Wastewater treatment systems that use microalgae have the potential to remove nutrients, heavy metals (HMs), dangerous compounds, biochemical oxygen demand (BOD), chemical oxygen demand (COD), and other pollutants. The microalgae treatment system is an environmentally friendly, economical, and long-term alternative for treating wastewater. Microalgae harvesting is an essential first step in processing algal biomass after growing in wastewater. The biomass of microalgae can be extracted using a variety of techniques, including filtering, flotation, gravity sedimentation, centrifugation, and flotation. Flocculation is currently the most promising approach for commercial-scale algal biomass harvesting. Innovative approaches to microalgal flocculation can drastically reduce the resources required for industrial-scale biomass production. Bio-based flocculation technologies have recently gained significant research interest because of their excellent efficacy, long-term viability, and ecologically friendly nature. Bioflocculation is safe and good for the environment, whereas chemical microalgae flocculation is effective but can damage the environment and the biomass it collects. Biological flocculation methods facilitate the integration of photosynthetic biorefineries with wastewater bioremediation, therefore enhancing the possibility of microalgae biotechnology for biofuel generation. Biochar, fertilizers, animal feed, and bioactive chemical extraction are some value-added products that may be made from harvested microalgae biomass because of their high protein, carbohydrate, lipid, vitamin, and antioxidant content. Thus, treating wastewater using microalgae contributes to sustainable wastewater management and satisfies the “reduce, reuse, and recycle” idea of the circular economy. Improving the efficacy of wastewater treatment and the productivity of algal biomass depends on understanding how microalgae extract pollutants and nutrients from wastewater. This chapter aims to explore recent advances in microalgal bioremediation for wastewater treatment and to summarize several cost-effective ways, including bio-based flocculation of harvesting microalgae biomass to recover and reuse it from wastewater treatment.
