Work out backwash water volume instantly with clear inputs, formula shown and shareable results.
Backwash volume is filter area times backwash rate times duration. Rates of 30-40 m/h are needed to fluidise and expand sand media by 20-30%. Backwash water typically consumes 2-4% of plant output, and recovering it after settling is standard practice where water is scarce.
Backwash volume
Volume = filter area x backwash rate (m/h) x duration (h)
Flow rate
Flow (L/s) = area x rate x 1000 / 3600
Yes, after solids removal, but recycling concentrates pathogens and disinfection by-product precursors. Many regulators cap the recycle rate and require it to be returned upstream of all treatment barriers.
The bed does not fluidise properly, mud balls form, and the filter progressively loses capacity and allows breakthrough. Air scour combined with a lower water rate is often more effective than water alone.