New York City’s Wastewater Treatment System
Where Sludge Goes
Sludge is the solid byproduct of wastewater treatment. Its use is regulated by both the federal and state governments. NYC’s sludge is digested, which is a form of processing that improves the quality of the material and creates biogas. After digestion, the sludge is then dewatered. Dewatering is a process where the solid components of sludge are separated from the liquid components. Not all of the city’s 14 wastewater treatment plants have onsite dewatering facilities. Those facilities without dewatering capabilities transport their sludge through force mains or sludge vessels to in-city treatment plants that have onsite dewatering capabilities. After dewatering, the leftover solid product of the processed sludge is generally referred to as “biosolids”. The city’s biosolids are managed by outside contractors who take it to landfills for disposal or further process it to recover its value as a nutrient-rich soil amendment.
As part of the mayor’s plan for OneNYC, we have a goal of zero-landfilling of biosolids by 2030. This means we will develop a program to reuse all biosolids beneficially. Some of the further processing technologies that can be used to qualify biosolids for reuse include composting, drying, and lime stabilization. NYC produces about 1,200 tons/day of biosolids or about 50 truckloads! Such a large quantity spread out over our 6 dewatering facilities means that our beneficial use program will need to be diverse and include multiple types of further treatment.
To learn more about biosolids, we recommend visiting the Water Environment Federation, Mid-Atlantic Biosolids Association, and Northeast Biosolids and Residuals Association websites.