Quality of Sewage | Environmental Engineering - Civil Engineering (CE) PDF Download

Aerobic Decomposition

1. Nitrogenous organic matter
   
   Nitrate
2. Carbonaceous organic matter
   
   Carbon dioxide
3. Sulphurous organic matter
   
   Sulphate

Anaerobic Decomposition

1. Nitrogenous organic matter
   
2. Carbonaceous organic matter
   
3. Sulphurous organic matter
   
4. Organic acids
   

Threshold Odour Number (TON)

V_s = The volume of the sewage
V_D = The volume of distilled water or odourless water.

Total Solids, Suspended Solids and Settleable Solids

1. 
   Where,
   S₃ = Dissolved solids plus colloidal or filterable solids in mg/lit
   S₂ = Non-filterable solids in mg/lit
   S₁ = The total amount of solids in mg/lit
   S₄ = Volatile suspended solids, in (mg/lit.)
   S₅ = Fixed solids
2. 
   
   Total Solids
   50% → Dissolved
   25% → Suspended
   25% → Settleable

Chemical Oxygen Demand

1. Biodegradable + non Biodegradable O.M.
2. K₂Cr₂O₇ + H₂SO₄ added and used is measured.

Theoretical Oxygen Demand

C₆H₆ + 7.5O₂ → 6O₂ + 3H₂O
Benzene
C₆H₁₂O₆ + 6O₂ → 6O₂ + 6H₂O
Glucose

1. 
   Where,
   Biochemical oxygen demand in ppm or mg/lit.
   Initial dissolved oxygen in mg/lit.
   Final dissolved oxygen in mg/lit.
2. 
   
   

(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.
L_t = O₂ the equivalent of organic matter present after t days.
(ii)  

Where,
k_D = Deoxygenation constant.
L = Organic matter present at t = 0
(iii)  

(iv)  

Where,
Y_t = The total amount of organic matter oxidized int days i.e. BOD.
(v)

(vi)  

Where,
Y_u = Ultimate B.O.D of  days.
(vii)  

(viii) Laboratory Estimations of k_D and L values
(Thomas Method)

Where,
m = Slope of the line
C = Intercept of the line on the y-axis.

Relative Stability (s)

Where
t₂₀ = time in days at 20^oC.
t₃₇ = time in days at 37^oC.