A Novel and rapid harvesting method of microalgae using saw dust coated polypyrrole

Abstract

Microalgae biomass harvesting is a big challenge and still a topic of great interest to develop economic and low energy technologies which could be capable both of managing large volumes of culture and efficiently recovering the biomass during upstream process. In this study, a simple and rapid harvesting method using electro conductive polymer coated saw dust had been presented as a new agent (flocculant) for separating Chlorella vulgaris from a highly diluted suspension. Polypyrrole (PPy) coated saw dust as a novel flocculant was prepared via in-situ polymerization of pyrrole (Py) monomer using FeCl3 oxidant in aqueous medium in which saw dust particles were suspended. The zeta potential of flocculant and Chlorella vulgaris and X-ray photoelectron spectroscopic (XPS) analysis of flocculant were characterized to understand the efficiency and mechanism of flocculant interaction with algae cell. PPy maintained predominantly positive charge over a wide pH range (2-10) with an isoelectric point at pH 10.4, while Chlorella vulgaris maintained negative surface charge from pH 5 and high with isoelectric point 3.8. The microalgae showed the highest separation efficiency at pH 10. The maximal recovery efficiency reached more than 90% for microalgae at a stirring speed of 120 rpm within 5 min. The maximal adsorption capacity of Chlorella vulgaris was 165 mg dry biomass/mg-saw dust coated PPy. Separation efficiencies were tested under various conditions such as different PPy/Saw dust dosage, pH and stirring speed. The concentration factor obtained was higher than 32 and high concentration factors saved energy and time associated with microalgal harvesting and .allowed a reduction in the equipment size necessary for biomass dewatering, thus improving the feasibility of using these microorganisms in biofuel or wastewater processes. The use of electro-conductive flocculant (PPy) allowed for efficient biomass recovery from freshwater microalgae cultures. The flocculant doses required were much lower than using other flocculants such as aluminium or iron salts, or chitosan.