Using Existing Facility to Maximize the Wet Weather Treatment Capacity of the Akron, Ohio, Water Reclamation Facility: Operating Step Feed and Improved Clarifiers to Process Peak Flow

The City of Akron, Ohio, is required to expand the peak wet-weather secondary treatment capacity of its water reclamation facility from 416,000 cubic meters per day (m3/day) to 1,060,000 m3/day, as one component of an overall combined sewer overflow abatement program. Secondary treatment train Unit 6 was modified to provide step feed capabilities. Units 5 and 6 secondary clarifiers were modified with density current baffles, larger and deeper center wells, and energy dissipating inlets in various combinations. Test results from clarifier stress tests and measurement of sludge characteristics were used to calibrate computational fluid dynamic (CFD) models. The results demonstrated that good performance could be sustained at surface overflow rates (SORs) in excess of 3 meters per hour (m/h) as long as the clarifier mixed liquor suspended solids (MLSS) concentration was controlled to below critical values. Redundancy in the system provided by step feed and possibly polymer addition are means to adjust to changing operating conditions.