Microfiltration open system

The microalgae are cultured in bioreactors under solar or artiflcial light in the presence of carbon dioxide and salts. The bioreactors may be closed systems made of polyethylene sleeves rather than open pools. Optimal conditions for pigment production are low to medium light intensity and medium temperatures (20 to 30°C). Pigment extraction is achieved by cell breakage, extraction into water or buffered solution, and centrifugation to separate out the filtrate. The filtrate may then be partly purified and sterilized by microfiltration and spray dried or lyophilized. 

Microfiltration and UF membranes can be asymmetric, with a denser side and a more open side, or uniform without macrovoids (See Figure 16.3). The open area behind the denser surface in an asymmetric design means there is less resistance to water permeating the membrane. Operating pressure can be lower and the membrane systems can be more productive. The limitation of the asymmetric design is that the material, predominately used in the hollow fiber configuration, is not as strong as the uniform cross section. 

Let us take polysulfone as an example. This is a polymer which is frequently used as a membrane material, both for microfiltration/ultrafiltration as well as a sublayer in composite membranes. These applications require an open porous structure, but in addition also asymmetric membranes with a dense nonporous top layer can also be obtained which are useful for pervaporation or gas separation applications. Some examples are given in table ni.S which clearly demonstrate the influence of various parameters on the membrane structure when the same system, DMAc/polysulfone(PSf), is employed in each case. How is it possible to obtain such different structures with one and the same system To understand this it is necessary to consider how each of the variables affects the phase inversion process. The ultimate structure arises through two mechanisms i) diffusion... 

Several investigators have attempted to address the issue of whether heterogeneous pacemakers are necessary for the initiation of waves in the BZ and other systems. By careful microfiltration of all solutions and maintenance of dust-free conditions, it is possible to increase greatly, but not to suppress completely, the average time required for the spontaneous appearance of waves in a BZ solution (Pagola and Vidal, 1987). The results suggest that dust particles do serve as pacemakers, but it remains an open question as to whether waves can arise from random concentration fluctuations or whether it was simply too difficult to eliminate all heterogeneities from the system. 

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