Establishing a functional biological community for wastewater treatment is essential when starting a new plant. Monitoring the growing biology during a startup provides the insight plant staff need to adjust operations to achieve a high treatment efficiency. Settleometer testing of aeration basin effluent in activated sludge processes can indicate whether the biomass will settle properly or cause bulking in the system. From evaluation of settleometer readings and facility mixed liquor suspended solids (MLSS) concentrations, operators can calculate sludge volume index (SVI) values that describe biomass settleability. SVI values are variable in activated sludge systems, but Jenkins et al. (2003) found that sludge bulking occurs at SVI numbers greater than 150 ml/g.1 The following case study outlines the startup of a 1 MGD integrated fixed-film activated sludge (IFAS) process using ProBiotic Scrubber® II (PBII) as seed.