BIOFILM START-UP AND CONTROL IN AERATED BIOFILTER

Bacterial colonization of an aerobic fixed bed reactor was studied as a function of reactor height and time. The amount of fixed biomass, its activity and the influence of periodic backwashing was measured. Rapid colonization was achieved during the first five days of pilot operation. A decreasing gradient of biomass from top to bottom of the reactor was observed. This zoning tended to disappear with time. Backwashing operation permitted the removal of 30 % of the fixed biomass, without affecting wastewater treatment efficiency. Removal rates remained stable with time and reached 90 % for total COD, from which 60 to 70 % was obtained in the first part of the reactor.