Background:
Bioactive compounds from various natural sources have been attracting more and more
attention, owing to their broad diversity of functionalities and availabilities. However, many of the bioactive
compounds often exist at an extremely low concentration in a mixture so that massive harvesting is needed to
obtain sufficient amounts for their practical usage. Thus, effective fractionation or separation technologies are
essential for the screening and production of the bioactive compound products. The applicatons of conventional
processes such as extraction, distillation and lyophilisation, etc. may be tedious, have high energy consumption or
cause denature or degradation of the bioactive compounds. Membrane separation processes operate at ambient
temperature, without the need for heating and therefore with less energy consumption. The “cold” separation
technology also prevents the possible degradation of the bioactive compounds. The separation process is mainly
physical and both fractions (permeate and retentate) of the membrane processes may be recovered. Thus, using
membrane separation technology is a promising approach to concentrate and separate bioactive compounds.
Methods:
A comprehensive survey of membrane operations used for the separation of bioactive compounds is
conducted. The available and established membrane separation processes are introduced and reviewed.
Results:
The most frequently used membrane processes are the pressure driven ones, including microfiltration
(MF), ultrafiltration (UF) and nanofiltration (NF). They are applied either individually as a single sieve or in
combination as an integrated membrane array to meet the different requirements in the separation of bioactive
compounds. Other new membrane processes with multiple functions have also been developed and employed for
the separation or fractionation of bioactive compounds. The hybrid electrodialysis (ED)-UF membrane process,
for example has been used to provide a solution for the separation of biomolecules with similar molecular weights
but different surface electrical properties. In contrast, the affinity membrane technology is shown to have the
advantages of increasing the separation efficiency at low operational pressures through selectively adsorbing
bioactive compounds during the filtration process.
Conclusion:
Individual membranes or membrane arrays are effectively used to separate bioactive compounds or
achieve multiple fractionation of them with different molecule weights or sizes. Pressure driven membrane processes
are highly efficient and widely used. Membrane fouling, especially irreversible organic and biological fouling,
is the inevitable problem. Multifunctional membranes and affinity membranes provide the possibility of
effectively separating bioactive compounds that are similar in sizes but different in other physical and chemical
properties. Surface modification methods are of great potential to increase membrane separation efficiency as
well as reduce the problem of membrane fouling. Developing membranes and optimizing the operational parameters
specifically for the applications of separation of various bioactive compounds should be taken as an important
part of ongoing or future membrane research in this field.
A Hybrid Modeling Framework for Membrane Separation Processes: Application to Lithium-Ion Recovery from Batteries