BAF, as well as the other fixed-film processes, is advantageous in comparison to the activated sludge systems due to higher volumetric loads, increased process stability, and compactness of the reactors, caused by higher biomass concentration and higher specific removal rates. Furthermore, organic material removal and nitrification can be carried out in a single unit.
Since the solids are entrapped into the filter, the settling phase isno more required and consequently the associated problems above described for the conventional AS process can be avoided.
The main limitation of this technology is the increase in the head losses during the operation as a result of solids accumulation within the filter and the attached biomass growth on the filter packed media which cause a progressive decrease of the bed porosity. This obliges periodic backwashing in order to maintain the headloss to a minimum.
Backwashing frequency can vary from few hours to several days depending on the operation characteristics of the filter and the biomass growth yield.
