The summative and formative fouling potential of industrial fermentation broth engineered to produce valuable industrial enzymes was investigated. A resistance-in-series approach was adapted to estimate the relative fouling potential of broth components at two different cross-flow conditions under high-loading scenarios. Bench-scale tests were executed in cross-flow cell modules fitted with polysulfone microfiltration (MF) membranes (0.2 mu m nominal pore size) where fermentation broth and its isolated components, i.e., bacterial cells, particle-free media, surrogate proteins, or virgin media, were separately introduced. Setting and fouling behavior were assessed in situ, using continuous ultrasonic and permeate flow observations. Fouled membranes were characterized using scanning electron microscopy (SEM) and scanning acoustic microscopy (SAM). The largest flux declines were observed when membranes were challenged with fresh industrial broth. Flux was least affected by virgin media that had been clarified by centrifugation and by a solution of washed bacterial cells. Acoustic spectra showed significant increases in reflected power immediately following broth challenges. Above a threshold of 14 mu g cm(-2), SAM showed that acoustic reflection patterns from fouled membranes were statistically different than their otherwise clean-condition counterparts. SEM observations were consistent with acoustic spectra and biochemical autopsy revealing rapid, progressive biomass build-up from dynamic conglomeration of "patchy", heterogeneous biomass deposits that are loosely anchored to the membrane surface. Results were interpreted via modeling approaches using resistance-in-series as well as combined pore-blockage and cake filtration. (C) 2009 Elsevier B.V. All rights reserved.