GreenTreat aims to develop a microalgal-based, integrative, sustainable process of tertiary wastewater treatment (WWT) and treated water reuse: a pilot process using microalgae to remove excess nitrogen and phosphorus along with pharmaceutical products, which conventional WWT technologies often fail to eliminate. In GreenTreat, the traditional aerobic/anaerobic bacterial treatment used in most wastewater treatment plants (WWTP) will be complemented with photobioreactors newly designed by Bluemater, a Portuguese biotechnology company, in which a microalgae (Tetraselmis sp., CTP4) recently developed by CCMAR is expected to complete the elimination of nutrients and increase the removal rates of pharmaceuticals. These photobioreactors are an innovative design conceived for the remediation of contaminated waters by microalgae and were selected for their good productivity/cost relationship. In addition, flotation will be used for microalgae harvesting and biomass recovery. CTP4 is a highly stress-tolerant microalgal isolate able to outcompete most contaminants even in wastewater, withstand high light intensity without apparent photoinhibition, and survive temperatures as high as 50°C, all indispensable features in outdoor cultivation. CTP4 is also able to deplete nutrients rapidly. Under low nutrient levels its lipid content can increase up to 50% of its dry weight. Hence, to decrease costs and carbon footprint of WWTP, lipids of the generated microalgal biomass will be used for biodiesel production, whereas the remaining biomass will be used as feedstock to produce biogas. During the project, the efficiency of nutrient and pharmaceutical removal and the population dynamics of the bacteria/microalgal communities in the pilots will be tested under different operational conditions (hydraulic and sludge retention times) and under different seasonal constraints (e.g. winter and summer extreme temperature and light conditions, and contaminants load due to population fluctuations). Treated water will be assessed for definition of water reuse scenarios. Lastly, a lifecycle assessment of the proposed technology will be conducted and its economical viability assessed.