Air Quality and Solid Waste Management for the FE Exam
Beyond water and wastewater treatment, the FE exam tests environmental engineering concepts related to air quality and solid waste management. These topics are particularly important for the FE Environmental exam but also appear on the FE Civil exam.
Air Quality Fundamentals
Major Air Pollutants
The EPA regulates six criteria air pollutants under the National Ambient Air Quality Standards (NAAQS):
- Particulate matter (PM10 and PM2.5): Solid or liquid particles suspended in air. PM2.5 (particles smaller than 2.5 micrometers) is especially harmful as it penetrates deep into the lungs.
- Ozone (O3): A secondary pollutant formed by reactions between NOx and volatile organic compounds (VOCs) in sunlight. Ground-level ozone is the primary component of smog.
- Carbon monoxide (CO): Formed by incomplete combustion. Colorless and odorless. Binds to hemoglobin, reducing oxygen delivery.
- Nitrogen dioxide (NO2): Formed during high-temperature combustion. Contributes to acid rain and ozone formation.
- Sulfur dioxide (SO2): Primarily from burning fossil fuels containing sulfur. Causes acid rain and respiratory problems.
- Lead (Pb): From industrial processes and historically from leaded gasoline. Neurotoxin, especially harmful to children.
Air Pollutant Concentration Units
- Mass concentration: micrograms per cubic meter (ug/m^3). Used for particulate matter.
- Volume mixing ratio: Parts per million (ppm) or parts per billion (ppb). Used for gaseous pollutants.
- Conversion: ppm = (ug/m^3) * 24.45 / M, where M is molecular weight and 24.45 is the molar volume at 25 degrees C and 1 atm.
Atmospheric Dispersion
The Gaussian plume model estimates pollutant concentrations downwind of a source:
- The plume is carried by wind in the downwind direction
- It spreads horizontally and vertically following Gaussian (bell-curve) distributions
- Dispersion depends on atmospheric stability (stable, neutral, unstable conditions)
- Unstable conditions (sunny, light winds) produce more mixing and lower ground-level concentrations close to the source
- Stable conditions (clear nights, temperature inversions) suppress mixing and can cause high concentrations
Air Pollution Control Technologies
- Particulate control: Cyclones (inertial separation), electrostatic precipitators (electrical charging), baghouses (fabric filtration), wet scrubbers (water contact)
- Gaseous pollutant control: Absorption (scrubbing with liquid), adsorption (activated carbon), catalytic conversion, thermal oxidation
- NOx control: Selective catalytic reduction (SCR), selective noncatalytic reduction (SNCR), low-NOx burners
- SO2 control: Flue gas desulfurization (FGD), commonly using lime or limestone scrubbing
Solid Waste Management
Municipal Solid Waste (MSW)
MSW includes household, commercial, and institutional waste. Key management strategies follow the waste management hierarchy:
- Source reduction: Reducing waste generation at the source (most preferred)
- Recycling and composting: Recovering materials for reuse or biological processing
- Energy recovery: Incineration with energy capture (waste-to-energy)
- Landfilling: Engineered disposal in sanitary landfills (least preferred but often necessary)
Sanitary Landfill Design
Modern sanitary landfills are engineered containment systems designed to protect human health and the environment:
- Liner system: Prevents leachate from contaminating groundwater. Typically includes a compacted clay liner overlain by a geomembrane (synthetic liner).
- Leachate collection system: Drainage layers and pipes that collect liquid that percolates through the waste. Leachate is treated before discharge.
- Gas collection system: Captures methane and other gases produced by decomposing organic waste. Gas can be flared or used for energy recovery.
- Final cover: After closure, a multi-layer cover system prevents water infiltration and controls gas emissions.
- Monitoring: Groundwater monitoring wells detect any contamination from the landfill.
Landfill Gas
Decomposing organic waste in a landfill produces landfill gas, primarily methane (50 to 60%) and carbon dioxide (40 to 50%). Methane is a potent greenhouse gas and a fire/explosion hazard. Large landfills are required to collect and control landfill gas.
Hazardous Waste
Hazardous waste is waste that poses a threat to human health or the environment due to its toxicity, ignitability, corrosivity, or reactivity.
- RCRA (Resource Conservation and Recovery Act): Regulates hazardous waste from "cradle to grave" (generation, transportation, treatment, storage, and disposal).
- Listed wastes: Wastes specifically listed in RCRA regulations as hazardous.
- Characteristic wastes: Wastes that exhibit one or more hazardous characteristics (ignitability, corrosivity, reactivity, toxicity as measured by the Toxicity Characteristic Leaching Procedure, or TCLP).
CERCLA (Superfund)
CERCLA governs the cleanup of contaminated sites. Key elements include:
- National Priorities List (NPL): A list of the most contaminated sites in the country that are prioritized for cleanup.
- Remedial investigation/feasibility study (RI/FS): Characterizes contamination and evaluates cleanup alternatives.
- Record of Decision (ROD): Documents the selected cleanup remedy.
- Potentially Responsible Parties (PRPs): Parties liable for cleanup costs, including current owners, past owners, generators, and transporters.
Noise Pollution
Sound is measured in decibels (dB). Key concepts:
- The decibel scale is logarithmic: a 10 dB increase represents a tenfold increase in sound intensity
- Sound levels from multiple sources do not add arithmetically; use: L_total = 10 * log10(10^(L1/10) + 10^(L2/10) + ...)
- Sound decreases with distance from a point source: for every doubling of distance, the sound level decreases by approximately 6 dB
Environmental engineering questions span a wide range of topics. Focus on understanding the fundamental principles (mass balance, kinetics, the waste hierarchy) and knowing the key regulations and their purposes.