Electro-flotation of Chlorella sp. assisted with flocculation by chitosan

Harvest of algal biomass from dilute culture medium at low cost remains a major hurdle to industrial scale processing. Conventional harvesting methods are not only costly, but also affect any later downstream processes partly because of the metal ions contamination by flocculants. This work constructed an electro-flotation technique including two steps of flocculation by chitosan first and then sequential bubbling flotation by non-sacrificial graphite electrodes. Laboratory work has been carried out to investigate the influences of chitosan dosage, pH value, cell density of algal culture, stirring rate and mixing time on flocculation efficiency, and the voltage and current intensity imposed on electrodes and the space between electrodes on flotation efficiency. Moreover, a 1000 L pilot bench of electro-flotator constructed to harvest Chlorella sp. was tested. Around 90% of total recovery efficiency and 50 times concentration rate have been reached, and only 23.7 g chitosan and 0.43 kWh of electricity are required to harvest 1 kg biomass. Above results proved electro-flotation by graphite electrodes assisted with chitosan is a safe and cost effective approach for microalgae harvesting.