CEE 202 - Environmental Engineering Midterm Theory Summary
1. Oxygen Demand
---------------- Measures how much oxygen is required to break down organic matter.
- Types:
* BOD (Biochemical Oxygen Demand): Oxygen used by microbes over 5 days.
* COD (Chemical Oxygen Demand): Oxygen needed to chemically oxidize all organics.
* THOD (Theoretical Oxygen Demand): Oxygen needed to fully oxidize a compound (via stoichiometry).
- For glucose (C6H12O6): THOD = (mg/L of glucose / 180) × 6 × 32
2. Alkalinity
------------- Capacity of water to neutralize acids (buffer against pH changes).
- Main contributors: HCO3-, CO3^2-, OH- Expressed as mg/L as CaCO3.
- Important in coagulation and softening.
- Conversion: mg/L as CaCO3 = (mg/L as ion × 50) / Equivalent Weight
3. Hardness
----------- Caused by multivalent cations (mainly Ca2+ and Mg2+).
- Types:
* Total Hardness (TH) = Ca + Mg (as CaCO3)
* Carbonate Hardness (CH) = Min(TH, Alkalinity)
* Non-Carbonate Hardness (NCH) = TH - CH
- Conversion: mg/L as CaCO3 = (mg/L as ion × 50) / EW
4. Jar Test
----------- Simulates coagulation and flocculation for water treatment.
- Procedure: add coagulant, mix, let settle, measure turbidity.
- Alum (Al2(SO4)3·12H2O):
* 1 mol = 594 g
* Consumes 6 mol HCO3- Alkalinity demand (mg/L as CaCO3) = (mg/L alum / 594) × 6 × 50
Key Notes:
- COD > BOD > THOD (typically)
- Hardness and alkalinity expressed as mg/L as CaCO3 for standardization.
- Know equivalent weights: Ca = 20, Mg = 12.15, HCO3 = 61, CO3 = 30.