Tertiary Treatments

Question 1

Objective

Answer 1

remove pollutants not adequately removed by secondary treatment. Only minor removal of nitrogen, phosphorous, soluble COD and heavy metals is achieved by secondary processes. If these pollutants are of major concern, tertiary treatment should be used.

Question 2

Final Effluent

Answer 2

99% BOD5 and phosphorus, all SS, bacteria and 95% of nitrogen removed. The pollutants are removed by physical and/or chemical and/or biological treatments

Question 3

Filtration

Answer 3

The typical BOD of secondary treatment effluent is approximately 20 to 50 mg/l.
Filtration processes remove the residual SS including the unsettled bacteria.
Sand Filters/Trickling filters/Plain filtration.

Question 4

Adsorption - Objective

Answer 4

remove refractory organics (soluble organic materials resistant to biological breakdown that persist in the secondary effluent)

Question 5

Adsorption - Method

Answer 5

The soluble organic materials could be removed by adsorbing them on activated carbon (AC): organic material accumulates on the surface of the AC.

Question 6

Phosphorous Removal

Answer 6

Accomplished by chemical precipitation using one of three compounds: ferric chloride (FeCl3), aluminium sulphate (Al2(SO4)3), or lime.