Environmental Engineering - Wastewater Characteristics Complete Study Notes

Characteristics of Sewage

Aerobic Decomposition

(i) Nitrogenous organic matter

 Nitrate

(ii) Carbonaceous organic matter

 Carbon dioxide

(iii) Sulphurous organic matter

 Sulphate

Nitrogen Cycle under Aerobic Decomposition

Anaerobic Decomposition

(i) Nitrogenous organic matter

(ii) Carbonaceous organic matter

(iii) Sulphurous organic matter

(iv) Organic acids

Threshold Odour Number (TON)

  The volume of the sewage

 The volume of distilled water or odourless water.

Total Solids, Suspended Solids and Settleable Solids

(i)  

 Where,

 Dissolved solids plus colloidal or filterable solids in mg/lit

 Non-filterable solids in mg/lit

 The total amount of solids in mg/lit

 Volatile suspended solids, in (mg/lit.)

 Fixed solids

(ii)  

Total Solids

50% → Dissolved

25% → Suspended

25% → Settlable

Chemical Oxygen Demand

 (i) Biodegradable + non Biodegrable O.M.

 (ii)  added and used is measured.

Theoretical Oxygen Demand

 Benzene

 Glucose

Biochemical Oxygen Demand

 Where,

Biochemical oxygen demand in ppm or mg/lit.

Initial dissolved oxygen in mg/lit.

Final dissolved oxygen in mg/lit.

(i)  

 Where,

k = Rate constant signifying the rate of oxidation of organic matter and it depends upon the nature of organic matter and temperature. Its unit is per day.

   the equivalent of organic matter present after t days.

(ii)  

 Where,

  Deoxygenation constant.

  Organic matter present at  

(iii)  

(iv)  

 Where,

 The total amount of organic matter oxidized int days i.e. BOD.

(v)

(vi)

 Where,

  Ultimate B.O.D of  days.

(vii)  

(viii) Laboratory Estimations of  and L values

 (Thomas Method)

 Where,

 m = Slope of the line

 C = Intercept of the line on the y-axis.

Relative Stability (s)

 Where time in days at 20^oC.

  time in days at 37^oC.

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