Sludge Boats
Out of Sight, but Never Out of Mind
Every day in New York City, aqueducts deliver over one billion gallons of fresh water from reservoirs in the Catskill Mountains. As quickly as this water is delivered, it is flushed down toilets and washed down the drains of sinks, showers and bathtubs. Rain, along with street waste, are sent down the drains too. The day ends with more liquid exiting the city through sewer pipes than entering by aqueduct.
The Story of Sludge
In the very earliest years of the city's history, the waste was simply sent to the rivers and bays around the city. At first, the local population was considered to be small enough that the tide, which pushed fresh saltwater past the city's shores, would take the wastewater with it when it retreated back to the vast ocean. This regular tidal action would seem to be sufficient until the city's population exploded in the late 1800s. At this point, that the city began building a sort of factory to clean the sewage (known as a ‘treatment plant’) before it emptied into the surrounding water.
A sewer line under construction in the 1930s. Image Credit: NYPL Digital Collections
One of the main byproducts of this cleaning process is called sludge. It's basically a thick 'soup' of what’s left over once the human waste, toilet paper and food bits have been ‘digested’ by helpful bacteria and the excess water has been removed.
The City tried several different solutions to dispose of the sludge. However, as more treatment plants were built, there were very few effective ways to deal with the growing amount of sludge produced. So, the sludge was piped into nearby bodies of water.
Much of the bacteria had been killed by the process, but it still did not smell or look very attractive. Of course, people living, working - and even swimming- nearby complained.
Image Credit: U.S. Fish and Wildlife Service via Wikimedia Commons
Once again, the vast ocean was seen as the answer. Because the goal of each new treatment plant was to return cleaner water to nearby bays and rivers, each plant was built alongside a body of water. This design made it easy for the city to bring boats to the plants.
Explore the map to discover treatment plants all across the city! Click on the arrows on the top right of you want to expand your map. Use the legend in the lower left-hand corner to help you.
Beginning in 1924, fleets of powerful tugboats would push (or pull) barges alongside the plants so that the sludge could be emptied into large floating containers.
A tugboat pushes a barge. Image Credit: Mitch Waxman via Flickr
After a twelve mile voyage to the edge of the harbor, all the sludge would be dumped into the ocean. At this location, the ocean was about 80 feet deep. (If you can envision a ten-story tall building, the water would only reach the top of the eighth floor windows at this depth.) The voyage was short enough that each barge could return by the end of the day, or even be re-filled and sent out to dump another load.
What do you think happened when the city dumped hundreds of barges of sludge here each day?
The map to the right shows the site, a 12-mile distance from shore. That's how far the sludge boats would travel!
At first the dilution principle (lots of ocean water + not as much sludge = a lot less pollution in local waters + a little more pollution in the ocean) seemed to work, but as more cities and towns used this solution, this part of the ocean began to be overwhelmed by the pollution, just as the rivers had in the early days of NYC. (One additional factor that added to the problem of ocean pollution was that many cities were also dumping their garbage in the ocean as well. This practice continued locally until the early 1930’s when New Jersey asked the Supreme Court to make NYC stop.)
One major complaint was that the addition of so much sludge in such shallow water caused a major reduction of oxygen levels in the water, which could cause fish to die, or force them to leave the area. The other major complaint was that harmful bacteria from the sludge seemed to be reaching shore, especially during the summer, causing sickness in some beach-goers.
Image Credit: Alexander Alland via NYPL Digital Collections
During this same period of time (known as the Great Depression) the U.S. Government paid for many people to do work such as upgrading sewage treatment plants and building new ships to haul sludge. NYC added three new sludge tankers to it’s ‘fleet’ during this time. These ships were named the 'Coney Island', the 'Wards Island” and the “Tallman Island”, all named for treatment plants. Each tanker could carry over four hundred thousand gallons of sludge which made them much more efficient than having to fill up multiple barges. As New York City grew, so did the fleet of tankers.
New vessels were added in the late 1950's through the late 1960's. These new vessels were also named for treatment plants: “Owls Head,” “Bowery Bay” and “Newtown Creek.” The “North River” was added to the fleet in the mid-1970s after big changes happened to the way we thought about dumping sludge.
A group celebrates the Newtown Creek. Image Credit: NYCDEP via Flickr
The new large vessels travel across New York Harbor. Image Credit: Alexander Hope, National Archives at College Park via Wikimedia Commons
Late 20th Century
After many activist groups created a growing awareness of environmental concerns, President Richard Nixon created the Environmental Protection Agency (or EPA) in 1970. By 1972 Congress had become concerned about worsening water pollution and passed the Clean Water Act. This law allowed the EPA to regulate the ways waste (including sludge) was released into our nation's rivers, bays and coastal ocean waters. The EPA quickly told NYC that this practice of dumping waste so close to shore would have to stop. The City replied that it would take time to follow this request: they didn't have a plan and they would need time to raise money to pay for whatever would be devised, and more time to build the solution, whatever it would be!
A microbiologist examines samples from the Wards Island Sewage Treatment Plant in 1948. Image Credit: NYC DEP via Flickr
Each time the EPA told the City they'd need to stop dumping, the City replied that they needed more time to figure out a solution. So, until 1987, the City continued to dump sludge at the 12-mile site. But at that time, the City proposed a compromise: a new location 106 miles out in the ocean. That far away, the ocean is over three thousand feet deep. If you can envision the tallest building in New York City, the water would be twice as deep as that building is high!
The city had its tankers, which could travel those distances into the rough waters of the open ocean, but none of the barges the city was using at the time could manage those waves on the three-day voyage. Many new barges needed to be found!
The map to the right shows the dumping site, 106 miles away from shore. What cities is it near?
One year later, Congress passed a new law called the Ocean Dumping Ban Act, which allowed the EPA to demand that NYC stop this new practice as well. Again, NYC told the EPA they needed time to figure out a solution. By the summer of 1992, the City stopped using the 106-mile site. In the end, close to 20 million wet tons of sludge had been dumped there. They were the last city to dump sludge into the ocean, and now that 'solution' is no longer practiced anywhere in the USA.
Many scientific studies have been done to determine the ecological impact of sludge dumping at the 106-mile site and there is still much to be learned. The organic material attracted many deep water scavengers, which seemed to thrive until the material began to be depleted. They were, in turn, eaten by predators who often moved on to other areas of the Atlantic. If these predators later showed signs of disease or harm, it was hard to find them to gather that information. We know that some of the material began to move further to the south along the deep ocean floor. We do not have enough conclusive data yet to determine whether it has been diluted enough to minimize the pollution.
The sea cucumber is an example of a creature that scavenges for organic material on the sea floor. Image Credit: Diego Delso via Wikimedia Commons
While the end of sludge dumping might have been good news nationally, New York City still had very little good news in terms of what alternative solutions would work best. Most experts involved in the process agree there are only a few practical options. All of them would be more expensive than ocean dumping. Using the ships to access the 106-mile site cost $20 million dollars each year. The first year afterwards, the City spent $250 Million dollars to dispose of the sludge.
Sludge Boats at Wards Island Sewage Treatment Plant. Image Credit: NYC DEP via Flickr
What to do? The main options available to the city are:
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Sewage Today
The City realized that all the best options would require that the sludge undergo a process called ‘dewatering’. You can probably guess that the process takes more water out of the sludge. Less watery sludge (about 65% water) means it’s easier to transport. Dewatering is a lot like what happens to your clothes right before the washing machine is done. Sludge is put into a perforated barrel and spun very quickly so that the centrifugal force pushes the water out the perforations (holes) and leaves behind much drier sludge.
These machines are expensive and need to be frequently maintained by workers with special training, so the city did not add one to every treatment plant. The Port Richmond plant in Staten Island sends its sludge to Oakwood Beach by pipe. The 26th Ward Plant receives sludge by pipe from the Coney Island and Jamaica Plants. You might think the City no longer had a need for all those ocean-going tankers. However, they were given a new job much closer to shore. Several plants have their sludge collected by boat and delivered to other plants for dewatering. For example, the City’s largest plant, Newtown Creek, has its sludge delivered by boat across Long Island Sound to the Hunts Point Plant in the Bronx. This kept the old tankers very busy for many years.
Dry, dewatered sludge. Image Credit: Hannes Grove via Wikimedia Commons.
When the United States had another financial crisis in 2008 (similar to the Great Depression in the 1930s) the Federal Government again helped the city improve its sewage infrastructure. In order to upgrade the ageing tankers, the City was given over $50 million dollars to help build three new boats. That money helped pay for about half the cost of the boats. Each would again be named for local Treatment Plants: Port Richmond, Rockaway and Hunts Point. These boats wouldn’t need to travel through the rough waters of the Atlantic, so they were built differently. They ‘sit’ lower in the water and are shorter above the water as well so they can carry more sludge and pass beneath low bridges. This will help them pick up and deliver sludge to any Plant in the City. Previously, the Newtown Creek Plant used to pipe its sludge to a tank along the East River because the bigger old boats couldn’t get close enough. Thanks to the design of the new boats, the tank was removed and was replaced by affordable housing and public space.
A close up view of the Hunts Point. Image Credit: NYC DEP via Flickr
Many of the old boats were sold to work for other industries, some were bought so their steel could be re-used for other purposes. One of the tankers, the Coney Island, was used for a very surprising purpose. It was cleaned up, towed out into the ocean, just past the mouth of New Jersey’s Shark River and it was sunk. That’s right, sunk! It was the first ship to become an artificial reef, creating habitat for coastal fish. Scuba divers have explored this intentional shipwreck and found many different fish and other species on and around the ship. It’s a popular spot for recreational fishing boats to visit as well!
A similar vessel is sunk to create an artificial reef in Florida. Image Credit: Florida Fish and Wildlife via Flickr
Today, all the dewatered sludge that NYC produces is delivered by truck or train to landfills and recently has been sent as far away as Texas and Alabama. Every day over sixty large tractor-trailer trucks leave the city loaded with sludge. Most critics still use the word ‘sludge’, but those who are eager to recycle this waste prefer to call it ‘biosolids.’ The City hopes that one day a good solution can be found for all this waste. Some engineers believe that by mixing sludge and food waste together, it will create a type of natural gas (called ‘biogas’) that can be used to heat buildings, for example. But this solution has not yet been perfected and it will be up to tomorrow’s scientists (maybe you!) to find the right answers to all these important questions.
We hope you enjoyed the tale of the humble, yet important sludge boat!
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