CPWM Waste Treatment Technologies 5 — Questions and Answers
Question 1: What is the primary purpose of the SNCR (Selective Non-Catalytic Reduction) system in a waste-to-energy plant?
- Remove dioxins from flue gas
- Reduce NOx emissions by injecting ammonia or urea into the furnace (Correct answer)
- Capture mercury using activated carbon
- Neutralize acid gases with lime injection
Correct answer: Reduce NOx emissions by injecting ammonia or urea into the furnace
SNCR reduces nitrogen oxides (NOx) by injecting ammonia or urea into the high-temperature furnace zone (850–1100°C), where reagents react with NOx to form nitrogen gas and water without a catalyst.
Question 2: Which treatment technology converts the organic fraction of municipal solid waste into a soil amendment through controlled biological decomposition?
- Mechanical biological treatment (MBT) — dry fraction only
- Anaerobic digestion followed by composting
- Source-separated organics composting
- All of the above can produce a soil amendment (Correct answer)
Correct answer: All of the above can produce a soil amendment
All three approaches — MBT, anaerobic digestion with digestate composting, and source-separated organics composting — can produce stabilized organic soil amendments when properly designed and operated.
Question 3: Under RCRA, which treatment standard applies to hazardous debris (contaminated equipment, containers, or soil) before land disposal?
- Universal Treatment Standards (UTS) for each constituent
- Debris-specific standards allowing extraction or destruction technologies (Correct answer)
- Characteristic hazardous waste treatment levels only
- Best Demonstrated Available Technology (BDAT) for listed wastes
Correct answer: Debris-specific standards allowing extraction or destruction technologies
RCRA's debris rule (40 CFR §268.45) allows hazardous debris to meet LDR standards through extraction technologies (washing, thermal desorption) or destruction/immobilization technologies specific to debris rather than UTS concentration levels.
Question 4: What is the function of a refuse-derived fuel (RDF) system in integrated waste management?
- Convert waste gases into liquid fuels using catalysts
- Process MSW to remove non-combustibles and produce a high-energy fuel pellet or fluff (Correct answer)
- Extract biodiesel from food waste through transesterification
- Generate hydrogen gas from plastic waste through steam reforming
Correct answer: Process MSW to remove non-combustibles and produce a high-energy fuel pellet or fluff
RDF systems shred, screen, and separate MSW to remove metals, glass, and inerts, producing a combustible fraction (pellets or fluff) with higher and more consistent energy content than raw MSW.
Question 5: Which chemical oxidation reagent is most commonly used for in situ chemical oxidation (ISCO) of chlorinated solvents in groundwater?
- Sodium hypochlorite
- Potassium permanganate (Correct answer)
- Hydrogen peroxide alone (non-Fenton)
- Peracetic acid
Correct answer: Potassium permanganate
Potassium permanganate (KMnO₄) is widely used in ISCO for chlorinated solvents (PCE, TCE) due to its stability, long persistence in the subsurface, and effective oxidation of the C=C double bond.
Question 6: A biogas-to-electricity facility generates 500 m³/hour of biogas at 60% methane content. If the electrical conversion efficiency is 35% and methane's heating value is 35.8 MJ/m³, what is the electrical output in kW?
- 1,074 kW (Correct answer)
- 3,783 kW
- 6,300 kW
- 2,655 kW
Correct answer: 1,074 kW
Methane flow = 500 × 0.60 = 300 m³/hr; energy input = 300 × 35.8 MJ/m³ = 10,740 MJ/hr = 2,983 kW; electrical output = 2,983 × 0.35 ≈ 1,044 kW, closest to 1,074 kW.
Question 7: Which emerging waste treatment technology uses microwave energy to treat medical and pharmaceutical waste without generating dioxins?
- Autoclave steam sterilization
- Microwave irradiation treatment systems (Correct answer)
- Chemical disinfection with chlorine dioxide
- Dry heat sterilization
Correct answer: Microwave irradiation treatment systems
Microwave irradiation systems use electromagnetic energy to heat waste internally, achieving sterilization of infectious medical waste without the combustion byproducts (dioxins, furans) associated with incineration.
CPWM Waste Treatment Technologies 5
What is the primary purpose of the SNCR (Selective Non-Catalytic Reduction) system in a waste-to-energy plant?