BIOCHEMICAL OXYGEN DEMAND Define 

Oxygen matter + bacteria + nutrients + O2  ➙ By products + CO2 + H2O + NH3

Significance of organic matter

  • Waste water contain organic matters.
  • Aerobic microbes speed on organic matter and demand oxygen.
  • More concentration of organic matter more is the dissolve oxygen require.

Water Bodies :

  • Has nutrients and microbes.
  • As aquatic life for which concentration of visual oxygen is important.

The amount of organic matters Degradate will depend on following factors

  1. Time
  2. Temperature
  3. Seeding ( microbial population )
  4. Characteristics of organic matters
  5. Toxicity
  6. Nutrients concentration
  7. Presence of nitrifying bacteria

Above factors of decrease the BOD value.

BIOCHEMICAL OXYGEN DEMAND My Nots

Where, 

  • Co = initial concentration of organic matter
  • DC = concentration of organic matter 

BIOCHEMICAL OXYGEN DEMAND My Nots

Important point : 

Rate of change of concentration is depend on the initial concentration of organic matters 

NOTE : 

  • BIOCHEMICAL OXYGEN DEMAND and CHEMICAL OXYGEN DEMAND so Biodegradable is low.
  • BOD AND COD ratio low = biodegradability low.
  • When we measure BOD and 5th day oxygen level is zero so BOD value also 0. 
  • BOD increase = sample size decrease.