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

Abstract

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 4.8L 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.