Simultaneous Carbon Capture, Biomass Production, and Diary Wastewater Purification by Spirulina maxima Photobioreaction

The feasibility of a two-stage process involving carbon dioxide capturing and a photobioreaction (containing microalgae cells of Spirulina maxima) was investigated for the dual purpose of CO2 sequestration and wastewater remediation. The study systematically demonstrated the capability of CO2 removal through wet scrubbing using diluted wastewater as the scrubbing liquid and the potential of biomass growth in the CO2-enriched wastewater. The NaOH-alkalized wastewater provided a CO2 absorption capacity approximately equal to 0.5 g CO2 g(-1) NaOH at 0.5 M, and the absorbed CO2 was effectively converted into usable bicarbonate to support the growth of S. maxima. The biomass productivity using the CO2-enriched wastewater (30% diluted) was 0.036 g L-1 d(-1), which was in line with the productivity obtained from the controlled growth tests using NaHCO3 as the carbon source. Dilution of raw dairy (milk processing) wastewater was necessary as high chemical oxygen demand (COD) loading inhibited the growth of S. maxima. However, with sufficient dilution, as the COD was less than 300 mg L-1, the COD was effectively removed (79%) during the microalgae cultivation period, as were NH4+ (51%) and PO4- (35%) to lesser extents. The uptake of organic carbon indicated that Spirulina grew mixotrophically in the wastewater. Furthermore, by virtue of the hydroxide reaction with CO2 that form aqueous carbonates (lowering the pH) and the photosynthetic activity that consumes carbonates (increase the pH), the solution pH can effectively be used as the controlling parameter in operation of the system.