Study of the filamentous microorganisms causing activated sludge bulking and biological foams formation
Prof. Ing. Jiří Wanner, DrSc.
Dissertation is aimed at the study of the characteristics two most common filamentous microorganisms causing filamentous bulking of activated sludge and biological foams formation, e.g. Microthrix parvicella and nocardioform actinomycetes.
The theoretical part summarizes the knowledge of activated sludge biocenosis composition, mechanism of bioflocculation, separation problems of activated sludge and its settling properties evaluation, compiles available information on filamentous microorganisms identification, classification and geographical distribution and on possibilities to control their growth in activated sludge and biological foams.
The aim of the work was to study the behaviour of activated sludge with the dominant fraction of Microthrix parvicella, to describe the effect of selected substrates, nutrients and cultivation conditions on its growth and morphological changes in mixed and pure culture, to verify the possible floc - forming microorganisms inhibition by denitrification intermetabolites, to check the applicability of described hydrofobicity measurement for routine analyses and to verify by means of molecular biology methods the microscopic identification of some filamentous microorganisms and detect main group of floc - forming organisms.
The experimental part contains the description of the studied laboratory systems, summarizes the used methodology of analytical techniques, kinetic tests, microscopic analyses, growth studies of filamentous microorganism Microthrix parvicella and modified procedure of activated sludge and biological foam hydrofobicity measurement. Its final chapter describes the methodology of fluorescent in situ hybridization (FISH), e.g. using of gene probes.
These main conclusions result from the obtained data:
- a steady state of laboratory anoxic - oxic (SBR and continuously plug flow) models with the simultaneous dominant position of filamentous microorganisms, Microthrix parvicella in the biocenosis has never been reached regardless of loading and synthetic wastewater composition; the dominant position of microthrix parvicella was kept by using the raw wastewater and bigger model both in anoxic - oxic and anaerobic - anoxic - oxic condition
- an increasing ammonia concentration in basic medium favour the tendency of Microthrix parvicella to grow in longer morpholocical forms, the strong dependence of its growth on oxygen concentration/cultivation conditions was observed. The combination of oxic - non-oxic conditions and ammonia addition led into the complete replacement of the spores by long filaments exhibiting all morphological features and Gram and Neisser staining characteristics typical of Microthrix parvicella, however, the ability of the filament to form spores has not been verified yet by other researchers
- no correlation was found between filamentous microorganism Microthrix parvicella abundance and denitrification rate or denitrification course in regard to the nitrite concentration, the hypothesis of floc - forming microorganisms inhibition by denitrification intermetabolites has not been unambiguously prove
- the probability of biological foam formation grows with the increase of filamentous microorganism Microthrix parvicella abundance and hydrofobicity of the biocenosis; a regular measurement of activated sludge hydrofobicity changes by described method could (together with the microscopic analysis) predict to a certain degree the biological form formation at WWTP
- the microscopic identification of Microthrix parvicella was verified by means of specific gene probes, the experiments confirmed the possibility to monitor filamentous microorganism presence independently of filament morphology. Furthermore, the application of FISH proved Acinetobacter spp. is not the dominant species of biological phosphorus removal mechanism.