Quantifying internal CO₂ recycling for high-rate carbon capture in mixotrophic Scenedesmus acuminatus.

Authors

Muhammad Muzammil Sultan, Muhammad Mubashar, Hira Ashfaq, Jing Li, Xuezhi Zhang

Published in

Bioresource technology. Pages 135560. Aug 02, 2026. Epub Aug 02, 2026.

Abstract

Mixotrophy, which simultaneously utilizes organic and inorganic carbon, offers a promising alternative to overcome the low biomass productivity and carbon utilization rates of conventional microalgal systems. However, its potential for enhanced CO₂ capture and the contribution of internal respired-CO₂ recycling remain poorly quantified. This study used a stoichiometric carbon-budget framework to estimate CO₂-equivalent carbon capture, carbon utilization, model-estimated internal CO₂ recycling, and evaluated biomass production in Scenedesmus acuminatus under autotrophy, heterotrophy, and mixotrophy, followed by optimization of organic carbon source, glucose loading, and feeding strategy. Under autotrophy, the CO₂-eq capture rate reached only 0.48 g L^-1d^-1, whereas CO₂ emission under heterotrophy reached 0.27g L^-1d^-1. Mixotrophy achieved a net CO₂ eq. capture rate of 1.19 g L^-1 d^-1, 148% higher than autotrophy. Among different organic carbon sources, glucose was the most effective carbon source for enhancing carbon utilization and biomass productivity. Batch glucose optimization showed that 5 g L^-1 glucose showed highest net CO_2-eq capture, whereas 6.5 g L^-1 favored biomass accumulation but reduced capture efficiency, demonstrating that biomass and carbon-capture optimal were not identical. Semi-continuous glucose feeding further improved performance: a total glucose input of 6 g L^-1 increased net CO₂ capture to 1.35 g L^-1 d^-1, enhanced total carbon utilization to 2.15 g L^-1 d^-1, and reduced unrecycled respiratory CO₂ emission by 80% relative to batch cultivation. These findings demonstrate that glucose-controlled mixotrophy enhances microalgal carbon capture by coordinating simultaneous organic/inorganic carbon utilization and internal CO₂ recycling, providing a basis for carbon-negative wastewater treatment and algal bio-refineries.

PMID:
42543101
Bibliographic data and abstract were imported from PubMed on 03 Aug 2026.

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