Who will be Staten Island’s next top sludge thickener?

Who will be Staten Island’s next top sludge thickener?

New York City’s Department of Environmental Protection (DEP) is seeking out an enterprising company to beef up aging infrastructure at its Oakwood Beach Wastewater Resource Recovery Facility on Staten Island, according to a solicitation published by the city late last year.

The project, set to begin this summer, involves “sludge thickening improvements” — tune-ups to the complex system of belts, pumps, pipes, valves, grinders and heat exchangers that turn solid waste into a slightly thicker slurry. It can then be digested by hungry bacteria into methane, carbon dioxide and other gasses.

DEP officials said the makeover will cost the city about $79 million — a big investment in an old and unglamorous piece of city infrastructure. But afterward, cleaning up the city’s waste will run smoother, and the upgraded machines will save energy, reduce carbon emissions and even produce fuel in the form of biogas.

The project’s PASSPort page shows that the agency received six bids, ranging from a mere $77 million to a hefty $113 million. All the vendors have done their fair share of wastewater business with the city before, according to data from the New York City comptroller’s office. One company, Jett Industries, has 11 active contracts with the city, totaling more than $373 million.

Sludge thickening is just one step in a massive municipal wastewater management enterprise. The city’s 14 wastewater treatment plants process more than 1 billion gallons of runoff each day from our sinks, showers and toilets. That’s enough to fill 1,500 Olympic-sized swimming pools and have a little bit leftover.

The pipes that carry the sludge to and from the thickeners are due for replacement.

Department of Environmental Protection

Workers, heavy machinery and bacteria work together to remove trash, food, waste and dangerous microorganisms from all those gallons and then release the treated water back into our waterways. The dirty work of wastewater treatment keeps our water in halfway-decent shape and even creates some useful byproducts, like biogas for fuel and fertilizer. (Wastewater can also be used to track the spread of polio, COVID-19 and other diseases.)

“We talk about the water cycle, but the model of water that we currently practice is not a circle at all. It’s a straight arrow where we mine clean water and then dump waste into the environment,” said Dr. Kartik Chandran, a professor of earth and environmental engineering at Columbia University. “Wastewater treatment is really the only way that we can close the loop.”

Why sludge gets thickened on Staten Island

For this project, DEP is hoping to improve sludge thickening at its Oakwood Beach Wastewater Resource Recovery Facility, which sits on Staten Island’s eastern shore and opens into the Lower New York Bay. It’s been in operation since the 1950s and serves more than 240 million people, according to the agency’s website.

DEP spokesperson Douglas Auer said the Oakwood Beach plant’s sludge thickeners have been hard at work for more than 40 years, and the decades have taken their toll on the gear. According to slides shared with prospective applicants late last year, the plant needs two new gravity thickeners, enormous tanks of wastewater with rotating scrapers that squeegee settled particles into a sludge hopper.

This DEP diagram shows how sludge, pictured in brown, settles to the bottom of wastewater tanks, where it can be taken away for thickening.

Department of Environmental Protection

The weight of the water on top of the particles squishes them down further, thickening the sediment even more. Once it’s been thickened, the sludge will sit for two weeks in digesters.

Those are body-temperature tanks where hungry bacteria can convert it into gas. The plants can even use that gas to power their equipment. Whatever’s left at the end of that process can be composted, mixed into soil or further dehydrated and disposed of.

Prior to the pandemic, loving couples could tour one facility’s egg-shaped digesters on Valentine’s Day.

Prior to the pandemic, loving couples could tour one facility’s egg-shaped digesters on Valentine’s Day, but Auer told Gothamist that there aren’t currently any plans to bring the popular date night offering back, at least in person.

Gravity thickening is already simpler and cheaper than some alternative methods, according to the U.S. Environmental Protection Agency, although it can be greasy and smelly. The proposed replacements will be more energy-efficient, the agency said, and the resulting sludge will make better biogas and fertilizer.

A sludge thickener at the Oakwood Beach Wastewater Resource Recovery Facility in Staten Island. This photo was shared with prospective bidders on the $79 million project.

Department of Environmental Protection

The plant will get a bunch of cool accessories to go with the new thickeners, including four heat exchangers and more than a dozen pumps to move the sludge around. It will also receive a new polymer mixing station, so workers can add chemicals to the sludge to make it even thicker.

Sludge thickeners aren’t the only components of the plant getting a facelift. The facility will also receive a new pumping station to help workers cope with increased flow during storms, a Federal Emergency Management Agency (FEMA) official told Fox 5 New York in October.

In 2015, DEP invested $30 million to make energy efficiency upgrades at a separate wastewater facility in Port Richmond, which included the installation of rooftop solar panels.

NYC Water via Flickr

That’s especially important for the Oakwood Beach plant, which serves parts of Staten Island hit hard by Hurricane Sandy. During the storm, city employees worked around the clock to pump 80 millions of contaminated stormwater through the plant rather than allowing it to run out into the streets. The plant itself sits on higher ground than the surrounding area, giving it some protection from floodwaters, SILive reported.

The surrounding neighborhoods were transformed by the 2012 storm. Some were emptied out almost completely thanks to buyouts. The area will also be protected by a seawall and levees, thanks to a $615 million Army Corps of Engineers project that was slated to break ground in the fall of 2022.

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