A PRACTICAL METHOD FOR QUANTIFICATION OF PAO AND GAO POPULATIONS IN ACTIVATED SLUDGE SYSTEMS

Enhanced Biological Phosphorus Removal (EBPR) from wastewater relies on the enrichment of activated sludge with Phosphorus Accumulating Organisms (PAO). Nevertheless, the presence and proliferation of Glycogen Accumulating Organisms (GAO) that compete for substrate against PAO may be detrimental for EBPR systems leading to deterioration and, in extreme cases, failure of the process. Therefore, from both process evaluation and modeling perspectives, the estimation of PAO and GAO populations in activated sludge systems rises as a relevant issue. A simple method for the quantification of PAO and GAO population fractions in activated sludge systems is presented in this paper. In order to develop such a method the activity observed in anaerobic batch tests executed under different PAO-GAO ratios by mixing highly enriched PAO and GAO cultures was studied. Strong correlations between PAO-GAO population ratios and biomass activity were observed (R2 > 0.97). This served as a basis for the proposal of a simple, practical and seemingly reliable method to quantify the PAO and GAO populations in activated sludge systems based on commonly measured and reliable analytical parameters such as mixed liquor suspended solids (MLVSS), acetate (HAc) and orthophosphate (PO43−-P). The proposed method was evaluated using activated sludge from municipal wastewater treatment plants. The results from the quantification performed following the proposed method were compared to direct population estimations carried out with FISH analysis (determining Candidatus Accumulibacter Phosphatis as PAO and Candidatus Competibacter Phosphatis as GAO). Average differences in the determination of PAO and GAO fractions were around 4 and 1%, respectively. The method showed to be potentially suitable to estimate the PAO and GAO populations regarding the total PAO-GAO biomass. It could be used not only to evaluate the performance of Enhanced Biological Phosphorus Removal (EBPR) systems but also in the calibration of potential activated sludge mathematical models regarding the PAO-GAO coexistence.