Mass and Viability Estimations of Nocardia in Activated Sludge and Anaerobic Digesters Using Conventional Stains and Immunofluorescent Methods

Abstract

An immunofluorescent method was developed to estimate the quantity and viability of Nocardia filaments in activated sludge and anaerobically digested sludge on both a mass and volume basis. The Gram stain counting technique of Vega-Rodriguez (1983) and Pitt (1988) was modified to estimate the mass of Nocardia in activated sludge and compared to the immunofluorescent method. Both methods were calibrated on a pure culture of chemostat grown Nocardia amarae. Using the immunofluorescence technique, Nocardia were estimated to comprise an average of 18% by weight of the VSS in a foaming activated sludge plant. Nocardia were found to be, on average, 79% viable as judged by INT reduction staining. Nocardia were found to comprise 13% of the VSS in a foaming anaerobic digester sludge and had an average viability of 63%. These organisms were estimated to be 30 to 50% viable in a mixed anaerobic digester with a hydraulic detention time of 14 days.