Kinetic and metabolic aspects of Defluviicoccus vanus- related organisms as competitors in EBPR systems A. B. Lanham, M. A. M Reis and P. C. Lemos ABSTRACT A. B. Lanham M. A. M Reis P. C. Lemos REQUIMTE/CQFB, Chemistry Department, FCT/UNL, 2829-516 Caparica, Portugal E-mail: analanham@dq.fct.unl.pt; amr@dq.fct.unl.pt; pac@dq.fct.unl.pt A reactor was successfully enriched (90% as shown by Fluorescence in situ Hybridization) in Defluviicoccus vanus-related organisms presenting a Glycogen Accumulating Organisms (GAO) phenotype. Initial batch tests were performed using anaerobic/aerobic conditions to assess the capacity of different carbon sources utilization frequently abundant in wastewater: acetate, propionate, butyrate, valerate and glucose. Acetate and propionate were totally consumed in the anaerobic phase as well as butyrate and valerate, though these last ones with a very low consumption rate. All substrates were converted to polyhydroxyalkanoates (PHA). Glucose had a very slight anaerobic consumption but failed to disclose a typical GAO phenotype. In aerobic conditions, again all carbon sources were readily consumed except for glucose, with acetate and propionate having the higher consumption rates. Therefore, glucose seems not be used by this type of organisms. Acetate and propionate consumption rates indicated that these GAOs could reveal good competition advantages in EBPR systems where these carbon sources are available, especially propionate. Volatile Fatty Acid (VFA) uptake in aerobic phase and consequential PHA production indicate these organisms as possible candidates for PHA production. Key words | carbon substrate, EBPR, GAOs, in vivo NMR INTRODUCTION Eutrophication has been considered a serious problem since it affects directly and indirectly water quality, landscape preservation and especially ecosystems. Since the 1970s a biological system, Enhanced Biological Phosphorus Removal or EBPR, has been developed and implemented. This system allows phosphorus removal from wastewater in a more sustainable alternative to chemical processes. How- ever, dealing with a biological system implies some variability that will result from differences in wastewater composition, environmental and climatic conditions. Therefore, a large interest has arisen in studying the process variables as well as the microbiology dynamics involved. EBPR systems function through a mixed cultures process mainly enriched in a group of organisms known as Polyphosphate Accumulating Organisms (PAOs). However, some system’s failures have been reported where phos- phorus removal capacity has decreased or ceased. These events have often been ascribed to another group of microrganisms known as Glycogen Accumulating Organ- isms (GAOs) that have a similar behaviour as PAOs, namely in the carbon cycling. GAOs can, therefore, compete with PAOs for carbon sources, but without storing internal polyphosphate reserves, and if the system’s conditions favour them, they will strive and deteriorate the EBPR capacity. Several types of GAOs have been identified although none has been isolated. From these, two major groups seem to play a possible leading role in this PAO-GAO competition: Candidatus Competibacter phosphatis and Defluviicoccus vanus-related organisms (clusters 1 and 2). doi: 10.2166/wst.2008.552 1693 Q IWA Publishing 2008 Water Science & Technology—WST | 58.8 | 2008