The City of Berne operates a Class II, 0.683 MGD controlled discharge waste stabilization lagoon facility consisting of a 16.42-acre lagoon (#1), a final 21.15-acre lagoon (#2), two clarifiers for phosphorus removal, and UV disinfection. The facility, which operates at approximately 146% of average design capacity, received ammonia-nitrogen effluent limits in their last NPDES permit renewal on August 1, 2012. The City received funding through the Indiana Finance Authority, State Revolving Loan Program to complete their WWTP Improvements Project with construction costs of $6,830,000 and total loan costs of $7,930,000.
Commonwealth Engineers’ solution to the regulatory and hydraulic overload conditions at the plant were set forth as follows: Lagoon No. 1 was converted to partial-mix with the addition of aeration with fine bubble diffusers, which helped increase the average design flow to 1.08 MGD and peak flow to 1.92 MGD. The selected treatment system for ammonia-nitrogen removal was the Nelson Environmental OPTAER Treatment Process which incorporated the Submerged Attached Growth Reactor (SAGR) technology to provide ammonia-nitrogen removal. The system uses a clean uniform gravel bed for the nitrifying bacteria to attach and the biological process occurs as the wastewater passes through this bed. Aeration was also provided for the process through an aeration bubbling system. The SAGR technology is very operator-friendly with little to no maintenance.
The SAGR system included four 262’ x 72’ cells at approximately 9’ deep to achieve ammonia-nitrogen removal. Due to elevation constraints, the existing clarifiers were demolished and replaced with a new disc filter after the SAGR system for continued phosphorus removal. The existing effluent pump stations were also upgraded with high and low service pumps for average and peak conditions. Lagoon No. 2 was used in the winter months for additional detention time and treatment and during wet weather events that exceed 1.92 MGD to maintain flow through the SAGR system at or below the rated peak flow. Due to the increased power requirements for aeration, the project also implemented emergency standby power.