Solid and Hazardous Waste Management II: Hazardous Waste — Types, Characteristics and Health Impacts, Treatment by Neutralisation, Oxidation-Reduction, Precipitation, Solidification, Stabilisation and Incineration, and Final Disposal — and E-Waste, Fly Ash and Plastic Waste

An incinerator's performance is expressed as the destruction and removal efficiency (DRE) of each principal organic hazardous constituent: DRE = (Win − Wout) ÷ Win × 100, where Win is the mass fed and Wout the mass emitted in the stack gas. If a constituent is fed at 1,000 kg/h and 0.1 kg/h leaves the stack, DRE = (1000 − 0.1) ÷ 1000 × 100 = 99.99%, the "four nines" standard long used for hazardous-waste incinerators, with "six nines", 99.9999%, required for the most toxic compounds such as PCBs and dioxins. Waste that remains after treatment goes to final disposal in a secure landfill, which has double composite liners with a leak-detection layer between them, leachate collection and treatment, and a cap, and receives only wastes that have been stabilised and pass the leaching limits. In India such landfills are part of common treatment, storage and disposal facilities (TSDFs) serving industrial areas, and the 2016 Rules also regulate the import and export of hazardous waste in line with the Basel Convention.

E-waste is discarded electrical and electronic equipment, whole or in part, together with rejects from manufacturing and repair. India's E-Waste (Management) Rules 2022, which replaced the Rules of 2016 and came into force on 1 April 2023, classify it in Schedule I under broad categories: information technology and telecommunication equipment; consumer electrical and electronics, including solar photovoltaic panels; large and small electrical and electronic equipment; electrical and electronic tools; toys, leisure and sports equipment; medical devices; and laboratory instruments. E-waste is a paradox: it contains valuable metals, gold, silver, copper, palladium and rare earths, often at higher concentrations than natural ores, and hazardous ones: lead in cathode-ray-tube glass and solder, mercury in switches and older flat-panel backlights, cadmium in nickel-cadmium batteries, hexavalent chromium, beryllium, brominated flame retardants and PVC, which forms dioxins and furans when burned.

Proper handling runs from collection through authorised channels, to dismantling and segregation of components, to recycling by mechanical shredding and separation followed by metal recovery through pyrometallurgy (smelting), hydrometallurgy (leaching and electrowinning) or emerging bioleaching, with residues sent to a secure landfill at a TSDF. Much of India's e-waste is still processed by the informal sector, in clusters such as Seelampur in Delhi, where open burning of cables and acid baths to extract gold expose workers, often children, and neighbourhoods to lead, dioxins and acid fumes. The 2022 Rules rest on extended producer responsibility: producers must meet annual collection and recycling targets by purchasing EPR certificates generated by registered recyclers through an online portal, with environmental compensation for shortfalls, and they must comply with limits on hazardous substances in new equipment, the reduction of hazardous substances provisions, which cap lead, mercury, hexavalent chromium and certain brominated flame retardants at 0.1% by weight and cadmium at 0.01%.

Fly ash is the fine residue of pulverised coal combustion carried out of the boiler with the flue gas and captured by electrostatic precipitators or fabric filters; the coarser bottom ash falls to the base of the furnace, and ash sluiced to lagoons is pond ash. Because Indian coal commonly contains 30 to 45% ash, India's coal-fired power stations generate fly ash on a scale of a few hundred million tonnes a year. It consists largely of glassy spherical particles, including hollow cenospheres, composed of silica, alumina and iron oxide, with lime and trace elements such as arsenic, boron, chromium, lead, mercury and selenium. Under ASTM C618, Class F fly ash, from bituminous and anthracite coal and typical of India, is low in calcium and pozzolanic, while Class C, from lignite and sub-bituminous coal, is high in calcium and partly self-cementing. A pozzolan has little binding power by itself, but in the presence of water it reacts with calcium hydroxide, released when cement hydrates, to form cementitious calcium silicate hydrates.

Unused fly ash occupies land in ash ponds, blows as fugitive dust, and can leach trace elements into groundwater, and breaches of ash-pond embankments have released slurries into rivers and farmland. Its utilisation turns a waste into a resource. The largest uses are in cement, as the pozzolanic component of Portland pozzolana cement, which may contain up to about 35% fly ash, and in concrete; fly ash bricks and blocks, made with lime and gypsum, which save fertile topsoil used for clay bricks; road and flyover embankments and pavement sub-bases; the filling of mine voids and the reclamation of low-lying land; and smaller uses in agriculture as a soil amendment, ceramics and the recovery of cenospheres. The Ministry of Environment has issued fly ash notifications since 1999, requiring its use in construction within set distances of power plants, and a notification of 2021 requires thermal power plants to utilise all the ash they generate, including accumulated legacy ash over a period of years, with environmental compensation for shortfalls. A mass balance shows the scale: a plant burning 1,000 tonnes of coal a day with 40% ash, of which 80% leaves as fly ash, produces 320 tonnes of fly ash daily; even with a precipitator capturing 99.5%, 1.6 tonnes a day escape to the air.

Packaging is the largest source of plastic waste, much of it used once and discarded within days; consumer goods, textiles, agriculture (mulch films and irrigation pipes) and fishing gear add the rest. Plastics are identified by resin codes: 1 PET (bottles), 2 HDPE, 3 PVC, 4 LDPE (films and carry bags), 5 PP, 6 PS and 7 others. Because most conventional plastics do not biodegrade, they persist for decades to centuries, fragmenting into microplastics smaller than 5 mm that are now found from mountain snow to the deep sea and in drinking water and food. Plastic litter clogs drains and aggravates urban floods, as in Mumbai in 2005; it is eaten by cattle, which die of blocked stomachs; it entangles and is swallowed by seabirds, turtles and marine mammals; it carries additives such as phthalates and bisphenol A and adsorbs other pollutants; and burning it in the open releases dioxins, furans and, from PVC, hydrochloric acid.

Management follows the waste hierarchy: reduce, reuse, recycle, recover energy and only then dispose. India's Plastic Waste Management Rules 2016 have been amended several times. The 2021 amendment raised the minimum thickness of plastic carry bags to 75 microns from 30 September 2021 and 120 microns from 31 December 2022, and banned the manufacture, import, stocking, distribution, sale and use of identified single-use plastic items, such as earbuds with plastic sticks, plastic cutlery, straws, stirrers, thin wrapping films and plastic decorations, from 1 July 2022. Extended producer responsibility guidelines of 2022 set targets for producers, importers and brand owners to collect and recycle or process their packaging, and require recycled content in packaging. Recycling may be mechanical (sorting, washing, shredding and re-melting, best for clean, single-polymer streams such as PET) or chemical (pyrolysis to fuel oil); low-value plastics are co-processed in cement kilns or used in bituminous roads, a technique pioneered in India by R. Vasudevan and adopted in road guidelines. Internationally, the UN Environment Assembly resolved in 2022 to negotiate a legally binding instrument on plastic pollution.