Enhancing the Removal of Highly Concentrated CO2 Through Synergism between Microalgae Consortium and Nutrient Ratio in Photobioreactor

Abstract

This research was carried out by developing the carbon capture and storage (CCS) technology to determine the synergism between microalgae consortium and the optimum nutrient ratio as an effort to obtain higher CO₂ removal efficiency and CO₂ utilization efficiency. The microalgae consortium consisting of Chlorella sp., Scenedesmus sp. and Ankistrodesmus sp. have been selected previously as potential candidates for Microbial Carbon Capture and Storage (MCCS) agent and already cultured continuously in PHM (Provasoli Haematococcus Media) artificial medium, in vertical column photobioreactor. Pure CO₂ gas at a high concentration of 10% (v/v) flowed from the bottom of vertical column photobioreactor continuously with optimum flow rate of 5 L.min^-1. A growth medium (PHM) containing artificial nutrients was flowed continuously at flow rate 7L.day^-1 and detention time 3.8 days. Four fluorescent lamps were positioned outside the photo-bioreactor to obtain light intensity of 4000 lux, set for 16 hours light exposure and 8 hours dark, with operating temperature 30°C maintained during the study. Three compositional variations of microalgae consortium were used. They are as follows;  Ch : Sc : An = 1: 1: 1; Ch : Sc = 1: 1; and Ch : An = 1: 1, where Ch, Sc, and An  were  Chlorella sp., Scenedesmus obliquus and Ankistrodesmus sp., respectively. The following variations of nutrient composition were used; C: N: P = 100: 10: 1, C: N: P = 100: 50: 1 and C: N: P = 100: 25: 1. The C, N, and P sources were CO₂ (inorganic), KNO₃, and KH₂PO₄, respectively. This study proves that synergism between the types making up the consortium also determined the ability to utilize inorganic carbon source. Without the presence of Ankistrodesmus sp., synergism between Scenedesmus obliquus and Chlorella sp. showed twice higher CO₂ utilization efficiency in comparison to the synergism between Ankistrodesmus sp and Chlorella sp. Increased nitrogen concentration in medium increased the growth of Chlorella sp and Scenedesmus obliquus as a consortium, the CO₂ removal efficiency, the CO₂ utilization efficiency and the Carbon Uptake Rate. The nutrient ratios C:N:P of 100:50:1 could increase CO₂ utilization efficiency upto 50% higher than the C:N:P of 100:10:1.