Quantifying Activated Sludge Bulking-Causative Filamentous Bacteria Using Molecular Methods

Abstract

Filamentous bulking is a widespread problem in activated sludge wastewater treatment plants. In North Carolina, 63% of wastewater treatment plants (WWTPs) surveyed have experienced bulking. Determining the dominant bulking-causative bacteria and their level of proliferation is a necessary step in bulking control. This study used molecular techniques, i.e. quantitative Fluorescent in situ Hybridization (FISH) and membrane hybridization to identify and quantify the specific filamentous microorganisms and their threshold values for causing bulking in both lab scale reactors and full scale treatment plants. Filament length of a specific filamentous organism, Eikelboom Type 1851, correlated strongly with the sludge volume index (SVI) and was identified to be the major bulking-causative microorganism in lab scale reactors and a full scale activated sludge plant. The full scale plant is a biological nutrient removal (BNR) plant, a common operational mode in North Carolina, suggesting that this organism may be prevalent in North Carolina WWTPs. The threshold value for Eikelboom Type 1851-caused-bulking was determined. This threshold value will allow the monitoring of incremental improvements in control methods and the delineation of the niche of Eikelboom Type 1851 in activated sludge. Furthermore, the lab scale experiments verified the kinetic selection theory and the filamentous backbone theory for Type 1851.