The paper presents the nature, properties, conversion methods and trends in the use of microalgae biomass in various branches of the economy, in particular in the food sector. Possibilities of practical use of microalgae culture as one of the stages of the post-production water purification process in the dairy industry were presented. The implementation of circular economy principles in this sector has been focused on creating closed water cycles through the use of membrane installations combined with a system for the management of activated sludge in the microalgae biomass cultivation process. Sludge from dairy production is rich in nutrients that are used for the growth of microalgae cells. Microalgae biomass can be used as a renewable raw material, e.g. for the production of bio-chars, sorption biomaterials, as a substitute for lubricants and many others. The article focuses on microalgae used as sorption biomaterials and their importance in closing production water cycles in the food industry. Post-production sewage from the dairy industry contains a sufficiently large amount of biogenic substances that can be used to cultivate microalgae with properties dedicated to processing into biochars with a structure and functional features suitable for processing into sorption biomaterials.