from metal-finishing industrial wastewater and also strive to reuse of this water for agricultural or other purposes. Although cyanide can be removed and recovered by several processes, while biological treatment process gained an impetus of efficient degradation ability. Biological treatment of cyanide has often been offered as a potentially economical, environmentally friendly alternative to conventional methods. For the treatment of cyanide-containing wastewater, the adsorption and biodegradation are two significant methods. The first one, that is, adsorption is better to other wastewater treatment techniques in terms of efficiency, ease of operation, and low cost. The second, biodegradation method of cyanides removal is better than physical and chemical methods. In cyanide biodegradation process; the cyanide is converted to carbon and nitrogen source by various enzymes present in microorganisms. Biological treatments with bacterial whole cells is another important route for cyanide removal from water in which whole cells are used either in bulk phase or are immobilized on a solid support (bioadsorbent). Immobilized whole cells produce biolayer on bioadsorbent surface and when treated with solution having cyanide, the bacterial cells biodegrade it within the cell as well as it gets adsorbed on bioadsorbent surface. This process is termed as simultaneous adsorption and biodegradation process. In this chapter, we are aimed to make comprehensive description about sustainable bioremoval techniques on the removal of most hazardous materials like cyanide which are released from metal-finishing industrial effluents.
Chapter
Fenton oxidation, coagulation/flocculation/sedimendation plus Fenton oxidation, and Fenton oxidation plus activated carbon adsorption were conducted to develop the effective processes for recycling a biologically treated coking plant effluent. Fenton oxidation enhanced adsorptive capacities of activated carbon for the residual organics and also made them more biodegradable. The Fenton oxidation followed by adsorption and biodegradation in a biological activated carbon (BAC) adsorber was the most cost-effective treatment process to recycle the final effluent for in-plant reuses while meeting the much more stringent discharge limits of the future. Batch experiments were also conducted to determine the effects of copper-loading and fixing methods on the capacity of granular activated carbon (GAC) for removing cyanide from KCN (pH = 11), K3Fe(CN)6 solutions and several Shanghai Coking Plant (SCP) effluent samples. KI-fixed carbon (Cu/KI-GAC) was the best GAC samples tested. Adsorption was the primary mechanism of cyanide removal; catalytic oxidation of the adsorbed cyanide on carbon surface contributed a minor amount of the observed removal. Four small adsorbers containing the base GAC and 0–100% of Cu/KI-GAC were employed for treating a Fenton-oxidized/precipitated SCP effluent sample. After the start-up period (<3 weeks) to establish the effective BAC function in the adsorbers, the effluents became stable and met the discharge limits (CODCr < 50 mg/L and TCN < 0.5 mg/L); with >30% Cu/KI-GAC in the adsorber, the effluent would meet the discharge limits during the start-up phase. The BAC function of the adsorber substantially reduced the carbon replacement cost, making the combined Fenton oxidation and BAC treatment process a cost-effective alternative for recycling the biotreated coking plant effluent.
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ZnO, NiO and ZnO@NiO nanocrystals were successfully synthesized and characterized by FTIR, XRD and SEM methods. The average particles sizes of ZnO, NiO and ZnO@NiO were 32, 50 and 48 nm, respectively. The nanocrystals were examined as sensors for cyanide removal. The cyanide sensing test revealed that, compared with the pure ZnO, NiO, the ZnO@NiO nanocrystals exhibited highly improved sensing performances. The ZnO@NiO nano crystals were found to have better capacity for iron cyanide than sodium cyanide. The effects of significant parameters such as contact time, pH (2–12), nanocrystal dose (0.02–0.4 g) and cyanide concentration (5–50 mg/L) on the removal of cyanide by nanocrystals were explored. At an optimum pH<5, over 90% removal of 20 mg/L cyanide was obtained for nanocrystal dose of 0.2 g after 30 min contact time for iron cyanide by ZnO@NiO nano crystals. Cyanide removal was followed by pseudo second order kinetic model for ZnO@NiO nano crystals (k2=4.66×10⁻² and R²=0.999). The values of standard entralpy change of 7.87 kJ/mol and standard free energy change of −18.62 kJ/mol at 298 K suggest the adsorption of cyanide on nanocrystals is an endothermic and spontaneous process. ZnO@NiO nanocrystal is an efficient sensor for removal of cyanide from water and wastewater.
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En el presente estudio, las comunidades bacterianas en muestras de suelo y agua, procedentes de pozas artesanales de lixiviación con cianuro, fueron caracterizadas por análisis dependientes e independientes de cultivo. Para la caracterización de la comunidad bacteriana cultivable, se emplearon técnicas clásicas de microbiología hasta la obtención de cepas puras, las cuales fueron identificadas a nivel molecular. Por otro lado, las comunidades bacterianas no cultivables fueron caracterizadas por secuenciación de próxima generación del gen ARNr 16S. La comunidad bacteriana cultivable estaba principalmente representada por los géneros Pseudomonas, Bacillus y Acinetobacter; mientras que las comunidades no cultivables, predominantes en muestras de suelo, fueron los filos Proteobacteria (12.91%), Firmicutes (11.32%), Actinobacteria (11.25%) y Bacteroidetes (10.16%). Por otro lado, en muestras de agua predominaron los filos Firmicutes (59.16%) y Actinobacteria (38.99%).
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Applications of biotechnology are in use or have been proposed for almost all sectors of the mining and minerals industries for metal extraction, metal recovery, and environmental control. A recently completed study in Canada reviewed the status of biotechnological process development in different sectors of the industry and by commodity. This paper provides an overview of the findings of the study including a discussion of the sectors of the industry in which biotechnology enjoys commercial success and those for which future applications are indicated. Special emphasis is given to the commercial metal extraction processes and to applications for environmental control for which future technical and economic advantages are likely as environmental regulations become more stringent.
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Cladosporium cladosporioides biomass was a highly efficient biosorbent of copper cyanide and nickel cyanide from aqueous solutions. A 32–38 fold concentration of initial 0.5mM metal cyanides could be achieved when biosorption process was carried out under standardised conditions. Residual, unrecoverable metal cyanide could be completely biodegraded in 5–6h. The solution treated with the combined biosorption-biodegradation process was fit for discharge in the environment.
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Cyanide hydratase, which converts cyanide to formamide, was induced in mycelia of Stemphylium loti by growth in the presence of low concentrations of cyanide. Mycelia were immobilised by several methods. The most useful system was found to be treatment with flocculating agents. This technique is applicable to a wide range of easily isolated fungi that contain cyanide hydratase.
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The effect of cyanide on the anaerobic treatment of synthetic wastewater, containing starch and volatile fatty acids, was evaluated. A laboratory-scale UASB reactor, operated at hydraulic retention time of 12 h, was successfully acclimatised to CN influent levels as high as 125 mg l−1. Evaluation of cyanide levels in the effluent demonstrated removal efficiencies of this compound of between 91 and 93% at volumetric CN loading rates of about 250 mg l d−1. First addition of CN at 5 mg l−1 and subsequent sudden increases in influent CN levels during the acclimatisation process resulted in temporary deterioration of reactor performance in terms of methane production and COD conversion, while CN levels in the effluent were temporarily increased. Recovery from CN inhibition was observed within 3–4 weeks, when effluent CN levels decreased again below about 10 mg l−1. Sludge activity measurements demonstrated an increased tolerance against CN, once sludge had been acclimatised to this toxic compound. The effect of CN inhibition on methanogenic activity was more pronounced for acetoclastic than for hydrogenotrophic methanogens. The findings of this study demonstrate the potential of anaerobic treatment for COD removal in CN contaminated waste waters. The results also suggest a potential application specifically for CN removal from waste streams.
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A cyanide-metabolizing bacterium, strain DF3, isolated from soil was identified as Alcaligenes xylosoxidans subsp. denitrificans. Whole cells and cell extracts of strain DF3 catalyzed hydrolysis of cyanide to formate and ammonia (HCN + 2H2O----HCOOH + NH3) without forming formamide as a free intermediate. The cyanide-hydrolyzing activity was inducibly produced in cells during growth in cyanide-containing media. Cyanate (OCN-) and a wide range of aliphatic and aromatic nitriles were not hydrolyzed by intact cells of A. xylosoxidans subsp. denitrificans DF3. Strain DF3 hydrolyzed cyanide with great efficacy. Thus, by using resting induced cells at a concentration of 11.3 mg (dry weight) per ml, the cyanide concentration could be reduced from 0.97 M (approximately 25,220 ppm) to less than 77 nM (approximately 0.002 ppm) in 55 h. Enzyme purification established that cyanide hydrolysis by A. xylosoxidans subsp. denitrificans DF3 was due to a single intracellular enzyme. The soluble enzyme was purified approximately 160-fold, and the first 25 NH2-terminal amino acids were determined by automated Edman degradation. The molecular mass of the active enzyme (purity, greater than 97% as determined by amino acid sequencing) was estimated to be greater than 300,000 Da. The cyanide-hydrolyzing enzyme of A. xylosoxidans subsp. denitrificans DF3 was tentatively named cyanidase to distinguish it from known nitrilases (EC 3.5.5.1) which act on organic nitriles.
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Cyanidation tailings disposed of in a surface impoundment experience a loss of cyanide due to natural attenuation, which frequently reduces the cyanide concentration to very low levels. Quantifying cyanide losses in terms of impoundment geometry, local weather conditions and feed-solution chemistry has been largely empirical in spite of the fact that, in many cases, mining operations rely on surface impoundments to reduce cyanide to below an internally regulated concentration or below an effluent limitation. To permit a quantitative evaluation of cyanide losses in an impoundment, a computer simulation was developed to estimate the losses of free, weak acid dissociable (WAD) and total cyanide due to dissociation, photolysis and volatilization. Results of the model are compared with data collected for a North American tailings impoundment in 1998.
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Cydnidation tailings disposed of in a surface impoundment experience a loss of cyanide due to natural attenuation, which frequently reduces the cyanide concentration to very low levels. Quantifying cyanide losses in terms of impoundment geometry, local weather conditions and feed-solution chemistry has been largely empirical in spite of the fact that, in many cases, mining operations rely on surface impoundments to reduce cyanide to below an internally regulated concentration or below an effluent limitation. To permit a quantitative evaluation of cyanide losses in an impoundment, a computer simulation was developed to estimate the losses of free, weak acid dissociable (WAD) and total cyanide due to dissociation, photolysis and volatilization. Results of the model are compared with data collected for a North American tailings impoundment in 1998.
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Cyanidation tailings which are disposed in a surface impoundment experience a loss of cyanide due to natural attenuation, frequently reducing the cyanide concentration to very low levels. Quantifying cyanide losses in terms of impoundment geometry, local weather conditions and feed solution chemistry has been largely empirical though in many cases mining operations rely on surface impoundments to reduce cyanide to below an internally regulated concentration or below an effluent limitation. To permit a more quantitative evaluation of cyanide losses in an impoundment, a computer simulation was developed to estimate the losses of free, weak acid dissociable (WAD) and total cyanide due to dissociation, photolysis and volatilization. Results of the model are compared against data collected for a North American tailings impoundment during 1998.
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The potential of sewage sludge for decomposition of cyanide has been investigated at different temperatures, ratio sewage sludge to cyanide, pH and also at prolonged and at four cycle repeated processes. Along with the kinetics of cyanide decomposition, the consumption of reagents necessary to maintain pH of the biosystem and the releasing of volatile cyanide have been examined. The positive effect of the activation of sewage sludge by means of aeration and its correlation to the kinetics of the bacterial growth have been also studied. Along with aeration, “carrier biology” has been employed to improve the characteristics of sewage sludge, using wood peels as a carrier material.
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Former gasworks sites are sometimes be heavily contaminated with spent oxide which contains cyanide complexed to metals (especially iron). In this study, mixed fungal cultures have been isolated from acidic gasworks soil by their ability to utilize iron or nickel cyanide as the sole source of nitrogen at acidic or neutral pH, respectively. A mixed culture comprising Fusarium solani and Trichoderma polysporum was obtained by enrichment on tetracyanonickelate [K2Ni(CN)4] at pH 4. A second mixed culture consisting of Fusarium oxysporum, Scytalidium thermophilum, and Penicillium miczynski was isolated on hexacyanoferrate [K4Fe(CN)6] also at pH 4. Both consortia were able to grow on K4Fe(CN)6 as the sole source of nitrogen under acidic conditions. Growth was associated with progressive removal of cyanide from the culture supernatant. After the termination of growth, at least 50% of the total cyanide had been degraded. Growth of the fungi on K2Ni(14CN)4 as a source of nitrogen at pH 7 yielded 14C-labelled carbon dioxide. Growth of the Fusarium isolates on K2Ni(CN)4 at pH 7, associated with the removal of cyanide, required 5 days as compared to 28 days on K4Fe(CN)6 at pH 4. Cyanide uptake by the fungi on K4Fe(CN)6 at pH 4 occurred simultaneously with removal of iron from the biomass-free medium. Pure cultures of F. solani and F. oxysporum were grown on K2Ni(CN)4 or K4Fe(CN)6 in pure culture at pH 7 or 4, respectively.
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Water-soluble iron cyanide compounds are widely used as anticaking agents in road salt, which creates potential contamination of surface and groundwater with these compounds when the salt dissolves and is washed off roads in runoff. This paper presents a summary of available information on iron cyanide use in road salt and its potential effects on water quality. Also, estimates of total cyanide concentrations in snow-melt runoff from roadways are presented as simple mass-balance calculations. Although available information does not indicate a widespread problem, it also is clear that the water-quality effects of cyanide in road salt have not been examined much. Considering the large, and increasing, volume of road salt used for deicing, studies are needed to determine levels of total and free cyanide in surface and groundwater adjacent to salt storage facilities and along roads with open drainage ditches. Results could be combined with current knowledge of the fate and transport of cyanide to assess water-quality effects of iron cyanide anticaking agents used in road salt.
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Biological treatment of a synthetic leachate containing cyanide was accomplished in a sequencing batch biofilm reactor (SBBR). A mixed culture of organisms growing on silicone tubing were provided with cyanide as a sole carbon and nitrogen source. Organisms consumed cyanide (20 mg/liter CN−WAD) and produced ammonia in an approximate 1:1 molar yield. The SBBR was operated on a 24-h cycle. Over the course of each cycle, 20 mg/liter of cyanide was degraded to below 0.5 mg/liter. Results from four track studies are presented. It was demonstrated that, when supplied with glucose, the organisms would readily consume excess ammonia. For each mole of glucose added, 10 moles of NH3-N were removed from solution. The SBBR can be used as a mobile system for treatment of leachate from gold-mining operations. Large volumes of low concentration wastewater can be treated in the SBBR since it is not necessary to maintain a consortium of settling organisms. © 1998 Elsevier Science Ltd. All rights reserved
Article
Tests were conducted at the Ryan Lode Mine near Fairbanks, Alaska, to determine the comparative costs of chemical and biological destruction of cyanide in mine wastewater. The main body of pond and rinse water was treated by the patented, INCO Air-SO2 process. A 250 ton test heap was built and inoculated with a cyanide-reducing bacterium Pseudomonas pseudoalcaligenes (UA7). The capital and operating costs for both processes were carefully recorded during the treatment. These costs were used as the basis for an analysis of the comparative costs of rinsing and detoxifying a hypothetical, two-million ton heap using each method. Four scenarios were analyzed. The biological method had a higher capital cost, but a significantly lower operating cost, so that the present-worth cost was significantly lower for the biological method.
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The presence of cyanide in industrial effluent waste presents a major environmental and ecological hazard. Although chemical methods of treating this compound are known, bacterial detoxification of cyanide is of interest both in order to understand how cyanide may be dealt with in the environment and to evaluate the economic viability of bacterial systems for cyanide detoxification. The enzyme rhodanese, which catalyzes the formation of thiocyanate and sulfite from cyanide and thiosulfate, has been found in various organisms including Bacillus subtilis and E. coli. Thiobacillus denitrificans was shown to have the highest levels of this enzyme, but growth conditions in continuous culture on defined media have recently been developed for the production of equally high rhodanese levels in the thermophile Bacillus stearothermophilus. Purified rhodanese from this latter organism has already proved to be of value as an antidote in experimental cyanide poisoning in small mammals. This communication reports on the use of a culture of B. stearothermophilus in a small chemical reactor for the continuous removal of cyanide in the form of thiocyanate. The capacity of B. stearothermophilus to remove cyanide in the form of thiocyanate in the process described is high (5 to 8 g NaCN/l culture/hr at 27°C); furthermore, both the rate of cyanide removal and the half life of the process were unaffected by the presence of 5x10-5M Zn2+, Cu2+, Ni2+, or Al3+ over a 12 day period. By running the process at temperatures at which B. stearothermophilus is capable of growth in normal media (i.e. above 35°C) higher rates of cyanide detoxification are possible (14 to 25 g NaCN/l culture/hr at 50°C), although preliminary evidence indicates a reduction in half life at higher temperature.
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Cyanide compounds are widely used in gold ore processing plants in order to facilitate the extraction and subsequent concentration of the precious metal. Owing to the high cyanide concentrations employed in gold processing, effluents generated have high contents of free cyanide as well as metallic cyanide complexes, which lend them a high degree of toxicity. The process under study, developed in laboratory scale with the use of a distillation apparatus, consists of highly decreasing the pH of the solution by adding sulfuric acid. Thus, the cyanide present in either free form or as a metallic complex is made volatile and the resulting cyanide gas is absorbed in an alkaline solution for reutilization. This work aims at recognizing the chemical relations between the cyanide and metals during distillation. The regeneration of cyanide from gold processing proved to be a viable procedure. Cyanide recoveries pointed to the fact that if a method for reutilization of cyanide contained in mining effluents is employed, the precious metal processing will become more efficient. Also, the environmental conditions in the area of the operation will be improved.
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Accumulation of UO 22 + by Scenedesmus obliquus 34 was rapid and energy-independent and the biosorption of UO 22 + could be described by the Freundlich adsorption isotherm below the maximum adsorption capacity (75 mg g-1 dry wt). The optimum pH for uranium uptake was between 5.0_8.5.0.1_2.0 M NaCl enhanced uranyl, while Cu2+, Ni2+, Zn2+, Cd2+ and Mn2+ competed slightly with uranyl. Pretreatment had an unexpected effect on biosorption. After being killed by 0.1 M HCl, S. Obliquus 34 showed 45% of the uptake capacity of the control in which fresh cells were suspended directly in uranyl solution, while the pretreatment of cells by 0.1 M NaOH, 2.0 M NaCl, ethanol or heating decreased uptake slightly. Fresh S. obliquus 34 at 1.2_2.4 mg dry wt mL-1 was able to decrease U from 5.0 to 0.05 mg L-1 after 4_6 equilibrium stages with batch adsorption. Deposited U could be desorbed by pH 4.0 buffer. It is suggested that U was captured by effective groups or by capillary action in the cell wall in the form of [UO2OH]+.
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A bacterial coculture capable of growing on thiocyanate has been isolated from thiocyanate adapted bacterial suspension of urban sewage treatment plant. The coculture is composed of two bacteria identified as species Acinetobacter johnsonii and Pseudomonas diminuta. The two end products of thiocyanate conversion are ammonia and sulfate. The thiosulfate has been identified as the sulfur intermediate product of the conversion of thiocyanate to sulfate.
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The present study compared the efficiency of two unicellular green algae, Chlorella vulgaris (a commercial species from Carolina Biological Supplies Company) and WW1 (an indigenous species isolated from a local sewage treatment works, tentatively identified as Chlorella miniata) in removing Ni2+ from nickel solutions with concentration ranges similar to that in electroplating effluents. The Ni2+ removal efficiency of C. vulgaris (around 33–41%) was significantly lower than that of WW1 (more than 99%) in nickel solutions from 10 to 40 μg ml−1. The maximum Ni2+ uptake by C. vulgaris and WW1 under the present batch experiment was 641.76 and 1367.62 μg g−1, respectively. According to Langmuir adsorption isotherms the nickel adsorption capacity of WW1 (2985.07 μg g−1) was two times greater than that of C. vulgaris (1282.05 μg g−1). These results demonstrated that WW1 was a more powerful Ni2+ biosorbent than C. vulgaris. In both species, most Ni2+ in solution was sequestered by the algal cells within the first few minutes of treatment. The cellular Ni2+ concentration increased with the concentrations of nickel in solution. After treating Ni-containing wastewater for 24 h, both species were still capable of cell division, but the growth rate was reduced in proportion to the concentrations of nickel in the wastewaters.
Article
Biological treatment is a proven process for the treatment of mining effluents such as tailings, wastewaters, acidic mine drainage etc. Several bacterial species (Pseudomonas sp.) can effectively degrade cyanide into less toxic products. During metabolism, they use cyanide as a nitrogen and carbon source converting it to ammonia and carbonate, if appropriate conditions are maintained. In this study, nine strains of Pseudomonas sp. were isolated and identified from a copper mine. Two (CM5 and CMN2) of the nine bacteria strains were used in a cyanide solution. Some important parameters in the biological treatment process were tested and controlled: pH, cell population and CN− concentration. Tests were conducted to determine the effect of the type of bacterial strains on the treatment of cyanide. Laboratory results indicated that biological treatment with Pseudomonas sp. might be competitive with other chemical treatment processes. This paper presents the results of an investigation of a biological treatment system for cyanide degradation in a laboratory batch process.
Article
The removal of heavy metals by a dry biomass of a brown seaweed was evaluated. A continuous system was used, with an effluent from a Brazilian zinc producing industry, containing zinc (88.0 mg/L), cadmium (1.4 mg/L), and manganese (11. 7 mg/L), as well as high levels of calcium (444 mg/L), magnesium (100 mg/L) and sodium (37.0 mg/L). Preliminary results, in batch conditions, indicated fast uptake kinetics for the heavy metals, whose equilibria were reached in a maximum of 30 minutes. The continuous run was conducted in a laboratory acrylic column, lm high, containing several samplers, filled with the dry biomass. The system operated in upflow condition, at a flow rate of 25 mL/min, f or approximately 70 hours, with high operational stability. The results showed high efficiency in the biosorption of heavy metals. Sodium, calcium and magnesium were not incorporated by the biomass, probably as they are present in the structural polysaccharides of the biomass, thus preventing the establishment of an effective ion-exchange process. Analysis of the obtained results did not indicate selective uptake of the metals, probably due to their marked concentration differences in solution. The continuous laboratory system initially showed an efficiency close to 100% in the biosorption of all heavy metals, followed by a gradual decrease, as a function of the saturation of binding sites in the biomass. A mathematical adjustment of the curves obtained for the uptake of the different metals was used for estimating the amount of biosorbed metals, through mathematical computer integration.
Article
In the history of Turkey the first use of cyanide for gold recovery has been at the Ovacik Gold Mine. During one-year test period, this mine has successfully been mining and processing after a complicated and extensive environmental impact procedure. In Turkey about 2500 ton of sodium cyanide are used with about 240 ton of sodium cyanide being used at this mine annually. During the test period, it has been shown that an effluent quality (CNWAD) between 0.06 ppm (min) and 1 ppm (max) was achievable after cyanide destruction with the Inco Process. It was also found that treated effluent values (CNWAD) of process water (decant) were between 0.04 ppm (min) and 0.59 ppm (max). This paper presents a review of the cyanidation and cyanide destruction processes at the Ovacik Gold Mine.
Article
Biosorption is considered a potential instrument for the removal of metals from waste solutions and for precious metals recovery, an alternative to the conventional processes, such as those based on ion exchange, or adsorption on activated carbon. In this work the state of the art of biosorption investigation is presented and results found in literature are compared.
Article
Combined biodegradation and internal diffusion effects on the biodegradation rate of ferrous(II) cyanide complex (ferrocyanide) ions by Ca-alginate gel immobilized Pseudomonas fluorescens beads were investigated as a function of initial ferrocyanide concentration and particle size in a batch system. Assuming first-order biodegradation kinetics (ν=kC), first-order biodegradation rate constants for free and different sized immobilized particles were predicted and at 100 mg l−1 bulk ferrocyanide ion concentration experimental effectiveness factors (η) were determined for each particle size. Then using these data, the Thiele modulus (φ) was evaluated for each particle size. Finally effective diffusion coefficient (De) was calculated from the Thiele modulus equation, which is a function of particle size, effective diffusion coefficient and first-order biodegradation rate constant. The results showed that the intraparticle diffusion resistance has a significant effect on the observed biodegradation rate.
Article
For over 100 years, cyanide has been the leach reagent of choice for the extraction of precious metals. Cyanide is used as a lixiviant in milling leach circuits, as well as in heap leach operations. Increasingly stringent environmental regulations have created much interest in a wide variety of methods to destroy residual cyanide. Traditional means of cyanide destruction include alkaline chlorination, hydrogen peroxide, and the INCOIS02 air process. Biological degradation of cyanide has often been offered as a potentially inexpensive, environmentally friendly alternative to conventional processes.In response to the costs of cyanide destruction, cyanide use has become increasingly efficient, and recovery and recycle processes are being employed in many operations. Because of this, and because the pilot studies necessary to develop a biological treatment process can be expensive and time consuming, biological treatment has not seen widespread use for the detoxification of cyanide. Recently, however, biological degradation of cyanide has received a great deal of consideration as a method for cyanide detoxification for heap leach closures.In the decommissioning of heap leaches, residual cyanide must be detoxified before the heap can be closed. Smaller heaps have been successfully decommissioned and larger heaps are in the process of decommissioning. During closure, residual concentrations in the heap must be reduced so that the leachate meets discharge requirements. This paper examines the various alternative methods of heap closure, and compares closing costs for 1.2 and 25 million ton heaps.
Article
utilizes cyanide as the sole source of carbon and nitrogen. Agar, alginate, and carrageenan were screened as the encapsulating matrices for P. putida. Alginate-immobilized cells of P. putida degraded sodium cyanide (NaCN) more efficiently than non-immobilized cells or cells immobilized in agar or carrageenan. The end products of biodegradation of cyanide were identified as ammonia (NH3) and carbon dioxide (CO2). These products changed the medium pH. In bioreactors, the rate of cyanide degradation increased with an increase in the rate of aeration. Maximum utilization of cyanide was observed at 200 ml min−1 of aeration. Immobilized cells of P. putida degraded cyanides, cyanates and thiocyanates to NH3 and CO2. Use of Na[14C]-CN showed that 70% of carbon of Na[14C]-CN was converted into 14CO2 and only 10% was associated with the cell biomass. The substrate-dependent kinetics indicated that the K m and V max values of P. putida for the substrate, NaCN were 14 mM and 29 nmol of oxygen consumed mg protein−1 min−1 respectively.
Article
The susceptibility of cytochrome oxidases to cyanide means that cyanide is toxic to living cells and cyanide pollution causes great damage to microbial and other ecosystems. Cyanide pollution comes from both industrial wastes and a number of plants, many of agricultural importance, which are cyanogenic and release cyanide into the soil. Despite some understanding of the pathway of cyanide assimilation by aerobic microorganisms, there is little known about cyanide assimilation by anaerobic microorganisms. The author discusses cyanide production, utilization, degradation, and resistance by microorganisms. He concludes that among the most primitive organisms were some that could metabolize cyanide, perhaps in conjunction with other carbon and nitrogen sources. 199 references, 4 figures, 2 tables.
Article
Cyanide is an important industrial chemical produced on a grand scale each year. Although extremely toxic to mammalian life, cyanide is a natural product generated by fungi and bacteria, and as a result microbial systems have evolved for the degradation of cyanide to less toxic compounds. The enzymes which utilize cyanide as a substrate can be categorized into the following reaction types: substitution/addition, hydrolysis, oxidation, and reduction. Each of these categories is reviewed with respect to the known biochemistry and feasibility for use in treatment of cyanide containing wastes.
Article
This chapter focuses on cyanide metabolism in micro-organisms. It is noted that cyanide is a relatively common product of microbial as well as plant metabolism. Cyanide production by micro-organisms has many characteristics typical of secondary metabolism. In addition, it is probably the simplest secondary metabolic system and a continued investigation of cyanide formation should greatly aid a better understanding of microbial secondary metabolism. Cyanide degradation by Chromobacterium violaceum, or C. violaceum, is known to synthesize at least three enzymes capable of metabolizing cyanide. These include rhodanese, γ-cyano-α-aminobutyric acid synthase, and β-cyanoalanine synthase. The concentrations of all three enzymes increase in the post-cyanogenic period. The buildup of β-cyanoalanine is particularly noteworthy in bacteria grown under conditions of high cyanogenesis. The suspensions of harvested C. violaceum cells are also able to form β-cyanoalanine when incubated with cyanide and serine.
Article
A strain of Bacillus pumilus was isolated from Fargo clay in a field near Fargo, North Dakota, which had been cropped in flax 73 consecutive years. This bacterium had an unusual ability to survive saturated solutions of potassium cyanide. The optimal growth conditions of this strain of Bacillus pumilus in the standard medium with 10−1 M cyanide as well as its morphological changes to a filamentous form under the influence of cyanide were established. Both 14CO2 and 15NH4+ were produced in cultures of the organism during labelling experiments in which K14C15N was fed, supporting the idea of cyanide utilization by this bacterium. Oxygen uptake studies by the filamentous form in the presence of 10−1 M KCN suggested that it has an extreme tolerance to cyanide. This is the first report of a bacterium being able to survive solutions of KCN up to 2.5 M.
Article
Our isolate, Pseudomonas putida, is known to be capable of utilizing cyanides as the sole source of carbon (C) and nitrogen (N) both in the form of free cells and cells immobilized in calcium alginate. In the present study, the cell-free extract(s) were prepared from the cells of P. putida grown in the presence of sodium cyanide. The ability of enzyme(s) to convert cyanides, cyanates, thiocyanates, formamide and cyanide-containing mine waters into ammonia (NH3) was studied at pH 7.5 and pH 9.5. The kinetic analysis of cyanide and formamide conversion into NH3 at pH 7.5 and pH 9.5 by the cell-free extract(s) of P. putida was also studied. The Km and Vmax values for cyanide/formamide were found to be 4.3/8 mM and 142/227 mumol NH3 released mg protein-1 min-1 respectively at pH 7.5 and 5/16.67 mM and 181/434 mumol NH3 released mg protein-1 h-1 respectively at pH 9.5. The study thus concludes that the cell-free extract(s) of P. putida is able to metabolize not only cyanides, cyanates, thiocyanates, and formamide but also cyanide-containing mine waters to NH3.
Article
Two living Chlorella species were used to remove nickel from solution containing 30 micrograms Ni ml-1 in 10 successive cycles. The present study also examined the continued viability of these two algal species after repeated exposure to nickel. The two species of Chlorella were Chlorella vulgaris (commercially available) and WW1 (indigenous species isolated from domestic sewage and was tentatively identified as Chlorella miniata). The nickel removal percentage of WW1 cells was maintained at around 85% in the first five cycles, then declined slightly from the fifth cycle onwards, and finally achieved around 70% removal at the end of the 10th cycle. On the contrary, the removal efficiency of C. vulgaris declined from 50 to 30% during the 10 cycles of nickel bisorption. At the end of these 10 successive cycles, WW1 accumulated a substantial amount of Ni2+ (the cumulative cellular Ni concentration was 0.92% dry w.), while the value was only 0.17% in the case of C. vulgaris. These results suggest that the local isolate, WW1, had more consistent and satisfactory ability for removing Ni than the commercial C. vulgaris. Both algal species were still capable of dividing after each nickel treatment cycle, suggesting that the cells were not killed even when significant amounts of nickel were adsorbed/absorbed. However, Ni exposure adversely affected the physiological activity of algal cells as reflected by the decline in division rate and chlorophyll-a activity in both species. Such negative effects became more obvious as the number of cyclic treatments was increased. Nevertheless, WW1 cells appeared to recover from nickel treatment when re-cultivated in commercial medium for 2 weeks.