Challenges and Perspectives for Alternative Media in Microalgae Cultivation: Main Substrates and Approaches and Potential of Alternative Derived Biomasses as Source of Bioactives

This chapter presents an overview of the utilization of food industrial waste/byproducts for cultivating freshwater microalgae biomasses, highlighting their main characteristics and potential application. The main industrial byproducts used in microalgae cultivation were dairy wastewater, cheese whey, starch wastewater, fruit peels or discarded fruits, oil mill waste, tofu, brewery and restaurant food wastes, and fish protein hydrolysate. The main microalgae species evaluated were Chlorella, Porphyridium, Ascochloris, Desmodesmus, Haematococcus, Lagerheimia, Monoraphidium, Scenedesmus, Crypthecodinium, Chlamydomonas, and Spirulina. Industrial byproduct utilization may increase microalgae growth rate and biomass productivity, resulting in biomasses with higher concentrations of bioactive compounds, such as carotenoids, phycoerythrin, phycocyanin, beta-carotene, lutein, zeaxanthin, astaxanthin, docosahexaenoic acid, omega fatty acids, and exopolysaccharides compared with the synthetic medium. This strategy can reduce the use of freshwater and growth medium for microalgae cultivation, reducing production costs. Besides, microalgae cultivation removes nutrients from wastewater, reduces possible environmental impacts, and improves the industry’s carbon footprint. Optimizing pretreatment and cultivation parameters may contribute to an increased concentration of bioactive compounds, such as using different pretreatment methods (maceration, aqueous extraction, heat-assisted extraction), control culture conditions (light time and intensity, pH, temperature), and optimizing byproduct concentration and promote nutritional manipulations in the culture medium (nutrient supplementation/privation), among others.