Aerobic cell factories on the other hand, are energetically advantaged compared to anaerobic cell factories (19). Therefore, the use of aerobic bacteria allows for the production of more complex chemicals via energy-intensive biochemical pathways (18), broadening the renewable chemical spectrum. However, a disadvantage of aerobic gas fermentation is its reliance on the Calvin-Benson-Bassham cycle. Whilst this cycle achieves favourable kinetics by investing appreciable energy into C1 fixation (20), it is consequently thermodynamically inefficient compared to the Wood-Ljungdahl pathway. Due to the greater heat generation, aerobic bioreactors require the installation of substantial cooling capacity, translating to both capital and operating cost burden (19). In addition, compressors are required to satisfy the oxygen demand and the presence of oxygen necessitates the use of more expensive stainless steel reactors. Historically, aerobic fermentation has been used for high value, low volume products (21). However, for the production of higher volume commodity products, where utility costs dominate (22), aerobic fermentation has been hindered by process economics. This is a result of the aforementioned cooling requirements, associated air compression and reduced economies of scale compared with anaerobic fermentation (23).
coulson and richardson volume 1 pdf 73
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