(5 PTS) THE SCHEMATIC DIAGRAM BELOW SHOWS PART OF A WASTEWATER TREA...

7. (5 pts) The schematic diagram below shows part of a wastewater treatment plant. The

primary settling tank removes 30% BOD and 60% suspended solids (SS) while the

biological treatment removes 90% BOD and 90% SS. The characteristics of the

wastewater are indicated at point A.

Aeration tank

V=215m

³

Secondary

• B • C • D

Primary

• A

settling tank

Q = 400 m

³

/d

BOD

5

=350 mg/l

R =30%

SS=250 mg/l

• E

SS=10,000 mg/l

Waste sludge= 7m

³

/d

A. The primary settling tank is usually designed assuming

(i) Type I settling (ii) Type II settling

(iii) Type III settling (iv) Type IV settling

B. The suspended solids (mg/l) entering the aeration tank (point B) is approximately

(i) 100 (ii) 2385 (iii) 2510 (iv) 10100

C. The expected BOD (mg/l) at point D

(i) 18-25 (ii) 28-35 (iii) zero (iv) above 35

D. What is the food-to-microorganisms ratio inside the aeration tank?

E. What is the sludge age?