The nation’s first use of glycerol to reduce nitrogen saves millions in capital investment for a New York City treatment plant and helps Jamaica Bay restoration.
Nitrogen from wastewater treatment plants isn’t a threat to human health, but it can reduce oxygen levels in water bodies and promote excess algae growth that can harm the ecosystem.
As part of efforts to restore Jamaica Bay, the New York City Department of Environmental Protection (DEP) is taking steps to cut nitrogen discharges. One of those projects was a test of glycerol for reducing nitrogen in effluent.
A $2 million research and development project was completed and the new system put online in December 2011 at 26th Ward Wastewater Treatment Plant. The technology, the first of its kind in the world, removes nitrogen from effluent by adding glycerol, a high-carbon byproduct of biodiesel production that is nonhazardous and nonflammable, to a dedicated separate centrate aeration tank. It has reduced the nitrogen discharges by 3,000 pounds per day (67 percent).
Saving the bay
That’s good news for Jamaica Bay, target of an extensive protection plan since 2007. The reduction from the 26th Ward facility amounts to 10 percent of the total nitrogen discharged to the bay. The project bodes well as the DEP continues efforts to reduce nitrogen loading from its treatment plants, which account for nearly 90 percent of the nitrogen reaching the sensitive 31-square-mile estuary between Long Island, Queens and Brooklyn.
As part of the bay restoration efforts, the state Department of Environmental Conservation set limits to reduce nitrogen discharges by 50 percent. “Jamaica Bay’s water quality has been impaired for the last several decades,” says Zainool Ali, 26th Ward plant superintendent. “Excessive nitrogen has caused a lot of algae blooms and low oxygen levels. Reducing nitrogen will help restore the natural plants and aquatic life.”
Before the new glycerol project was put online, the Ward plant was putting about 5,000 pounds of nitrogen per day into Jamaica Bay. That has been cut to 1,900 pounds, helping to meet the current aggregate permitted level for the bay of 36,500 pounds per day. The long-term goal is to essentially eliminate nitrogen discharges to the bay.
For the successful project, the DEP and its research consultants, the New York offices of Hazen and Sawyer and CH2M Hill, received the 2013 American Council of Engineering Companies of New York’s Empire Award, the group’s top engineering excellence honor. “It was a very successful study that demonstrated a new wastewater treatment technique that is so important to New York and other municipalities around the globe,” adds Ali. “The discovery represents an important step toward more efficient and sustainable wastewater treatment.”
The glycerol process is a variation of biological nutrient removal and enhances denitrification. As ammonia undergoes treatment, it is converted to nitrites and nitrate. When glycerol is added to the aeration tanks in the anoxic zone, it helps convert the nitrate and nitrite to nitrogen gas, which is released into the atmosphere. The process uses 1,400 gpd of neat glycerin. “It is a very simple solution,” says Ali. “It was a seamless transition for the operators when we added it.”
The glycerol alternative prevented an expenditure of $30 million for an ammonia recovery system. Another alternative was to use methanol, used by about 200 treatment plants in the U.S. “As opposed to glycerol, methanol is more challenging for operators to safely handle, and it costs much more to store given its composition,” says Ali. Glycerol is also a byproduct of the biodiesel industry and so it is readily available as producers seek alternatives to expensive treatment needed to make it useful in other ways, such as for pharmaceuticals and cosmetics.
The DEP has committed $115 million to remove nitrogen discharges into Jamaica Bay as part of a 2010 agreement to restore the bay’s wildlife habitat. DEP’s Research and Development Section is testing a next-generation use of anamox. While it is in its infancy, Ali says, it shows promise for saving a considerable amount of money while cutting nitrogen emissions further.
Ali expects DEP to add the glycerol system to at least some of its seven other wastewater treatment plants that discharge to Jamaica Bay or the East River, which flows to the Bay. The 26th Ward plant has a design capacity of 85 mgd, and it can treat up to 170 mgd of wet weather flow. It also receives sludge for treatment from four other DEP facilities.
As successful the glycerol process has been, work continues on refining it. “Even though it has significantly helped nitrogen reduction, it is still being perfected,” says Ali. One thing under study is additional air treatment in the aeration tank to see if that could save energy or reduce chemical usage.