Treatment and disposal of hazardous waste

The approach follows the waste management hierarchy: minimise first, treat second, dispose of safely last. The "cradle to grave" principle means the generator remains responsible from production to final disposal.

1. Waste minimisation

• Source reduction (process change, material substitution, good housekeeping).
• Recycling, reuse and recovery (solvent recovery, metal recovery, waste exchange).

2. Physical and chemical treatment

• Neutralisation of acids and alkalis.
• Precipitation of heavy metals as hydroxides or sulphides, followed by filtration.
• Oxidation and reduction, e.g. cyanide oxidised by chlorine; chromium(VI) reduced to chromium(III).
• Adsorption on activated carbon, air stripping and ion exchange.

3. Thermal treatment

• Incineration above 1000 $^\circ$C with a 2 s residence time destroys organics (about 99.99% destruction), with flue gas cleaning; the rotary kiln is the most common type. It is the standard method for pesticides, solvents and biomedical waste.

4. Biological treatment

• Activated sludge, land farming and bioremediation for biodegradable organics.

5. Solidification and stabilisation

• Mixing with cement, lime, fly ash or bitumen to make a solid block that reduces leaching of metals before landfilling.

6. Secure (hazardous) landfill

Double liner (clay + HDPE), leachate collection, leak detection, cap, groundwater monitoring, and a site far from water sources; deep-well injection is sometimes used for liquids.

Transport must follow a manifest system, and storage must use labelled, compatible containers. The Basel Convention controls the cross-border movement of hazardous wastes.