Microthrix Parvicella Research Articles

Effect of environmental conditions on the occurrence of Microthrix parvicella in activated sludge

The filamentous bacterium Microthrix parvicella often causes poor settling of activated sludge in oxidation ditches supplied with domestic sewage. This organism utilizes preferably fatty acids as a carbon and energy source and it requires reduced nitrogen and reduced sulphur compounds for growth. In activated sludge fed with a synthetic wastewater containing oleic acid, abundant growth of M. parvicella was obtained in a bench scale plant operated at a low oxygen concentration. On the other hand, in control plants operated at a high oxygen concentration or fed with a synthetic wastewater containing glucose, this organism disappeared. These results may explain the excessive growth of M. parvicella in oxidation ditches supplied with raw domestic sewage as this type of wastewater contains a considerable amount of fatty matter and the process is usually operated at a low oxygen concentration in the mixed liquor. Bulking of sludge caused by M. parvicella can be cured by an enhanced oxygen supply.

Stable foams in activated sludge plants

A study of several full-scale activated sludge plants has confirmed that whilst stable foam formation is associated with a dominance of the sludge flora by Nocardia or Microthrix parvicella, the degree of dominance is not related to the foaming potential as measured by a novel ‘foam index’. The data also show the significance that the suspended solids concentration has on foaming.

Microthrix parvicella, a filamentous bacterium from activated sludge: growth on Tween 80 as carbon and energy source.

Microthrix parvicella, cultivated in a medium with Tween 80 and Casamino acids, utilized only the oleic acid moiety of Tween 80 as carbon and energy source. The cell yield from Tween 80 was about 0.32 g dry weight of cells per g of Tween 80 consumed. As only the oleic acid moiety of Tween 80 was utilized, the cell yield from oleic acid was 1.3 g dry weight of cells per g oleic acid consumed. The amount of carbon produced as CO2 was less than 30% of the oleic acid-carbon and this low value was in agreement with the high cell yield. In batch culture M. parvicella stored large amounts of lipid material during the early growth phase. The fatty acids of the lipid globules were similar to the fatty acids supplied as carbon source. The percentage composition of the biomass changed to give C/N percentage ratios of about 15 during the early growth phase due to the high concentration of internal lipids and the low concentration of protein. The growth rate in batch culture was about 0.016 h-1 but was affected by the concentration of Casamino acids in the medium.