Chapter 11 — Waste Management

Waste is any material, substance or by-product that is discarded because it is no longer wanted or useful after its primary use. The vegetable peel in the kitchen, the broken plastic bucket, the smoke from a chimney, the used water from a bathroom and the ash from a power station are all waste. The word is relative: what is waste to one person may be raw material to another, and much of waste management consists of turning discarded material back into something useful. In nature there is no waste, because the dead leaf becomes soil and the dead animal feeds other creatures; waste is a human problem that arises when materials are produced and discarded faster than nature can absorb them.

The first way of classifying waste is by its physical state.

• Solid waste is the refuse of homes, markets, offices, factories, farms and building sites: kitchen scraps, paper, plastic, glass, metal, cloth, rubble, ash, crop stalks, animal dung and industrial slag. The waste collected by a municipality from households and shops is called municipal solid waste. An Indian city produces about 300 to 600 grams per person per day; Kolkata produces roughly 4,000 to 4,500 tonnes a day.
• Liquid waste is water that has been used and fouled: sewage from toilets, sullage from kitchens and bathrooms, effluent from tanneries, dye works, paper mills and chemical plants, drainage from farms carrying fertiliser and pesticide, and oil from ships and garages. It is the largest waste stream by volume; a city discharges nearly as much waste water as it consumes.
• Gaseous waste is the smoke, fumes and gases released into the air: carbon dioxide and sulphur dioxide from burning coal and oil, carbon monoxide and nitrogen oxides from vehicle exhausts, methane from rotting garbage and paddy fields, chlorofluorocarbons from old refrigerators and dust from cement and stone-crushing works.

The three states are linked. A rubbish heap is solid, but rain washing through it produces a liquid waste called leachate, and the rotting of the heap gives off methane, a gaseous waste. A treatment plant that cleans liquid sewage produces a solid sludge. Good management therefore has to consider all three together, which is why this chapter, though it deals mostly with solid waste, keeps liquid and gaseous waste in view.

Waste is also classified by where it comes from, because the source decides its composition and the way it should be handled.

• Domestic or household waste from homes, hotels and markets: food scraps, vegetable and fruit peel, paper, packaging, plastic bags, bottles, cans, old clothes, broken furniture and sweepings. Most of it, by weight, is organic.
• Industrial waste from factories and mines: fly ash from thermal power stations, slag from iron and steel works, chemical sludge, dye, acid, oil, scrap metal, sawdust and overburden from mines. It is often toxic and is the most difficult to treat.
• Agricultural waste from farms: straw and stubble, husks, sugar-cane bagasse, weeds, animal dung, and the residue of chemical fertilisers and pesticides that washes into ponds and rivers. Most agricultural waste is biodegradable and can be returned to the soil.
• Biomedical waste from hospitals, clinics, nursing homes and laboratories: used syringes, needles, bandages, blood-stained cotton, body tissues, expired medicines and cultures. It carries infection and must be kept separate and destroyed.
• Electronic waste or e-waste: discarded mobile phones, computers, televisions, batteries and wires, containing lead, mercury, cadmium and other poisons.
• Construction and demolition waste: bricks, concrete, tiles, sand and timber from building sites.
• Mining waste, commercial waste from shops and offices, and radioactive waste from nuclear plants and hospitals are further categories.

The third classification, by nature, is the most important for management. Biodegradable waste is waste that bacteria, fungi and other living organisms can break down into simple, harmless substances within a short time: food, peel, paper, cotton, leaves, wood, dung and dead animals. It can be composted or turned into biogas. Non-biodegradable waste cannot be decomposed by living organisms, or only over hundreds of years: plastics, glass, metals, synthetic cloth, rubber, ceramics and most chemical wastes. A plastic bag may lie in the soil for 500 years and a glass bottle for a million. Such waste must be reused, recycled or safely stored. Between the two lies waste that is biodegradable only slowly, such as thick wood, bone and leather. The single most useful habit in waste management is to segregate waste at the source into these two classes, the wet and the dry bin, so that each can go to the right treatment.

Waste that is not managed does not disappear; it spreads into the soil, the water and the air and degrades all three.

Effects on land and soil. Open dumping of garbage on the outskirts of towns, as on the Dhapa dumping ground east of Kolkata or the Deonar ground in Mumbai, buries fertile land under mountains of refuse forty or fifty metres high. Plastic bags and sheets mixed into farmland block the passage of water and air and stop roots from growing; chemical and industrial waste, fly ash and heavy metals such as lead, cadmium and chromium poison the soil and enter the crops grown on it. Rain water seeping through a dump dissolves salts, acids and metals and forms a dark, foul liquid called leachate, which sinks into the soil and contaminates the groundwater below. Dumps breed rats, flies and stray dogs and ruin the value of the surrounding land.

Effects on water. Untreated sewage and industrial effluent poured into rivers, ponds and the sea are the main cause of water pollution in India. Organic waste is decomposed by bacteria that use up the dissolved oxygen in the water, so that fish and other life suffocate; this demand for oxygen is called the biochemical oxygen demand and is the standard measure of how polluted a river is. Nutrients from sewage and fertiliser feed an explosive growth of algae, called eutrophication, which turns ponds green, blocks sunlight and finally kills the pond. Toxic effluent from tanneries, dye works and paper mills carries chromium, mercury and acids that kill fish and accumulate in the bodies of those who eat them. The Ganga at Kanpur, the Yamuna below Delhi and the Hooghly below Kolkata are among the most polluted stretches of river in the world, and the canals of Kolkata are open sewers. Plastic waste that reaches the sea kills turtles and fish that swallow it and breaks down into microplastic that enters the food chain.

Effects on air. Burning garbage in the open, a common practice in every Indian town, releases smoke, carbon monoxide and, when plastic burns, dioxins, among the most poisonous substances known. Rotting organic waste in dumps gives off methane, a greenhouse gas twenty times more powerful than carbon dioxide, and hydrogen sulphide, the smell of rotten eggs that hangs over Dhapa. Dumps sometimes catch fire and burn for weeks. Industrial chimneys and vehicles add sulphur dioxide and nitrogen oxides that form acid rain, which corrodes buildings and acidifies soil and lakes. Dust from construction waste and stone crushers fills the air of expanding cities.

The damage that waste does to soil, water and air returns to human beings as disease, and to the environment as ugliness and loss of life.

Health. Uncollected garbage is the breeding ground of the organisms that carry disease. Flies that settle on refuse and then on food spread cholera, typhoid, diarrhoea and dysentery, the greatest killers of children in India. Rats that live in dumps carry plague and leptospirosis. Stagnant water in discarded tyres, cans and coconut shells breeds the mosquitoes that carry malaria and dengue, and the dengue epidemics of Kolkata every monsoon are traced directly to the containers of rubbish that collect rain. Contaminated drinking water from wells near dumps and from rivers receiving sewage causes hepatitis and jaundice. Smoke from burning garbage and from dumps aggravates asthma and bronchitis, and dioxins from burning plastic cause cancer and birth defects. Heavy metals in the vegetables and fish raised on polluted land and water accumulate in the body: mercury damages the nervous system, lead retards the mental development of children and cadmium destroys the kidneys. The waste-pickers, often children, who sort garbage with bare hands on the dumps suffer cuts, infections and tetanus, and the hospital waste that is illegally mixed with ordinary refuse spreads hepatitis B and even HIV through discarded needles.

Environment and economy. Waste that clogs drains and canals is the main cause of the water-logging that paralyses Kolkata after every heavy shower; the Dhapa canals and the Tolly's Nullah are choked with plastic. Waste dumped in mangrove creeks and on beaches such as Digha destroys the habitat of birds, crabs and fish and spoils tourism. Plastic eaten by cows and street animals kills them. Landfills occupy land that could feed people, and the methane they release adds to global warming. The cost of illness, of lost workdays and of cleaning up pollution runs into thousands of crores of rupees a year, and the foul and ugly surroundings lower the quality of life for everyone, most of all for the poor who live nearest the dumps.

These effects are the argument for waste management. A society that collects, separates, treats and recovers its waste avoids most of them; a society that simply throws its waste away pays for it in sickness and squalor.

Waste management is the collection, transport, processing, recycling and disposal of waste in ways that protect health and the environment and recover as much value as possible. It is a chain of steps: waste is generated, stored in the home or factory, collected by the local body, transported to a transfer station, treated by one of several methods and finally disposed of. The modern approach is guided by a hierarchy of preferences: first prevent the waste, then reduce it, then reuse, then recycle, then recover energy, and only as the last resort dispose of it in a landfill. This hierarchy is summed up in the principle of the three Rs: Reduce, Reuse, Recycle. Some add a fourth R, Refuse, or Recover.

Reduce means producing less waste in the first place. A shopper who carries a cloth bag refuses the plastic one; a family that buys loose rice and dal instead of packets, drinks tap water instead of bottled water, prints on both sides of the paper and repairs a chair instead of replacing it reduces the waste it creates. Industry reduces waste by designing lighter packaging and longer-lasting goods. Reduction is the cheapest and best of the three because the waste never exists.

Reuse means using a thing again, for the same or a different purpose, without reprocessing it. Glass milk bottles and soft-drink bottles returned to the dairy or bottling plant, jam jars used to store spices, old clothes passed to a younger child or cut into dusters, a tin used as a flower pot, and the second-hand market for books, furniture and cars are all reuse. Reuse extends the life of an object and saves the energy that would be needed to make a new one.

Recycle means collecting a used material and reprocessing it into new products. Waste paper is pulped into new paper; broken glass, called cullet, is melted into new bottles; aluminium cans, iron scrap and copper wire are melted and recast; plastic bottles are shredded and spun into fibre for carpets and jackets; and kitchen waste is composted into manure, which is the recycling of organic matter. Recycling saves raw material, energy and landfill space: recycling a tonne of paper saves about seventeen trees and recycling aluminium uses only five per cent of the energy of making it from ore. India has a large informal recycling economy of rag-pickers and kabadiwalas who recover paper, metal and plastic from waste.

All three depend on segregation at source, the sorting of waste into wet, dry and hazardous at the home or shop, without which recyclable material is spoiled by food waste and organic waste is contaminated by plastic and batteries.

Before waste can be treated it must be collected, and in Indian cities collection is the weakest link. The chain begins in the home with storage and segregation. The Solid Waste Management Rules of 2016 require every household, shop and office to keep waste in three separate containers: a green bin for wet biodegradable waste, a blue bin for dry recyclable waste such as paper, plastic, glass and metal, and a red or black container for domestic hazardous waste such as batteries, tube lights, paint tins, expired medicines and sanitary waste. Segregation at source is the single step on which every later method depends: mixed waste can only be dumped, while segregated waste can be composted, recycled or safely destroyed.

Primary collection is the door-to-door collection from houses by municipal workers or contracted self-help groups with handcarts, tricycles and small vans, usually every morning. Where door-to-door collection does not exist people dump waste at street corners or in community bins, which overflow, are scattered by animals and become the open dumps that disfigure every Indian town. Street sweeping and the cleaning of drains produce silt and litter that join the stream.

Secondary collection and transport take the waste from the collection points to a transfer station, where it is compacted and loaded into large covered trucks for the long haul to the treatment plant or landfill. Compactor trucks reduce the volume by half or more and covered bodies prevent spillage and smell on the road. Kolkata Municipal Corporation runs a fleet of compactors and moves its waste from about 150 compactor stations to Dhapa and the newer site at Rajarhat.

Sorting takes place at a materials recovery facility, where dry waste is separated by hand or machine into paper, cardboard, the several kinds of plastic, glass, ferrous metal picked out by magnets and non-ferrous metal, and baled for sale to recyclers. In India much of this work is done by the informal sector of waste-pickers, and modern policy tries to bring them into the formal system with identity cards, gloves and fair prices rather than to displace them.

The costs of collection and transport are the largest part of a municipality's waste budget, often 70 to 80 per cent, which is why reducing waste at source and treating it close to where it is produced, in ward-level compost plants and neighbourhood recycling centres, are the goals of modern planning. A city that collects its waste every day and keeps it segregated has solved half of its waste problem.

The oldest way of dealing with solid waste is to dump it on low ground outside the town. This open dumping is not a method of management but the absence of one: the dump stinks, smokes, leaches poison into the groundwater, breeds vermin and eventually rises into a hill. The sanitary landfill is the engineered replacement for open dumping and remains the final destination of whatever waste cannot be composted, recycled or burnt.

A sanitary landfill is a carefully chosen and prepared site. It must be away from houses, airports, rivers, wetlands and flood plains, on ground where the water table is deep and the soil is clay rather than sand. A large pit or cell is excavated and its floor and sides are lined with a layer of compacted clay and a thick sheet of high-density polyethylene to stop leachate escaping into the ground. Above the liner a layer of gravel with perforated pipes collects the leachate and carries it to a treatment plant, where it is cleaned before release. Waste is brought in, spread in thin layers, compacted by heavy machines and covered every day with 15 to 20 centimetres of soil, so that flies, rats, birds and smell are kept down and rain runs off instead of soaking in. Layer upon layer, the cell is built up in the form of a low hill. Vertical pipes sunk through the mass collect the methane produced by the decomposing waste, which is flared or, in a modern landfill, burnt in engines to generate electricity. When the cell is full it is capped with a thick layer of clay and soil, planted with grass and monitored for years, because the settling and gas production continue for decades.

Advantages. A sanitary landfill is simple, can take almost any kind of waste, is cheaper to build than an incinerator, and, if properly run, protects the groundwater and the air. The reclaimed land can become a park or playground, as some old landfills of Delhi and Mumbai have.

Disadvantages. It uses a great deal of land, which is scarce near large cities; it wastes the value of the recyclable and compostable materials thrown into it; the liner may eventually leak; methane and leachate must be managed for years after closure; and residents object to living near one. India's older sites, including Dhapa, Ghazipur in Delhi and Deonar in Mumbai, are open dumps that have grown into unstable, burning mountains, and their conversion into sanitary landfills or their bio-mining, the digging out and sorting of the old waste, is a major task of the Swachh Bharat Mission.

Half or more of Indian municipal waste is biodegradable kitchen, market and garden waste, and the best thing to do with it is to turn it back into soil. Composting is the controlled decomposition of organic waste by micro-organisms, bacteria and fungi, in the presence of air, producing a dark, crumbly, earthy-smelling material called compost or humus that is an excellent manure. Composting is recycling done by nature with human help.

In the simplest method, used in villages and school gardens, organic waste is heaped in a pit or a ring of bricks about a metre deep, in layers alternating with a little soil, dung or old compost to supply the micro-organisms, kept moist but not wet, and turned every two or three weeks so that air reaches the whole heap. The bacteria work fast and the heap heats up to 60 or 70 degrees Celsius in its first weeks, which kills weed seeds and disease germs; after two to three months the heap cools and the compost is ready. The Indore method and the Bangalore method are Indian systems of pit composting developed in the 1920s and 1930s. Municipal compost plants do the same thing on a large scale in long windrows turned by machines, and Kolkata has such plants at Dhapa. Anaerobic composting, without air, is slower and smelly and is better done in a closed biogas plant.

Vermicomposting uses earthworms to do the work. Kitchen and garden waste is spread in shallow beds or tanks, kept shaded and moist, and stocked with the red wriggler worm, Eisenia fetida, or the Indian blue worm. The worms eat the decaying matter and pass it out as fine granular castings that are rich in nitrogen, phosphorus, potassium and beneficial microbes, a better manure than ordinary compost. A bed produces vermicompost in about 45 to 60 days, needs no turning and gives off no smell, and the worms multiply so that the farmer can sell them too. Vermicomposting has spread rapidly among the farmers and self-help groups of West Bengal because it is cheap, needs little space and yields a product that sells at a good price.

Advantages of composting: it deals with the largest fraction of the waste; it returns organic matter and nutrients to soils exhausted by chemical fertiliser; it reduces the weight going to landfill by half; it produces no toxic ash or smoke; and it can be done at every scale from a flower pot on a balcony to a city plant. Limitations: it needs the waste to be segregated, because plastic, glass and batteries mixed in spoil the compost and poison the soil; it takes time and space; it cannot treat non-biodegradable waste; and the compost must find buyers, which the government supports by requiring fertiliser companies to market city compost.

Some waste is neither compostable nor recyclable, and some, like hospital waste, is too dangerous to store at all. For such waste the methods are thermal: destroying it by heat.

Incineration is the burning of waste at a high temperature, usually 850 to 1,200 degrees Celsius, in a specially designed furnace called an incinerator, under controlled conditions with a supply of air, so that the combustible part is turned into carbon dioxide, water vapour and a small residue of ash. A modern incinerator has a feeding hopper, a combustion chamber with moving grates, a secondary chamber where the flue gases are held at high temperature for at least two seconds to destroy dioxins, a boiler that recovers the heat to raise steam and generate electricity, and a chain of scrubbers, filters and electrostatic precipitators that remove acid gases, heavy metals and fly ash before the cleaned gas leaves the chimney. When the heat is used to generate power the plant is called a waste-to-energy plant; Delhi has such plants at Okhla and Ghazipur.

Advantages: incineration reduces the volume of waste by about 90 per cent and its weight by 70 to 75 per cent, so very little goes to landfill; it destroys pathogens and is the standard treatment for biomedical waste; it needs little land and can be sited near the city; and it recovers energy. Disadvantages: it is expensive to build and run and needs skilled operation; Indian waste, wet and low in calorific value, burns poorly and often needs added fuel; if the temperature is too low or the gas cleaning fails, the chimney releases dioxins, furans and heavy metals that are among the most poisonous pollutants known; the ash still contains concentrated toxins and needs a secure landfill; and it destroys materials that could have been recycled. Open burning of garbage on streets and dumps is the uncontrolled and wholly harmful version of incineration.

Pyrolysis is the thermal decomposition of waste at 400 to 800 degrees Celsius in the absence of oxygen, so that the material does not burn but breaks down into a combustible gas called syngas, a liquid oil and a solid char. The gas and oil can be burnt as fuel or refined, and the char can be used as activated carbon or buried. Pyrolysis suits plastics, rubber tyres, and other organic wastes with high energy content; a tyre pyrolysis plant yields oil, carbon black and steel wire. Because no air is admitted, pyrolysis produces far fewer toxic gases than incineration and recovers products rather than only heat, but it needs well-sorted dry feedstock and its plants are still few in India. Gasification, a related process using a limited supply of air or steam, converts waste mainly into gas for power generation.

When organic waste decomposes without air, in a closed container, the bacteria that work under these anaerobic conditions release biogas, a mixture of about 55 to 70 per cent methane and 30 to 45 per cent carbon dioxide with traces of hydrogen sulphide. Methane burns with a clean blue flame, so biogas is a fuel for cooking, lighting and running engines, and the process turns the smelly waste of a farmyard into energy and manure at the same time. It is the ideal way to treat cattle dung, kitchen and market waste, sewage sludge and the waste of slaughter-houses and sugar mills.

The common Indian biogas plant, or gobar gas plant, is a digester tank built of brick below ground. Dung and other organic waste are mixed with an equal quantity of water into a slurry and fed through an inlet pipe into the digester, where they stay for 30 to 50 days at about 35 degrees Celsius while the anaerobic bacteria break them down. The gas collects at the top. In the floating drum or KVIC type a steel drum floating on the slurry rises as gas collects and its weight provides the pressure; in the fixed dome or Deenbandhu type, cheaper and more common, a dome of masonry holds the gas and the slurry level rises and falls. The gas is piped to the kitchen stove or a lamp. The digested slurry flowing out of the outlet is an excellent, odourless manure, richer in nitrogen than raw dung because none of it has been lost by burning.

A family plant of 2 cubic metres, fed with the dung of three or four cattle, supplies the cooking needs of a family of five and saves them the smoke of a dung-cake or wood fire, the labour of gathering fuel and the cost of kerosene or LPG. Community plants and large plants at dairies, vegetable markets and sewage works feed engines that generate electricity or produce compressed biogas for vehicles. West Bengal, with its cattle and its dense villages, has tens of thousands of household plants, and Kolkata's large markets have set up plants that run on vegetable waste.

Advantages: biogas turns waste into energy and manure, gives a clean fuel that reduces the cutting of trees for firewood, captures methane that would otherwise escape into the atmosphere as a greenhouse gas, kills most of the pathogens in the dung and improves village sanitation. Limitations: the plant needs a steady supply of dung or wet waste and of water, works slowly in cold weather, needs some skill to run and repair, and produces much less gas from dry or woody material. Together with the methane collected from sanitary landfills and the power generated by incinerators, biogas is part of the wider idea of energy recovery from waste, the fourth step of the waste hierarchy.

The liquid waste of a city, its sewage from toilets, sullage from kitchens and bathrooms and effluent from factories, must be cleaned before it is returned to a river, otherwise the river becomes a drain. The cleaning is done in a sewage treatment plant in stages.

Preliminary and primary treatment removes the solids. The sewage first passes through bar screens that catch rags, plastic and sticks, then through a grit chamber where sand and gravel settle. It then flows slowly through a large primary settling tank, where about half of the suspended organic matter sinks to the bottom as sludge and grease floats to the top to be skimmed off. Primary treatment is a physical process.

Secondary treatment is biological. The settled sewage is fed into aeration tanks where air is bubbled through it and a mass of bacteria, the activated sludge, feeds on the dissolved organic matter and converts it into carbon dioxide, water and more bacteria. An older method trickles the sewage over beds of stones coated with bacterial slime, the trickling filter. After several hours the liquid passes to a secondary settling tank where the bacterial floc settles; part is returned to seed the aeration tank and the rest joins the primary sludge. Secondary treatment removes 85 to 95 per cent of the biochemical oxygen demand.

Tertiary treatment, used where the water is to be reused or the river is sensitive, removes nitrogen, phosphorus and remaining germs by filtration through sand, by chemical treatment and by disinfection with chlorine or ultraviolet light. The sludge from the settling tanks is thickened, digested in anaerobic tanks that yield biogas, dried on beds and used as manure or sent to landfill.

Kolkata has a unique natural system. Much of the city's sewage flows east through canals to the East Kolkata Wetlands, a 12,500 hectare expanse of shallow ponds, called bheris, where sunlight, algae and fish clean the water while the fish and the vegetables grown on the banks feed the city. It is the largest sewage-fed fishery in the world and has been declared a wetland of international importance.

Industrial effluent from tanneries, textile mills, chemical works and paper mills contains acids, alkalis, dyes, oils and heavy metals that bacteria cannot remove, so factories must have their own effluent treatment plants, using neutralisation, chemical precipitation, filtration and adsorption, or share a common effluent treatment plant, like the one serving the tanneries relocated to Bantala. The Water Act of 1974 and the Pollution Control Boards set the standards that the effluent must meet before discharge, and the Ganga Action Plan and the Namami Gange programme have built sewage plants along the Ganga and Hooghly, though many towns still discharge untreated sewage.

Three kinds of waste are so dangerous that they need their own rules and their own treatment.

Electronic waste or e-waste is the fastest-growing waste stream in the world. Discarded computers, mobile phones, televisions, refrigerators, air conditioners, printers, wires, chargers and batteries contain valuable materials, gold, silver, copper and rare metals, and also poisons: lead in solder and cathode-ray tubes, mercury in switches and flat screens, cadmium in batteries, chromium in coatings, brominated flame retardants in plastic casings. India generates over 1.6 million tonnes a year and is a dumping ground for imports. Most of it is broken up by hand in informal workshops, in Delhi, Moradabad and the Chandni Chowk and Tangra areas of Kolkata, where workers burn wires to recover copper and dip circuit boards in acid to extract gold, poisoning themselves, the soil and the drains. The proper method is collection through take-back schemes and authorised collection centres, dismantling in registered recyclers with protective equipment, recovery of metals in smelters and safe disposal of the residue. The E-Waste Management Rules of 2016 make the manufacturer responsible for taking back its products, a principle called extended producer responsibility. The citizen's duty is never to throw a battery or phone into the ordinary bin.

Hazardous waste is waste that is toxic, corrosive, flammable, explosive or reactive: acids and cyanides from electroplating, pesticides, paint, solvents, asbestos, used oil, chemical sludge, fly ash with heavy metals, and the mercury of tube lights. It must be stored in sealed labelled containers, transported by licensed carriers and treated by neutralisation, solidification in cement or incineration at very high temperature, and the residue buried in a secure landfill with double liners, as at the Haldia hazardous waste facility. Radioactive waste from nuclear power stations, research reactors and hospitals is the most hazardous of all, because it stays dangerous for thousands of years; it is stored in shielded vaults and, for the highest level, vitrified into glass blocks for deep burial.

Biomedical waste from hospitals, nursing homes, pathology laboratories and veterinary clinics, about 15 per cent of a hospital's total waste, carries infection. The Biomedical Waste Management Rules require it to be segregated at the bedside into colour-coded bags, yellow for tissues and infected dressings to be incinerated, red for contaminated plastics to be disinfected and recycled, white translucent for needles and sharps, and blue for glass, and to be treated within 48 hours in a common treatment facility by incineration, autoclaving at high pressure steam, microwaving or chemical disinfection. Mixing biomedical waste with ordinary garbage, and the trade in used syringes, are crimes that spread hepatitis and HIV.

Kolkata's waste. The Kolkata Municipal Corporation collects roughly 4,000 to 4,500 tonnes of solid waste a day from its 144 wards, about half of it organic. Waste is picked up from houses and from street vats, moved to compactor stations and trucked to the Dhapa dumping ground on the eastern edge of the city, in use since 1865, where it has risen into a hill more than 30 metres high. A compost plant at Dhapa treats part of the organic waste, and the old dump is being capped and a new engineered landfill developed, with a further site at Rajarhat. Sewage flows by canal to the East Kolkata Wetlands, where the bheris treat it naturally. The city's problems are the usual Indian ones: incomplete segregation, waste thrown into canals and drains that causes water-logging, open burning, and the informal recycling economy of thousands of rag-pickers and kabadiwalas who nonetheless recover a great deal of paper, plastic and metal. Howrah, Durgapur, Asansol and Siliguri face the same difficulties on a smaller scale, and the villages of Bengal, where waste was once entirely organic, are now littered with plastic that no one collects.

Laws. India's waste is governed by the Environment Protection Act of 1986, under which the central government has issued rules for each stream: the Solid Waste Management Rules 2016, which require segregation at source, door-to-door collection, composting or biomethanation of wet waste, and sanitary landfills only for residual waste; the Plastic Waste Management Rules 2016, amended in 2021 to ban single-use plastic items such as thin carry bags, straws and cutlery; the E-Waste Rules; the Biomedical Waste Rules; the Hazardous Waste Rules; and the Construction and Demolition Waste Rules. The Water Act of 1974 and the Air Act of 1981 control liquid and gaseous waste through the Central and State Pollution Control Boards.

Programmes. The Swachh Bharat Mission, launched on 2 October 2014, aimed to end open defecation by building toilets and to achieve scientific management of solid waste in every town, and its Swachh Survekshan survey ranks cities every year on cleanliness, which has spurred Indore, Surat and others to segregate and compost almost all their waste. The Namami Gange programme, started in 2014, builds sewage treatment plants and river-front works to clean the Ganga and its tributaries including the Hooghly, continuing the Ganga Action Plan of 1985. The Mission LiFE campaign asks citizens to reduce consumption. West Bengal's own Mission Nirmal Bangla carries the sanitation programme into the districts. The principle behind all these is that waste is a shared responsibility of the producer, the citizen and the local body, and that the cheapest waste to manage is the waste that is never created.

Waste management is not only the work of engineers and municipalities; it begins in the home and the school, and no city has become clean without its citizens. This section sets out what an individual and a community can do.

At home. Keep two bins and segregate wet and dry waste every day; hand batteries, tube lights, medicines and electronic items to the separate collection. Compost kitchen waste in a pot, bin or pit if there is any space, or send it to a community compost. Carry a cloth or jute bag and refuse plastic carry bags and single-use cups, straws and cutlery. Buy loose goods, avoid excess packaging, use a steel water bottle and a lunch box. Repair, reuse and give away before throwing away. Sell paper, glass and metal to the kabadiwala. Never burn garbage, never throw waste into a drain, pond, river or on the street, and empty and cover every container that could hold rain water so that mosquitoes cannot breed.

At school. A school is a small town and can practise everything the chapter teaches. Colour-coded bins in every classroom and corridor; a compost pit or vermicompost bed for canteen and garden waste, with the compost used on the school garden; a paper recycling drive; a ban on plastic in the tiffin and the canteen; an eco-club that holds cleanliness drives, surveys the neighbourhood's waste, runs a poster and street-play campaign and observes World Environment Day on 5 June and Swachhata Diwas on 2 October; and projects in which students measure how much waste the school produces and how much can be diverted from the dump. Students who learn these habits carry them home, and the parent learns from the child.

In the community. Residents' associations and self-help groups can organise door-to-door collection where the municipality does not, set up neighbourhood compost and recycling centres, plant and clean the local pond, and press the councillor for regular collection and against open dumping. Public awareness through rallies, posters, radio and social media changes habits; the Swachh Bharat Mission spread partly because it made cleanliness a matter of pride. Waste-pickers deserve recognition and safe conditions, because they do the city's recycling. Shopkeepers can offer jute bags and take back bottles, and hotels and markets can run their own biogas plants.

The attitude behind it. The deepest change is to see waste not as something that disappears when the truck comes but as a resource that we have made and must answer for. The sweet-shop box, the polythene packet and the old phone will still be somewhere on earth long after we forget them. Reduce first, reuse next, recycle always, and dispose of only what nothing else can take: that is the whole of this chapter, and a habit that a student of Class 10 can begin today.