OP-II-3

PP-III-24THE PROCESS FOR PRODUCING LACTIC ACID BY MEMBRANEBIOREACTOR SYSTEMIlushka I.V., Kolbakov V.V.Nordbiochem Ltd, Polva, Estonia, agro3000@inbox.ruLactic acid has been manufactured by employing the batch-type fermentationprocess which comprises the steps of culturing lactic acid bacteria for more than60 hours after inoculation and isolating lactic acid from the culture medium. Thebatch process has an advantage of high-concentration lactic acid production of over120 g/L, though it has revealed a critical shortcoming of low volumetric productivity ofless than 5 g/L/h. To compensate for the low productivity, the fermentation volume isenlarged, which in turn increases the cost for the construction of fermentationfacilities and the maintenance of the facilities. As an alternative approach toovercome the low productivity of batch-type fermentation process, cell-recyclingprocess by which microorganisms are concentrated in a fermenter to increase theproductivity, has been suggested.According to present experiments, the lactic acid can be produced in a simple andinexpensive manner, so as to eliminate the disadvantages of the prior processesdiscussed above. It has been surprisingly found, that if to create such conditions at whichgrowth rate of cells is minimal but sufficient for replacement cells death, in this casedecrease of the specific consumption of carbohydrates per unit of lactate is take place.The growth rate of cells can be reduced by increase of temperature and decreaseof pH up to critical and supercritical values for each microorganism and as well bydecrease of amounts nutrients fed into the fermenter and by use of additivesbacteriostatics.It has been surprisingly found, that for each microorganism there are optimal conditions- temperature, рН, amounts of nutrients and bacteriostatics fed into the fermenter, at whichgrowth rate of cells is minimal but sufficient for replacement cells death.Preferably, the optimal growth rate of cells reach by combination of temperature,рН, by amount of used nutrients and bacteriostatics fed into the fermenter.Concentration of cells of microorganisms has been reached value 100 g/L (dried cellweight) and more, in the membrane recycle bioreactor system. With combinations ofparametres described above, we can get volumetric productivity more 100 g/L/h.484