================================== DOCUMENT 4: SESSION 4 (S4) ================================== POLLUTION ABATEMENT (21CHO105T) Unit 2 - Session 4 I. MULTIPLE CHOICE QUESTIONS (MCQs) 1. The solid residue obtained after anaerobic digestion is called: ● Answer: B. Digestate ● Explanation: Digestate is the nutrient-rich solid and liquid residual material remaining after the anaerobic digestion of organic matter. 2. Refuse-Derived Fuel (RDF) is prepared from: ● Answer: B. Combustible fraction of waste ● Explanation: RDF is processed from the high calorific, combustible components of municipal solid waste, such as plastics, paper, cardboard, and textiles. 3. RDF is commonly used in: ● Answer: B. Cement kilns ● Explanation: Cement manufacturing plants utilize RDF as an alternative auxiliary fuel source in high-temperature kilns to substitute fossil fuels like coal. 4. Pyrolysis is carried out in the: ● Answer: C. Absence of oxygen ● Explanation: Pyrolysis is the thermal decomposition of carbonaceous materials at elevated temperatures in the complete absence of oxygen, preventing combustion. 5. Pyrolysis of solid waste produces: ● Answer: C. Oil, gas, and char ● Explanation: The thermal breakdown of waste via pyrolysis yields three primary products: condensable bio-oil, non-condensable syngas, and solid carbonaceous char. II. SHORT ANSWER QUESTIONS 1. What is meant by value extraction from solid waste? ● Answer: Value extraction refers to recovering useful resources, materials, or energy from solid waste streams through mechanical sorting, recycling, biological digestion, or thermal conversion, transforming waste liabilities into secondary raw commodities. 2. What are Material Recovery Facilities (MRFs)? ● Answer: Material Recovery Facilities (MRFs) are specialized plant facilities where comingled dry recyclable solid wastes are received, sorted, processed, and baled into marketable commodities (such as clean metals, paper, glass, and plastics) using manual and automated mechanical separation technologies. III. LONG ANSWER QUESTION 1. Explain the concept and methods of value extraction from solid waste. ● Answer: 1. Concept of Value Extraction Value extraction shifts waste management paradigms away from linear "take-make-dispose" models toward circular economic systems where waste functions as a valuable raw material input. 2. Key Methods of Value Extraction ● Material Recycling & MRFs: Mechanical sorting of dry recyclables using trommels, magnetic separators, eddy current separators, and optical scanners to recover ferrous/non-ferrous metals, paper, and plastics. ● Refuse-Derived Fuel (RDF) Production: Shredding, drying, and pelletizing combustible municipal waste fractions to produce high-calorific fuel for industrial boilers and cement kilns. ● Biological Value Extraction (Composting & Anaerobic Digestion): Processing organic food and garden waste into nutrient-rich compost or biogas and digestate through controlled microbial action. ● Thermochemical Conversion (Pyrolysis & Gasification): Breaking down complex organic waste polymers without oxygen into high-value syngas, bio-oil, and solid carbon char.