Solid Waste Management and Power Supply: Collection, Processing, Disposal, Siting, Rules, Transformers and Substations
2. Collection, storage and transportation
The chain is generation, on-site storage, collection, transfer and transport, processing, disposal. Storage at the source starts with segregation: separate bins for wet and dry waste, with sanitary and domestic hazardous items kept apart, so that nothing is mixed that will later have to be pulled apart. Primary collection is door-to-door, by tricycle, hand cart or auto-tipper on a fixed schedule, which supports segregation and keeps bins off the street; community bins are secondary storage points, served by dumper placers or compactors, and a bin-free city aims to replace them with doorstep collection. Street sweeping and drain cleaning are collected separately, and informal waste-pickers and community groups can be brought into the system.
In a hot, humid climate wet waste is collected daily: it decomposes fast, breeds flies and rodents and leaks leachate. A transfer station is a facility where small collection vehicles unload into large trailers or compactors for the long haul to the processing or disposal site. It pays when the haul is long, since the saving in vehicle time and fuel exceeds the cost of the station, and it belongs near the centre of the collection area on a good road. Vehicles are covered to stop spillage and blowing, and routes are planned, now with GPS, to cut dead mileage.
Worked example: a town of 2,40,000 at 0.35 kg/capita/day produces 240,000 × 0.35 = 84,000 kg = 84 tonnes per day. If each collection vehicle carries 6 tonnes in one trip a day, the fleet needed is 84 / 6 = 14 vehicles, before any allowance for breakdown spares or a second trip. The same waste at a loose density of 300 kg/m³ is 84,000/300 = 280 m³ a day, which is why volume, not weight, often limits a vehicle.
3. Recycling, reuse and processing of waste
Recycling returns materials to use: paper, plastics, metals and glass are sorted from the dry stream at a material recovery facility (MRF) and sold to recyclers, with waste-pickers integrated into the chain; C&D waste can be crushed into recycled aggregate; e-waste goes to authorised recyclers. Reuse keeps an item in service without reprocessing. Both rest on a clean dry stream. The wet and residual streams need processing.
| Route | Principle | Conditions and notes |
|---|---|---|
| Composting | aerobic decay of organics into stable, humus-like compost | segregated organic feed; starting C:N about 25 to 30:1; moisture about 50 to 60%; the thermophilic stage near 55 to 65 °C kills pathogens; turning or forced air; windrow, aerated static pile, in-vessel or vermicomposting |
| Biomethanation (anaerobic digestion) | organics digested without oxygen into biogas (about 55 to 65% methane) and a digestate | suits wet, high-moisture food waste; no aeration power; gas for cooking, electricity or compressed gas; needs clean feed and gas safety |
| Incineration (waste-to-energy) | controlled combustion with excess air at high temperature, around 850 °C or more, with heat recovery to make power | cuts volume by about nine-tenths and mass by about three-quarters; needs enough calorific value, gas cleaning for dioxins and acid gases, and ash disposal; poorly suited to wet mixed waste |
| Refuse-derived fuel (RDF) | the dry, high-calorific fraction (paper, plastics, textiles) separated, shredded and dried into a fuel | burnt in cement kilns or boilers as a coal substitute; needs a buyer; chlorine from PVC corrodes; cuts landfill |
Worked example for yield: a city produces 400 t/day of MSW, of which 55% is organic and delivered segregated to a composting plant whose yield is 30% of the organic input by mass. Organic input = 0.55 × 400 = 220 t/day; compost = 0.30 × 220 = 66 t/day. The rest is mostly water and carbon dioxide lost in decay, and rejects.
4. Landfills and disposal
A sanitary landfill is the engineered, last-resort disposal of the residue that cannot be recycled or processed: waste is placed in layers, compacted and covered each day. It is the opposite of open dumping, which pollutes groundwater with leachate, burns, breeds vectors and releases methane. Its parts are a liner (compacted clay, a geomembrane, or both) that stops leachate leaving; a leachate collection and treatment system, since the leachate is strong in BOD, ammonia and metals; gas collection, since landfill gas is about half methane, which is explosive in air between roughly 5 and 15%, and is flared or used; daily and final soil cover; surface-water drains that keep rain out; monitoring wells for groundwater; and post-closure care for decades.
The landfill area follows from volume and height: V = (tonnes per day × days) / compacted density, plus the soil cover that takes up part of the space, and A = V / H. Example: 100 t/day at a compacted density of 500 kg/m³ is 200 m³/day. Over 10 years, with 365 days a year, V = 200 × 3,650 = 730,000 m³; soil cover adds 20% of the volume, giving 876,000 m³; at a lift height of 10 m, A = 876,000 / 10 = 87,600 m² = 8.76 ha. Without the cover it would be 7.3 ha, so ignoring the cover leaves the land about one-sixth short (7.3 against 8.76 ha). Methods are trench (flat land, deep water table), area and ramp, or depression filling.
5. Area requirements and location criteria for facilities
A planner reserves land for each facility at the master-plan stage, with its area from the throughput and the process, and its location from what it needs and what it harms. Land area is not a fixed norm: a landfill’s area is volume over height, a compost yard’s follows throughput and retention time, and a waste-stabilisation-pond sewage plant needs many times the land of an activated-sludge plant for the same flow. Every facility that smells, makes noise or carries a hazard also needs a buffer, often planted as a green belt.
| Facility | Where it belongs | Why |
|---|---|---|
| Water intake and treatment plant | intake upstream of the town’s outfalls; plant near the source on ground above flood level | clean raw water, short raw mains, protection from flood |
| Elevated reservoir | high ground near the centre of its zone | even pressure with short mains |
| Sewage treatment plant | at the low end of the sewer system, downstream and downwind of the town, above flood level, near the point of disposal or reuse | gravity flow, odour kept away, effluent safe from floods |
| Transfer station | near the centre of the collection area, on a good road toward the disposal site, enclosed | shortest haul by small vehicles, quick transfer |
| Compost and biomethanation plant | city fringe, near farms that use the compost, downwind of housing, with a buffer and leachate control | odour and flies; market for the product |
| Waste-to-energy plant | industrial land with good road access and a grid connection nearby, with a buffer | feed in, power out, stack emissions kept from housing |
| Sanitary landfill | low-permeability soil, deep water table, outside flood plain, clear of rivers, lakes, wells, habitation and the bird-strike zone of airports, with adequate capacity and access | protects groundwater and air safety; long life; reasonable haul |
| Electric substation | at the load centre of its service area, on an accessible road, with safety clearances | short feeders mean low losses and low voltage drop |
6. Standards, rules and codes
The legal frame for waste is the Solid Waste Management Rules, made under the Environment (Protection) Act, 1986, which replaced the older Municipal Solid Wastes (Management and Handling) Rules, 2000, and have since been revised. Their principles matter more than their clause numbers.
- Segregation at source: every generator must keep waste apart, wet, dry, and the special categories such as sanitary and domestic hazardous items, and hand it over to the authorised collector; littering and burning are barred.
- Polluter pays and extended producer responsibility: the generator pays user charges, and bulk waste generators such as large complexes, hotels and institutions carry stricter duties, including processing their wet waste on site; and, under the related plastic-waste and e-waste rules, producers and brand owners of plastic packaging and electronics are responsible for the end-of-life of their products.
- Local-body duty: door-to-door collection, secondary storage, transport, processing into compost, biogas or fuel, and landfilling of only the inert residue, to engineering and siting standards, with no open dumping; and land earmarked for processing facilities in the plan.
- Related rules under the same Act cover construction and demolition waste, plastic waste, e-waste, bio-medical waste and hazardous waste; each assigns duties to the generator, the producer and the local body.
The technical standards are the CPHEEO manuals (water supply and treatment, sewerage and sewage treatment, municipal solid waste management) and the BIS codes: IS 10500 (drinking water), IS 1172 (basic requirements for water supply, drainage and sanitation), IS 2470 (septic tanks) and IS 1742 (building drainage). The National Building Code, Part 9, Plumbing Services, brings water supply, drainage and sanitation, solid waste management and gas supply into building regulation. Programmes such as Swachh Bharat Mission (Urban) and AMRUT have funded such works, and service-level benchmarks measure the result. For electricity, the Electricity Act, 2003, the Central Electricity Authority’s technical standards and the Indian Electricity Rules apply, with NBC Part 8 covering electrical installations in buildings.
7. Fundamentals of power transmission and distribution
Power flows from the generating station through transmission to the load centres and then through distribution to the consumer, with transformers stepping the voltage up at the start and down in stages. In India alternating current is the norm, with HVDC links for very long, undersea or asynchronous connections.
| Level | Standard voltages | Role |
|---|---|---|
| Generation | about 11 to 25 kV at the generator | stepped up at once by the generator transformer |
| Transmission (extra-high voltage) | 765, 400 and 220 kV | bulk power over long distances between stations and grid substations |
| Sub-transmission | 132 and 66 kV | from the grid substation to the city and large industrial load |
| Primary distribution (HT) | 33 and 11 kV | along feeders to the distribution substations |
| Secondary distribution (LT) | 415 V three-phase, 230 V single-phase | from the distribution transformer to the consumer |
Why transmit at high voltage? The power is P = √3 V I cos φ for a three-phase line, so for the same power the current falls as 1/V, and the line loss I²R falls as 1/V². Tripling the voltage cuts the loss to one-ninth for the same conductor, or lets a much thinner conductor do the work. The price is dearer insulation, taller towers, wider right-of-way and costlier substations, so each power and distance has an economic voltage. Example: a line that loses 90 kW at 11 kV loses 90/9 = 10 kW at 33 kV for the same power and conductor.
Losses are technical (I²R heating in lines, transformer core and copper losses, poor power factor, overloading, unbalanced phases, over-long low-tension lines) and commercial (theft, metering and billing faults); together they are the AT&C (aggregate technical and commercial) loss. They are cut by distributing at higher voltage with small transformers near the load (HVDS) instead of long LT lines, by right-sized conductors, by capacitors for power factor, by load balancing and by metering. Overhead lines are cheaper and easier to repair but need a right-of-way and are exposed; underground cables suit dense, built-up areas for safety and appearance but cost far more.
8. Transformers, feeders and substations
A transformer transfers AC power between circuits by mutual induction, changing voltage and current but not frequency. For an ideal one, V₁/V₂ = N₁/N₂ = I₂/I₁. A step-up transformer (more secondary turns) raises voltage at the generating station; a step-down transformer lowers it at each substation. It is rated in kVA, not kW, because its losses depend on voltage and current and not on the power factor. The core (iron) loss is nearly constant whenever it is energised; the copper loss varies with the square of the load; efficiency is greatest when the two are equal. Example: a single-phase transformer with 1,100 primary turns working from 11 kV to 440 V has 1,100 × 440/11,000 = 44 secondary turns.
A distribution transformer (11 kV to 415 V) is sized for the diversified maximum demand of the area: kVA = connected load × demand factor / power factor. Example: 150 flats at 3 kW connected load each is 450 kW; at a demand factor of 0.4 the maximum demand is 180 kW; at a power factor of 0.9 the transformer must supply 180/0.9 = 200 kVA, and the next standard rating above the need is chosen. For a three-phase transformer, the line current is I = S / (√3 V): a 250 kVA unit draws 250,000 / (√3 × 11,000) = 13.12 A on the 11 kV side.
The conductors that carry the power have three roles. A feeder runs from a substation to the distribution area with no tapping on the way, so its current is constant and it is designed for current-carrying capacity. A distributor runs through the area and is tapped by consumers along its length, so it is designed for voltage drop. A service main is the final connection from the distributor to the consumer. Feeders are laid radial (one path from the source: cheap and simple, but a fault interrupts everything beyond it), ring or loop (two paths, so supply can be restored by switching) or interconnected (several sources, the most reliable and the dearest).
A substation changes voltage, switches and protects the network. By function there are step-up (at the power station), grid or transmission, sub-transmission and distribution substations (11 kV to 415 V). Its equipment includes transformers, circuit breakers, isolators, lightning arresters, busbars, current and voltage transformers, protective relays, capacitor banks and earthing. By construction, outdoor air-insulated (AIS) substations are cheap but need a lot of land; gas-insulated (GIS) substations, insulated by SF₆, are compact, needing a fraction of the land, and suit dense, land-scarce cities but cost more; pole-mounted and compact (kiosk) units serve small loads. A substation is sited at the load centre of the area it serves, so that feeders are short and losses and voltage drop low, and the plan reserves the land and its safety clearances.
Key takeaways
- Waste generated = population × per capita rate; Indian MSW is wet, inert-rich and low in calorific value, so collect wet waste daily, segregate at source, and keep tonnes and cubic metres tied by their density.
- The waste hierarchy runs reduce, reuse, recycle, recover, dispose; match the route to the stream: wet to compost or biomethanation, dry combustibles to RDF, recyclables to the MRF, only inert residue to landfill.
- A sanitary landfill has a liner, leachate and gas collection, daily cover and monitoring; its area is volume over height with the cover soil included (V = mass / compacted density, A = V / H).
- Siting follows hydrology, soil, flood level, wind, access, buffer and haul distance: intake upstream, sewage plant downstream, landfill clear of water, wells, flood plain and airports, substation at the load centre.
- The Solid Waste Management Rules, made under the Environment (Protection) Act, rest on segregation at source, polluter pays and producer responsibility, and local-body duty; IS 10500, IS 1172, IS 2470, CPHEEO manuals and NBC Part 9 carry the technical standards.
- Power runs 765/400/220 kV transmission, 132/66 kV sub-transmission, 33/11 kV primary and 415/230 V secondary distribution; loss falls as 1/V², transformers are rated in kVA with core loss constant and copper loss varying with load squared, a feeder is designed for current and a distributor for voltage drop, and a substation sits at the load centre.
Practice questions (18)
Attempt each one before opening the answer. Every explanation names the tempting wrong option as well as the right one, because that is where marks are lost.
Which sequence lists the waste hierarchy from the most preferred to the least preferred response?
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Answer: C — reduce, reuse, recycle, recover, dispose
The hierarchy prefers not making the waste (reduce), then keeping items in use (reuse), then reprocessing materials (recycle), then recovering value such as compost, biogas or energy (recover), and landfilling the residue last. The sequence that begins with disposal is the exact reverse, and the others place recycling or reuse above reduction.Direct incineration of raw mixed municipal waste from an Indian city is generally unsuitable mainly because
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Answer: A — its moisture and inerts give it a low calorific value, so it will not burn unaided
Wet food waste and inert silt and ash pull the heating value down, so mixed waste needs supplementary fuel unless it is first segregated, dried or made into RDF. Incineration does cut volume strongly when the waste burns; the real trouble is the poor burn, not any inability to reduce volume.A waste transfer station is economical when
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Answer: D — the haul to the disposal site is long, so the time and fuel saved exceed its cost
A transfer station lets small collection vehicles unload and return quickly, while large trailers or compactors make the long haul, so it pays only when the haul is long. With a short haul the extra handling is a pure cost. Segregation at source is needed for processing, but it does not decide whether transfer is economical.A vegetable market and a hotel cluster produce 30 t/day of segregated, wet, high-moisture food waste. The operator wants fuel for a nearby kitchen and an output usable as manure. The best processing route is
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Answer: B — biomethanation, giving biogas for the kitchen and a digestate usable as manure
Wet, high-moisture food waste is the ideal feed for anaerobic digestion, which yields biogas and a nutrient-rich digestate, matching both wishes. Wet waste burns poorly, so incineration and RDF are the tempting but wrong routes; burying it in a landfill wastes the resource and produces heavy leachate and methane.Four sites are proposed for a sanitary landfill. The most suitable is
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Answer: A — a clay plateau with a deep water table, outside the flood plain, clear of wells, homes and airport bird-strike zones
A landfill needs low-permeability soil and a deep water table to protect groundwater, a site outside the flood plain and clear of water sources and homes, and distance from airports, where the birds that gather at waste are a collision hazard. Each rival site fails one of these tests; the short haul of the flood-plain site does not repay its hydrological risk.In India’s waste-management rules, the principle of “polluter pays” means that
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Answer: C — generators pay user charges and fines, and producers answer for the end-of-life of their goods
The principle puts the cost on whoever creates the waste: user fees and spot fines on the generator, and, under the related plastic-waste and e-waste rules, extended producer responsibility for packaging and electronics. It is not a rule that the municipality absorbs everything, nor one that exempts households or spreads the cost over the whole state.Which list gives the supply voltages in the correct descending order along the chain from transmission to the consumer?
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Answer: B — 400 kV, 132 kV, 33 kV, 11 kV, 415 V
The chain steps down from extra-high-voltage transmission (400 kV) through sub-transmission (132 kV) and primary distribution (33 kV, 11 kV) to 415 V at the consumer. The other lists place 132 kV above 400 kV, or 33 kV above 132 kV, or put 400 kV below 220 kV.In a dense city where land is very scarce, the preferred substation type, and the reason, is
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Answer: D — gas-insulated (GIS), because it is compact and needs a fraction of the land, though dearer
A gas-insulated substation packs the equipment in SF₆-filled enclosures that need a small fraction of the land of an air-insulated yard, which is worth the extra cost where land is dear. Outdoor air-insulated yards are cheaper but land-hungry, and a pole-mounted unit serves only small loads.A three-phase transformer of 400 kVA is fed at 11 kV. Ignoring losses, the line current on the 11 kV side is nearly
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Answer: A — 20.99 A
For three phase, I = S / (√3 V) = 400,000 / (1.732 × 11,000) = 20.99 A. The figure 36.36 A is S/V and forgets the √3, which is the tempting slip; 62.98 A multiplies by √3 instead of dividing.Which statement correctly contrasts a feeder with a distributor?
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Answer: C — A feeder runs from a substation to the area untapped and is designed for current capacity, while a distributor is tapped along its length and designed for voltage drop
A feeder carries bulk power from the substation to the distribution area with no tappings, so its current is constant and its limit is current-carrying capacity. A distributor is tapped along its length, so voltage drop at the far consumers governs it. The final connection to the premises is the service main, not a feeder.Which of the following statements about a sanitary landfill are correct?
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Answer: A — The leachate must be collected above a liner and treated; B — Landfill gas contains methane, which is explosive in air, so it is collected and flared or used
A landfill must contain its leachate with a liner and a collection system and must manage its methane. Burying wet waste produces heavy leachate and gas rather than safe compost, and open burning is barred because it releases toxic smoke and defeats the engineered cover.Which of the following pairs of waste stream and processing route are appropriate?
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Answer: A — Segregated wet kitchen waste: composting or biomethanation; B — The dry combustible fraction (paper, plastics, textiles): RDF for a cement kiln or boiler
Wet organics suit biological processing and the dry, high-calorific fraction suits RDF. Inert silt and debris have no fuel value, so burning them recovers nothing and they go to recycled aggregate or landfill; and mixed waste composted directly gives compost contaminated with glass, plastic and metals.Which of the following statements about transformers are correct?
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Answer: A — The rating is in kVA because the losses depend on voltage and current, not on power factor; B — The core loss is nearly constant while the transformer is energised, and the copper loss varies as the square of the load; C — The efficiency is greatest when the copper loss equals the core loss
Iron loss depends on the voltage and frequency, copper loss on the current squared, and the maximum efficiency lies where the two are equal. A step-up transformer raises the voltage, which needs more turns on the secondary, so the claim of fewer secondary turns is reversed.A town of 3,20,000 people generates waste at 0.45 kg/capita/day. Each collection vehicle carries 8 tonnes in one trip a day. The number of vehicles needed to lift the whole day’s waste, with no spare vehicles, is ____.
Numerical answer — type the value.
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Answer: 18
Waste = 320,000 × 0.45 = 144,000 kg = 144 tonnes/day. Vehicles = 144 / 8 = 18 exactly, so no rounding up is needed. Check: 18 × 8 = 144.A landfill receives 120 t/day at a compacted density of 600 kg/m³ for 8 years of 365 days. Daily and intermediate soil cover adds 25% to the waste volume, and the landfill is filled to a height of 10 m. The land area required, in hectares to one decimal place, is ____.
Numerical answer — type the value.
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Answer: 7.3
Daily volume = 120,000 kg / 600 kg/m³ = 200 m³. Over 8 × 365 = 2,920 days: 584,000 m³. With 25% cover: 584,000 × 1.25 = 730,000 m³. Area = 730,000 / 10 = 73,000 m² = 7.3 ha (1 ha = 10,000 m²). Without the cover the area would be 5.84 ha.A city generates 250 t/day of municipal waste, of which 60% is organic. Only 80% of the organic fraction reaches the composting plant properly segregated, and the plant’s yield is 25% of the input by mass. The compost produced, in tonnes per day, is ____.
Numerical answer — type the value.
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Answer: 30
Organic fraction = 0.60 × 250 = 150 t/day. Reaching the plant = 0.80 × 150 = 120 t/day. Compost = 0.25 × 120 = 30 t/day. Check: 0.6 × 0.8 × 0.25 = 0.12, and 0.12 × 250 = 30.A housing block has 200 flats with a connected load of 2.5 kW each. The demand factor is 0.45 and the power factor is 0.9. The minimum transformer kVA needed to meet the maximum demand is ____.
Numerical answer — type the value.
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Answer: 250
Connected load = 200 × 2.5 = 500 kW. Maximum demand = 0.45 × 500 = 225 kW. kVA = 225 / 0.9 = 250 kVA. The kVA, not the 225 kW, is what the rating must cover.A line transmitting a fixed power at 33 kV loses 64 kW. The same power is sent at the same power factor and over the same conductor at 132 kV. The line loss, in kW, becomes ____.
Numerical answer — type the value.
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Answer: 4
For fixed power the current varies as 1/V, and the loss I²R as 1/V². The voltage rises by 132/33 = 4, so the loss falls by 4² = 16: 64/16 = 4 kW. Dividing by 4 instead of 16 is the common slip.