The BIOTIM^® AF (Anaerobic Filter) process uses bacterial immobilization by means of slime films on an inert support material and the entrapment of sludge flocs within the macro-porous structure of the carrier material to retain as much of the active sludge as possible.

Especially designed carrier materials are available, usually made of polyethylene or polypropylene. They are highly voided to reduce the risk of clogging and have high specific surfaces between 100 and 200 m² per m³ carrier material.

Anaerobic filters are used whenever non-granular or non settleable sludge is expected and when available area is limited. The high biomass concentration inside the reactor allows volumetric loading rates of 5 to 10 kg COD/m³ per day. The carrier material is relatively expensive.

BIOTIM^® AF, ADM-Pfizer, Ireland