7) An activated sludge with a suspended solids concentration of 3000 mg/l is set

Question

7) An activated sludge with a suspended solids concentration of 3000 mg/l is settled in the secondary clarifier. The secondary sludge removed has a suspended solids concentration of 1.5%. Wastewater flows into the secondary clarifier process at the rate of 120 cubic meters per minute.

a) calculate the total volume of wastewater going into the secondary clarifier each hour.

b) Assuming that all the solids are settled, calculate the percent volume reduction that was achieved in the secondary sludge.

c) Calculate the total volume of secondary sludge that would be pumped from the secondary clarifier each hour.

d) Calculate the sludge flow rate and the clarifier effluent flow rate (in m3/min).

Explanation / Answer

Since, Wastewater flows into the secondary clarifier process at the rate of 120 cubic meters per minute.

a) So, total volume of wastewater going into the secondary clarifier each hour = 120x60

=7200 cubic metre

---------------------------------------------------------------------------------------------------------------------------------------------------------------------

b) Initail sludge = 3000 mg/l = 3 g/l

= 3 %

Sludge removed = Initial sludge in waste water - Final sludge

= 3 - 1.5

= 1.5 %

Volume reduction is due to removal of sludge

So, percentage volume reduction = 1.5 %

---------------------------------------------------------------------------------------------------------------------------

c) Total volume of secondary sludge pumped each hour = 1.5% of 7200 cubic metre

= 1.5x7200/100

= 108 cubic metre

--------------------------------------------------------------------------------------------------------------------------------------------------

d) Sludge removed in one hour = 108 cubic metre

Sludge flow rate = 108/60 cubic metre per min

= 1.8 m3/min

Clarifier effluent flow in one hour = 7200 - 108 cubic metre

= 7092 cubic metre

Clarifier effluent flow rate = 7092/60

= 118.2 m3/min

Related Questions

Navigate

• Browse (All)
• Browse 7
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.