Physical, chemical, and biological processes are used for the purification of water. The primary stages of treatment are meant to remove solids that form in the upper surface of the water. Secondary stages remove the substances that are remnants of the primary treatment. Dissolved organics and suspended solids are removed. Tertiary methods remove nutrients and carry the polishing of wastewater. The final step is disinfection which removes and destroys pathogens. The generated sludge is separated and removed and is used for land purposes.