Solid and Hazardous Waste Management: MSW, Processing and Landfills, Hazardous Waste and Special Streams

Integrated solid waste management (ISWM) treats generation, storage, collection, transfer and transport, processing and disposal as one system, choosing a combination of methods for each waste stream and judging it on environmental, economic and social grounds together, rather than optimising one stage in isolation. Its ordering principle is the waste hierarchy, from most to least preferred: prevention and reduction at source, reuse, recycling (including composting), recovery of energy, and disposal in a landfill last. Each step down the hierarchy recovers less of the value embodied in the material and leaves more for the environment to absorb. The hierarchy is a default, not a law of nature: a life-cycle comparison can occasionally favour energy recovery over recycling a badly contaminated stream.

In India each waste stream has its own rules, framed under the Environment (Protection) Act, 1986. The Solid Waste Management Rules, 2016 replaced the Municipal Solid Waste (Management and Handling) Rules, 2000, extended responsibility beyond municipal limits to other generators, and required segregation at source into three streams — biodegradable (wet), non-biodegradable (dry) and domestic hazardous waste. Alongside them are the Plastic Waste Management Rules, 2016, the Bio-Medical Waste Management Rules, 2016, the Construction and Demolition Waste Management Rules, 2016, and the Hazardous and Other Wastes (Management and Transboundary Movement) Rules, 2016; e-waste and batteries have rules of 2022, the E-Waste (Management) Rules, 2022 and the Battery Waste Management Rules, 2022. A thread running through the newer rules is extended producer responsibility (EPR), which makes producers responsible for collecting and processing their products at the end of life.

Sources of MSW are residential, commercial, institutional, market, street sweeping and construction debris; generation in Indian cities is typically a few hundred grams per person per day, rising with income, and the daily quantity is simply population × per-capita rate. Indian MSW is characteristically rich in wet organic matter and inerts and poor in paper and plastics compared with high-income cities, which gives it a high moisture content and a low calorific value — the central fact behind the difficulties of incinerating it. Characteristics are physical (composition, density, moisture, particle size, field capacity), chemical — the proximate analysis of moisture, volatile matter, fixed carbon and ash, and the ultimate analysis of C, H, O, N, S and ash — and energetic. The moisture content of a mixture is the mass-weighted average of its components’ moisture contents, and the energy content can be estimated from the ultimate analysis by Dulong’s formula, HHV (kJ/kg) = 337C + 1428(H − O/8) + 95S, with C, H, O and S in per cent by mass.

Collection begins with segregated storage at the source and door-to-door collection. Two vehicle systems are compared by the time per trip: in the hauled container system the vehicle carries each full container to the processing site and brings it back empty, which suits large generators such as markets; in the stationary container system the containers stay put and are emptied into a compactor truck that returns only when full, which suits households. Transfer stations are used where the processing or disposal site is far away: small collection vehicles unload into large transfer vehicles, reducing the haul cost per tonne. Routing, crew size and collection frequency are then optimised, and the whole chain is the most expensive part of MSW management — typically well over half its cost.

Reuse and material recovery facilities come first, sorting the dry fraction into saleable streams. The wet fraction is treated biologically. Composting is aerobic decomposition to a stable humus: it runs best at a C/N ratio of about 25–30, a moisture of about 50–60%, with aeration by turning or forced air, and a thermophilic phase of about 55–65 °C that kills pathogens and weed seeds. Vermicomposting uses earthworms at lower temperatures. Anaerobic digestion yields biogas and a digestate, and suits wet, homogeneous feed such as kitchen and market waste. Energy recovery treats what cannot be recycled: incineration (mass burning with heat recovery and flue-gas cleaning) needs a waste of adequate calorific value and low moisture; refuse-derived fuel (RDF) is the dry, combustible fraction shredded and densified for co-firing; pyrolysis heats the waste in the absence of oxygen to char, oil and gas; gasification uses a limited supply of oxygen or steam to make a combustible syngas (CO and H₂); plasma arc systems reach very high temperatures. Because Indian MSW is wet and low in calorific value, waste-to-energy plants depend on segregation and pre-drying.

What remains goes to an engineered sanitary landfill, which isolates the waste from groundwater and air: a composite liner of compacted clay (hydraulic conductivity of the order of 10⁻⁷ cm/s or less) and an HDPE geomembrane; a leachate collection layer and drains above it; the waste placed in cells, compacted and covered daily with soil; gas collection wells; and a final cover and cap. Decomposition passes from a short aerobic phase through an acid phase to a long methanogenic phase, in which the gas is roughly half methane and half CO₂. Leachate is estimated from a water balance, the percolation through the cover being precipitation less runoff and evapotranspiration. The landfill volume is the mass per day divided by the compacted density, increased for daily cover, over the design life; the area is that volume divided by the fill depth. Around these technologies sit four system ideas. The circular economy keeps materials in use at their highest value — design for durability, repair and disassembly, reuse and remanufacture, recycling — so that waste becomes an input. Life-cycle energy analysis counts the energy used from extraction to disposal, including the energy embodied in materials, to compare options such as recycling and virgin production. Decentralised renewable systems — household or community biogas plants, compost units, solar driers — process waste close to where it arises. Urban metabolism treats a city like an organism, tracing the flows of water, energy, materials and nutrients into it, their accumulation as stocks, and their release as wastes and emissions, as the basis for closing its loops.

A waste is hazardous if it is ignitable (flammable), corrosive (strongly acidic or alkaline, or corroding steel), reactive (unstable, explosive, or releasing toxic gas with water or acid) or toxic — the ICRT characteristics — or if it appears on a list of hazardous processes and substances. Toxicity for disposal is judged by a leaching test that asks what a landfill leachate would extract from it. It is generated by industries such as chemicals, pharmaceuticals, petroleum refining, electroplating, tanneries and pesticide manufacture, and in households as batteries, paints, solvents and fluorescent lamps. Its fate in the environment depends on the substance: volatile organics escape to air, soluble ones travel with groundwater, and hydrophobic ones sorb to soil organic matter, with a distribution coefficient K_d = f_oc × K_oc. Sorption slows a dissolved contaminant relative to the water by the retardation factor R = 1 + ρ_bK_d/n (ρ_b the dry bulk density, n the porosity), so it moves at v/R; biodegradation, hydrolysis and radioactive decay may remove it along the way.

Treatment is chosen to destroy, detoxify or immobilise: physical (separation, evaporation, air stripping, adsorption), chemical (neutralisation, oxidation–reduction such as reducing Cr(VI) to Cr(III) or oxidising cyanide, precipitation of metals), biological, thermal — incineration at high temperature, judged by the destruction and removal efficiency, DRE = (W_in − W_out)/W_in × 100 for the principal organic hazardous constituent — and stabilisation/solidification with cement or lime to bind metals before disposal. What remains goes to a secure landfill with double composite liners and leak detection between them, usually within a treatment, storage and disposal facility (TSDF). Soil contamination comes from spills, leaking tanks, dumps and disposal of sludges; leaching carries soluble contaminants down through the vadose zone to the water table, where they form a plume that moves with the groundwater. Light non-aqueous liquids (LNAPLs such as petrol) float on the water table; dense ones (DNAPLs such as chlorinated solvents) sink to the aquifer floor and bleed slowly for decades. Remediation includes excavation, pump-and-treat, soil vapour extraction, in-situ bioremediation, permeable reactive barriers and natural attenuation.

Biomedical waste arises in hospitals, clinics, laboratories and blood banks; only a part of it is infectious, but mixing makes all of it so, which is why the rules begin with segregation at the point of generation into colour-coded containers. Under the Bio-Medical Waste Management Rules, 2016: yellow for anatomical waste, soiled dressings, expired medicines and chemical waste, sent for incineration or other permitted treatment; red for contaminated recyclable items such as tubing, bottles, intravenous sets, catheters, gloves and syringes without needles, which are autoclaved or microwaved and shredded before recycling; white (translucent), puncture-proof containers for sharps; and blue for glassware and metallic body implants. Treatment is at a common bio-medical waste treatment facility.

Plastic waste is durable, light and bulky, so it litters, blocks drains and fragments into microplastics; thermoplastics (PET, HDPE, PVC, LDPE, PP, PS, coded 1–6) can be mechanically recycled if segregated and clean, while multilayered packaging is difficult and goes to co-processing in cement kilns or to energy recovery. Management rests on segregation, EPR for producers and brand owners, restrictions on thin carry bags and specified single-use items, and the phasing out of the least recyclable forms. Waste from the energy sector is a growing stream: end-of-life solar photovoltaic panels (mostly glass and aluminium, with silicon, silver, and lead or cadmium in some types), wind turbine blades of glass- or carbon-fibre composite that are hard to recycle, batteries — lead–acid, with a mature recycling chain, and lithium-ion, carrying lithium, cobalt and nickel and a fire risk — and fly ash from coal-fired power stations, used in cement, bricks and fills. Construction and demolition (C&D) waste — concrete, brick, soil, steel, timber — is heavy and largely inert; it is segregated at site, stored separately, and crushed into recycled aggregate and products. E-waste — discarded computers, phones, appliances — contains valuable metals (copper, gold, silver, palladium) alongside hazardous ones (lead, mercury, cadmium, brominated flame retardants); the danger lies in informal recycling by open burning and acid leaching, so the rules channel it through producers’ EPR to authorised dismantlers and recyclers via collection centres.