Abstract
BackgroundA 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.ResultsTo 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 9 7.4± 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.ConclusionsThis 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.
Highlights
A bicarbonate-based integrated carbon capture and algae production system (BICCAPS) uses carbonate to capture CO2 and produce bicarbonate for alkalihalophilic microalgal cultivation
Biomass concentration and pH were measured during 5 days of cultivation with different concentrations of sodium bicarbonate
In this study, N. oleoabundans was selected for semi-continuous recycling culture with BICCAPS, and this was the first proof of the recyclability of a BICCAPS
Summary
A bicarbonate-based integrated carbon capture and algae production system (BICCAPS) uses carbonate to capture CO2 and produce bicarbonate for alkalihalophilic microalgal cultivation. This culture resulted in an algal biomass productivity of up to 1.2 g L−1 day−1, indicating that high productivity is achievable at this extreme condition [7] This high concentration of bicarbonate can supply sufficient carbon at the beginning of each culture, with no continuous C O2 bubbling or interval feeding necessary. A low-cost horizontal floating photobioreactor without gas bubbling and/or an agitation system that uses waves as the only energy for mixing was developed in our previous study [8] This progress systematically reduced the cost of photobioreactor manufacturing, carbon supply, energy consumption, and culture condition control (pH, DO, temperature) [8] and showed great potential to reduce microalgal biomass production cost. The feasibility of using spent medium enriched with carbonate to absorb CO2 and conducting culture recycling must be proven by experiment
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