Fundamentals of Engineering Exam (FE) Chemistry, Biology and Environmental Engineering Flashcards

24 sample cards from the Chemistry, Biology and Environmental Engineering deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. Define the bacterial doubling/generation time and give the growth formula.

   Generation time is the time for a population to double. Exponential growth: $$N = N_0\,2^{(t/t_d)}$$ where $t_d$ is doubling time. Equivalently $N = N_0 e^{\mu t}$ with specific growth rate $\mu$.

2. What distinguishes Gram-positive from Gram-negative bacteria?

   Gram-positive: thick peptidoglycan cell wall, retains crystal violet (stains purple). Gram-negative: thin peptidoglycan plus an outer lipopolysaccharide membrane, stains pink with safranin counterstain.

3. Define LD50 and explain its significance in toxicology.

   $\text{LD}_{50}$ is the dose lethal to 50% of a test population, usually in mg of substance per kg body weight. A lower $\text{LD}_{50}$ means higher acute toxicity.

4. Distinguish acute vs chronic toxicity and a carcinogen vs a teratogen.

   Acute toxicity: harmful effect from a single/short high exposure. Chronic toxicity: from prolonged low-level exposure. A carcinogen causes cancer; a teratogen causes birth defects in a developing fetus.

5. What is bioaccumulation versus biomagnification?

   Bioaccumulation: buildup of a substance in an individual organism over time (uptake > excretion). Biomagnification: increasing concentration of that substance at successively higher trophic levels of a food chain (e.g. mercury, DDT).

6. Define BOD and COD and how they differ.

   BOD (Biochemical Oxygen Demand): oxygen consumed by microbes degrading organics, typically measured over 5 days ($\text{BOD}_5$). COD (Chemical Oxygen Demand): oxygen equivalent to chemically oxidize all organics. COD $\geq$ BOD because COD includes non-biodegradable matter.

7. What are the primary indicators of water quality regulated for drinking water?

   Turbidity, pH, dissolved oxygen, total dissolved solids (TDS), hardness, coliform/E. coli bacteria, nitrates, and disinfection byproducts. Coliforms indicate possible fecal contamination.

8. List the conventional steps of a surface-water treatment plant in order.

   Coagulation $\to$ Flocculation $\to$ Sedimentation (clarification) $\to$ Filtration $\to$ Disinfection. Coagulation/flocculation aggregate particles; sedimentation/filtration remove them; disinfection (e.g. chlorine) kills pathogens.

9. What is water hardness and how is it commonly expressed?

   Hardness is the concentration of multivalent cations, mainly $\ce{Ca^2+}$ and $\ce{Mg^2+}$, expressed as mg/L equivalent $\ce{CaCO3}$. It causes scale and soap-scum. Removed by lime-soda softening or ion exchange.

10. Distinguish primary, secondary, and tertiary wastewater treatment.

    Primary: physical settling of solids (sedimentation). Secondary: biological removal of dissolved organics (e.g. activated sludge, trickling filter). Tertiary: advanced polishing — nutrient (N, P) removal, filtration, disinfection.

11. How does the activated sludge process work?

    Wastewater is aerated with a microbial floc that metabolizes dissolved organics. The mixed liquor passes to a clarifier where biomass settles; part is recycled (return activated sludge) to maintain the population and the rest is wasted.

12. Define the food-to-microorganism (F/M) ratio in activated sludge.

    $$\frac{F}{M} = \frac{Q\,S_0}{V\,X}$$ where $Q$ is flow, $S_0$ influent BOD, $V$ aeration volume, and $X$ MLSS concentration. It expresses the organic loading per unit biomass and controls sludge performance.

13. What is the order of the solid waste management hierarchy (most to least preferred)?

    Source reduction/prevention $\to$ Reuse $\to$ Recycling/composting $\to$ Energy recovery (incineration with heat capture) $\to$ Treatment/Landfill disposal (least preferred).

14. What is leachate and why is it a concern at landfills?

    Leachate is contaminated liquid that percolates through waste, carrying dissolved and suspended pollutants. It can contaminate groundwater, so modern landfills use liners and leachate collection systems; landfill gas (mostly $\ce{CH4}$ and $\ce{CO2}$) is also collected.

15. Name the six EPA criteria air pollutants.

    Particulate matter ($\text{PM}_{10}/\text{PM}_{2.5}$), ground-level ozone ($\ce{O3}$), carbon monoxide ($\ce{CO}$), sulfur dioxide ($\ce{SO2}$), nitrogen oxides ($\ce{NO_x}$), and lead ($\ce{Pb}$).

16. What causes acid rain and what is its chemistry?

    $\ce{SO2}$ and $\ce{NO_x}$ emissions react with water and oxygen in the atmosphere to form sulfuric and nitric acids: $$\ce{SO2 + H2O -> H2SO3},\quad \ce{2SO2 + O2 + 2H2O -> 2H2SO4}$$ lowering rain pH below ~5.6.

17. Differentiate primary and secondary air pollutants, and give the ozone example.

    Primary pollutants are emitted directly (e.g. $\ce{NO}$, $\ce{SO2}$, $\ce{CO}$). Secondary pollutants form in the atmosphere via reactions; ground-level ozone is secondary, formed photochemically from $\ce{NO_x}$ and VOCs in sunlight.

18. What air pollution control device is used for particulates versus gaseous pollutants?

    Particulates: cyclones, baghouses (fabric filters), electrostatic precipitators (ESPs). Gases: wet/dry scrubbers and absorbers (e.g. flue-gas desulfurization for $\ce{SO2}$), and catalytic converters/SCR for $\ce{NO_x}$.

19. State the general steady-state mass balance equation.

    $$\text{Accumulation} = \text{In} - \text{Out} + \text{Generation} - \text{Consumption}$$ At steady state, accumulation $= 0$, so In $+$ Generation $=$ Out $+$ Consumption.

20. Write the mass balance for a CSTR (completely mixed reactor) with first-order reaction at steady state.

    For $V\frac{dC}{dt}=QC_0 - QC - kVC = 0$: $$C = \frac{C_0}{1 + k\tau}$$ where $\tau = V/Q$ is the hydraulic residence time.

21. Give the effluent relation for an ideal plug-flow reactor (PFR) with first-order kinetics.

    $$\frac{C}{C_0} = e^{-k\tau}$$ where $\tau = V/Q$. For the same conversion of a positive-order reaction, a PFR requires less volume than a CSTR.

22. What is hydraulic (or detention) retention time and how is it calculated?

    Retention time is the average time a fluid parcel stays in a reactor or tank: $$\tau = \frac{V}{Q}$$ where $V$ is volume and $Q$ is volumetric flow rate.

23. Define a contaminant's half-life for first-order decay and the relationship to the rate constant.

    For first-order decay $C = C_0 e^{-kt}$, the half-life is $$t_{1/2} = \frac{\ln 2}{k} = \frac{0.693}{k}$$ the time for the concentration to fall to half its initial value, independent of $C_0$.

24. What is dilution, and how do you compute a mixed concentration when two streams combine?

    By conservation of mass (flow-weighted average): $$C_{mix} = \frac{Q_1 C_1 + Q_2 C_2}{Q_1 + Q_2}$$ where $Q$ are flow rates and $C$ are concentrations of each stream.

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