Non-destructive in situ monitoring of photosynthetic quotient in open microalgae cultivation.

Photosynthetic quotient (PQ)-based feedback strategy is emerging as a promising approach for precise optimization the cultivation of microalgae. However, the absence of in situ and non-destructive monitoring methods remains a critical bottleneck in open systems. Here, an intermittent aeration (IA) cultivation mode was constructed for measuring PQ of Nannochloropsis oceanica. A daily IA cycle with 1:23 h non-aeration to aeration ratio enabled real-time PQ calculation using dissolved oxygen and carbon dioxide concentrations. The measured PQ (PQm) closely aligned with the theoretical PQ (PQc) under both nitrogen-sufficient and nitrogen-limited conditions, (R2 > 0.80, P < 0.05). Under nitrogen-limited, PQm also exhibited a strong correlation with lipid content (R2 = 0.86), highlighting its potential as a real-time indicator of lipid productivity. This scalable, low-cost method eliminates the need for tail gas analyzer, enabling dynamic carbon flux assessment and adaptive process control for enhanced efficient in open microalgae cultivation.