Biomedical subjects

C T Frijters

Publications and source records attributed to C T Frijters.

3 recordsLinked to original sources

PubMed2001

Future perspectives in bioreactor development.

The paper discusses conversion capacities of both anaerobic and aerobic wastewater treatment systems in relation to growth kinetics, hydrodynamics and biomass concentration. In the current modern anaerobic high-rate reactors the conversion potentials are optimally exploited. This is not yet true for aerobic systems since operation of aerobic systems under conditions of low biomass growth reduces the maximum applicable loading rates significantly. Both the concept of granulation and the introduction of fluidised bed systems have increased conversion capacities for both anaerobic and aerobic systems significantly. One of the latest development concerns the SBR with granular biomass. The grazing concept, in which ciliates convert aerobically grown dispersed cells, offers a possibility for significant improvement of aerobic systems. In the fields of psychrophilic and thermophilic anaerobic treatment, specific reactor development may contribute to further enhance volumetric conversion capacities. Due to reduced water usage, both COD and salt concentrations tend to increase for industrial effluents. As a consequence, there is a need for the development of anaerobic reactors retaining flocculant biomass. The membrane bioreactors offer a solution for certain niches in wastewater treatment. However the oxygen transfer economy is poor. There is a need for fundamental knowledge development to obtain a realistic image of this technology.

Bacteria, Aerobic↗

PubMed1993

Effects of acetate, propionate, and butyrate on the thermophilic anaerobic degradation of propionate by methanogenic sludge and defined cultures.

The effects of acetate, propionate, and butyrate on the anaerobic thermophilic conversion of propionate by methanogenic sludge and by enriched propionate-oxidizing bacteria in syntrophy with Methanobacterium thermoautotrophicum delta H were studied. The methanogenic sludge was cultivated in an upflow anaerobic sludge bed (UASB) reactor fed with propionate (35 mM) as the sole substrate for a period of 80 days. Propionate degradation was shown to be severely inhibited by the addition of 50 mM acetate to the influent of the UASB reactor. The inhibitory effect remained even when the acetate concentration in the effluent was below the level of detection. Recovery of propionate oxidation occurred only when acetate was omitted from the influent medium. Propionate degradation by the methanogenic sludge in the UASB reactor was not affected by the addition of an equimolar concentration (35 mM) of butyrate to the influent. However, butyrate had a strong inhibitory effect on the growth of the propionate-oxidizing enrichment culture. In that case, the conversion of propionate was almost completely inhibited at a butyrate concentration of 10 mM. However, addition of a butyrate-oxidizing enrichment culture abolished the inhibitory effect, and propionate oxidation was even stimulated. All experiments were conducted at pH 7.0 to 7.7. The thermophilic syntrophic culture showed a sensitivity to acetate and propionate similar to that of mesophilic cultures described in the literature. Additions of butyrate or acetate to the propionate medium had no effect on the hydrogen partial pressure in the biogas of an UASB reactor, nor was the hydrogen partial pressure in propionate-degrading cultures affected by the two acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetates↗

PubMed1992

Enrichment of Thermophilic Propionate-Oxidizing Bacteria in Syntrophy with Methanobacterium thermoautotrophicum or Methanobacterium thermoformicicum.

Thermophilic propionate-oxidizing, proton-reducing bacteria were enriched from the granular methanogenic sludge of a bench-scale upflow anaerobic sludge bed reactor operated at 55 degrees C with a mixture of volatile fatty acids as feed. Thermophilic hydrogenotrophic methanogens had a high decay rate. Therefore, stable, thermophilic propionate-oxidizing cultures could not be obtained by using the usual enrichment procedures. Stable and reproducible cultivation was possible by enrichment in hydrogen-pregrown cultures of Methanobacterium thermoautotrophicum DeltaH which were embedded in precipitates of FeS, achieved by addition of FeCl(2) to the media. The propionate-oxidizing bacteria formed spores which resisted pasteurization for 30 min at 90 degrees C or 10 min at 100 degrees C. Highly purified cultures were obtained with either M. thermoautotrophicum DeltaH or Methanobacterium thermoformicicum Z245 as the syntrophic partner organism. The optimum temperature for the two cultures was 55 degrees C. Maximum specific growth rates of cultures with M. thermoautotrophicum DeltaH were somewhat lower than those of cultures with M. thermoformicicum Z245 (0.15 and 0.19 day, respectively). Growth rates were even higher (0.32 day) when aceticlastic methanogens were present as well. M. thermoautotrophicum DeltaH is an obligately hydrogen-utilizing methanogen, showing that interspecies hydrogen transfer is the mechanism by which reducing equivalents are channelled from the acetogens to this methanogen. Boundaries of hydrogen partial pressures at which propionate oxidation occurred were between 6 and 34 Pa. Formate had a strong inhibitory effect on propionate oxidation in cultures with M. thermoautotrophicum. Inhibition by formate was neutralized by addition of the formate-utilizing methanogen or by addition of fumarate. Results indicate that formate inhibited succinate oxidation to fumarate, an intermediate step in the biochemical pathway of propionate oxidation.

Journal Article↗