Studies of microbial purification of a model waste water containing 4-nitrophenol were carried out in a continuously working aerobic solid-bed reactor. The main emphasis was on the dynamic behaviour of the system after a sudden change in cultivation conditions and on the steady state performance of the reactor as a function of the pollution load. A change from ammonium-free to ammonium-containing medium hardly influenced the nitrophenol degradation. The reactor responded differently to an increase in pollutant load, which was brought about by increasing either the 4-nitrophenol content or the flow of the waste water. Up to a load of 270 mg l-1 h-1 the pollutant was stably and almost completely degraded. At a higher load, only a partial 4-nitrophenol degradation took place. A mathematical model was derived to describe the processes that occurred in the reactor. By segregation into two compartments--the aqueous phase and the biofilm--account was taken of the fact that the pollutant is carried into the biofilm by diffusion and is degraded there. The observed relations between the pollutant load, the pollutant concentration in the outlet of the reactor and the reactor performance agreed with the simulated process behaviour. As the model simulation showed, the incomplete pollutant degradation at a higher reactor load was caused by oxygen limitation.
A toluene-degrading Pseudomonas species isolated from waste water was studied with regard to its growth behaviour. The dependence of the growth rate on the pH value, on the toluene concentration and on temperature, as well as the O2 consumption of the isolate were determined. The fact that toluene is a highly volatile substrate, which is present both in the liquid and in the gas phase of a reactor, was considered in the experiments. It is shown that the volatility of toluene has to be taken into consideration for an accurate determination of the toluene concentration. in the medium.
The microbial aerobic decontamination of waste waters contaminated with highly volatile pollutants was experimentally investigated in a closed chemostat in [I]. The experiments, using a previously isolated Pseudoinonus strain, were carried out with synthetic waste water containing toluene and saturated with either nitrogen or oxygen. A model for the interpretation of the experimentally determined process behaviour has been derived in this study. A comparison of the process curves obtained by simulation (numerical solutions of the model equations) with the experimentally determined results confirmed the model concepts. The model analysis supplied equations describing the process in a steady state as a function of the technical process parameters. These equations were used to draw conclusions for the practical operation of waste-water purification processes in closed chemostats.
A mathematical model has been developed to describe the stability behaviour of the pBR322 plasmid derivative pBB210 with the plactamase gene and the human interferon-a1 gene in Ercherichia coli TG1 under non-selective, selective and modified selective conditions in a chemostat The model was formulated on the basis of experimental investigations. It includes the interaction between plactam antibiotics (ampicillin and sulbactam) and cells (with and without plasmids). in particular the correlation between the growth rate of plasmid-free cells and ampicillin concentration in the medium; ampicillin transport into the periplasm of the plasmid-bearing cells, ampicillin degradation in the periplasm by plasmid-encoded plactamase and the inhibition of the latter by sulbactam. The results obtained by the simulation of chemostat cultivations under various conditions and by steady state analyses are closely related to the results of experiments. Under non-selective conditions, the fraction of plasmid-bearing cells was approaching zero. Under selective and modified selective conditions, a coexistence between plasmid-free and plasmid-bearing cells was reached at steady state. Under these conditions, the steady state fraction of plasmid-bearing cells was proportional to the ampicillin concentration in the feed and inversely proportional to the cell concentration in the chemostat. During highdensity cultivation, a large amount of ampicillin is necessary to suppress plasmid-free cells. Even small concentrations of the plactamase inhihitor sulhactam in the feed increased the steady state fraction of plasmid-bearing cells (from 17.2% to 99.6% at sulbactam-Na concentrations of0 to 5 mg/l).
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