A recycling culture of Neochloris oleoabundans in a bicarbonate-based integrated carbon capture and algae production system with harvesting by auto-flocculation

Background: A bicarbonate-based integrated carbon capture and algae production system (BICCAPS) uses carbonate to capture-CO2 and produce bicarbonate for alkalihalophilic microalgal cultivation. In this process, carbonate is regenerated and re-used for-CO2 capture. However, a practical example of a recycling culture to prove its feasibility is still absent. Results: To reach this goal, a recycling culture of Neochloris oleoabundans was created in this study. The effect of bicarbonate concentration on N. oleoabundans growth showed that the highest productivity was obtained at 0.3 mol L-1, but the highest apparent carbon utilization efficiency was obtained at 0.1 mol L-1. The harvest of algal biomass was tested with alkaline flocculation, which is induced by high pH due to bicarbonate consumption. The result showed that the maximum recovery rate of 97.7 +/- 0.29% was reached with a supplement of 20 mM-Ca2+. Compared with this, alkaline flocculation without-Ca2+ also resulted in a high recovery rate of up to 97.4 +/- 0.21% in culture with 0.7 mol L-1 bicarbonate. In recycling culture, the spent medium was bubbled with-CO2 and re-used for algal culture. After eight times of recycling, biomass productivity in recycling culture with 0.1 and 0.3 mol L-1 bicarbonate was 0.24 and 0.39 g L-1 day(-1), respectively, higher than the 0.20 and 0.30 g-L-1 day(-1) in the control. The apparent carbon utilization efficiencies achieved in these semi-continuous cultures with 0.1 mol L-1 bicarbonate were 242 +/- 3.1 and 266 +/- 11% for recycling and control culture, respectively, while those with 0.3 mol L-1 bicarbonate were 98 +/- 0.78 and 87 +/- 3.6%, respectively. Conclusions: This study proved the feasibility of BICCAPS recycling culture with the first practical example. More importantly, the produced algal biomass can be harvested without any flocculant supplement. Thus, this process can reduce both culturing and harvesting costs in algal biomass production.