Different mechanisms for the anaerobic storage of organic substrates and their effect on enhanced biological phosphate removal (EBPR)

The driving force for Enhanced Biological Phosphorus Removal (EBPR) is the presence of an anaerobic zone that enriches the activated sludge for P-accu mulating microorganisms (PAOs). According ro accepted models, PAOs anaerobi cally store volatile fatty acids (VFAs) as polyhydroxyalkanoates (PHAs) uti lising polyphosphate hydrolysis as the energy source. For substrates other than VFAs, one hypothesis is that other heterotrophs convert them to VFAs, so acting in favour of PAOs. However, particular glycogen accumulating micr oorganisms have been described (GAOs), that compete against PAOs being able to store anaerobically many substrates into PHAs, by transforming intracel lular carbohydrates (glycogen) into PHAs, as the energy source. In this per spective, the paper presents a summary (with new findings) of a long experi mental work to study EBPR processes with a lab-scale Sequencing Batch React or fed with different organic substrates (peptone, glucose and acetate, sep arate or in mixtures). Our results show that EBPR can be obtained with subs trates other than VFAs with neither their pre-conversion to VFAs nor their storage as PHA. Moreover, in different periods anaerobic uptake of glucose was possible with and without EBPR. In both cases, the stored polymer was g lycogen while the energy source was either polyphosphate hydrolysis or lact ic fermentation, respectively. These results are not consistent with the re ported behaviour of PAOs or GAOs, so showing that many different mechanisms of anaerobic uptake and storage of substrates can art in Favour of, or aga inst EBPR, Deeper insight on these mechanisms is needed to improve design a nd operation of EBPR plants. (C) 1999 IAWQ Published by Elsevier Science Lt d. All rights reserved.