================================== 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: ● Answer: B. Biogas ● 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: ● Answer: C. Methane and carbon dioxide ● Explanation: Landfill gas generated by anaerobic decomposition of buried organic waste typically consists of roughly 50-60% methane ( ) and 40-50% 𝐶𝐻 4 carbon dioxide ( ). 𝐶𝑂 2 3. Recovery of landfill gas helps in: ● Answer: B. Reducing methane emissions ● 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: ● Answer: C. Cement kilns ● 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? ● Answer: C. Refuse-Derived Fuel ● 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. ● Answer: Incineration involves the controlled high-temperature combustion (850 ° C to 1100 ° 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. ● Answer: Advanced waste-to-energy technologies include: ○ Gasification: Converting carbonaceous waste into syngas using sub-stoichiometric oxygen at high temperatures. ○ Pyrolysis: Thermal cracking of waste in the absence of oxygen to produce bio-oil, syngas, and char. ○ 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. ● Answer: 1. Direct Combustion (Incineration) ● Mechanism: Burning solid waste in excess oxygen inside refractory-lined furnaces. Heat exchange boilers recover thermal energy to produce electricity or district heating. ● 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) ● Pyrolysis: Thermal degradation without oxygen yielding bio-oil, combustible gases, and char. ● Gasification: Partial oxidation at high temperatures (700 ° C - 1400 ° C) producing clean syngas ( ) used for power generation or chemical synthesis. 𝐶𝑂 + 𝐻 2 3. Biochemical Conversion (Anaerobic Digestion / Landfill Gas Recovery) ● Biogas Generation: Processing segregated wet organic waste in sealed anaerobic digesters to produce methane-rich gas. ● 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 ● Utilizing the high temperatures (~1450 ° 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.