Cities have been expanding at alarming rates; more and more people are entering in to cities for better livelihood and standard of living, which leads to the generation of enormous wastewater. Due to limited resources and unplanned settlement, most of the volume of this increased municipal wastewater remains untreated or partially treated, which exert pressure on aquatic ecosystems, as municipalities find the escape route for discharging the wastewater in to nearby lakes, wetlands, steam or rivers. Conventional treatment involves the physical, chemical and biological treatment processes that are able to remove most of the organic matter (BOD) from the wastewater; but it still contains excess nutrients and pathogenic microbes that create the problem of eutrophication in the receiving water bodies. To remove these excess nutrients, many advanced processes could be used, which require high cost of building and operation; which are not feasible for low-income countries.

Microalgal remediation could be low-cost and a sustainable treatment approach that provides an efficient wastewater treatment and affordable for all the countries. Microalgae have proved to be efficient nitrogen and phosphorous sequesters and remove heavy metals from the wastewater; further they remove the color and odor through oxygenation of water. They could be applied to untreated or secondary treated wastewater; applied either in suspended culture form or in the form of microalgal biofilms.