Today’s concerns about greenhouse gases (GHG) are a worldwide issue. Wastewater treatment plants (WWTPs) partially contribute to this problem. Furthermore, water recycling can help the environment and can contribute to reducing waterborne diseases. Processes performed in WWTPs vary, but they typically include headworks, grit removal, mixing, clarifying, nutrients removal, filtering, disinfection, discharging to local water bodies or open fields, and handling and proper disposal of solid objects. In some plants, biogas is generated. Although wastewater treatment is a mature technology, there is significant potential for improvements from the standpoints of their economics, their energy efficiency, and their potential to reducing greenhouse gas emissions.