The New York City Department of Environmental Protection (DEP) operates a fleet of 5 small tankers that can frequently be seen in the waterways around the city. The tankers transport residual solids that remain after wastewater has been treated (called sludge) between city sewage treatment plants. The city operates 14 wastewater treatment plants but only six of those plants have the centrifuges needed to fully dewater sludge. Wet sludge is transported daily by tanker from the other 8 plants to one of the six that can dry it out, and some is also shipped to New Jersey where the Passaic Valley Sewage Commission dewaters it. Once dried out, the sludge can next be trucked to various processors and converted into fertilizer or other agricultural products.

The DEP tanker North River travelled up the Hudson Wednesday morning, having begun the day at the Bowery Bay treatment plant in Queens. The tanker stopped at the North River plant on the Hudson at 140th Street to deliver sludge, and then proceeded to the Passaic Valley Sewage Commission’s dock in Newark, presumably to deliver some more.

For more on the process for treating sludge, see the NYC DEP’s web site: https://www1.nyc.gov/site/dep/water/wastewater-treatment-process.page
The DEP site does not discuss the contract with Passaic Valley but the agreement is referred to in this report from 2008 and the visit by the North River to the PVSC dock suggests the arrangement remains in place: https://www1.nyc.gov/assets/dep/downloads/pdf/water/wastewater/safe-disposal-harmful-products/commercial-food-waste-disposal-study.pdf