================================== DOCUMENT 5: SESSION 5 (S5) ================================== POLLUTION ABATEMENT (21CHO105T) Unit 2 - Session 5 I. MULTIPLE CHOICE QUESTIONS (MCQs) 1. The main product of anaerobic digestion is: β Answer: B. Biogas β Explanation: Anaerobic digestion breaks down organic matter by bacterial action in an oxygen-free environment, primarily producing biogas (rich in methane and carbon dioxide). 2. Landfill gas mainly consists of: β Answer: C. Methane and carbon dioxide β Explanation: Landfill gas generated by anaerobic decomposition of buried organic waste typically consists of roughly 50-60% methane ( ) and 40-50% πΆπ» 4 carbon dioxide ( ). πΆπ 2 3. Recovery of landfill gas helps in: β Answer: B. Reducing methane emissions β Explanation: Capturing and flaring or utilizing landfill gas prevents fugitive emissions of methane, a potent greenhouse gas, while recovering energy. 4. Co-processing of waste is commonly carried out in: β Answer: C. Cement kilns β Explanation: Co-processing utilizes industrial cement kilns to simultaneously recover energy and material from waste streams under extremely high temperatures. 5. Which of the following wastes is suitable for co-processing? β Answer: C. Refuse-Derived Fuel β Explanation: Refuse-Derived Fuel (RDF) and high-calorific industrial wastes are ideal feedstocks for co-processing in cement kilns. II. SHORT ANSWER QUESTIONS 1. Explain incineration as a method of energy recovery. β Answer: Incineration involves the controlled high-temperature combustion (850 Β° C to 1100 Β° C) of solid waste in specialized furnaces. The heat released during combustion is used to generate high-pressure steam, which drives turbines to produce electricity, simultaneously reducing waste volume by up to 90%. 2. Explain advanced waste-to-energy technologies. β Answer: Advanced waste-to-energy technologies include: β Gasification: Converting carbonaceous waste into syngas using sub-stoichiometric oxygen at high temperatures. β Pyrolysis: Thermal cracking of waste in the absence of oxygen to produce bio-oil, syngas, and char. β Anaerobic Digestion (Biomethanation): Microbial conversion of wet organic waste into methane-rich biogas under oxygen-free conditions. III. LONG ANSWER QUESTION 1. Explain the methods of energy recovery from solid waste. β Answer: 1. Direct Combustion (Incineration) β Mechanism: Burning solid waste in excess oxygen inside refractory-lined furnaces. Heat exchange boilers recover thermal energy to produce electricity or district heating. β Advantages: High volume reduction and energy generation. Requires strict flue-gas cleaning (scrubbers, bag filters) to control dioxins and acid gases. 2. Thermochemical Conversion (Pyrolysis and Gasification) β Pyrolysis: Thermal degradation without oxygen yielding bio-oil, combustible gases, and char. β Gasification: Partial oxidation at high temperatures (700 Β° C - 1400 Β° C) producing clean syngas ( ) used for power generation or chemical synthesis. πΆπ + π» 2 3. Biochemical Conversion (Anaerobic Digestion / Landfill Gas Recovery) β Biogas Generation: Processing segregated wet organic waste in sealed anaerobic digesters to produce methane-rich gas. β Landfill Gas Capture: Installing extraction wells across sanitary landfills to collect fugitive landfill gas for electricity generation or direct thermal utilization. 4. Co-Processing in Cement Kilns β Utilizing the high temperatures (~1450 Β° C clinker burning zone) and long residence times of cement kilns to safely destroy hazardous and non-hazardous waste while recovering energy and substituting raw materials.