Influence of the Presence of Long Chain Fatty Acids (Lcfas) in the Sewage on the Growth of M. Parvicella in Activated Sludge Wastewater Treatment Plants

Foaming and bulking problems in activated sludge treatment plants are associated to the
presence of a variety of filamentous bacteria. However, it has been observed that M.
parvicella is the most frequent filamentous microorganism causing sludge bulking and
foaming, especially in treatment plants involving nutrients removal.
High sludge retention time, low DO, low temperature, presence of anoxic, anaerobic, and
intermittently aerated zones, are the most commonly cited conditions associated with its
growth. Substrate composition is another significant factor, as it has been found that slowly
degradable organic material may favour the growth of M. parvicella. If has also been
suggested that M. parvicella may preferably store long chain fatty acids (LCFAs) under
anaerobic conditions and subsequently use it for growth.
The paper presents the results of an investigation conducted at the wastewater treatment
plant of Ioannina, aiming to establish a cause-effect relationship between the presence of
LCFAs and the abundance of M. parvicella. This investigation is a part of a wider study
sponsored by the Greek Secretariat for Research, under the PENED programme.
The duration of the investigation covers 8 months, from January 2004 to August 2004. During
this period samples were taken from the sewage collection network and wastewater treatment
plant of Ioannina and analysed for, among other parameters, LCFAs and total fatty acids
while samples of the mixed liquor and the foam in the biological reactors were microscopically
analysed in order to determine the presence and amount of various types of filamentous
bacteria.
Two main conclusions were drawn. The first is related to the effect of temperature on the
growth of M. parvicella, indicating that the growth of this specific filamentous bacterium is
favoured by low temperatures (generally below 20 oC), while higher temperatures cause the
practical elimination of M. parvicella, irrespectively of other factors. This conclusion verifies
previous studies in pilot units and full scale plants. The second conclusion is that during
winter periods there seems to be a positive correlation, between the presence of fatty acids
and more specifically LCFAs and the amount of M. parvicella.