eliminating pollutants lowering pollutants lessen pollutants waterborne illness ensuring adherence human activity negative effects rivers lakes ecosystem importance people animals wholesome environment goals guarantee extraneous nutrients freshwater resources air soil primary objectives safely released activated sludge biological techniques physical chemical eliminating impurities environmental requirements avoid contaminating environmental standards treating wastewater drinking water industrial water bodies clean provide treated water satisfies environmental standards protect aquatic habitats treating wastewater makes regulations avoid fines wastewater treatment wtp