CPWM Waste Treatment Technologies and Disposal Methods 5 — Questions and Answers
Question 1: Plasma arc gasification differs from conventional gasification primarily in that it:
- Operates at lower temperatures to preserve recyclable metals
- Uses electrically generated plasma reaching temperatures above 5,000°C to destroy virtually all waste constituents (Correct answer)
- Requires pre-sorted homogeneous feedstocks only
- Produces primarily carbon dioxide and water with no syngas
Correct answer: Uses electrically generated plasma reaching temperatures above 5,000°C to destroy virtually all waste constituents
Plasma arc gasification uses an electrically generated plasma torch at extremely high temperatures (>5,000°C) to fully decompose waste into syngas and vitrified slag.
Question 2: What is the primary advantage of anaerobic digestion over aerobic composting for organic waste treatment?
- Faster decomposition rates with shorter processing times
- Production of biogas (methane-rich) that can be used for energy recovery (Correct answer)
- Lower capital costs for facility construction
- Better pathogen destruction for all waste types
Correct answer: Production of biogas (methane-rich) that can be used for energy recovery
Anaerobic digestion generates biogas (approximately 60% methane) as a recoverable energy product, unlike aerobic composting which releases heat to the atmosphere.
Question 3: Which post-closure care requirement for Subtitle D landfills specifies the minimum duration of monitoring and maintenance obligations?
- 5 years after closure
- 10 years after closure
- 30 years after closure (Correct answer)
- Until the landfill has fully degraded with no environmental risk
Correct answer: 30 years after closure
EPA Subtitle D regulations require a minimum 30-year post-closure care period, though regulators may adjust this period based on site-specific conditions.
Question 4: Selective catalytic reduction (SCR) in waste-to-energy facilities is used to control emissions of:
- Mercury and dioxins
- Nitrogen oxides (NOₓ) (Correct answer)
- Hydrogen chloride and sulfur dioxide
- Particulate matter and heavy metals
Correct answer: Nitrogen oxides (NOₓ)
SCR systems inject ammonia or urea into flue gas over a catalyst bed to convert nitrogen oxides to harmless nitrogen gas and water.
Question 5: Which waste treatment technology is classified as 'thermal desorption' and how does it work?
- Burning contaminated soil at temperatures above 1,200°C to destroy organic contaminants
- Heating contaminated soil or waste to volatilize contaminants for separate capture and treatment without destroying the soil matrix (Correct answer)
- Applying radiant heat to sterilize medical waste in sealed containers
- Using steam injection to drive contaminants deeper into soil for immobilization
Correct answer: Heating contaminated soil or waste to volatilize contaminants for separate capture and treatment without destroying the soil matrix
Thermal desorption heats contaminated media to volatilize organic contaminants which are then captured and treated separately, leaving the soil matrix largely intact.
Question 6: Under RCRA, what constitutes a 'contained-in' determination for contaminated environmental media such as soil and groundwater?
- A finding that the media is located within a permitted containment structure
- A regulatory agency determination that contaminated media no longer contains a listed hazardous waste and is exempt from hazardous waste regulations (Correct answer)
- A laboratory certification that contaminant levels are below detection limits
- A finding that the media is surrounded by a physical barrier preventing migration
Correct answer: A regulatory agency determination that contaminated media no longer contains a listed hazardous waste and is exempt from hazardous waste regulations
A 'contained-in' determination is a state or EPA finding that contaminated soil or groundwater no longer contains listed hazardous waste, allowing management under non-hazardous waste rules.
Question 7: When evaluating disposal alternatives for low-level radioactive waste (LLRW) mixed with hazardous waste (mixed waste), the applicable regulatory framework requires compliance with:
- RCRA only, since RCRA supersedes nuclear regulations for land disposal
- Both RCRA hazardous waste requirements and the Atomic Energy Act/NRC regulations simultaneously (Correct answer)
- Only NRC regulations because radioactivity overrides RCRA classification
- State solid waste regulations exclusively under Subtitle D
Correct answer: Both RCRA hazardous waste requirements and the Atomic Energy Act/NRC regulations simultaneously
Mixed waste containing both hazardous waste characteristics and radioactivity is subject to dual regulation under both RCRA and the Atomic Energy Act/NRC, requiring compliance with both simultaneously.
CPWM Waste Treatment Technologies and Disposal Methods 5
Plasma arc gasification differs from conventional gasification primarily in that it: