A design of the following water treatment units for a town with a population of 100,000 people and a freshwater consumption rate of 200 Lpcd. The required units are: 

(1) Softening (if needed),
(2) Sedimentation: 

(3) Carbon adsorption

The sedimentation process is expected to remove 90% of all settle able material.
Disinfection is to be achieved using chlorine, where a free residual chlorine of 0.30 mg/L is needed.
A continuous carbon adsorption process is to be carried out to remove the taste and odor resulting from the presence of 30 mg/L of trichlorobenzene in the source water, which must be reduced to less than 1 mg/L. It is advisable to employ the Bohart-Adams approach for the design and analysis of the adsorption process.

The source water has the following relevant composition:

• Turbidity of 150NTU which corresponds to a TSS of about 120 mg/L,
• pH of 8.5 and an Alkalinity of about 300 mg/L as CaCO3,
• Required alum dose of 80 mg/L for proper coagulation,
• Ca-Hardness of 250 mg/L as CaCO3,
• Mg-Hardness of 100 mg/L as CaCO3
• Ammonia (NH3) of 5 mg/L,
• Ferrous iron ion of 3 mg/L
• Ionic Manganese of 2 mg/L
• Sulfide ion of 1 mg/L.

Answer rating: 100% (QA)

Calculations Softening if needed The source water has a CaHardness of 250 mgL as CaCO3 This is above ... View the full answer