*3.3. Separation Physical Methods*

Filtration, dialysis and centrifugation, either for the algal biomass or precipitates, are also among the downstream processes after pre-treatment and extraction steps [131–133]. Cross-flow filtration and dialysis against water are usually performed using different molecular weight cut-off (MWCO) membranes for isolation of fucoidans from smaller compounds depending on the high molecular weight of fucoidans [134] and also for fractionation purposes, where low molecular weight fucoidans (LMWF) can be separated from high molecular weight analogues (HMWF) [49].

In addition, filtration, concentration, and fractionation are simultaneously performed using centrifugal concentrators (Vivaspin®) equipped with membranes with certain MWCO, like in protein purification. However, in some cases, especially in the presence of bulk masses or high concentrations of salts and small contaminants, the use of centrifugal concentrators becomes practically and economically unsuitable for fucoidans purification. In such cases, bulky contaminants result in membrane clogging leading to its deterioration and increasing the production cost.
