Harvesting Microalgae With Chitosan

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.