Fixed-Growth Nitrification of Secondary Effluent

A downflow submerged-bed, fixed-growth nitrification process has been successfully applied to the effluents of an activated sludge process and an independent physical-chemical treatment process. The empty-bed detention time, gas/water ratio, backwashing frequency, water temperature, supporting medium, and the ammonia limit in the nitrified effluent are identified as the major parameters for efficient process control. The relationship between the empty-bed detention time and the water temperature has been fully illustrated. Both air and industrially pure oxygen are shown to be equally effective in providing the necessary oxygen source for the biological oxidation of ammonia. The gravel is demonstrated to be superior over the sand, stone, and activated carbon as the supporting medium for the fixed-growth nitrification process. The air or oxygen is bubbled through the sparging system at the bottom of the supporting medium. The cost estimate for nitrifying 10,000,000-gal/day (37,850-m³/day) activated sludge plant effluent is shown.