Microalgae play crucial roles in carbon sequestration, nutrient removal, biosorption, and biodegradation of pollutants in aquatic ecosystems. They are used for effective nutrient removal in conventional wastewater treatment systems and in phycoremediation of effluents from various industries, including petrochemical, pharmaceutical, and textile industries. Wastewater treatment based on microalgae is a sustainable solution for efficient nutrient removal and degradation of both organic and non-organic pollutants. Unlike traditional methods, the biomass produced in wastewater can be utilized for the production of economically valuable products in a biorefinery mode, contributing to the circular economy through waste management. The advances in cultivation methods, technical designs, and the introduction of unconventional microalgal systems have enhanced the sustainability and effectiveness of wastewater treatment technology, along with additional benefits like carbon sequestration and biomass production. Microalgal wastewater treatment has emerged as a promising technique to meet the industrial commitment to responsible practice by integrating several chemical and biochemical techniques. Sequential microalgal water treatment systems, where different microalgal species or strains are grown in a sequential or stage dependent manner, have emerged as an effective mechanism in many industrial and municipal sectors. This chapter discusses the recent technological developments in microalgae-based wastewater treatment systems, including the sequential systems, their designs, the strains used, and the mechanisms involved for treatment and monitoring. It also discusses the potential and challenges in the establishment of large scale sequential microalgal wastewater treatment plants in industries and possible solutions for the integration of the technology based on the concepts of circular economy towards sustainability.