Question

Using the following assumptions, determine the sludge age, cell wastage flow rate, and return sludge flow rate for the Turkey Run WWTP. Assume: - X=1500mg/L - S 0

​
=130mg/L - Four (4) Aeration tanks (Each dimension: 7.0 m W×32.0 m L×4mH ) - Q=0.135 m 3
/s - Suspended solids in the effluent are negligible. - Bacterial decay rate =0.040 day-1 - Yield coefficient =0.40 - Effluent BOD 5
​
=5.0mg/L (soluble) - Return sludge concentration =9130mg/L - Up to first decimal points, do now include unit in your answer. a) HRT= days b) SRT= days c) Qw= m 3
/d d) Qr= m 3
/d

Answer 1

To determine the sludge age, calculate the Hydraulic Retention Time (HRT) and the Solids Retention Time (SRT). HRT is approximately 7.36 hours and SRT is approximately 12.8 years. The waste flow rate is 0.273 m³/s and the sludge recirculation flow rate is 2493.3 m³/d.

Step-by-step explanation:

To determine the sludge age, we need to calculate the Hydraulic Retention Time (HRT) and the Solids Retention Time (SRT).

(a) HRT = Volume of Aeration Tanks / Influent Flow Rate. Since there are four tanks, the total volume is (7m x 32m x 4m) x 4 = 3584 m³. Therefore, HRT = 3584 m³ / 0.135 m³/s = 26523.7 seconds or approximately 7.36 hours.

(b) SRT = Sludge Age = X / (μ - kd). Where X is the mixed liquor suspended solids (MLSS) concentration and the term (μ - kd) is the net growth rate of microorganisms. Given X = 1500 mg/L, kd = 0.040 day⁻¹, and μ = Yield coefficient x BOD₅ removal efficiency = 0.40 x 1 (since all BOD₅ is being removed), SRT = 1500 mg/L / (0.40 - 0.040 day⁻¹) = 4687.5 days or approximately 12.8 years.

(c) Qw = Waste Flow Rate = Influent Flow Rate - Effluent Flow Rate = 0.135 m³/s - (0.005 m³/s x 130 mg/L / 5 mg/L) = 0.273 m³/s.

(d) Qr = Sludge Recirculation Flow Rate = Xr x Qw = 9130 mg/L x 0.273 m³/s = 2493.3 m³/d.