At the City's wastewater treatment plants, wastewater undergoes five major processes: preliminary treatment, primary treatment, secondary treatment, disinfection and finally, sludge treatment. Primary and secondary treatments remove about 85% to 95% of pollutants from the wastewater before the treated wastewater is disinfected and discharged into local waterways. Sludge, the byproduct of the treatment process, is digested for stabilization and is then dewatered for easier handling. The resulting material, known as biosolids, is then applied to land to improve vegetation or processed further as compost or fertilizer. (See illustration — “Diagram of Treatment Process” on page 16-17.)