FE Environmental flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Mass balance equation

Accumulation = inputs − outputs + generation − consumption. At steady state, accumulation is zero, so inputs + generation = outputs + consumption. Used to model reactors, airsheds, and watersheds.

Ideal gas law

PV = nRT, where P is absolute pressure, V is volume, n is moles, R is the universal gas constant (0.08206 L·atm/mol·K), and T is absolute temperature in kelvin.

Henry's law constant

Relates partial pressure of a gas to its dissolved concentration: p = H·x or C_air = H'·C_water. Higher H means lower water solubility; H increases with temperature.

First-order reaction

Rate = kC, integrated as C = C0·e^(−kt). Half-life t½ = ln2/k ≈ 0.693/k. Common for BOD exertion, disinfection, and radioactive decay.

Zero-order reaction

Rate = k, independent of concentration. Integrated form C = C0 − kt. Half-life t½ = C0/(2k). Often used for saturated systems such as some biological treatment.

Darcy's law

Q = K·i·A, where Q is flow, K is hydraulic conductivity, i is hydraulic gradient (Δh/ΔL), and A is cross-sectional area. Describes groundwater flow through porous media.

Reynolds number

Re = ρVD/μ = VD/ν. In pipes, Re < 2,100 is laminar, 2,100–4,000 transitional, and > 4,000 turbulent. Used to determine flow regime and friction factor.

Theoretical oxygen demand

ThOD is the oxygen required to completely oxidize a compound to CO₂, H₂O, and other end products, calculated from stoichiometry. For glucose (C₆H₁₂O₆), ThOD = 192 g O₂ per mol.

Concentration conversion ppm

In water, 1 mg/L ≈ 1 ppm (density ≈ 1 kg/L); 1 µg/L = 1 ppb. In air, 1 ppmv = 1 volume of contaminant per 10⁶ volumes of air.

BOD exertion curve

BOD exerted over time follows first-order kinetics: BOD_t = BOD_ult(1 − e^(−kt)). The rate constant k is temperature-dependent, typically 0.1–0.3 day⁻¹ at 20°C.

Settling velocity

For discrete particles in dilute suspension, Stokes' law: v_s = g(ρ_p − ρ_w)d²/(18μ). Valid for Re < 1. Used in grit chambers and sedimentation basins.

Porosity and void ratio

Porosity n = V_voids/V_total; void ratio e = V_voids/V_solids. Relationship: n = e/(1+e). Important for groundwater storage and soil transport calculations.

Dilution factor

Dilution factor = (Q_stream + Q_waste)/Q_waste. Used to estimate downstream concentration after mixing: C_down = (Q_s·C_s + Q_w·C_w)/(Q_s + Q_w).

Acid dissociation constant Ka

Ka measures acid strength; pKa = −log Ka. For weak acids, pH ≈ pKa + log([A⁻]/[HA]) (Henderson–Hasselbalch). Lower pKa means stronger acid.

Solubility product Ksp

Ksp is the equilibrium constant for dissolution of a sparingly soluble salt. For AgCl(s) ⇌ Ag⁺ + Cl⁻, Ksp = [Ag⁺][Cl⁻]. Used to predict precipitation and scaling.

Logarithmic scale pH

pH = −log[H⁺]. Each unit change represents a tenfold change in hydrogen ion concentration. Neutral water at 25°C has pH 7 and [H⁺] = 10⁻⁷ M.

Alkalinity definition

Alkalinity is the acid-neutralizing capacity of water, mainly from bicarbonate (HCO₃⁻), carbonate (CO₃²⁻), and hydroxide (OH⁻). Expressed as mg/L as CaCO₃.

Hardness

Hardness is the sum of divalent metal ions, primarily Ca²⁺ and Mg²⁺, expressed as mg/L as CaCO₃. It causes scaling and reduces soap lathering.

Hydraulic retention time

HRT = V/Q, where V is reactor volume and Q is flow rate. Also called detention time. Used to size tanks, clarifiers, and lagoons.

Hydraulic loading rate

HLR = Q/A, where Q is flow and A is surface area. Applied to clarifiers, trickling filters, and land treatment systems. Units: m³/(m²·d) or gal/(ft²·d).

Organic loading rate

OLR = (Q·S)/V, where S is substrate concentration (e.g., BOD) and V is reactor volume. Units: kg BOD/(m³·d). Used to design biological treatment systems.

Food-to-microorganism ratio

F/M = (Q·S)/(V·X), where X is biomass concentration. Low F/M favors endogenous respiration and nitrification; high F/M favors rapid growth and sludge production.

Mean cell residence time

MCRT (sludge age) = mass of solids in system / mass of solids wasted per day. Controls effluent quality and sludge production in activated sludge.

Dispersion coefficient

Longitudinal dispersion coefficient D_L = α_L·v + D_m, where α_L is dispersivity and v is seepage velocity. Used in contaminant transport modeling.

Retardation factor

R = 1 + (ρ_b/θ)·K_d, where ρ_b is bulk density, θ is porosity, and K_d is distribution coefficient. Contaminant velocity = seepage velocity / R.

Distribution coefficient Kd

Kd = C_solid/C_water at equilibrium. Higher Kd means greater sorption and slower contaminant migration. Used in retardation and fate-transport calculations.

Octanol-water partition coefficient

Kow (log Kow) measures hydrophobicity. High log Kow (>3) indicates bioaccumulation potential and sorption to organic matter. Used in environmental fate screening.

Bioconcentration factor

BCF = C_organism/C_water at steady state. Estimated from Kow: log BCF ≈ 0.76 log Kow − 0.23 for organic chemicals. Used in ecological risk assessment.

Volatilization rate

Volatilization from water to air is driven by Henry's law and mass transfer. Flux = K_L·(C_water − C_air/H'), where K_L is overall mass transfer coefficient.

Photolysis rate

Photolysis rate depends on light intensity, molar absorptivity, and quantum yield. Rate = k_p·C, where k_p is pseudo-first-order photolysis rate constant.

Hydrolysis reaction

Hydrolysis is a reaction with water that breaks chemical bonds, often pH-dependent. Rate = k_h·C, where k_h is hydrolysis rate constant. Important for pesticides and esters.

Biodegradation kinetics

Monod kinetics: μ = μ_max·S/(K_s + S). At low S, first-order; at high S, zero-order. Used to model biological treatment and natural attenuation.