A NOVEL CONTROL STRATEGY FOR IMPROVED NITROGEN REMOVAL IN AN ALTERNATING ACTIVATED-SLUDGE PROCESS .1. PROCESS ANALYSIS

Increasing demands on discharged water quality have led to the develop ment of activated sludge processes which incorporate the biologically mediated removal of nitrogen and phosphorus. A major obstacle in the d evelopment of new control strategies for such processes is the lack of variables which can effectively alter process behavior and can feasib ly be manipulated This two part paper deals with a novel means to impr ove the nitrogen removal in an alternating type nutrient removal activ ated sludge process through control of the cycle length. In this first part, an analysis of process dynamics is undertaken. Using a simple m odel to describe the nitrogen dynamics in the alternating process, the existence of an optimal cycle length as a function of process conditi ons is demonstrated and explained. A graphical technique is developed which allows quick visualization of nitrogen dynamics under constant p rocess conditions. This also serves as a means to assess whether a sel ected cycle length is optimal, too long, or too short for a given set of conditions. Based on the findings of this first part, the second pa rt of the paper develops and demonstrates control strategies which ser ve to automatically adjust the cycle length to compensate for changing process conditions.