Novel Bio-regeneration Concept via Using Rich Solution as Nutrition Resource for Microalgae Cultivation: Effect of pH and Feeding Modes

Absorption–bioconversion hybrid process has the advantages of capturing CO 2 in the form of bicarbonate in the absorber and utilizing bicarbonate as a carbon source for microalgae growth in the photoreactor. It can simultaneously achieve CO 2 capture and utilization and avoid energy consumption of rich solvent regeneration in conventional absorption processes. As a promising solvent for hybrid process, NH 3 could capture CO 2 at low cost and with high efficiency. However, a high concentration of regenerated NH 3 in a photoreactor would adversely affect microalgae growth. Previous work indicated that batch-feeding cultivation and pH adjustment might be a promising alternative to reduce NH 3 release rate and its inhibition to microalgae. In this work, the influence of batch-feeding interval (i.e., 3, 6, and 9 days) and pH (i.e., 7, 8, and unadjusted) on the performance of absorption–microalgae hybrid system was investigated. The experimental results indicated that pH control has a significant influence on the growth of microalgae ( Chlorella sp. L38) and value-added ingredient yield. NH 3 escape ratio could be kept at lower than 34% when the pH was controlled at 7. In addition, a shortened batch-feeding interval would be also beneficial to increase the growth of microalgae, with the NH 3 escape ratio decreased to 19%. It could be observed that the performance of the absorption–microalgae hybrid system could be intensified by the pH control and batch-feeding interval optimization.