Hybrid operation of photobioreactor and wastewater-fed open raceway ponds enhances the dominance of target algal species and algal biomass production

Abstract Successful cultivation of algal biomass in outdoor open systems depends on maintaining the growth of desirable species against algal invaders that diminish biomass production potential by posing competitive pressure on target algal species. This study demonstrates a photobioreactor (PBR)-open raceway pond (ORP) hybrid system that enables the operation of PBR as a continuous source of the inoculum of desirable algal species to sustain the growth of target algal species in small-scale open raceway ponds (sORPs). A 47-day long operation of PBR-ORP hybrid system indicated that hybrid operation allowed sORPs to maintain the predominant growth of Parachlorella sp. JD076, a target microalga, whereas the sORP operated in conventional semi-continuous mode completely lost the desirable algal species. Moreover, the sORP assigned to PBR-ORP hybrid operation exhibited 40% and 62% increased algal biomass and lipid productivities compared to the sORP operated in conventional semi-continuous mode. The hybrid system produced significantly more biomass and lipids than the conventional semi-continuous system with CO 2 amendment, and the hybrid system with CO 2 amendment was also more productive than the same system with only aeration. These results thus align well with previous studies that suggested the operation of PBR-ORP hybrid system as a promising crop maintenance strategy to improve the growth and yield of target species at industrial algal cultivation.