Environmentalists, wildlife activists, and locals recently sought immediate intervention by the Union Environment Ministry into the recurring illegal discharge of highly toxic, untreated leachate into the Aravalis.
About Leachate
Leachate is a toxic liquid produced when water passes through decomposing waste in a landfill, dissolving contaminants in the process. Without proper management, this foul-smelling substance can contaminate groundwater, soil, and surface water, posing significant risks to human health and the environment. 
How leachate is formed
Leachate is formed by the infiltration of water into a landfill, primarily from precipitation like rainfall. Several processes contribute to its formation: 

• Percolation: Water trickles down through the layers of solid waste, extracting soluble materials.
• Decomposition: The biological breakdown of organic waste by bacteria and fungi releases byproducts and additional water, which are carried by the percolating fluid.
• Chemical reactions: As waste decomposes, it promotes chemical reactions that can alter the composition of the liquid. For instance, the pH can drop, causing metal ions that were originally insoluble to dissolve into the leachate. 

Composition
The exact chemical makeup of leachate varies depending on the landfill's age, the types of waste it contains, and the local climate. It is a complex mixture that can include: 

• Dissolved organic matter: A complex mix of organic acids, alcohols, sugars, and phenols.
• Inorganic compounds: High concentrations of salts, including chlorides, sulfates, sodium, potassium, calcium, and magnesium.
• Heavy metals: Toxic metals such as lead, mercury, cadmium, and arsenic.
• Nitrogen compounds: Elevated levels of ammonia and other nitrogenous compounds are common, resulting from the breakdown of organic material like proteins.
• Xenobiotic organic compounds (XOCs): Synthetic chemicals that are resistant to degradation, such as pesticides and other industrial chemicals.
• Pathogens: Microorganisms derived from biodegradable waste that pose health risks. 

Environmental and health impacts
The environmental risks posed by uncontrolled leachate are severe and long-lasting. 

• Groundwater contamination: When leachate escapes from a landfill, it can seep into underground aquifers, contaminating drinking water sources.
• Surface water pollution: Runoff from landfills can transport leachate to nearby rivers, lakes, and streams. High nutrient levels can cause eutrophication, which depletes oxygen and kills aquatic life.
• Soil degradation: Toxic compounds can accumulate in the soil, harming beneficial microorganisms and reducing fertility, potentially rendering the land barren.
• Air pollution: Volatile compounds in leachate can evaporate and contribute to air quality issues. The decomposition process also releases gases like methane and carbon dioxide, which are potent greenhouse gases. 

Management and treatment
Modern landfills are engineered with systems to collect and manage leachate, minimizing its environmental impact. 

• Collection systems: Perforated pipes and drainage layers are installed at the bottom of the landfill, above impermeable liners, to collect leachate in sumps.
• Impermeable liners: Natural and synthetic materials like high-density polyethylene (HDPE) are used to create a barrier between the waste and the surrounding soil and groundwater.
• Treatment: Once collected, leachate is transported for treatment. Because of its complex composition, treatment often requires a combination of methods:
• Physical methods: Such as filtration and reverse osmosis to remove suspended solids and dissolved contaminants.
• Chemical methods: Including coagulation, flocculation, and advanced oxidation processes to remove metals and organic pollutants.
• Biological methods: Using microorganisms to break down organic matter in treatment processes like activated sludge or membrane bioreactors.
• Monitoring: Regular monitoring of groundwater and leachate quality is essential to detect any potential leaks and ensure the system is working effectively.

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