CPWM Waste Treatment Technologies 3 — Questions and Answers
Question 1: In a fluidized bed combustor treating municipal solid waste, what material is typically used as the bed medium?
- Activated carbon
- Sand or limestone (Correct answer)
- Crushed glass
- Iron filings
Correct answer: Sand or limestone
Sand or limestone particles serve as the bed medium in fluidized bed combustors; limestone also helps neutralize acid gases formed during combustion.
Question 2: Which treatment technology is most appropriate for highly concentrated organic liquid hazardous wastes that are difficult to biodegrade?
- Composting
- Constructed wetlands
- High-temperature incineration (Correct answer)
- Windrow turning
Correct answer: High-temperature incineration
High-temperature incineration (>1200°C) destroys recalcitrant organic compounds through thermal oxidation, achieving destruction and removal efficiencies (DRE) of 99.99% or higher.
Question 3: What is the Destruction and Removal Efficiency (DRE) standard required by the US EPA for principal organic hazardous constituents (POHCs) in hazardous waste incinerators?
- 99.9%
- 99.99% (Correct answer)
- 99.999%
- 95%
Correct answer: 99.99%
EPA's RCRA regulations require hazardous waste incinerators to achieve a DRE of at least 99.99% (four nines) for each POHC listed in the waste feed.
Question 4: In composting, what is the ideal carbon-to-nitrogen (C:N) ratio for optimal microbial activity?
- 5:1 to 10:1
- 25:1 to 30:1 (Correct answer)
- 50:1 to 60:1
- 100:1 to 150:1
Correct answer: 25:1 to 30:1
A C:N ratio of 25:1 to 30:1 provides optimal nutrient balance for microbial decomposition; ratios below 20:1 cause nitrogen loss as ammonia, while ratios above 40:1 slow decomposition.
Question 5: Which membrane technology is most commonly used in leachate treatment at modern landfills?
- Microfiltration
- Ultrafiltration
- Reverse osmosis (Correct answer)
- Electrodialysis
Correct answer: Reverse osmosis
Reverse osmosis uses semi-permeable membranes under high pressure to remove dissolved contaminants, heavy metals, and organics from landfill leachate, achieving high removal efficiencies.
Question 6: What is the main advantage of in-vessel composting over windrow composting?
- Lower capital cost
- Better odor control and faster processing time (Correct answer)
- Higher finished compost yield
- Elimination of the need for oxygen
Correct answer: Better odor control and faster processing time
In-vessel systems enclose the composting process, providing better odor control, temperature regulation, and faster decomposition (days vs. weeks) compared to open windrow systems.
Question 7: Which regulatory standard governs air emissions from municipal waste combustors (MWCs) in the United States?
- RCRA Subtitle C
- EPA 40 CFR Part 60 Subpart Eb (Correct answer)
- TSCA Section 6
- CAA Title IV Acid Rain Program
Correct answer: EPA 40 CFR Part 60 Subpart Eb
EPA 40 CFR Part 60 Subpart Eb establishes New Source Performance Standards (NSPS) for large municipal waste combustors, setting emission limits for dioxins, mercury, particulates, and acid gases.
CPWM Waste Treatment Technologies 3
In a fluidized bed combustor treating municipal solid waste, what material is typically used as the bed medium?