Mixotrophic and heterotrophic growth of microalgae using acetate from different production processes

Abstract

The high metabolic flexibility and biodiversity of microalgae make them promising systems for the production of chemicals and high-value metabolites to be utilized in various industrial applications. Currently, microalgae are primarily cultivated in phototrophic processes or in fermenters using glucose as substrate. However, such configurations are often too costly for the majority of potential applications and require improvements. The use of acetate as substrate to enhance biomass productivity and reduce cost and environmental impacts is a promising solution. In a future bio-based economy, acetate can serve as an excellent intermediate to link many industrial facilities, as it can be synthesized using different technologies from renewable resources as CO2 and waste. This work provides a detailed description of acetate synthesis processes alternative to the conventional methanol carbonylation, including the pros and cons of each: aerobic and anaerobic fermentations; thermochemical treatments; C1 gas fermentation; microbial electrosynthesis and artificial photosynthesis. Additionally, the utilization of acetate as substrate for microalgae growth in mixotrophic and heterotrophic conditions is reviewed, covering key metabolic and engineering aspects (strains, yields, growth rate, inhibition, productivity, process configuration). These aspects serve as guidelines for a rationale design of an algal cultivation process based on acetate as a carbon source. Finally, the review critically assesses the state of the art of coupling of acetate-rich streams with algal biomass production, highlighting the pros and cons and addressing the main knowledge gaps to be filled through future research.