Physical Characteristics of sewage:

1. Turbidity
2. Color
3. Odour
4. Temperature

Chemical Characteristics of sewage:

1. Total solids , suspended solids , settleable solids
2. pH value
3. chloride content
4. nitrogen
5. presence of fats , greases and oils
6. sulphides , sulphates and H2S gas
7. dissolved oxygen
8. Chemcial Oxygen Demand (COD)
9. Bio Chemical Oxygen Demand (BOD)

Nitrogen Content : The presence of nitrogen in sewage indicates the presence of organic matter , and may occur in one or more of the following forms .

1. Free ammonia , called ammonia nitrogen
2. Albuminoid nitrogen called as organic nitrogen
3. Nitrites and
4. Nitrates

Sludge Bulking

The Biological Sludge which does not settle well and compacts poorly in the secondary settling tank , leaving a small amount of clear supernatant at the top is Bulking Sludge.
Bulking occur due to the presence of toxic substances , insufficient aeration , frequent shock loadings and excessive rate of supply of substrate.
Bulking of Sludge is controlled by a mixture of copper sulphate and lime in 1:1 ratio by weight