UGC NET Environmental Science Unit-VII: Solid and Hazardous Waste Management Syllabus

What are the three main collection methods for municipal solid waste?

Hauled-container system (HCS), stationary-container system (SCS), and kerbside/community-bin collection.

In the hauled-container system, how are containers handled?

Containers are picked up, hauled to the disposal/transfer site, emptied, and returned to their original or another location — suited to high generation-rate sources.

In the stationary-container system, how is waste collected?

Containers remain at the point of generation; the collection vehicle travels to each, empties the waste into the truck, and the container stays in place.

What is source segregation of solid waste?

Separation of waste at the point of generation into categories (e.g., wet/biodegradable, dry recyclable, domestic hazardous) to enable efficient recovery and treatment.

What is a transfer station and when is it economical?

A facility where waste from collection vehicles is consolidated into larger transport vehicles; it is economical when disposal sites are far from collection areas, reducing haul cost and time.

What are the three types of transfer stations based on loading method?

Direct-discharge (direct-load), storage-discharge (storage-load), and combined direct- and storage-discharge stations.

What is the purpose of route optimization in waste collection?

To minimize haul distance, time, fuel, and labour by designing efficient collection routes (heuristic routing) while covering all pickup points.

What is materials recovery facility (MRF)?

A facility where commingled or source-separated recyclables are received, sorted, processed, and baled for sale to markets.

What mechanical processing techniques are used to recover materials from waste?

Size reduction (shredding/grinding), size separation (screening/trommels), density separation (air classification), magnetic separation (ferrous), and eddy-current separation (non-ferrous).

What is air classification in waste processing?

A density-based separation that uses an air stream to separate light (paper, plastic) from heavy (glass, metal) fractions of shredded waste.

How does magnetic separation work in waste recovery?

A magnetic field (e.g., overband or drum magnet) extracts ferrous metals from the mixed waste stream.

What is composting?

The aerobic, controlled biological decomposition of the organic fraction of solid waste by microorganisms into a stable, humus-like product (compost).

What are the optimum conditions (C/N, moisture, temperature, pH) for aerobic composting?

C/N ratio ~25–30:1, moisture 50–60%, thermophilic temperature 55–60°C, and pH ~6.5–8.0.

What is vermicomposting?

Composting using earthworms (e.g., Eisenia fetida) to break down organic waste into nutrient-rich worm castings (vermicompost), operating at mesophilic temperatures.

What is anaerobic digestion of organic waste?

Biological decomposition of organic matter by microbes in the absence of oxygen, producing biogas (CH4 + CO2) and a digestate, with energy recovery.

What is refuse-derived fuel (RDF)?

A fuel produced by shredding, drying, and processing the combustible (high-calorific) fraction of MSW into pellets or fluff for use in incinerators/boilers.

What is incineration of solid waste?

Controlled high-temperature (≈850–1000°C) combustion that reduces waste volume by 80–90% and mass by ~70%, with optional energy (waste-to-energy) recovery.

What is pyrolysis in waste processing?

Thermal decomposition of organic waste at 400–800°C in the absence of oxygen, yielding char (solid), pyrolytic oil (liquid), and syngas (gas).

How does gasification differ from incineration and pyrolysis?

Gasification is partial oxidation at high temperature in a limited (sub-stoichiometric) oxygen supply, producing combustible syngas — unlike full-oxygen incineration or oxygen-free pyrolysis.

What is a sanitary landfill?

An engineered method of disposing of solid waste on land by spreading in thin layers, compacting to the smallest practical volume, and covering with soil daily to minimize environmental impact.

What are the essential engineered components of a sanitary landfill?

A liner system (clay/geomembrane), leachate collection and treatment system, landfill gas collection system, daily/final cover, and groundwater monitoring wells.

What is leachate?

The contaminated liquid that percolates through the waste in a landfill, carrying dissolved and suspended pollutants, requiring collection and treatment to protect groundwater.

What is landfill gas and its main constituents?

Gas produced by anaerobic decomposition of waste, composed mainly of methane (~50–55%) and carbon dioxide (~45–50%), with trace gases; methane is recoverable as energy.

What are the phases of gas generation in a landfill?

Phase I aerobic; Phase II anaerobic acid (acidogenic); Phase III unsteady methanogenic; Phase IV steady methanogenic; Phase V maturation/stabilization.

What is a hazardous waste?

A waste that, due to its physical, chemical, or biological characteristics, poses a substantial present or potential threat to human health or the environment when improperly managed.

What are the four characteristic properties that classify a waste as hazardous?

Ignitability, corrosivity, reactivity, and toxicity (the ICRT characteristics).

What defines the 'corrosivity' characteristic of hazardous waste?

Aqueous wastes with pH ≤ 2 or ≥ 12.5, or those able to corrode steel at a specified rate — capable of damaging tissues and containers.

What is the TCLP test used for?

The Toxicity Characteristic Leaching Procedure simulates leaching in a landfill to determine whether a waste's leachate exceeds regulatory toxicity limits for specified contaminants.

What are the major treatment methods for hazardous waste?

Physical (sedimentation, filtration, adsorption), chemical (neutralization, oxidation/reduction, precipitation), biological (bioremediation), thermal (incineration), and stabilization/solidification before secure landfilling.

What is solidification/stabilization of hazardous waste?

Treatment that immobilizes contaminants by binding them in a solid matrix (e.g., cement, lime, fly ash) to reduce mobility, leachability, and toxicity before secure land disposal.

What is a secure landfill for hazardous waste?

A highly engineered disposal facility with double liners, leachate detection/collection, leak-detection layers, and continuous monitoring designed to isolate hazardous waste from the environment.