CIVL 2240: Introduction to Environmental Engineering - Water Pollution (Organic)

Types of Water Pollutants
  • Water pollutants can be categorized in various ways:
    • Pathogens
    • Organic/Inorganic substances
    • Nutrients
    • Chemical pollutants
    • Sediments
    • Radio nuclides
    • Emerging contaminants
Organic Water Pollution
  • An organic molecule is defined as any compound containing carbon, with exceptions including:
    • Carbon monoxide (CO)
    • Carbon dioxide (CO2)
    • Bicarbonate (HCO3−)
    • Carbonate (CO32−)
Biodegradation of Organic Matter
  • The process of biodegradation includes:
    • Substrate (Feed)
    • Nutrients (N, P, Fe, etc.)
    • Oxygen (O2)
    • Produces:
    • New cells
    • Carbon dioxide (CO2)
    • Water (H2O)
  • Reaction: Organic matter + O2 → CO2 + H2O + New Cells
Measuring Organic Matter

  • Biochemical Oxygen Demand (BOD):

    • Indicator for organic matter concentration.

    • Defined as the amount of oxygen utilized by microorganisms to oxidize organic matter.

    • Measured by incubating a contaminated sample with microorganisms for 5 days at 25°C, comparing initial and final dissolved oxygen.

    • Example:

    • Sample (1): 500 mg O2 drawn

    • Sample (2): 3000 mg O2 drawn

Chemical Oxygen Demand (COD)
  • Chemical Oxygen Demand (COD):
    • Measures total oxygen required to oxidize organic matter using strong oxidizing agents (e.g., potassium dichromate (K2Cr2O7), potassium permanganate (KMnO4)).
    • Generally, COD values are higher than BOD values:
    • Microorganisms may not oxidize all organic matter.
Calculating Oxygen Requirements for Oxidation

  • Four essential steps are:

    1. Write the chemical equation for the oxidation process.
    2. Balance the equation (moles for C, H, O).
    3. Convert moles to grams.
    4. Assess the mass of oxygen required per gram of organic matter.

  • General reaction:
    [ \text{Organic matter} + O2 \rightarrow CO2 + H_2O ]

  • Example Calculation (Glucose):

    • Write balanced equation: [ C6H{12}O6 + ZO2 \rightarrow XCO2 + YH2O ]
    • Balancing yields: [ C6H{12}O6 + 6O2 \rightarrow 6CO2 + 6H2O ]
    • Analysis leads to:
    • 1 mole of glucose requires 6 moles of oxygen.
    • Grams calculation (1 mole of oxygen = 32 g):
    • 6 x 32 g O2 = 192 g O2 for 180 g glucose ( \Rightarrow 1.07 \, \text{g O2/g glucose} )
Other Organic Compounds and Their COD Equivalents

  • Butyric Acid (C4H8O2):

    • Balanced: [ C4H8O2 + 5O2 \rightarrow 4CO2 + 4H2O ]
    • Calculated COD equivalent: [ 1.82 \, \text{g COD/g Butyric acid} ]

  • Glycine (C2H5O2N):

    • Balanced: [ C2H5O2N + 1.5O2 \rightarrow 2CO2 + H2O + NH_3 ]
    • Calculated COD equivalent: [ 0.64 \, \text{g COD/g Glycine} ]
Measurement of Biomass in Wastewater

  • Biomass Concentration Measurement Methods:

    • Cell number (visual count under microscope).
    • Cell mass metrics (Dry weight, Optical density/Turbidity using wavelengths of 600-700 nm).

  • Total Solids (TS):

    • Composed of:
    • Total Suspended Solids (TSS) + Total Dissolved Solids (TDS)
    • Measurement temp range: 103-105 °C.
Total Suspended Solids (TSS)
  • Types of Solids:
    • Fixed Solids (FS) post-combustion at 500 °C (indicator of inorganic matter).
    • Volatile Solids (VS) loss of mass post-combustion at 500 °C (indicator of organic matter).
COD Fractions
  • Classifications based on Size:
    • Particulate COD, Soluble COD, Colloidal COD, Semi-soluble COD.
  • Generally, Total COD = Particulate COD + Soluble COD.
  • COD can be used to estimate biomass through: [ pCOD = 1.42 \times VSS ]
Nutrients for Bacterial Growth
  • Major components of bacterial cells include:
    • Water ~75%, organic compounds 22.5%, inorganic components 2.5%.
    • Nutritional elements needed are:
    • Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, and other trace elements (Sulfur, Potassium, etc.).
Theoretical Biomass Yield from Substrates
  • Example for glucose:
    • Biomass yield from glucose calculated as:
      [ Biomass Yield = \frac{226}{540} = 0.42 \, g cell/g glucose ]
References
  • Essential readings:
    • "Introduction to Environmental Engineering and Science" by Gilbert M. Masters and Wendell P. Ela (2008).
    • "Introduction to Environmental Engineering" by Vesilind, Morgan, & Heine (2010).