The optimization task was performed using the gluconic acid synthesis by the Acefobucter methonolicrrs MB 58 strain. The microorganisms were grown continuously on methanol as the growth substrate. After finishing the growth process by the deficiency of N and P, the gluconic acid synthesis was started by adding glucose. The synthesis process was performed continuously. The oxygen transfer rate depended on the gluconic acid concentration. During the growth process, the oxygen transfer rate reached a value of about 13 g 0,. kg-I . h -I using a 30-1 glass fermenter equipped with a 6 blade stirrer and fully baffled. This rate declined to a value of between 2 and 5 g 0, . kg-I . h -' in the presence of gluconic acid concentrations above 150 g gluconic acid . kg-' medium. The yield (g gluconic acid . g-glucose) depended on the gluconic acid concentration and amounted to y = 0.7 in relation to 150 g gluconic acid . kg-I medium and y = 0.8 in relation to 200 g . kg-medium, respectively.The fermenters were coupled with ultrafiltration moduls (Fa. ROMICON and Fa. SARTORIUS). The biomass concentrations amounted from 5 to 40 g dry mass kg-' medium. The ultrafiltration modules retained the biomass within the fermentation system. A glucose solution (30 t o 50 weight percent glucose) was continuously dosed into the fermenter. The retention time was chosen between 2 and 30 h. The gluconic acid synthesis rate reached values of up to 32 g gluconic acid. kg-I . h-'. Within a range of up to 250 g gluconic acid . kg-' medium, the acid concentration had no influence on the enzyme activity.

In a process running more than five months it was proved that a nonsterile processing is possible at a stable microbial composition as well as stable performance parameters like productivity, growth yield, and product quality. For the stable processing it is important that methanol and dissolved oxygen concentration must not simultaneously exceed the threshold values (methanol> 1 g/1; dissolved oxygen > 0,5 mg/1). The postulated transfer rate obstructs at higher biomass concentrations did not occur in the examined ranges up to 80 kg biomass/1. Consequently, the growth rate did not depend on high biomass concentrations in this range.

The article contains sections titled: 1. Introduction 2. Substrates and Organisms 3. Efficiency Considerations in the Selection of Substrates and Microorganisms 4. Technology and Equipment 5. Products and Uses 6. Economic Aspects 7. Outlook

Two methane utilizing bacteria strains, GB 21 and WSB 874, were cultivated with methane as sole carbon and energy source in a submerged continuous fermentation process. The aim of the investigations was to reach high biomass concentrations (> 25 g BDM . kg-' medium) and high productivities (> 3 g BDM . kg-' . h-I). A precondition for the high-performance fermentation process was to ensure a transfer rate of methane and oxygen in quantities required by the microorganisms. For this purposes a high performance stirred pressure fermenter was used. The fermentation process is characterized by the transfer of two gaseous substrates. In order to develop a technical process it was necessary to investigate both the correlations between the two gases and the productivity of the fermentation process and the influence of system pressure on the microorganisms.Within a pressure range of up to 0.7 MPa a biomass concentration of up to 50 g BDM . kg-' medium and a productivity of up to 9 g BDM . kg-' . h-' was reached in a continuously running fermentation process under nonstenle conditions. Under these fermentation conditions the microbial population consisted of a dominating main culture GB 21 or WSB 874, respectively, and an accompanying flora (type 11). The microbial population was very stable in its composition during the fermentation process running continuously for weeks and months.

Using a methanol utilizing acidophilic MB 58 bacteria strain (IMET 109453, a stable fermentation process was performed in a pilot plant pressure fermenter of 250 I total volume for more than four months. Under the fermentation conditions (system pressure and retention time) used, productivities ranged between 2.3 and 9.4 BDM kg-l. h-l and growth yields between 0.31 and 0.42. Models describe the correlations between yield and retention time. The mean value of growth yield amounts to 0.41 at a retention time of 6.5 h.