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Membrane distillation (MD) is a thermally driven separation process that employs a hydrophobic membrane as a barrier for IntroductionMembrane distillation (MD) is a thermally driven separation technique using microporous hydrophobic membranes and performing on the principles of vapor-liquid equilibrium under different configurations. In this process, only volatile compounds (mainly water) of the feed stream evaporate at the membrane pore entrance, cross the membrane pores in vapor phase to finally be either condensed or removed as a vapor from a membrane module. The hydrophobic nature of the membrane prevents the pores from wetting by capillary forces. MD is known as a promising technology for many applications such as desalting seawater, brackish water, highly saline water [1,2], and removing organic compounds and heavy metals from aqueous solutions [3,4]. MD has also been used to manage waste water such as radioactive waste waters, oily waste waters [5], where the product could be safely discharged to the environment or the waste streams could be reused in an appropriate industrial activity. In biotechnology and food processing applications, MD has also been found as a promising tool, for instance, for removing ethanol and other metabolites from fermentation broths [6], for gentle concentration of valuable compounds in fruit juices [7], and in herb extract such as Ginseng [8].MD has many attractive features as compared to conventional separation processes. Low operating temperatures (~30-70°C) is one of them since the feed is not necessarily heated up to the boiling point like in thermal distillation. Thus, MD may advantageously utilize alternative energy sources, such as solar energy, geothermal energy, waste heats from power plant, etc. [9]. Compared with pressure driven membrane filtration processes such as nanofiltration or reverse osmosis, lower operating pressure translates to lower equipment costs and increased process safety. It is worth highlighting that membrane fouling in MD seems to be less of a problem for many applications than that in pressure-driven filtration processes [10].MD is, however, attended by some drawbacks. Compared to reverse osmosis, MD is known to have a lower permeate flux, and the susceptibility of permeate flux to processing conditions, particularly to temperature and concentration, is considerably high. Also, the trapped air within the membrane pores

Galacto-oligosaccharides (GOS) are prebiotic compounds widely used for their health-promoting effects. Conventionally, GOS is produced by the enzymatic conversion of lactose in stirred tank reactors (STR). The high operational costs associated with enzyme inactivation and removal might be reduced by the application of enzyme membrane reactors (EMR). In this study, we aimed to assess the potential of continuous GOS production by EMR using soluble Biolacta N5, a Bacillus circulans-derived commercial enzyme preparation. The steady-state performance of the EMR equipped with an ultrafiltration module was investigated as function of residence time (1.1–2.8 h) and enzyme load (17–190 U·g−1) under fixed operational settings of temperature (50 °C), pH (6.0), lactose feed concentration (300 g·kg−1), and recirculation flow-rate (0.18 m3·h−1). Results indicate that the yield of oligosaccharides with higher degree of polymerization (DP3-6) in STR (approx. 38% on total carbohydrate basis) exceeds that measured in EMR (ranging from 24% to 33%). However, a stable catalytic performance without a significant deterioration in product quality was observed when operating the EMR for an extended period of time (>120 h). Approx. 1.4 kg of DP3-6 was produced per one gram of crude enzyme preparation over the long-term campaigns, indicating that EMR efficiently recovers enzyme activity.

The market for prebiotics is steadily growing. To satisfy this increasing worldwide demand, the introduction of effective bioprocessing methods and implementation strategies is required. In this chapter, we review recent developments in the manufacture of galactooligosaccharides (GOS) and fructooligosaccharides (FOS). These well-established oligosaccharides (OS) provide several health benefits and have excellent technological properties that make their use as food ingredients especially attractive. The biosyntheses of lactose-based GOS and sucrose-based FOS show similarities in terms of reaction mechanisms and product formation. Both GOS and FOS can be synthesized using whole cells or (partially) purified enzymes in immobilized or free forms. The biocatalysis results in a final product that consists of OS, unreacted disaccharides, and monosaccharides. This incomplete conversion poses a challenge to manufacturers because an enrichment of OS in this mixture adds value to the product. For removing digestible carbohydrates from OS, a variety of bioengineering techniques have been investigated, including downstream separation technologies, additional bioconversion steps applying enzymes, and selective fermentation strategies. This chapter summarizes the state-of-the-art manufacturing strategies and recent advances in bioprocessing technologies that can lead to new possibilities for manufacturing and purifying sucrose-based FOS and lactose-based GOS.