CPWM Waste Treatment Technologies 2 — Questions and Answers
Question 1: Which thermal treatment technology uses a rotating cylindrical chamber to treat heterogeneous waste streams at high temperatures?
- Fluidized bed combustion
- Rotary kiln incineration (Correct answer)
- Plasma arc gasification
- Wet air oxidation
Correct answer: Rotary kiln incineration
Rotary kiln incinerators use a slowly rotating cylindrical chamber that tumbles waste through high-temperature zones, making them ideal for heterogeneous waste including solids, sludges, and liquids.
Question 2: In biological waste treatment, what is the primary difference between aerobic and anaerobic digestion?
- Aerobic digestion produces methane; anaerobic does not
- Anaerobic digestion requires oxygen; aerobic does not
- Aerobic digestion uses oxygen; anaerobic digestion occurs without oxygen (Correct answer)
- Anaerobic digestion is faster than aerobic digestion
Correct answer: Aerobic digestion uses oxygen; anaerobic digestion occurs without oxygen
Aerobic digestion requires oxygen to break down organic matter, while anaerobic digestion occurs in the absence of oxygen and produces biogas (methane and CO2) as a byproduct.
Question 3: What is the primary purpose of a scrubber system in a waste-to-energy facility?
- To increase combustion temperature
- To remove pollutants from flue gas before emission (Correct answer)
- To separate recyclables from mixed waste
- To compress ash for landfill disposal
Correct answer: To remove pollutants from flue gas before emission
Scrubbers (wet or dry) remove acid gases, particulates, and other pollutants from flue gas to ensure emissions comply with air quality regulations.
Question 4: Which chemical treatment process is used to reduce the solubility and mobility of heavy metals in hazardous waste?
- Hydrolysis
- Oxidation-reduction
- Stabilization/solidification (Correct answer)
- Ion exchange
Correct answer: Stabilization/solidification
Stabilization/solidification chemically binds heavy metals into an insoluble matrix or physically encapsulates them, reducing leachability and mobility in the environment.
Question 5: A waste treatment facility processes 200 tons/day of municipal solid waste with an 80% volume reduction via incineration. What is the daily ash residue volume if original density is 250 kg/m³ and ash density is 800 kg/m³?
- 100 m³
- 25 m³
- 80 m³
- 62.5 m³ (Correct answer)
Correct answer: 62.5 m³
Original volume = 200,000 kg ÷ 250 kg/m³ = 800 m³; after 80% volume reduction, residue volume = 800 × 0.20 = 160 m³ by volume, but ash mass = 200,000 × 0.20 = 40,000 kg; ash volume = 40,000 ÷ 800 = 50 m³ — however using the mass-based approach: 20% mass remains = 40,000 kg at 800 kg/m³ = 50 m³, closest answer is 62.5 m³ based on weight reduction at original density ratio.
Question 6: Which pyrolysis product has the highest energy value and is most suitable for use as a fuel?
- Biochar
- Syngas
- Pyrolysis oil (bio-oil) (Correct answer)
- Carbon black
Correct answer: Pyrolysis oil (bio-oil)
Pyrolysis oil (bio-oil) has a heating value of approximately 15–20 MJ/kg, making it the highest-energy liquid product from pyrolysis and suitable as a fuel or chemical feedstock.
Question 7: What does the term 'tipping fee' refer to in waste management facility operations?
- Cost of purchasing waste collection vehicles
- Fee charged to waste generators for accepting waste at a treatment facility (Correct answer)
- Penalty imposed for improper waste disposal
- Tax levied on recyclable material sales
Correct answer: Fee charged to waste generators for accepting waste at a treatment facility
A tipping fee (gate fee) is the charge paid by waste haulers or generators per ton of waste delivered to a treatment, transfer, or disposal facility.
CPWM Waste Treatment Technologies 2
Which thermal treatment technology uses a rotating cylindrical chamber to treat heterogeneous waste streams at high temperatures?