Sometimes the purified wastewater (from secondary or biological treatment) is not yet of good enough quality for discharge. In such cases additional processes might be needed. Examples are:

• Phosphate removal. Often with coagulation and filtration solutions.
• Solids or TSS reduction. Often with filtration solutions.
• Disinfection. Possibly with ozonation, chlorination or UV solutions.
• Carbon filtration. For removal of remaining contaminants and impurities (like drug or medicine residues) by absorption.