Proton and nutrient balanced medium for scalable, practical pH control in high-density Chlorella vulgaris cultures

pH of microalgal cultures increases with cell growth particularly in nitrate-based growth media, which requires chemical pH adjustment such as CO2 injection to prevent 'culture crash'. The CO2 injection however, is expensive and technically challenging in large-scale cultures. This study reports a unique and practical pH control mechanism through a new medium formulation with nutrient and proton balances, called B-8 medium. Comparison of B-8 to a common nutrient-balanced M-8 medium for growing Chlorella vulgaris showed that B-8 stabilized pH, supported 10-20% more biomass and was 60% less expensive than M-8. The scalability of the B-8 medium to facilitate pH control was further demonstrated by achieving pH stability in 4.8 L photobioreactor cultures without additional chemical buffering. This demonstrates for the first time, that practical and scalable pH control in high-density microalgal cultures can be achieved through growth medium optimization for nutrient and proton balances-an easier and more economical alternative to those achieved chemically.