Microalgae is one type of photosynthetic microorganism which can utilize carbon dioxide (CO2) through photosynthesis and convert exogenous carbon into microalgal biomass. Microalgal cultivation is considered as one of promising ways for carbon capture to reduce greenhouse gas effects. Formate is known as a single-carbon chemical, which possesses good solubility and stability under a wide range of pH. This work represents a comprehensive examination of microalgal culture of the green microalgae Chlorella sorokiniana by utilizing formate and effects of formate on this symbiotic algal-bacterial system.In Chapter 2, an algal-bacterial symbiotic system was explored to investigate utilization of formate as a carbon source. The algal-bacterial assemblage, after a 400-day adaptive evolution using the formate medium, has demonstrated a new capability to assimilate both formate and CO2 to promote biomass production. 13C isotope tracing and microbial community analysis were conducted to indicate a uniquely evolved formate utilizing culture. This study demonstrates a new route of using electrochemical-derived formate to support mutualistic algae-bacteria biorefinery while the formate as an alternative carbon source could repel pests for outdoor algal cultivations.In Chapter 3, cultivation parameters including light intensity, formate feeding rate and a novel approach of alternating carbon feeding were tested for enhancing microalgal biomass and productivity during the culture. Effects of formate on microbial communities and algal assemblage were reported. The results showed that formate was a good carbon source for microalgal cultivation, and the highest biomass concentration of 1.4 g/L was achieved during the culture. Microbial community analysis revealed a stable microalgal-bacteria consortia under the formate feeding system. Microalgal biomass was further increased to 1.6 g/L compared to the℗ formate feeding method with the alternating carbon feeding method.℗ In Chapter 4, effects of formate as an additional carbon source for microalgal culture with pumping flue gas within a 100 L photobioreactor (PBR) were investigated. Results showed that formate addition group exhibited better carbon capture efficiency than group without formate addition. Mass and energy balance analysis showed that formate group required 20% less energy consumption and showed nearly 33% higher biomass yield on average compared to control group.In summary, this work presents a symbiotic algal-bacterial system of utilizing formate. The work establishes a stable microalgal cultivation method with formate feeding in both bench-scale and pilot-scale PBRs. Notably, this work advances carbon capture efficiency in microalgal cultivation field, as well as innovative methods and techniques that elucidate the viability of formate utilization in microalgal cultivation for carbon capture.℗
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