--- title: "Physical and chemical characteristics of solid waste" subject: "Environment and Pollution Control" chapter: 5 key: "semester_7/environment_and_pollution_control:solid-waste-characteristics" source: https://www.bctengineer.com/q/semester_7/environment_and_pollution_control/solid-waste-characteristics site: BCT Engineering --- # Physical and chemical characteristics of solid waste Environment and Pollution Control · Chapter 5: Solid waste - Asked in: year not given, 6 marks - Video: [11 Physical and Chemical characteristics of solid wastes](https://www.youtube.com/watch?v=1BcklVqmpf8) — Learning Online - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/environment_and_pollution_control/solid-waste-characteristics - Whole chapter: https://www.bctengineer.com/md/semester_7/environment_and_pollution_control/chapter-5 ## Question Explain the physical and chemical characteristics of municipal solid waste and state why each is important in the management of solid waste. ## Short answer Physical: composition (organic, paper, plastics) guides treatment; density (loose 100–300, compacted 400–700 kg/m³) sizes bins; moisture (20–60%) affects calorific value; particle size determines shredder design. Chemical: proximate (moisture, volatile, ash) and ultimate (C,H,O,N,S) analyses predict combustion; calorific value 3000–4500 kJ/kg decides incineration feasibility; C/N 25–30 for composting; hazardous constituents affect safety. ## Answer Municipal solid waste (MSW) is the solid waste generated by households, markets, offices, institutions and streets. Its characteristics decide the methods of collection, treatment and disposal. #### Physical characteristics | Property | Meaning | Importance | |---|---|---| | Composition | Percentage of food/organic, paper, plastics, glass, metal, textile, inert | Selection of recycling, composting or incineration; developing countries have 50-70% organic waste | | Density | Mass per unit volume (loose 100-300; compacted 400-700 kg/m$^3$) | Design of bins, vehicles, landfill volume | | Moisture content | Water in the waste, typically 20-60% | Affects heating value, composting and leachate | | Particle size | Size distribution | Design of shredders, separators | | Generation rate | kg/person/day, depends on income and season | Planning of services | #### Chemical characteristics - **Proximate analysis:** moisture, volatile matter, fixed carbon and ash. Indicates how well the waste burns and how much ash must be disposed of. - **Ultimate analysis:** percentage of C, H, O, N, S and ash; used to compute the energy value, the air requirement and the gases formed in incineration. - **Calorific (heating) value:** energy per kg, about 3000-4500 kJ/kg for MSW in developing countries (higher in developed countries). Incineration needs at least about 6000-7000 kJ/kg, or an auxiliary fuel. - **C/N ratio:** best 25-30:1 for composting. - **pH, lipids, carbohydrates, proteins, fusing point of ash (clinkering):** relate to biodegradability and furnace operation. - **Hazardous constituents:** heavy metals and toxic chemicals that affect compost quality and leachate toxicity. Sampling is carried out by quartering, and sorting the sample gives the composition by weight. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why is the composition of MSW (percentage of organic, paper, plastic, etc.) important? A. It fixes the colour of the leachate B. It determines how much the vehicle weighs when empty C. It decides whether recycling, composting or incineration is suitable D. It sets the C/N ratio of incinerator ash Answer: C. Composition guides the choice of recycling, composting or incineration; a high organic fraction favours composting. (Key point: Importance of composition) 2. MSW in developing countries has a calorific value of about 3000-4500 kJ/kg. What does this imply for incineration? A. It burns well without any extra fuel B. It is below the roughly 6000-7000 kJ/kg needed, so auxiliary fuel would be required C. It cannot produce any ash D. It makes the waste ideal for composting only because of its density Answer: B. Incineration needs at least about 6000-7000 kJ/kg or an auxiliary fuel, so low-calorific MSW is poorly suited. (Key point: Calorific value and incineration) 3. Which analysis gives percentages of C, H, O, N, S and ash and is used to compute energy value and gases formed in incineration? A. Proximate analysis B. Ultimate analysis C. Particle size analysis D. Moisture analysis Answer: B. Ultimate analysis gives elemental composition; proximate analysis gives moisture, volatile matter, fixed carbon and ash. (Key point: Ultimate vs proximate analysis) ## Related in Environment and Pollution Control - [Solid waste management system and techniques](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Asolid-waste-management-techniques) — Environment and Pollution Control, chapter 5 - [Hazardous waste: definition and classification](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Ahazardous-waste-definition-classification) — Environment and Pollution Control, chapter 5 ## Related in other subjects - [Chemical waste leakage; boss asks silence](https://www.bctengineer.com/question.md?key=semester_8%2Fengineering_professional_practice%3Ahazardous-waste-leak-boss-silent) — Engineering Professional Practice, chapter 7 - [Importance and methods of waste management](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Aimportance-waste-management-methods) — Sanitary Engineering, chapter 1, asked 7× - [Methods of solid waste disposal](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Asolid-waste-disposal-methods) — Sanitary Engineering, chapter 10, asked 2× - [Physical and chemical weathering](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aphysical-and-chemical-weathering) — Engineering Geology I, chapter 6, asked 5×