ABSTRACT
The various modes of operation were discussed in Chapter 6. Typically, a decision must be made regarding the mode of operation ahead of all the other design parameters as all the latter are dependent on the former. Factors affecting the decision making include the following:
• Feedstock supply. Generally speaking, if the unit operation upstream foam fractionation is in batch mode (for instance, if it is a batch fermentation process), semi-batch (continuous with respect to gas and batch with respect to liquid) foam fractionation is the logical choice. While it is possible to adapt continuous foam fractionation to match the schedule of the batch mode fermentation, an intermediate liquid vessel is required to hold the solution. However, due to the fickle nature of the foam fractionation process, precise control is difficult. One could easily experience situations where a new batch of feedstock arrives but the old batch has not yet been completely processed, or situations where the feedstock from a previous batch has been used up but a new batch is not yet ready so the foam fractionation has to pause, which essentially forces the foam fractionation into a batch mode. Conversely, if the feedstock is supplied in continuous mode, such as a relatively constant stream of wastewater or from a continuous fermentation, a continuous foam fractionation is better suited. Continuous operation is also better suited for high throughput operations.
