Leachate Treatment

Freshkills Park, located in Staten Island, NY, is the largest landfill-to-park transformation project in the world. From 1948 to 2001, over 150 million tons of New York City's trash were brought to four sections, or "mounds," of the Fresh Kills Landfill. Fresh Kills is in the final stages of landfill closure, and the New York City Department of Sanitation (DSNY) uses state-of-the-art landfill engineering systems to contain solid wastes and manage the by-products of landfilling.

Landfill leachate, a landfill by-product, is created when rain water filters through buried wastes in a landfill. The rainwater leaches, or dissolves, constituents that are in those wastes. This process is somewhat similar to the process of making a cup of coffee; the coffee is created when water percolates through the ground coffee beans.  

Our tour guide today will be Mr. Ted Nabavi who has served as the Director of Waste Management Engineering at DSNY for more than 30 years. He is an Environmental Chemist and part of his job is to manage the operation and maintenance of the Landfill Leachate Control System. He also manages the Landfill Gas Production and Purification System at the former Fresh Kills Landfill and a similar system at Edgemere Landfill in Queens.

At Fresh Kills, the leachate is pumped from the landfill to influent tanks for holding, and from there it undergoes a series treatment steps: biological treatment, chemical treatment, and the polishing stage.

Leachate naturally migrates from the center of the mound laterally outward toward the edges of the mound. The leachate collection system, which is located around the periphery of each mound, takes advantage of this natural flow path. The system consists of a series of collection trenches, collection trench piping, cut-off walls, pumping stations and transmission piping that collect the leachate and pump it to the treatment plant. Once it arrives at the plant, the leachate is pumped into influent tanks.

The purpose of leachate or wastewater treatment is to remove harmful constituents so the treated water can be safely discharged to "receiving waters." Leachate is high in ammonia which is toxic to fish and so must be removed prior to discharge. In the biological treatment step, ammonia is broken down by a process called nitrification or ammonia oxidation.

During chemical treatment, sodium hydroxide and aluminum sulfate are added to the leachate to transform soluble metals into their non-soluble form. The mixture of solids and liquid is then sent to a clarifier where the solids settle out and are removed.

After the clarifier tanks, the treated leachate is then discharged to sand filters where the solids are removed in what is referred to as a "polishing stage." The solids collected from the sand filter are processed with the sludge from the SBRs and the clarifiers.

Watery solids are generated during the treatment process, and they are referred to as "sludge". The easiest way to handle the sludge is to remove the water, which happens in equipment called "filter presses" shown in the following pictures. Layers of dewatered sludge are pressed together to create "sludge cakes."  

Landfill leachate that has gone through biological treatment, chemical treatment, and the final polishing stage is ready to be discharged to the Arthur Kill.