Phase segregation in the poly(styrene-co-acrylonitrile)/poly(methyl methacrylate) (SAN/PMMA) blend with lower critical solution temperature (LCST) was assessed by linear viscoelastic rheology, optical microscopy, and inverse gas chromatography (IGC) techniques for various blend compositions. At low temperatures, the blends showed a classical behavior of homogeneous polymer melts, whereas in the vicinity of phase segregation, a shoulder in the storage modulus and in the linear relaxation modulus G(t) was observed. The width of such a low-frequency/longer-time plateau and the terminal relaxation time were found to increase with temperature. Such a behavior was attributed to variable morphologies appearing at different temperatures. The development of the morphology was found to take place within a given interval of temperature rather than at a single critical temperature. Optical microscopy and IGC analyses supported the observed peculiar behavior of such a blend. Time−temperature superposition, origin of elasticity, and the Fredrickson and Larson theory were discussed in light of the obtained results.

Autoflocculation and bioflocculation are considered to be the most promising means for the economical harvesting of microalgae. We have therefore studied these phenomena with cultures of Scenedesmus obliquus produced during biological tertiary wastewater treatment. The quantity of extracellular polymers produced during ageing of the cultures proved insufficient to initiate bio-flocculation while the concentration of Ca(2+) and PO(4) (3-) of the treated effluent were too low to induce autoflocculation. It has been shown, however, that the algae sediment more readily upon ageing, possibly as a result of increased cell density. The use of density gradients made with Percoll (a colloidal solution of silica particles) allowed measurement of the true cell density and showed that this increases when cultures enter the declining growth phase. The quality of the biomass thus harvested is, however, considerably impaired, protein content decreasing from 62.7% (dry wt) during the exponential growth phase (day 5) to 14% at the end of cultures (day 21).

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We have studied the use of chitosan as a non‐toxic flocculant to concentrate freshwater cultures of microalgae; these are part of a biological tertiary treatment system of urban wastewaters intended to produce biomasses for animal feeding. The sedimentation rate measured at increasing concentrations of chitosan showed that, under appropriate conditions (pH, stirring, etc.), a recovery of 95% or more of the algae was obtained at chitosan concentrations lower than 40 mg/liter. This result was obtained with temperatures ranging from 5 to 25°C and with an algal biomass concentration of 100–150 mg dry weight/liter. Results are also presented for biomass concentrations up to 1 g dry weight/liter. On the basis of these results, economic feasibility is examined by comparison with synthetic polyelectrolytes which appear to be the only other flocculants leading to a similar efficiency. Extension of the process to marine algae is also presented.