It is known that bioflocculation is successfully used for harvesting microalgae in facilities where microalgae are used in wastewater treatment. Some microalgal species flocculate more readily than others and such naturally bioflocculating microalgae can be mixed with other species to induce flocculation. In many researches have been shown that some bacteria and fungi have ability to induce efficient bioflocculation of microalgae (Zhang and Hu, 2012, Surendhiran and Vijay, 2013 and Talukder et al., 2014). Also it was proposed new effective method for harvesting of microalgae by bioflocculation of a non-flocculating microalga with another autoflocculating microalga (Salim et al., 2011). The advantage of this method in comparison with other applied flocculating microorganisms (such as bacteria or fungi) is that it does not require different cultivation conditions and therefore avoids additional costs and prevents undesired contaminations.
In this study the flocculation efficiency of commercial PEO compared with PAA and coagulant (i.e., ferric chloride) on harvesting Chlorella vulgaris. The technology of simultaneously employing coagulant and flocculant for drinking water purification and sewage treatment was used for harvesting of microalgae. The flocculated biomass was used as ballast agent for harvesting of microalgae ( Fig. 1). Also the supernatant after flocculated biomass separation was reused for microalgae cultivation.