Ergosterol determination in activated sludge and its application as a biochemical marker for monitoring fungal biomass

Abstract

Establishment of a routine fungal biomass monitoring program in activated sludge wastewater treatment plants (ASWTP) is of the utmost importance because it provides the bility to predict fungal infestations before they affect clarifier performance (bulking sludge). Ergosterol, a major fungal steroid, has been successfully used to determine fungal biomass in many different environments; this study sought to determine its efficacy for ASWTP. Ergosterol analysis was performed by high performance liquid chromatography. Initially, pure cultures of Geotrichum candidum were used because this organism was implicated in past clarifier problems. During a 62-h batch culture, ergosterol concentrations were found to be in direct proportion with both optical density and dry weight measurements; correlation coefficients of r = 0.95 and r= 0.99 were obtained, respectively. A mean value of 2.2 ± 0.6 μg ergosterol/mg fungal dry weight was obtained. A more stringent test of ergosterol's ability to predict fungal biomass changes was performed in a batch reactor which stimulated an ASWTP. Prior to an artificially induced fungal infestation, microscopic analysis revealed low fungal levels; ergosterol measured 86 ppb. Nine days later, extensive fungal growth was evident microscopically; ergosterol values increased 57-fold, to 4880 ppb. In contrast to viable plate counts, ergosterol determinations in activated sludge provided a superior method to measure fungal biomass. Furthermore, ergosterol determinations enhanced the information obtained by microscopic examination.