Investigation into Causes of a Permeability Crisis at Large Membrane Bioreactor

The Traverse City Regional Wastewater Treatment Plant was the largest operating membrane bioreactor (MBR) in North America upon start-up in 2004. In 2011, in its seventh winter of operation, the plant experienced an upset that severely reduced permeability even while routinely tracked operational parameters remained normal. Our staff optimized operations of the membranes to maximize permeability in a difficult biology while working to identify and control root causes. Investigation revealed a proliferation of a dispersed Gram-positive-staining bacteria and zoogloea in the activated sludge, which appeared to cause the decline in permeability. This paper describes the nature of the challenge faced at the Traverse City MBR, the measures we took to maintain sufficient permeation rates during the crisis, the sequence of measures we took to understand and abate the causes, and the lessons taken from the experience.