Concentration of Chlorella Sorokiniana Microalga Biomass at Combined Usage of Coagulants and Flocculants

Abstract

In this work we studied various methods for concentrating the algae biomass, and mechanisms of concentration processes of the microalgae cells. Presented are papers devoted to usage of various coagulants and flocculants (iron (III) chlorides and sulphates, titanium tetrachloride, slaked lime, potassium chloride, potassium permanganat, aluminum potassium sulphates, Flopam FO 4550 SH). In the experimental part we studied usage of FeCl₃^*6H₂O coagulant in the amount of 4, 6, 8, 10, 20, 30 mg/l of microalga Chlorella Sorokiniana suspension. Microstructure investigations have shown that at addition of ferrous chloride of concentration more than 20 mg/l, the cell death is more than 50%. Concentrations from 4 to 10 mg/l achieve low degree of precipitation (not more than 18%). Aiming at increasing degree of precipitation we investigated usage of two-component system coagulant-flocculant. Usage of two-component system results in a significant increase of precipitation degree of microalga Chlorella Sorokiniana: at addition of chitosan the degree reaches 53%, at addition of PAA it is 79%. We determined volume of the thickened biomass sludge. It shows that usage of chitosan results in more tightened biomass layer, which occupies minimal volume (V = 140 ml). The following three-component mixture is an optimum variant for high-efficient precipitation of biomass: coagulant FeCl₃ in the amount of 6 mg/l; flocculants as a mixture of chitosan 2% and PAA 1% in the amount of 10 ml/l. Addition of chitosan solution as a flocculant results in decrease of pH value, which is caused by usage of acetic acid for preparation of chitosan solution. Microstucture analysis of the precipitated biomass shows that at coloration of Chlorella Sorokiniana cells by methylene blue, the amount of dead (colored) cells is not less than 5%. Consequently, the precipitated biomass might be used for obtaining of valuable components.