Customer Question: How do you calculate expected dry weather flow and Volume of effluent to be discharged per day?

Dry Weather Flow is in essence the sewage flow, from a premises without the addition of any surface water.

Dry Weather Flow (DWF) Full Definition: The average daily sewage flow entering a Sewage Treatment Plant or sewer measured following 7 days without rain (excluding local or Bank holidays etc) and during which on the preceding 7 days, rainfall did not exceed 25 mm on any day.

The volume of effluent is usually calculated using population equivalents (PE) 1 PE is the amount of sewage generated by one person living in a domestic dwelling and is generally taken as 200 L of flow and 60 g of BOD/day.  Therefore, the DWF for a 10 PE premises would be:

10 x 200 L = 2000 L.

Full worked examples of how to calculate PE in different situations can be found in our Education Blog in Sewage Parameters 3: Population Equivalent (PE) Parts 1 & Population Equivalents (PE) Part 2.  If you have any further questions please do not hesitate to contact Butler Manufacturing Services Ltd (BMS)  We will be continuing to be update our education blog with helpful straightforward information on sewage treatment and the terminology surrounding it.

A bit about BMS

BMS is a quality manufacturer of package products for wastewater and stormwater treatment. BMS started in 1986 and has exported products to over 50 countries around the world.  It is a third generation family business with huge expertise in wastewater and stormwater.
BMS also manufacture a full range of products for surface water and wastewater treatment including our pioneering next generation RBC system the Aerotor, which forms part of our world leading Blivet package sewage treatment plant, a ‘one stop shop’ for all surface water products from design to installation including attenuation, interceptors, holding tanks (incl. chemical resistant), hydrobrakes, rainwater harvesting tanks & vortex silt/oil/debris separators, fully fitted pumping stations, our plug & play vehicle wash water recycling system; the Recyclone and much more.  Please see our enclosed Company & Product Profile for a full summary or View our full product/services catalogue at this link

BMS also can provide a Free Design Service for Sewage Treatment, Pump Stations or Surface Water and a full O&M, Repair, Advice and Testing service for existing installations.  We also can do free CPD Presentations on Sewage Treatment/Surface Water Management at any location.  Let us know when suits.

We would be delighted to discuss any requirements you might have, and we are available to meet you at your convenience.  Please do not hesitate to contact us.