The physiology of the filamentous bacterium Microthrix parvicella
A study has been made of the physiology of Microthrix parvicella. This filamentous bacterium often causes poor settleability of activated sludge in oxidation ditches supplied with domestic sewage. The organism was found to utilize only long chain fatty acids (preferably in esterified form) as carbon and energy source. Short chain fatty acids and glycerol are only utilized together with long chain fatty acids; other organic substrates are not consumed. The organism requires ammonium salts and reduced-sulphur compounds for growth. Thiamin and cyanocobalamin were found to be essential vitamins. Optimum temperature is 25°C and the pH of the medium has to be above 7. During the early growth phase in batch culture with an oleic acid ester (Tween 80) as the limiting substrate , M. parvicella stores large amount of lipids, mainly oleic acid in esterified form in its cells. In a subsequent period the stored lipids are used for energy supply and synthesis of cell protein.Growth kinetics were studied by cultivating the organism in a chemostat. The maximum specific growth rate was found to be 0.06 h -1 ; the K S value for Tween 80 was too low to be determined. The maximum yield coefficient and the maintenance on Tween 80 were 0.34 g cell dry weight/ g Tween 80 consumed and 6.3 mg Tween 80/g cell dry weight.h, respectively. As only the oleic acid moiety of Tween 80 is consumed, these values must be corrected for the non-fatty acid moiety (76%) of the Tween 80 molecule.Although oleic acid is an excellent substrate for M. parvicella, the organism was found to be inhibited at higher concentrations of this compound. Decreasing pH and decreasing biomass concentration promote the inhibiting action of oleic acid in washed cell suspensions. Various surface-active compounds which are not utilized as carbon source enhance the oxygen uptake rate of washed cells. The increase of the oxygen uptake due to added Tween 80 or oleic acid is probably caused by substrate respiration as well as a non-substrate-specific stimulation caused by surfaceactive properties of these compounds. The affinity for oxygen of M. parvicella is high (K S value < 0.016 mg/l).Abundant growth of M. parvicella was obtained in activated sludge in a bench- scale plant fed with waste water containing oleic acid and supplied with a limited amount of oxygen. These results explain the excessive growth of M.parvicella in activated sludge supplied with raw domestic sewage. This type of sewage contains a considerable amount of fatty matter and the activated-sludge process is usually operated at a low oxygen concentration in the mixed liquor.
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| Format: | Doctoral thesis biblioteca |
| Language: | English |
| Published: |
Landbouwhogeschool
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| Subjects: | activated sludge, aeration, microbiology, waste treatment, waste water treatment, water treatment, afvalverwerking, afvalwaterbehandeling, beluchting, geactiveerd slib, microbiologie, waterzuivering, |
| Online Access: | https://research.wur.nl/en/publications/the-physiology-of-the-filamentous-bacterium-microthrix-parvicella |
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| Summary: | A study has been made of the physiology of Microthrix parvicella. This filamentous bacterium often causes poor settleability of activated sludge in oxidation ditches supplied with domestic sewage. The organism was found to utilize only long chain fatty acids (preferably in esterified form) as carbon and energy source. Short chain fatty acids and glycerol are only utilized together with long chain fatty acids; other organic substrates are not consumed. The organism requires ammonium salts and reduced-sulphur compounds for growth. Thiamin and cyanocobalamin were found to be essential vitamins. Optimum temperature is 25°C and the pH of the medium has to be above 7. During the early growth phase in batch culture with an oleic acid ester (Tween 80) as the limiting substrate , M. parvicella stores large amount of lipids, mainly oleic acid in esterified form in its cells. In a subsequent period the stored lipids are used for energy supply and synthesis of cell protein.Growth kinetics were studied by cultivating the organism in a chemostat. The maximum specific growth rate was found to be 0.06 h -1 ; the K S value for Tween 80 was too low to be determined. The maximum yield coefficient and the maintenance on Tween 80 were 0.34 g cell dry weight/ g Tween 80 consumed and 6.3 mg Tween 80/g cell dry weight.h, respectively. As only the oleic acid moiety of Tween 80 is consumed, these values must be corrected for the non-fatty acid moiety (76%) of the Tween 80 molecule.Although oleic acid is an excellent substrate for M. parvicella, the organism was found to be inhibited at higher concentrations of this compound. Decreasing pH and decreasing biomass concentration promote the inhibiting action of oleic acid in washed cell suspensions. Various surface-active compounds which are not utilized as carbon source enhance the oxygen uptake rate of washed cells. The increase of the oxygen uptake due to added Tween 80 or oleic acid is probably caused by substrate respiration as well as a non-substrate-specific stimulation caused by surfaceactive properties of these compounds. The affinity for oxygen of M. parvicella is high (K S value < 0.016 mg/l).Abundant growth of M. parvicella was obtained in activated sludge in a bench- scale plant fed with waste water containing oleic acid and supplied with a limited amount of oxygen. These results explain the excessive growth of M.parvicella in activated sludge supplied with raw domestic sewage. This type of sewage contains a considerable amount of fatty matter and the activated-sludge process is usually operated at a low oxygen concentration in the mixed liquor. |
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