Many fermentations have a high daily water usage (Table 12.8). As charges for water increase, many of
Table 12.8. Daily water usage in fermentation processes
Industry m of water used day
Brewing 10;000 Distilling 320 Antibiotics 245 Antibiotics 5 200 Acetic acid 700 Single cell protein (methanol substrate) 4,000 to 12,000
Yeast (alkane substrate) 18,200
Bacteria (methanol substrate) 45,500
Bacteria (methane substrate) 18,200
Hastings and Jackson (1965) Pape(1977)
Taylor and Senior (1978) Ratledge (1975)
these processes will become vulnerable to cost escalation because of the relatively large volumes of water required per unit volume of product.
There is now a widespread interest in reducing overall consumption. In a bacitracin plant described by Inskeep et al. (1951), the water from the mash cooler was collected and reused to charge the mashing vessels and wash the fermenters. Water from the cooler coils was used to wash down the discharge cake from the filter presses. Bernstein et al. (1977) designed a 'closed-loop' system for fermenting cheese whey in which effluents were completely recycled.
Recycling of water was an integral stage of large scale SCP processes developed during the 1970s to minimize water consumption, reduce effluent treatment costs and reduce media costs by recycling of spent media (Sharp, 1989). When ICI pic's SCP Pru-teen plant was operating, it was designed to recycle most of the fermenter medium water (Ashley and Rodgers, 1986). Under optimum conditions they claimed that the water loss could be reduced to 3% of the flow through the fermenter using water recovery systems.
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