Basic Wastewater Operator Practice Exam

Calculate SRT given: MLSS = 2400 mg/L, Aeration basin volume = 35,000 gallons, WAS concentration = 3500 mg/L, WAS flow rate = 0.001 MGD.

1. 6 hours

2. 6 days

3. 24 hours

4. 24 days

The correct answer is: 24 days

To calculate the Solids Retention Time (SRT), you need to use the formula: \[ SRT = \frac{(MLSS) \times (V)}{(WAS \, \text{concentration}) \times (WAS \, \text{flow rate})} \] Where: - MLSS is the Mixed Liquor Suspended Solids (2400 mg/L). - V is the volume of the aeration basin in gallons (35,000 gallons). - WAS concentration is the Waste Activated Sludge concentration (3500 mg/L). - WAS flow rate is the flow rate of the Waste Activated Sludge (0.001 MGD). First, convert the volume from gallons to liters, as the other units are in mg/L: 1 gallon = 3.78541 liters, so: \[ 35,000 \, \text{gallons} \approx 132,489.5 \, \text{liters} \] Next, calculate the SRT using the given numbers: 1. Convert the WAS flow rate from MGD to liters per day: \[ 0.001 \, \text{MGD} = 0.001 \times 3785