OCCURRENCE OF GLYCOGEN ACCUMULATING ORGANISMS (GAO) AT FULL-SCALE ENHANCED BIOLOGICAL PHOSPHORUS REMOVAL (EBPR) WASTEWATER TREATMENT PLANTS

The presence of Glycogen Accumulating Organisms (GAO), that compete for substrate with Phosphorus Accumulating Organisms (PAO), has been associated with the deterioration and even failure of the Enhanced Biological Phosphorus Removal (EBPR) process in wastewater treatment plants. In the present paper the occurrence of GAO (Competibacter) at full-scale plants designed for EBPR in the Netherlands and the influence of operating and environmental conditions on the PAO and GAO populations present at those plants were studied. Eight municipal wastewater treatment plants were surveyed during (Dutch) winter conditions (water temperature around 12°C). Data regarding their operational and environmental conditions and process configurations were compiled. The EBPR activity from each plant was determined through anaerobic-aerobic batch tests performed with fresh activated sludge. Meanwhile, PAO (Accumulibacter) and GAO (Competibacter) fractions were quantified using Fluorescence in situ Hybridization (FISH). The effects of plant process configuration and operational and environmental conditions were examined and correlated with the activity and occurrence of PAO and GAO fractions. Accumulibacter fractions comprised 9 ± 1 % of total bacterial populations (as EUBacteria) while Competibacter were present in relatively lower fractions (2 ± 2 %). Wastewater treatment plants designed and operated with separate pre-denitrification tanks seemed to favour the growth of Accumulibacter populations than plants where a separate denitrification stage was absent. Besides, higher pH values (pH > 7.0) seemed to have a positive effect on the occurrence of Accumulibacter. Despite their low observed fractions, the potential detrimental effects that Competibacter could cause on biological P-removal systems were observed. However, GAO did not cause a major effect on the evaluated EBPR processes. It seems that observed GAO's appearance was not in the range that would have led to EBPR deterioration. Presumably, the effects of environmental conditions (such as temperature) limited their proliferation.