What is the size of imhoff tank for 22 users?

Answer 1

there, first what will be the amount of water

for 22 users is almost 4,000 gallons per day, so according to an Italian manufacturer the size is, 5'-6" x 8'-3" x 7'- 3" (model IMO / O 26 @ http://www.euromec.net/public/files/IMO-94.pdf)

But also recommend before Imhoff tank a trash tank (septic) with the following dimensions (@ http://www.mtmdrains.co.uk/tankoperation.html):

13' x 6'-6" x 6'-6" (vol = 4,200 gallons) for primary treatment, so you'll reduce up to 65% solids before entering Imhoff.

Treatment level should be at best 30/30 mg/l BOD/TSS

Regards