Question

EXAMPLE 6.8 Sizing a Primary Clarifier A town of 30,000 sends 0.5 m3 of wastewater per person per day to the waste- water treatment plant. A conventional circular primary clarifier would be designed to have an average detention time of 2.0 hours and an average overtlow rate of 40 m/d, whereas a high-rate clarifier would have an average overflow rate of 1,500 m/d.

Answer 1

Given overflow rate V_0 = 40 m/day Q = 15000 m^3/day [30.000 times 0.5n^3/day] we have V_0 = Q/A_b therefore A_b = Q /V_0 = 15000 m^3/day/40 m/day therefore A_0 = 375 m^2 pi/4 d^2_b = squareroot 4 times 375/pi therefore d_b = 21.85 therefore d_b = 21.85 therefore d_b = 22m we have deletion time = volume 2 hr = A_b times D_b/625 m^3/hr D_b = 2 times 625/ (pi/4 times 22^2) therefore D_b = 3.28m therefore eltechine deply = 3.3 m of conventional clavfier = 22m times 3.3m for iigh rate clarifies, V_0 = Q/A_b A_b = Q/V_0 = 15000 m^3 blay/1500 m/day = 10 m^2 for conechenar clautier, A_b = pi/4 times 22^2 = 380.13 m^2 therefore % sames in area = 380.13 - 10/380.13 = 97.34%