Design criteria of continuously operating biological aerated filters

Biological Aerated Filter (BAF) represent a compact wastewater technology aimed at improving treatment effectiveness by contemporarily minimizing the volume of the sludge-to-water contactor. BAFs can be classified as three-phase systems as far as their hydrodynamics is concerned and make use of granulated activated carbon (GAC) as a solid support; the macro-pores of this solid immobilize the growing biomass and assure a high sludge-to wastewater flow rate ratio. Our study stars from the standard design criteria adopted for a batch unit and extends the application of BAFs to continuous systems to attain simpler operations. The new concept unit is implemented with an air-lift regulated GAC recirculation and a section for separating the sludge from GAC. The treated water is segregated from the sludge suspension thanks to a careful regulation of flow rates in the biological reactor, which has some similarities with the so-called “backwash upflow sand filter”. The experimental work, ahead of treating wastewater from textile industries, defines all the operating variables suitable to steadily maintain the contact time between the liquid and solid phases, the hold-up and recirculation time of GAC and the flow rate ratio between the cleared stream and purge liquid. The experimentation has brought to define: the geometrical features of the unit, GAC hold-up and recirculation rate, main and air lift flow rates. In this research program a 0.28 m ID, 2 m high Perspex unit is used for the hydrodynamical study and an identical geometry SS biological contactor for real industrial wastewater treatment