Photosynthesis-fermentation hybrid system to produce lipid feedstock for algal biofuel

To avoid bacterial contamination due to medium replacement in the expanded application of a photosynthesis–fermentation model, an integrated photosynthesis-fermentation hybrid system was set up and evaluated for algal lipid production using <i>Chlorella protothecoides</i>. In this system, the CO₂-rich off-gas from the fermentation process was recycled to agitate medium in the photobioreactor, which could provide initial cells for the heterotrophic fermentation. The cell concentration reached 1.03±0.07 g/L during photoautotrophic growth and then the concentrated green cells were switched to heterotrophic fermentation after removing over 99.5% of nitrogen in the medium by a nitrogen removal device. At the end of fermentation in the system, the cell concentration could reach as high as 100.51±2.03 g/L, and 60.05±1.38% lipid content was achieved simultaneously. The lipid yield (60.36±2.63 g/L) in the hybrid system was over 700 times higher than that in a photobioreactor and exceeded that by fermentation alone (47.56±7.31 g/L). The developed photosynthesis-fermentation hybrid system in this study was not only a feasible option to enhance microalgal lipid production, but also an environment-friendly approach to produce biofuel feedstock through concurrent utilization of ammonia nitrogen, CO₂, and organic carbons.

为避免光合-发酵模型扩大应用中因培养基更换引发的细菌污染，本研究构建并评估了一套整合型光合-发酵混合系统，以原壳小球藻（Chlorella protothecoides）为生产菌株开展藻类油脂合成研究。该系统将发酵过程产生的富CO₂尾气回收，用于搅拌光生物反应器内的培养基，同时可为异养发酵提供初始接种细胞。光自养生长阶段，细胞浓度可达1.03±0.07 g/L；随后通过脱氮装置去除培养基中99.5%以上的氮源后，将浓缩的绿色藻细胞切换至异养发酵阶段。系统发酵结束时，细胞浓度可高达100.51±2.03 g/L，同时油脂含量达到60.05±1.38%。该混合系统的油脂产率（60.36±2.63 g/L）较单一光生物反应器体系提升超700倍，也优于单一发酵体系（47.56±7.31 g/L）。本研究开发的光合-发酵混合系统，不仅是提升微藻油脂产率的可行方案，同时也是一种环境友好的生物燃料原料生产途径，可同步利用氨氮、CO₂及有机碳源。