Valorisation of food waste with distinct carbon-to-nitrogen ratios by the microalga Isochrysis galbana: laboratory demonstration and techno-economic assessment†

The use of microorganisms to convert food waste into high-value products is a promising biorefinery approach for not only the reduction of food waste but also its recycling and valorisation. Moreover, microalgae are increasingly recognised as cellular factories capable of producing various value-added metabolites by utilising organic nutrients. In this regard, this study examined different food waste with distinct carbon-to-nitrogen ratios as nutrient sources for the production of diverse value-added products via mixotrophic cultivation of the microalga Isochrysis galbana. It was demonstrated that, while both hydrolysates enhanced the microalgal growth compared to the autotrophic cultivation, steamed bun waste hydrolysate with a high carbon-to-nitrogen ratio led to improved lipid accumulation and the nitrogen-rich shrimp waste hydrolysate favoured the production of fucoxanthin. Based on these experimental results, techno-economic analyses were conducted and demonstrated that the strategies examined on a laboratory scale would be economically viable at pilot-plant scale, especially if a nitrogen-rich hydrolysate such as that derived from shrimp waste were used, as this promotes microalgal growth. This study highlighted the significance of adopting various kinds of food waste in microalgae-based biorefineries, and hopes to provide insights to relevant sectors from both experimental and economic perspectives.