A new generation of biological aerated filters

Biological filters with fixed submerged beds are normally used for secondar y or tertiary treatment and are recognized for their good performance. Thes e processes are designed to meet, simultaneously, strict requirements of qu ality and operation. The achievement of the discharge consent requires the use of fine media which features a large support surface for the growth of biomass. On the other hand, the achievement of long filter run times is int rinsically related to the use of coarse media. Nowadays, all biological fil ters have mono-media, which offers a compromise between these two conflicti ng criteria. The B2A process is a newly developed compact filter which ensures high filt ration performance and long filter run times, even when used for crude sewa ge. The technology has been in use since 1992 for nitrification/denitrifica tion using an applied load of 0.7 kg/m(3). d to obtain an effluent quality of 20 mg/l total nitrogen. Further tests have proved its efficiency in the removal of carbonaceous pollution. The B2A process is the first compact filter capable of treating screened cr ude sewage yet producing effluent qualities which are equal to that from co nventional biological filters receiving settled sewage.