The Big Apple is planning an expansion of its anaerobic digester (AD) pilot program launched last summer at the Newton Creek Wastewater Treatment Plant in Greenpoint.
The purpose of the one-year pilot was to test the logistics of source separating food waste, collection of the waste, preprocessing by Waste Management and injection into the wastewater treatment plant (WTTP) digesters, according to Anthony Fiore, director of New York City’s Department of Environmental Protection Office of Energy. “The volume of source separated organics was too small during this initial pilot in order to determine benefits or costs of treating food waste through this pathway,” he said.
The densely populated city’s DEP hopes to prioritize increasing recycling rates and investing in clean, affordable renewable energy using the knowledge gained from the pilot program expansion. “There is a strong nexus between these two initiatives when it comes to food waste and wastewater treatment,” Fiore said.
This nexus is brought to life with the colocation of AD at the Newton WWTP. The DEP works with the NYC Department of Sanitation, the Department of Education and Waste Management to source separate organic waste (SSO) and remove residual contamination of the feedstock. This pretreatment creates a bioslurry for injection into the digesters. Fiore describes Waste Management’s part in preprocessing the food scraps as unique and crucial to seamless integration in the AD process. “The Waste Management system will provide specifications that are important to the digestion process such as pH, alkalinity, total suspended solids, and carbanaceous biological oxygen demand,” Fiore said.
From April 2013 to May 2014, the facility processed between 1.5 and 2 tons of SSO a day. This winter, the project will be scaled up over a three-year period beginning at 50 tons per day to 250 tons per day. “This volume of SSO will allow us to better understand the ability to source separate waste from both residential and commercial sectors, the efficiency of processing the material into a consistent bioslurry and the costs and benefits of treating food waste in anaerobic digesters,” Fiore said.
In the expansion plans, a bump in waste volume is accompanied by a new use for the created biogas. “The biogas that is produced at the plant today is used as fuel in boilers for both process and building heating needs, which accounts for about 40 percent of the gas that is produced,” Fiore said.
Fiore added that the remaining 60 percent is flared. In order to put the remaining biogas to use, the DEP is working on a biogas-to-grid energy project. “The DEP is working with National Grid to put that flared gas to beneficial use by cleaning it to pipeline-quality gas and injecting it into the local natural gas distribution system for community use,” Fiore said.
The residual gas produced from just the domestic sludge is estimated to heat 2,300 homes a day. Even more is possible at capacity if the demonstration project if successful. “We believe we have enough capacity at the Newtown Creek WWTP to handle 500 tons per day of SSO, or about eight percent of the city’s total organic waste load,” Fiore said. “All told, this would result in enough heat for approximately 5,100 homes per day and the avoidance of 90,000 metric tons of greenhouse gas emission—landfill, diversion, vehicle miles traveled, offsetting carbon intensive sources of natural gas and reduction in flaring—equivalent to removing approximately 19,000 vehicles from the road.”
Overall the project’s emphasis is on increasing the knowledge of the systems capabilities and resulting effects. The project is teaming up with the New York State Research and Development Authority as well as other academic institutions to develop a monitoring and testing program. The program will address operational parameters, codigestion benefits both operationally and financially, as well as additional parameters like digester chemistry, rheology and centrate quality among others.
Fiore believes that biogas serves as a good source of renewable energy, because in cities like New York, millions of tons of discarded food have potential as fuel. “Renewable natural gas produced from digestion serves as a model of how to affordably integrate clean, renewable energy into dense urban environments by leveraging existing assets.”