Benefits of integrated off-gas separation
15 Jan 2000
One of the main benefits of the Turbosep system is that the control of foam is totally automated, and depends on the requirements of the fermentation at any particular instant.
An increase in the working volume for the condenser of up to 10 per cent is possible, as foam is allowed to enter the off-gas leg without compromising the fermentation. As antifoam injection is linked to differential pressure, the possibility of loss of product is eliminated; and the vent losses associated with the fermentation are reduced, as separated entrained aerosol and foam are returned to the fermenter.
CRITICAL PARAMETERS
There are a number of critical parameters which govern the optimised growth of an organism. For example, in the fermentation of glutamic acid the critical parameters are aeration rate; temperature; pH and antifoam dosage.
The reduction in the use of antifoam compounds can have a number of beneficial effects on the fermentation system. An increase in the rate of oxygen transfer can lead to increase in yield: the rate of aeration and/or the speed of agitation can be reduced, leading to a consequent reduction in power consumption, while the growth rate within the fermenter is maintained.
The efficiency of the expulsion of unwanted by-products which can inhibit growth, such as carbon dioxide, can also be increased. Moreover, the reduced fouling of micro- and ultrafiltration membranes means that the efficiency of downstream processing will also increase.
REDUCING ANTIFOAM
The reduction in anti-foam usage will also impact on running costs of the fermentation, which can lead to short paybacks for the installation.
Increasing the rate at which nutrients are added to the fermentation invariably leads to the increase in the generation of foam. If this increase in foam generation can be adequately controlled using Turbosep, there is the possibility to reduce fermentation times with the subsequent increase in annual productivity per fermentation capacity.
MORE FOAM, MORE OXYGEN
The generation of foam may result in the increase oxygen transfer at the important gas bubble/liquid phase boundary. It has been reported that microbial cells near gas bubbles may absorb oxygen directly through the phase boundary, which increases the rate of oxygen transfer to these cells. The promotion of foam within the broth could therefore have an additional benefit with regard to oxygen transfer.
The efficiency of the Turbosep means that a substantial reduction in micro-organisms is achieved. Tests on a 6m3 E. coli fermentation show that there is typically a 3.5-4 fold magnitude reduction in number of organisms in the off gas, while entrained foam is continually separated and returned to the fermenter.
