CPWM Waste Treatment Technologies & Disposal Methods — Questions and Answers
Question 1: Which technology generates methane‑rich biogas from biodegradable waste?
- Aerated static pile composting
- Anaerobic digestion (Correct answer)
- Chemical oxidation
- Windrow composting
Correct answer: Anaerobic digestion
Anaerobic digestion is a biological process where microorganisms break down organic matter in the absence of oxygen. This process efficiently converts biodegradable waste into methane-rich biogas, a valuable renewable energy source, and a nutrient-rich digestate. It is a sustainable method for waste treatment and energy recovery.
Question 2: For efficient composting, the optimal carbon‑to‑nitrogen (C:N) ratio is approximately:
- 10:1
- 25–30:1 (Correct answer)
- 50:1
- 5:1
Correct answer: 25–30:1
For efficient composting, microorganisms require a balanced diet of carbon (energy source) and nitrogen (protein source). An optimal carbon-to-nitrogen (C:N) ratio of approximately 25–30:1 ensures rapid and effective decomposition. Ratios outside this range can lead to slow decomposition (too much carbon) or nitrogen loss as ammonia (too much nitrogen).
Question 3: The PRIMARY function of a composite liner in a sanitary landfill is to:
- Increase settlement of waste layers
- Prevent leachate from reaching groundwater (Correct answer)
- Capture landfill gas exclusively
- Support heavy equipment traffic
Correct answer: Prevent leachate from reaching groundwater
A composite liner in a sanitary landfill typically consists of a geomembrane (synthetic liner) placed over a compacted clay layer. Its primary function is to create an impermeable barrier that prevents leachate, the contaminated liquid generated within the landfill, from migrating into and polluting the underlying groundwater. This is crucial for environmental protection.
Question 4: High‑temperature rotary kiln incinerators are BEST suited to treat:
- Yard trimmings
- Hazardous organic liquids and sludges (Correct answer)
- Glass cullet
- Mixed recyclables
Correct answer: Hazardous organic liquids and sludges
High-temperature rotary kiln incinerators are specifically designed to achieve very high temperatures and long residence times, making them highly effective for the complete destruction of complex and hazardous organic wastes. This includes hazardous organic liquids and sludges, where thorough thermal treatment is necessary to break down persistent pollutants and ensure safe disposal.
Question 5: Steam autoclaving is a disinfection method MOST commonly applied to:
- Scrap metal
- Infectious medical waste (Correct answer)
- Construction debris
- Spent solvents
Correct answer: Infectious medical waste
Steam autoclaving uses high-pressure saturated steam to achieve sterilization, effectively killing microorganisms present in waste. This method is widely recognized and utilized for the disinfection and treatment of infectious medical waste, such as sharps, contaminated lab materials, and pathological waste, rendering it safe for subsequent disposal.
Question 6: After combustion in a mass‑burn waste‑to‑energy facility, the main solid residue requiring management is:
- Leachate
- Bottom ash and fly ash (Correct answer)
- Compost
- Biogas digestate
Correct answer: Bottom ash and fly ash
After the combustion of waste in a mass-burn waste-to-energy facility, the main solid residues that require management are bottom ash and fly ash. Bottom ash is the non-combustible material collected at the bottom of the furnace, while fly ash consists of fine particulate matter captured by air pollution control systems. Both contain concentrated contaminants and need proper disposal.
Question 7: Stabilization/solidification of hazardous waste primarily aims to:
- Increase biodegradability
- Reduce contaminant leachability (Correct answer)
- Enhance calorific value
- Decrease pH dramatically
Correct answer: Reduce contaminant leachability
Stabilization/solidification (S/S) is a treatment process for hazardous waste that aims to reduce the mobility and leachability of contaminants. This is achieved by physically encapsulating the waste or chemically reacting with it to form a more stable, less soluble matrix. The primary goal is to prevent harmful substances from leaching into the environment, making the waste safer for disposal.
Question 8: Solar evaporation ponds are MOST appropriately used to manage:
- Municipal solid waste
- Brine or saline wastewater (Correct answer)
- Household recyclables
- Biomedical sharps
Correct answer: Brine or saline wastewater
Solar evaporation ponds are shallow impoundments designed to evaporate water from liquid waste using solar energy and wind. They are most appropriately used for managing brine or saline wastewater, where the goal is to concentrate the dissolved solids for easier disposal or recovery. This method is cost-effective for large volumes of high-salinity liquids in arid regions.
Question 9: Deep‑well injection is generally permitted for which waste type?
- Radioactive waste
- Compatible non‑hazardous liquid waste (Correct answer)
- Household sharps
- Municipal solid waste
Correct answer: Compatible non‑hazardous liquid waste
Deep-well injection involves injecting liquid waste into porous rock formations deep underground, below potable water sources. This method is generally permitted for specific types of compatible non-hazardous liquid industrial wastes that are suitable for the geological formation and will not migrate to contaminate groundwater. Strict regulations govern its use to ensure environmental safety.
CPWM Waste Treatment Technologies & Disposal Methods
Which technology generates methane‑rich biogas from biodegradable waste?