How do you calculate expected dry weather flow and volume of effluent to be discharged per day?
Customer Question:
How do you calculate expected dry weather flow and the volume of effluent to be discharged per day?
What is Dry Weather Flow (DWF)?
Definition:
Dry Weather Flow is the average daily sewage flow entering a sewage treatment plant or sewer, excluding any addition of surface water.Conditions for Measurement:
Measured following 7 consecutive days without rainfall, excluding holidays.
Rainfall during the preceding 7 days should not exceed 25 mm on any given day.
How to Calculate DWF:
The volume of effluent is calculated using Population Equivalents (PE).
Population Equivalent (PE):
1 PE is defined as the amount of sewage generated by one person living in a domestic dwelling.
Assumed sewage flow:
200 litres of flow/day
60 grams of BOD/day
Formula for DWF:
DWF=Population Equivalent (PE)×Flow per PE (200 L/day)\text{DWF} = \text{Population Equivalent (PE)} \times \text{Flow per PE (200 L/day)}DWF=Population Equivalent (PE)×Flow per PE (200 L/day)Example Calculation:
For a premises serving 10 PE:
10×200=2000 litres/day (2 m³/day)10 \times 200 = 2000 \, \text{litres/day (2 m³/day)}10×200=2000litres/day (2 m³/day)
Additional Information:
Worked Examples:
Detailed examples for calculating PE in various scenarios are available in our Education Blog, specifically:Contact for Queries:
For further questions or guidance, please reach out to Butler Manufacturing Services Ltd (BMS).
Our Education Blog is continuously updated with clear and helpful information about sewage treatment and related terminology.
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