Microalgae harvesting technique using ballasted flotation: A review

Microalgae biomass as a promising bioenergy feedstock is considered to have huge potential to produce biofuels. However, a main barrier in microalgae biomass production is the economical and efficient harvesting and dewatering process of microalgae in large scale, which significantly restricts the development of microalgae biotechnology industries. Ballasted flotation, can be viewed as inverted ballasted sedimentation techniques, has recently been used to harvest microalgae. In this process, low-density materials (LDMs) are used to replace the bubbles in the dissolved air flotation process and attach to the microalgae cells, so that the microalgae cells float to the liquid surface and implement solid–liquid separation. This paper reviews the research progress of ballasted flotation technique for microalgae harvesting by revealing the principles of ballasted flotation process, summarizing the advantages and disadvantages, analyzing the operating parameters and energy consumption. This review expands our understanding about ballasted flotation, intends to provide guidance for the future research and practical applications of ballasted flotation. Finally, this review also suggests the directions for challenges and further perspectives of ballasted flotation for microalgae harvesting in the development of new LDMs and flocculants, the detachment of microalgae cell-LDM aggregates, the recovery and utilization of the harvest water, etc.