Improvement of Photoautotrophic Algal Biomass Production after Interrupted CO2 Supply by Urea and KH2PO4 Injection

Abstract

Microalgae-derived biomass is currently considered a sustainable feedstock for making biofuels, including biodiesel and direct combustion fuel. The photoautotrophic cultivation of microalgae using flue gas from power plants has been continuously investigated to improve the economic feasibility of microalgae processes. The utilization of waste CO2 from power plants is advantageous in reducing carbon footprints and the cost of carbon sources. Nonetheless, the sudden interruption of CO2 supply during microalgal cultivation leads to a severe reduction in biomass productivity. Herein, chemical fertilizers including urea and KH2PO4 were added to the culture medium when CO2 supply was halted. Urea (5 mM) and KH2PO4 (5 mM) were present in the culture medium in the form of CO2/NH4+ and K+/H2PO4−, respectively, preventing cell growth inhibition. The culture with urea and KH2PO4 supplementation exhibited 10.02-fold higher and 7.28-fold higher biomass and lipid productivity, respectively, compared to the culture with ambient CO2 supply due to the maintenance of a stable pH and dissolved inorganic carbon in the medium. In the mass cultivation of microalgae using flue gas from coal-fired power plants, urea and KH2PO4 were supplied while the flue gas supply was shut off. Consequently, the microalgae were grown successfully without cell death.

A Low-Cost Fertilizer Medium Supplemented with Urea for the Lutein Production of Chlorella sp. and the Ability of the Lutein to Protect Cells against Blue Light Irradiation

“…was 5.36 mg/L/day with the addition of 20 mM urea in 20 g/L fertilizer. In addition, urea is a widely used and cheap nutrient source for microalgal cultivation [71,72]. Therefore, when 20 mM urea was added to the 20 g/L fertilizer medium to replace the f/2 medium, the cost of media was reduced from USD 16.35 to USD 0.665 per gram lutein, a reduction of 96% (Table 1).…”

CO2 Sequestration Using Sodium Hydroxide and Its Utilization for Chlorella sorokiniana Biomass Production

“…Furthermore, the highest carbon consumption was 691.8 mg.L -1 as also seen in NaOH60 medium, followed by NaOH120, and NaOH30 (Figure 3). Carbon consumption was determined by acidic-alkalimetric titration method, based on the absorption reaction equation between CO2 gas and NaOH, as in equations ( 1) and ( 2) (Molazadeh et al, 2018;Yu et al, 2021).…”

“…The use of alkaline solutions to increase CO2 retention in microalgae cultivation has been carried out using different microalgae or with different concentrations and types of alkaline solutions (Nayak et al, 2013;Song et al, 2019;Yu et al, 2021), but optimization of NaOH concentration to bind CO2 in photoautotrophic cultivated C. sorokiniana has never been done before. The results of this study enrich knowledge about the potential of microalgae C. sorokiniana as a CO2 mitigation agent and an alternative source of energy and nutrition.…”

“…Moreover, the total protein content in Chlorella can be up to 43% dry weight according to the growth conditions, and 12-55% for total carbohydrate content (Ru et al, 2020). The involvement of NaOH solution also facilitates cell growth by absorbing CO2 into bicarbonate ions (HCO3-) (Yu et al, 2021). However, HCO3− as weak acid can lower the intracellular pH of the cytoplasm at a high concentration of dissolved (Ma et al, 2017).…”