The City of Akron, Ohio must expand the secondary treatment capacity of its Water Reclamation Facility from 416,000 m 3 /day (110 mgd) to 644,000 m 3 /day (170 mgd) as one component of an overall combined sewer overflow abatement program. Preliminary process analysis indicated that providing step-feed modifications to the aeration basins and modifications to the shallow secondary clarifiers could significantly increase the wet weather secondary treatment capacity. Secondary treatment train Unit 6 was modified to provide step-feed capabilities, and its secondary clarifiers were modified with baffles, improved center wells, and energy dissipating inlets in various combinations. Testing of the upgraded clarifiers along with actual wet weather events indicates the increase in capacity to 492,000 m 3 /day (130 mgd) required with only the modified Unit 6 was achieved, subject to final stress testing and a report on revising the Water Reclamation Facility's control measures. Higher capacities may be possible.KEYWORDS: wet weather treatment, secondary clarifiers, computational fluid dynamics, step feed
INTRODUCTIONThe City of Akron, Ohio, owns and operates a Water Reclamation Facility (WRF) with a preliminary treatment firm capacity of 795,000 m 3 /day (210 mgd), a primary treatment firm capacity of 568,000 m 3 /day (150 mgd), and a biological treatment firm capacity of 416,000 m 3 /day (110 mgd). Combined sewers form part of the City's wastewater collection system. As one component of an overall combined sewer overflow (CSO) abatement program, the City must expand the conventional secondary treatment capacity of its WRF to 644,000 m 3 /day (170 mgd) and install BIOACTIFLO™ at a capacity of 416,000 m 3 /day (110 mgd). The existing activated sludge system consists of six parallel and independent activated sludge trains (Units 1 through 6), each consisting of one four-pass plug flow activated sludge basin and three secondary clarifiers 30.5 m (100 feet) in diameter. The system treats the dry weather flow, which ranges from 151,000 to 303,000 m 3 /day (40 to 80 mgd), and a peak wet weather flow of 416,500 m 3 /day (110 mgd). All flows between 416,000 m 3 /day (110 mgd) and 568,000 m 3 /day (150 mgd) receive primary equivalent treatment before discharge.