Cyanide's Watery Grave: Understanding Aquatic Pollution

Cyanide is a fast-acting poison that can be lethal. It is introduced into the human body through inhalation, ingestion, and skin contact. Cyanide ions are released into the environment through various industrial activities, such as mining, metallurgy, and chemical production, and they can contaminate water sources. Due to its toxicity, the removal of cyanide from wastewater is crucial, and various methods, including biological, chemical, and physical processes, are employed to treat cyanide-containing water.

Sources of cyanide pollution

Cyanide is a fast-acting poison that can be lethal. It is introduced into the environment through various natural and human-led processes.

Industrial Activities

Some industrial processes, such as iron and steel production, chemical industries, wastewater treatment, and mining can create and release cyanide compounds into the environment. This includes fires at industrial workshops and houses.

Natural Sources

Certain bacteria, fungi, and algae can produce cyanide.

Exhaust Gases

Vehicle exhaust gases are a source of cyanide pollution.

Cigarettes

Cigarettes are a major source of cyanide exposure for people who do not work in industries related to this chemical.

Food

Cyanide is also found in certain foods such as spinach, bamboo shoots, almonds, lima beans, fruit pits, and tapioca.

Water Treatment

During water chlorination, low levels of cyanogen chloride may be produced.

Gold Mining

Residues produced in gold mining operations can be a source of cyanide pollution.

Plastic Production

Cyanide is used in the plastic production of all kinds of dyes.

Metallurgical Plants

Metallurgical plants are another source of cyanide pollution, especially when fires occur.

Biological Materials

Biological materials such as blood, urine, and saliva can contain cyanide and contribute to environmental pollution.

Industrial activities and cyanide

Cyanide is released into the environment as a result of various industrial activities. The bulk of cyanide pollution is due to the metal finishing and mining industries. Cyanide is also extensively used in the galvanic, metallurgical, and chemical industries.

Sources of cyanide in water include wastewater, industrial fires, and tobacco smoke. It is also produced during underground coal gasification. Cyanide can enter surface water through releases from metal finishing industries, iron and steel mills, runoff from disposal of cyanide wastes in landfills, pesticides, and the use of cyanide-containing road salts.

In the metal finishing industry, cyanide is used for electroplating, metal cleaning, and metal processing. In mining, cyanide is used in gold extraction processes. In addition, cyanide is used in the production of plastics, dyes, and pesticides.

The presence of cyanide in wastewater has led to the development of various treatment methods, including biological, physical, and chemical processes. Biological treatment methods, which utilize microorganisms to remove pollutants, are considered optimal due to their cost-effectiveness and ability to reduce cyanide concentrations to environmentally acceptable levels. Physical and chemical processes, such as adsorption and ozonation, are also used but may have drawbacks such as the generation of toxic by-products or the transfer of pollutants to another medium.

While the primary objective is to remove cyanide from wastewater, there is also a focus on exploring the potential value of cyanide waste in different industries. For example, cyanide residues from gold mining operations could be used for new extraction processes, reducing the need to purchase cyanide.

Cyanide's impact on human health

Cyanide is a fast-acting, lethal poison that can be inhaled, ingested, or absorbed through the skin. It is a colourless gas with a bitter almond odour and quickly enters the bloodstream. Cyanide is found in cigarette smoke, vehicle exhaust, and foods such as spinach, bamboo shoots, almonds, lima beans, fruit pits, and tapioca. It is also used in industrial processes such as iron and steel production, chemical industries, wastewater treatment, and mining.

The impact of cyanide on human health can vary depending on the level of exposure and the route of entry into the body. Inhalation and intravenous injection of cyanide produce a more rapid onset of symptoms than ingestion or transdermal exposure. This is because the former routes provide faster diffusion into the bloodstream. The toxicity of cyanide is mainly linked to the cessation of aerobic cell metabolism.

When exposed to cyanide, it is crucial to move to fresh air immediately. Washing any cyanide from the skin and eyes with soap and water is essential, and medical attention should be sought right away. Oxygen therapy and antidotes, such as sodium nitrite and sodium thiosulfate, are often used to treat cyanide poisoning. Other drugs may be necessary to control additional health effects, such as seizures.

In small doses, the body can convert cyanide into the less harmful thiocyanate, which is excreted in urine. Additionally, cyanide can combine with another chemical in the body to form vitamin B12, which helps maintain healthy nerve and red blood cells. However, in large doses, the body's ability to detoxify cyanide is overwhelmed, leading to severe health consequences.

Memory impairment has been reported as a delayed effect in individuals who survived cyanide poisoning with antidotal treatment. Studies have also indicated a possible link between cyanide exposure and Parkinsonism, but further research is needed to establish a cause-and-effect relationship.

Methods to remove cyanide from water

Cyanide is a contaminant that can accumulate in groundwater and surface waters through natural processes. It is produced by the decomposition of some plants and can be present in foods such as green almonds, cassava, and bamboo shoots. It is also used in industrial processes such as gold and silver extraction from ores, iron and steel production, and chemical industries. The removal of cyanide from wastewater is essential to prevent its accumulation and potential harm to human health and the environment. Here are some methods to remove cyanide from water:

Chemical Oxidation Methods:

Chemical oxidation methods, such as alkaline chlorination (using bleach) and hydrogen peroxide degradation, are commonly used to treat cyanide in wastewater. These methods break down the cyanide molecule, forming less toxic products like cyanate (OCN–), which is less persistent in the environment. However, these methods may not be as environmentally friendly as other available technologies.

Physicochemical Methods:

Physicochemical methods, such as adsorption, offer a cost-effective approach to cyanide removal. Adsorption utilizes forces of molecular attraction to remove cyanide and other contaminants from wastewater. It is simple to operate and suitable for low cyanide concentrations. The adsorbed cyanide can even be recycled and reused in some cases. However, physicochemical methods do not eliminate contaminants from their original source but transfer them to another medium for further treatment.

Biological Treatment:

Biological treatment utilizes microorganisms, such as plants, bacteria, fungi, or microalgae, to remove or reduce cyanide concentrations in water. This approach is simple, cost-effective, and environmentally friendly, as it produces fewer harmful by-products. Phytoremediation, for example, employs plants that can utilize cyanide to fulfill their nitrogen needs, thereby reducing cyanide levels in water or soil.

Ion Exchange (IX):

IX is a physical-chemical treatment process where a liquid stream containing cyanide is passed through a resin substrate. The resin selectively captures cyanide anions, temporarily retaining them until the resin is regenerated. This method is suitable for facilities aiming to reduce cyanide content below regulatory limits or treat large volumes of water with relatively low cyanide concentrations.

Membrane Separation:

Membrane separation techniques, such as membrane filtration, can be used to physically separate cyanide from water. While effective, this method has some drawbacks, including high costs for system maintenance and membrane replacement, as well as relatively high energy consumption and flow rate limitations.

The choice of the best cyanide removal technology depends on the specific needs of the facility, the concentration of cyanide in the wastewater, and environmental considerations. Continuous research and development aim to find more efficient, cost-effective, and environmentally friendly methods to address the challenge of cyanide pollution in water.

Biological treatment of cyanide

Biological treatment methods include phytoremediation and microbial bioremediation. Phytoremediation involves the use of plants to remove or reduce cyanide concentrations in water or soil. Plants can utilize cyanide to fulfil their nitrogen needs. This method is effective for cyanide concentrations of 0-10 mg/mL. However, it is important to note that the specific treatment approach depends on the type of wastewater, as cyanide concentration varies across different industries. For instance, concentrations range from ≤100,000 mg/mL in electroplating baths to 5-10 mg/mL in coal gasification processes.

Microbial bioremediation, on the other hand, relies on the metabolic activities of bacteria, fungi, or microalgae to degrade cyanide. Bacterial strains such as Pseudomonas, Bacillus, and Klebsiella have been examined for their ability to bioremediate free cyanide and metallic-complexed cyanide. In one study, the bacterial strain Pseudomonas pseudoalcaligenes CECT5344 was used in a batch reactor to biologically detoxify water containing cyanide. The operational procedure was optimized to assess cyanide biodegradation at variable pH values and dissolved oxygen concentrations. It was found that a high pH and low dissolved oxygen saturation minimized the release of toxic hydrogen cyanide (HCN).

In addition to these methods, an integrated biological approach for the treatment of cyanidation wastewater has also been explored. A sequencing batch biofilm reactor (SBBR) is a mobile, closed system capable of treating dilute cyanide waste streams. The SBBR was tested and found to be effective in removing cyanide, with a treatment capacity of 0.5 mg cyanide/liter-hour.

Overall, biological treatment methods offer a simple, cost-effective, and environmentally friendly approach to reducing cyanide concentrations in wastewater. By utilizing the metabolic activities of various organisms, these methods can effectively degrade cyanide and reduce its potential hazards to human health and ecosystems.

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