Traditionally, ethanol has been produced batch wise. However, high labor costs and the low productivity offered by the batch process have led many commercial operators to consider the continuous fermentation. Continuous fermentation can be performed in different kind of bioreactors — stirred tank reactors or plug flow reactors. Continuous fermentation often gives a higher productivity, offers ease of control and is less labor intensive than batch fermentation (Cheng et al., 2007). However contamination is more serious in this operation (Skinner & Leathers, 2004). In the fuel ethanol industry, control of bacterial contamination is achieved by acidification and using antibiotics such as penicillin G, streptomycin, tetracycline (Aquarone E,1960; Day et al., 1954), virginiamycin(Hamdy et al., 1996; Hynes et

al., 1997; Islam et al., 1999), monensin(Stroppa et al., 2000), or mixtures thereof. Fig 9 shows the process of continuous fermentation of molasses and sugarcane juice to produce ethanol. A high cell density of microbes in the continuous fermenter is locked in the exponential phase, which allows high productivity and overall short processing of 6 — 12 h as compared to the conventional batch fermentation (30 — 60 h). This results in substantial savings in labor and minimizes investment costs by achieving a given production level with a much smaller plant.

Fig. 7. Approach for evolutionary engineering
Temperature
• л	8 °С
Ethanol 15%(V/V)