Microalgae and cyanobacteria polysaccharides: Important link for nutrient recycling and revalorization of agro-industrial wastewater

•Microalgae polysaccharides production is enhanced under stress conditions.•Agro-industrial wastewater is a growth media for the production of polysaccharides.•Polysaccharides extraction facilitates their use as functional ingredients in foods.•Cianobacteria and microalgae polysaccharides have potential use in agriculture. Despite the high amount of wastewater generated by agroindustry around the world, only a limited number of alternatives for its reuse or revalorization have been applied. One of the most suitable alternatives for agro-industrial wastewater revalorization is the production of extracellular polysaccharides (EPS) from microalgae and cyanobacteria. Due to the complex carbohydrate metabolic pathway in microalgae and cyanobacteria, the EPS produced can be employed for residual water treatment, emulsification, gelling, and as a prebiotic ingredient, among others. EPS biological activities, including antioxidant, anti-inflammatory, antitumor, and antimicrobial have been related to their molecular weight, sulfate, uronic acid, or charged group content. In this review, microalgae and cyanobacteria EPS production, their functional properties, and sustainable production from agro-industrial wastewater are addressed. Microalgal polysaccharide sustainable production by agro-industrial wastewaters has the potential to become a standard for transforming linear food processing systems into circular economy alternatives. [Display omitted]