Nearly 25 years ago, the consulting engineering firm Banner & Associate, Inc. designed an efficient wastewater treatment facility for the city of Madison, S.D., that featured process control, flexibility and treatment efficiency while minimizing operating and maintenance costs. Key to the system was the aspirator aeration system that supplied reliable oxygenation and mixing to the oxidation ditch.
After decades of service, the aerators will be retrofitted this spring with an advanced process aerator/mixer system that will be able to provide “more for less” to the city’s next generation. The advanced Aire-O2 Triton process aerator/mixer system, manufactured by Aeration Industries International, Inc. , has the unique ability to mix and aerate independently to facilitate biological nutrient removal. Fewer units are required to meet permit, which translates into increased energy savings.
The wastewater treatment facility was constructed in 1984. Wastewater entering the plant is 70% municipal and 30% commercial/industrial. The plant’s average flow is 1.07 million gal per day (mgd), and the system’s design peak day flow is 4.04 mgd.
Current average influent characteristics are 139 mg/L BOD5 and 137 mg/L TSS. Following pretreatment and primary treatment, the wastewater flows into an oxidation ditch for secondary treatment. The oval-shaped ditch is 123 ft long with a 20-ft channel width and 9-ft depth. Effluent meets or exceeds 10 mg/L BOD and is discharged by infiltration percolation.