CPWM Waste Treatment Technologies 4 — Questions and Answers
Question 1: What is the primary mechanism by which plasma arc gasification converts waste into syngas?
- Biological fermentation at high temperatures
- Electrical plasma reaching 3,000–10,000°C that dissociates molecular bonds (Correct answer)
- Catalytic cracking similar to petroleum refining
- Steam reforming under moderate pressure
Correct answer: Electrical plasma reaching 3,000–10,000°C that dissociates molecular bonds
Plasma arc gasification uses electrically generated plasma at extremely high temperatures (3,000–10,000°C) to break all molecular bonds, converting organic matter to syngas (H₂ + CO) and vitrifying inorganic materials into slag.
Question 2: In hazardous waste treatment, what is 'land disposal restrictions' (LDR) treatment designed to accomplish?
- Maximize waste volume before landfilling
- Ensure hazardous waste meets treatment standards before land disposal (Correct answer)
- Classify waste for transportation manifests
- Determine the appropriate landfill liner system
Correct answer: Ensure hazardous waste meets treatment standards before land disposal
LDR regulations under RCRA require hazardous waste to be treated to specific standards that reduce toxicity or mobility before it can be land disposed, preventing future contamination.
Question 3: Which biological treatment process is most effective for treating petroleum-contaminated soil in situ?
- Phytoremediation using deep-rooted trees
- Bioventing with forced air injection to stimulate indigenous microbes (Correct answer)
- Chemical oxidation with permanganate
- Thermal desorption
Correct answer: Bioventing with forced air injection to stimulate indigenous microbes
Bioventing injects air into the vadose zone to stimulate indigenous aerobic microorganisms that naturally degrade petroleum hydrocarbons, making it cost-effective for in situ treatment.
Question 4: A waste treatment facility reports a heat recovery efficiency of 65% from an incinerator processing waste with a heating value of 10 MJ/kg at 100 tons/day. What is the daily energy recovered in GJ?
- 650 GJ (Correct answer)
- 1,000 GJ
- 6,500 GJ
- 1,538 GJ
Correct answer: 650 GJ
Daily energy input = 100,000 kg × 10 MJ/kg = 1,000,000 MJ = 1,000 GJ; recovered energy = 1,000 GJ × 0.65 = 650 GJ.
Question 5: What distinguishes supercritical water oxidation (SCWO) from conventional wet air oxidation (WAO)?
- SCWO operates below water's boiling point; WAO operates above it
- SCWO operates above water's critical point (374°C, 218 atm) achieving complete oxidation; WAO operates at lower conditions (Correct answer)
- WAO requires pure oxygen injection; SCWO uses air only
- SCWO is a biological process; WAO is purely chemical
Correct answer: SCWO operates above water's critical point (374°C, 218 atm) achieving complete oxidation; WAO operates at lower conditions
SCWO operates above water's critical point where water becomes a supercritical fluid that is miscible with oxygen and organic compounds, achieving near-complete destruction (>99.99%) versus the partial oxidation of conventional WAO.
Question 6: Which air pollution control device is specifically designed to remove fine particulates (PM2.5) from incinerator flue gas using electrostatic charge?
- Cyclone separator
- Electrostatic precipitator (ESP) (Correct answer)
- Venturi scrubber
- Fabric filter baghouse
Correct answer: Electrostatic precipitator (ESP)
Electrostatic precipitators charge particles using high-voltage electrodes and collect them on oppositely charged collection plates, effectively removing fine PM2.5 particles from flue gas streams.
Question 7: In anaerobic digestion, which operational parameter most directly affects the methane content of the produced biogas?
- pH of the feedstock
- Volatile solids (VS) loading rate
- Temperature (mesophilic vs. thermophilic) (Correct answer)
- Hydraulic retention time (HRT)
Correct answer: Temperature (mesophilic vs. thermophilic)
Operating temperature regime (mesophilic ~35°C vs. thermophilic ~55°C) most directly affects microbial community composition, reaction rates, and biogas quality, with thermophilic digestion generally producing higher methane yields.
CPWM Waste Treatment Technologies 4
What is the primary mechanism by which plasma arc gasification converts waste into syngas?