The study looked at the quality of wastewater leaving treatment plants in Tehran, Iran, which is crucial for protecting water sources from pollution. Researchers checked certain key factors like oxygen levels, solids, and acidity in the water. They analyzed the data using statistical programs and found that the pH level, oxygen demand, and solid content in most of the wastewater met Iran's standards. Plant C was the most effective in this study. The research didn't name the specific treatment plants but found that most were doing a good job of treating the water before releasing it.