More risks to the environment and public health arise from the use of wastewater, particularly in the developing nations where large quantities of untreated wastewater are used in agriculture and wastewater treatment is rare. Wastewater treatment is becoming increasingly important. Food, energy, and water security are becoming increasingly important for India and other countries. In India, most river basins have closed or drained completely. Untreated waste water discharged into surface and ground waters is the primary source for creating pollution in India. Due to the effects of urbanization, industrialization, and agricultural growth, the area also experiences moderate to severe water shortages. Approximately, 73,000 MLD (megaliters per day) are generated in the major cities of India. Large amounts of highly polluted wastewater are produced by biorefineries that are used to produce fuel ethanol. Municipal water is another type of waste water collected from homes, offices, shops, and restaurants in urban areas. Loaded waste water collected from biorefineries is first treated by a biological process named anaerobic digestion. Use of algae is another approach to treat waste water. In a similar way, for the treatment of municipal wastewater, constructed wetlands (CWs) provide an affordable alternative. An overview of the research on various waste water treatment plants and techniques is given in this chapter.