Solid Waste

Municipal solid waste must be collected, processed and disposed of safely. Learn generation and composition, the waste hierarchy, collection and transport, composting and waste-to-energy, sanitary landfill design (volume, liners, leachate, gas) and circular economy.

A city of a million people produces around 500 tonnes of waste every day. Poorly managed, it clogs drains, pollutes groundwater, releases methane and spreads disease; well managed, it becomes compost, recycled material and energy.

Solid waste engineering plans the whole chain from the household bin to the engineered landfill.

An analogy

Waste management is like a sorting office for materials: reduce what arrives, redirect what can be reused, recover value, and only then bury what's left.

Waste hierarchy

Prevent → reduce → reuse → recycle → recover (compost, energy) → dispose. Source segregation (wet/dry/hazardous) is the single biggest enabler of effective processing.

Characteristics and collection

Generation 0.3–0.6 kg/cap/day (developing cities) to 1.5–2 (high-income). Composition in many Indian cities is ~50 % organic, making composting and biomethanation attractive. Collection and transport can be 60–70 % of the cost — route optimisation and transfer stations help.

Processing

Aerobic composting (windrows, C/N ≈ 25–30, moisture 50–60 %), anaerobic digestion (biogas), material recovery facilities for recyclables, refuse-derived fuel and incineration with energy recovery (needs LHV > ~7 MJ/kg).

Sanitary landfills

Engineered landfills have composite liners (compacted clay + HDPE geomembrane), leachate collection and treatment, daily cover, landfill gas collection (methane for energy or flaring), and final capping. Siting avoids floodplains, aquifers and airports. Old dumps are remediated by biomining.

Formulas

• Daily generation: W = population × g
• Landfill volume: V = (W × 365 × years / ρ) × (1 + cover fraction)
• Energy potential: P = W × LHV / 86 400 × η [MW if W in t/d, LHV MJ/t]

Worked example: Landfill capacity

Given: 100 000 people, 0.5 kg/cap/d; 20-year life, compacted 0.8 t/m³, cover 20 %, depth 15 m

Find: Volume and footprint.

• W = 50 t/d → 365 000 t over 20 years
• V = 365 000/0.8 × 1.2 = 547 500 m³
• Area = 547 500/15 = 36 500 m² ≈ 3.65 ha

Answer: ≈ 5.5 × 10⁵ m³, ≈ 3.7 ha

Worked example: Energy from waste

Given: 50 t/d, LHV 8 MJ/kg; Electrical efficiency 20 %

Find: Power output.

• Thermal = 50 000 × 8/86 400 = 4.63 MW
• Electric = 0.93 MW

Answer: ≈ 0.9 MWe

Common mistakes

• Wrong: Planning landfill capacity without diversion targets. — Right: Segregation and composting can halve landfill needs.
• Wrong: Burning high-moisture mixed waste for energy. — Right: Check LHV; wet organics suit biomethanation, not incineration.

Applications

• Municipal services: Door-to-door collection, transfer stations and processing plants.
• Landfill engineering: Liner design, leachate treatment and gas-to-energy.
• Legacy dumpsite remediation: Biomining and capping of old open dumps.

Key takeaways

• Reduce, reuse, recycle, recover, then dispose.
• Segregation at source enables everything else.
• V = W·365·years/ρ × (1 + cover).
• Engineered landfills need liners, leachate and gas control.

Going further

• Leachate generation: HELP model water balance estimates leachate volumes for treatment design.
• Life-cycle assessment: Compares GHG and costs of recycling, composting, WtE and landfill.
• Extended producer responsibility: Makes producers fund end-of-life management of packaging and e-waste.