Operating Experience with Computer Control of Air Nitrification

Computer control of the air nitrification process in a 30-mgd advanced wastewater treatment plant is described. The computer system automatically starts and stops multiple centrifugal blowers, protects the blowers from surge, regulates the pressure in the air header, controls dissolved oxygen in two passes to desired setpoints, and provides minimum air flow for adequate mixing. Five months of computer control are compared to 5 months of manual control. Computer control reduced energy costs per unit loading (W/g) by about 34% with no adverse effects on the treatment process. Dissolved oxygen was closely regulated so that air flow was precisely matched to changing air demand.