Evaluating the Trade-offs Between Microalgal Biomass Production Rate and Nutrient Reduction in Dairy Waste Whey Permeate-amended Culture

Abstract

Leveraging microalgae for food production and aquaculture feeds utilizing waste offers an economically efficient and circular solution to food challenges while promoting nutritional sustainability. This research investigates the potential of whey permeate (WP), a by-product of cheese making, as a nutrient-rich substrate for algal cultivation. The first part (Chapter 2) delves into the preparation of WP powder and its integration into culture media, revealing that autoclaving WP with NaOH, resulting in browning reactions, supported algal growth, especially with 1 M NaOH. Media adjustments at pH 7 optimized biomass, and aging enhanced growth of the green alga Tetraselmis suecica, possibly due to calcium phosphate resolubilization. The solvent used with WP influenced phosphorus availability, while a light exposure experiment explored WP degradation. The cryptophyte Chroomonas mesostigmatica had higher growth in WP media with a headspace, emphasizing the importance of gas exchange. A second part (Chapter 3) extends to larger-scale exploration by characterizing biomass from four algal species in closed systems using WP as a phosphorus substitute and organic carbon source. Signs of mixotrophic growth were observed in T. suecica and the diatom Chaetoceros muelleri, suggesting lactose assimilation from WP. The pinguiophyte Pinguiococcus pyrenoidosus showed comparable eicosapentaenoic acid (EPA) productivity rates in WP media during exponential phase, highlighting a promising strain for omega-3 production. C. muelleri had significant fatty acid accumulation in stationary phase with WP media, hinting at its suitability for biofuel production. T. suecica and C. mesostigmatica emerged as potential candidates for protein production, and C. muelleri and C. mesostigmatica seemed suitable for WP remediation, given their luxury uptake of phosphorus. This work lays the foundation for large-scale production of algae-based valuable compounds using dairy waste WP as a growth substrate.