A Sustainable BNR Solution Combines EBPR With Struvite Recovery to Reduce Cost and Energy and Increase Reliability

This paper evaluates alternatives investigated to reduce chemical addition at a water reclamation facility with anaerobic digestion recycle streams. The alternatives evaluated were: 1. the MLE process with alum addition for P removal and denitrifying filters for N removal (MLE alternative), and 2. the 5-stage Bardenpho alternative process of biological phosphorus removal, activated sludge biological denitrification using methanol addition, and the Ostara struviterecovery recycles treatment (Bardenpho alternative). The Bardenpho alternative resulted in annual cost operational savings of 640,000–770,000 compared to MLE alternative under present load conditions and 700,000–800,000 under future load conditions. Reduced chemical and electrical energy consumption and increase net digester methane gas production are other major benefits. The cost of a 5-stage Bardenpho conversion was estimated at 6.1 million. The cost of the Ostara facility was estimated at 5.1 million at present load conditions, with an additional 1.4 million at future load conditions. Process performance would significantly increase: the 14 percent reduction in future average MLSS concentration would reduce the secondary clarifiers load and increase process stability; the effluent total phosphorus concentration would be reduced from about 0.9 mg/L to about 0.4 to 0.5 mg/L. In addition, since the filters would need to remove only about 1.9 to 3.1 mg/L nitrate under the Bardenpho alternative, compared to about 7.4 to 7.7 mg/L under the MLE alternative, this would significantly reduce the risk of methanol or nitrate effluent breakthrough.