Controlling Microthrix parvicella with Foam Control and “Ammonia-SRT”

The Bozeman Water Reclamation Facility (WRF) is a biological phosphorus and nitrogen removal system located in Bozeman, Montana. The cold-weather and spring run-off make filament control and ammonia removal a very delicate balance. This paper documents the extent of the Microthrix parvicella foaming at the Bozeman WRF and the methods used to significantly reduce this foaming. First it covers the three things done to reduce the foam trapping. The ducking skimmers were submerged to allow the foam to flow over them to the final clarifiers, where it was skimmed off. Second, the end channels that carried the flow from the first half to the second half of the folded bio-train design need ed to be aerated to raise their level to the aerated zone they discharged to. Third, two of the three flow-through windows in the partition walls were plugged to increase the hydraulic profile in the first half of the bio-trains. In conjunction with the foam trapping removal, an ammonia set point was used to safely reduce the solids retention time (SRT) of the system to a point that seems to inhibit M. parvicella foaming.