Imhoff type biological tanks consist of two overlapping and hydraulically communicating compartments. In the upper compartment the sedimentable solids fall to the bottom of the sedimentation chamber by gravity. The chamber is suitably inclined to allow the sludge to pass into the lower compartment where digestion takes place.

USE: primary treatment of sewage from toilets.

REFERENCE REGULATIONS: Inter-ministerial Committee for the Protection of Waters Resolution No.48/77, Legislative Decree No.152/06, Emilia Romagna Regional Resolution No.1053/03, Umbria Regional Resolution No.1171/07, D.A.C.R. Resolution No.145/10 Marches Water Protection Plan, Decree by the President of the Independent Province of Bolzano No.6/08