Бурение грунтовых зондов, установка энергетических колодцев

Fermentation pH is another parameter related to the culture media capable of regulating the substrate metabolism and altering the physiological parameters, including the internal pH of cells, mem­brane potential and proton-motive force. As a result, the medium pH affects the product selectivity, composition release and meta­bolic byproducts. The effect of pH on syngas fermentation is dis­cussed in recent publications and in reviews [1,2,3,25]. The optimum pH value varies with the organism, and there is a narrow range for every organism, in which the cells are metabolically active. Any large deviations in pH can lead to damage or death of the cells and consequently results in loss of biological activity. Lowering the fer­mentation broth pH can weaken the cell growth and affect the over­all productivity of the process because of the reduced flow of carbon and electron from the substrate toward the cell mass. However, in the case of acetogenic bacteria, this effect can be considered as an advantage because the reaction path can shift from acetogenic to sol — ventogenic phase, which supports the production of more reduced alcohol products such as ethanol. In such cases, the generated acetic acid, which is a weak organic acid, permeates through the cell mem­brane, as it is a lipophilic acid in the undissociated form. Acetic acid conducts H+ ions while diffusing through the cell membrane, thus reducing the intracellular pH. At the low internal pH values, exter­nal pH plays an important role in counteracting this situation [21].

Kundiyana and Wilkins have recently studied the effect of fer­mentation medium pH together with other parameters like tem­perature, and presence or absence of media buffer [25]. They have found that the temperature dependence on the gas solubility is an important factor as well. This may be due to the fact that carbon monoxide and hydrogen components of syngas show decreased solubility with increasing temperature. These studies revealed that Clostridium species preferentially switch from acetogenesis to sol- ventogenesis phase at pH below 5.0, and morpholinoethanesul — fonic acid (MES) added as media buffer has been shown to increase lag time for ethanol production. Furthermore, this study showed syngas fermentation using Clostridium ragsdalei at 32°C in a media without a buffer was associated with higher ethanol concentra­tion and reduced lag time as a result of switching to solventogen — esis. The optimization study concluded that temperature above 40°C and pH below 5.0 were outside the most favorable range for growth and metabolism of the Clostridium ragsdalei [25]. Probably the most important finding from this study was that it is possible to conduct syngas fermentation using Clostridium ragsdalei in the 32 to 37°C without any buffer addition as seen in the results of Table 12.2.

Additionally, temperatures above 37°C greatly reduced C. ragsdalei cell growth and performance resulting in significantly lower etha­nol production [25].

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