Enhanced nutrient removal by limiting dissolved oxygen concentration in a continuously fed, intermittently decanted, activated sludge plant

A large scale pilot treatment system has been used to study the effect of limiting the dissolved oxygen concentration on phosphorus removal, and the effect of different solids retention time (SRT) on nitrogen removal in continuously fed and intermittently decanted (CFID) activated sludge system. A basic operations schedule for biochemical oxygen demand (BOD) removal was employed in the study. The objective of the study was to develop operating data and to establish and verify that operational conditions conducive to enhanced nutrient removal can be maintained. It was established that simultaneous nitrification, denitrification and phosphorus uptake occur during the react phase. Nitrogen removal was enhanced by increasing SRT under normal operating conditions, nearly complete nitrification with a total nitrogen removal of 70 percent took place in the reactor operating at an SRT of 20 days. Phosphorus removal was improved by limiting the dissolved oxygen (DO) concentration during the aeration phase. Total phosphorus content in the reactor increases over time unless a phosphorus removal strategy is implemented.