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Heavy Metal Contaminants in Groundwater
Context:
Researchers at the Centre for Sustainable Technologies (CST), Indian Institute of Science (IISc) have developed a novel remediation process for removing heavy metal contaminants such as arsenic from groundwater.
More on News:
- The process ensures that removed heavy metals are disposed of in an environmentally friendly and sustainable manner.
- Prevents untreated heavy metal-rich sludge from being sent to landfills, which could lead to recontamination of groundwater.
- CST, highlighted the issue with existing technologies: While they remove arsenic and provide clean water, they do not adequately address the disposal of arsenic to prevent re-entry into the environment.
- The new three-step process was specifically designed to solve this problem.
Remediation Process Overview:
- Adsorption Stage:
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- Utilises a biodegradable adsorbent made of chitosan doped with bimetallic hydroxide/oxyhydroxide.
- Toxic inorganic arsenic is captured through electrostatic forces and complex formation.
- Novel aspect: Alkaline wash is recycled to regenerate the adsorbent bed.
- Membrane Separation:
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- Alkaline wash solution (sodium hydroxide and arsenic) is passed through a membrane system.
- Sodium hydroxide solution is reused to regenerate the adsorbent bed.
- Arsenic concentrate is separated for further treatment.
Bioremediation:
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- Arsenic concentrate undergoes a bioremediation process.
- Bioremediation is a branch of biotechnology that employs the use of living organisms in the removal of contaminants, pollutants, and toxins from soil, water, and other environments.
- These organisms can include microbes and bacteria.
- Microbes in cow dung methylate toxic inorganic arsenic into low-toxicity organic arsenic.
- Result: Toxicity reduced to below WHO standards within eight days.
- Cow dung sludge containing locked-in organic arsenic can be safely disposed of in landfills.
- Arsenic concentrate undergoes a bioremediation process.
Benefits and Adaptability:
- Organic arsenic species generated 50 times less toxic than inorganic form.
- Process adaptable to fluoride removal, with the last step modified to form calcium fluoride.
- Easy assembly and operation, with successful pilot-scale tests for safe drinking water generation.
- Collaboration with NGOs for deployment and testing in rural areas like Bhagalpur and Chikkaballapur.
Extent of Contamination in India:
- Arsenic Levels: 113 districts in 21 states exceed permissible arsenic levels of 0.01 mg per litre.
- Fluoride Levels: 223 districts in 23 states surpass permissible fluoride levels of 1.5 mg per litre.
- Permissible Limits and Regulatory Bodies: Bureau of Indian Standards (BIS) and WHO Standards:
- Contamination levels exceed standards set by both BIS and WHO.
- Health Implications: Human and Animal Health Impact: Contaminants pose significant health risks to both humans and animals.
- Need for Remediation: Efficient Removal and Safe Disposal:
- Necessitates effective methods for removing and disposing of contaminants to safeguard public health.
Heavy Metals in Drinking Water:
- Heavy metals are a group of metals and metalloids that have relatively high density and are toxic even at ppb levels.
- Examples include Pb, As, Hg, Cd, Zn, Ag, Cu, Fe, Cr, Ni, Pd, and Pt.
- Heavy metals contaminate drinking water from diverse sources: plumbing, mining, refineries, electronics, waste disposal, cement plants, and natural deposits.
- Private wells can get contaminated through groundwater and surface water seepage.
- High heavy metal consumption risks: acute/chronic toxicity, liver/kidney damage, anaemia, cancer.
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Geographic information system (GIS)-Based Assessment of Groundwater Vulnerability to Heavy Metal Contamination in Urban Aligarh:
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