By depth filtration of suspended material in effluent after treatment using contact filtration process, the total Zn and Cd concentration in the effluent discharge can be dropped to 1.

Cheap sand was used as filtration material in the biological contact oxidation filter to study the effects of fe removal under different conditions.

The concept of contact flocculation was originated from direct filtration, which refers to flocculation among suspended particles in the presence of contact media.