Microalgae are naturally gifted microorganisms that provide oxygen and clean environment by consuming wastewater nutrients and carbon dioxide. Operating conditions (retention time, temperature, light, sludge retention time, etc.) and unique consortium help in achieving higher degree of wastewater treatment. The growth of microalgae is mainly inhibited by the concentration level of pollutant in the wastewater. Pollutants like phosphorus, ammonia, carbon, etc., are consumed by algae and result in biomass production. This chapter provides comprehensive review on microalgae cultivation modes in wastewater, challenges and biomass applications for recovery of value-added products. Microalgae pave way for circular economy in achieving sustainable development goals. © 2023 Elsevier B.V., All rights reserved.