Environmental Engineering for the FE Exam
Environmental engineering topics on the FE Civil exam cover water and wastewater treatment, water quality, and environmental regulations. These questions test your understanding of treatment processes and your ability to apply mass balance and kinetic equations to environmental systems.
Water Quality Parameters
Understanding key water quality parameters is the foundation of environmental engineering:
- Biochemical Oxygen Demand (BOD): The amount of dissolved oxygen consumed by microorganisms to decompose organic matter. Measured over 5 days (BOD5) at 20 degrees C. Higher BOD indicates more organic pollution.
- Chemical Oxygen Demand (COD): The total amount of oxygen required to oxidize all organic matter (both biodegradable and non-biodegradable) using a strong chemical oxidant.
- Dissolved Oxygen (DO): The concentration of oxygen dissolved in water. Essential for aquatic life. Saturation depends on temperature and pressure.
- Total Suspended Solids (TSS): Solid particles suspended in water that can be removed by filtration.
- pH: Measure of hydrogen ion concentration. Most natural waters have pH between 6.5 and 8.5.
- Turbidity: Measure of water cloudiness caused by suspended particles.
- Coliform bacteria: Indicator organisms for fecal contamination. Measured as most probable number (MPN) or colony forming units (CFU) per 100 mL.
Water Treatment Processes
Drinking water treatment typically follows this sequence:
Coagulation and Flocculation
Chemical coagulants (typically aluminum sulfate or ferric chloride) are added to destabilize colloidal particles. Gentle mixing (flocculation) promotes particle aggregation into larger flocs that can be removed by settling.
Sedimentation
Flocculated water flows into sedimentation basins where gravity settles the flocs. Design parameters include:
- Surface overflow rate: Q/A (flow rate divided by surface area), typically 600 to 1,200 gal/day/ft^2 for conventional treatment.
- Detention time: Volume/Q, typically 2 to 4 hours.
- Settling velocity: Particles with settling velocity greater than the overflow rate will be removed.
Filtration
After sedimentation, water passes through granular media filters (sand, anthracite, or dual media) to remove remaining suspended particles. Filtration is essential for removing pathogens and achieving low turbidity levels.
Disinfection
Disinfection kills or inactivates pathogenic microorganisms. Common methods:
- Chlorination: Most common method. Residual chlorine provides ongoing protection in the distribution system.
- UV disinfection: Effective against Cryptosporidium and Giardia. No residual.
- Ozonation: Powerful oxidant. No residual.
The CT concept (concentration times contact time) is used to determine disinfection effectiveness. Required CT values depend on the target pathogen and the disinfectant used.
Wastewater Treatment
Primary Treatment
Physical processes to remove settleable solids and floating material:
- Screening: Removes large debris
- Grit removal: Removes sand and gravel
- Primary clarification: Settles suspended solids (typically removes 50 to 65% of TSS and 25 to 40% of BOD)
Secondary Treatment
Biological processes to remove dissolved organic matter:
- Activated sludge: Aerobic biological process using a mixed culture of microorganisms. Design parameters include food-to-microorganism ratio (F/M), sludge age (SRT), and mixed liquor suspended solids (MLSS).
- Trickling filters: Wastewater trickles over a bed of media covered with microbial biofilm. Simpler operation than activated sludge.
- Rotating biological contactors: Rotating discs partially submerged in wastewater support biofilm growth.
Tertiary Treatment
Advanced processes for additional pollutant removal:
- Nutrient removal (nitrogen and phosphorus)
- Filtration for additional TSS removal
- Advanced oxidation
- Membrane filtration
Mass Balance
Mass balance is the fundamental tool for analyzing environmental systems:
Accumulation = Inputs - Outputs + Generation - Consumption
For steady-state systems (no accumulation): Inputs + Generation = Outputs + Consumption
Apply mass balance to:
- Mixing problems (dilution of pollutants)
- Reactor design (CSTR and plug flow reactors)
- Sedimentation basin design
- Activated sludge system design
First-Order Kinetics
Many environmental reactions follow first-order kinetics:
C(t) = C_0 * e^(-k*t)
Where C_0 is the initial concentration, k is the rate constant, and t is time. BOD decay and disinfection kinetics often follow this model.
BOD Kinetics
BOD exertion follows first-order kinetics:
BOD_t = L_0 * (1 - e^(-k*t))
Where L_0 is the ultimate BOD and k is the BOD rate constant. BOD5 (the standard 5-day BOD) is the most commonly reported value.
Environmental Regulations
Key regulations to know for the FE exam:
- Clean Water Act: Regulates discharge of pollutants to surface waters. Establishes the NPDES permit system.
- Safe Drinking Water Act: Sets maximum contaminant levels (MCLs) for drinking water.
- CERCLA (Superfund): Governs cleanup of contaminated sites.
- RCRA: Regulates hazardous waste from generation through disposal.
Environmental engineering questions on the FE exam are very manageable with an understanding of treatment processes, mass balance, and first-order kinetics. These concepts are interconnected and build on each other logically.