Using seawater-based Na2CO3 medium for scrubbing the CO2 released from Bio-CNG plant for enhanced biomass production of Pseudanabaena limnetica

Abstract

The concentration of CO2, one of the most important greenhouse gases (GHG), has reached to 409.8 ± 0.1 ppm in 2019. Although there are many carbon capture and storage (CCS) methods, they are very costly and their long term use raises concern about environmental safety. Alternatively, bio-sequestration of CO2 using microalgal cell factories has emerged as a promising way of recycling CO2 into biomass via photosynthesis. In the present study, Indigenous algal strain Pseudanabaena limnetica was cultivated in pneumatically agitated 60-L flat-panel photobioreactor system. The gas was released from Bio-CNG plant as by-product into Na2CO3-rich medium and cultivated in semicontinuous mode of operation. It was observed that when CO2 was sparged in seawater-based 0.02 M Na2CO3 solution, maximum CO2 was dissolved in the system and was used for algal cultivation. Control system produced 0.64 ± 0.035 g/L of biomass at the end of 15 days, whereas CO2 sparged Na2CO3 medium produced 0.81 ± 0.046 g/L of biomass. When CO2 from Bio-CNG station was fed, it resulted in biomass production of 1.62 ± 0.070 g/L at the end of 18 days compared to 1.46 ± 0.066 g/L of biomass produced in control system which was not fed with gas released from Bio-CNG plant as by-product. Thus, feeding CO2 directly into Na2CO3 medium and operating the system semicontinuously would be efficient for scrubbing CO2 from commercial Bio-CNG plant. This study proves that feeding CO2 gas from Bio-CNG plant into Na2CO3-rich alkaline system can be used to feed algae for enhanced biomass production.