A new way to dispose of NYC's sewage biosolids can save money and counter the climate crisis at the same time
The big picture of NYC municipal solid waste
NYC is trying to change the way it processes its municipal solid waste (MSW). The City has set a goal of reducing waste sent to landfills to zero. (See the NYC DSNY Strategic Plan 2019 update.)
How much waste does NYC generate? NYC Department of Sanitation handles about 12,000 tons of waste a day, about 50% of the City's total waste, from residential and institutional sources. Private haulers take the other half, from commercial waste sources. Altogether, Sanitation reports that NYC generates around 14 million tons of waste per year.
Landfilling relies on trucks. The NYC 2006 Comprehensive Solid Waste Management Plan (SWMP) aims to gradually eliminate long-haul truck transport of municipal solid waste by expanding rail and barge transport infrastructure.
The City has also been looking into new technologies to convert MSW. A 2006 study commissioned by NYC recommended anaerobic digestion and thermal processing. This category includes both gasification and pyrolysis, which heat waste in low or no-oxygen environments, compared to incineration, in which wastes are heated in the presence of oxygen and burst into flame. Waste to energy (WTE) plants combine incineration with material recovery. There haven't been other DEP-commissioned studies on this topic since then. DEP planning goes on constantly, but very little is public.
NYC's sewage sludge and biosolids
One of NYC’s biggest municipal solid waste streams is sewage sludge, which after treatment is discreetly referred to as biosolids. NYC produces about 1,400 tons per day of biosolids, or over 500,000 tons per year, and pays contractors about $50 million a year to remove it.
The NYC Dept. of Environmental Protection, which manages the City’s water and sewer system, collects sludge from 14 wastewater recovery plants to centralized facilities for dewatering.
"Under OneNYC: The Plan for a Strong and Just City, Mayor Bill de Blasio pledged to dramatically reduce overall greenhouse gas emissions 80 percent by 2050 (80x50), specifically reducing emissions from City government operations 35 percent by 2025. Emissions from the water and wastewater systems are responsible for nearly 20 percent of City government emissions and wastewater treatment accounts for 90 percent of that. Improving the efficiency of wastewater treatment, increasing the production of biogas, and capturing and beneficially using all biogas as a renewable energy source significantly reduces carbon emissions, offsets emissions from energy originating from traditional fossil-fuel sources, and creates financial benefits through the creation of marketable Renewable Energy Credits...." - NYC DEP 2018 Strategic Plan, p. 29.
About 85% of NYC biosolids go to landfills in states across the easter US including Alabama, Ohio, Georgia, Pennsylvania, and upstate NY. The remaining 15% is composted or used in abandoned mine reclamation.
NYC put its sludge on barges and dumped it in the ocean until 1992, when Congress banned ocean dumping. NYC then put most of its sludge on rail to Colorado to be spread as fertilizer, or to a plant in the South Bronx to be converted to fertilizer pellets. But shipping to Colorado got too expensive, and complaints about the smell led to the shutdown of the Bronx facility in 2010.
Future biosolids disposal options?
While landfilling is currently the least expensive solution, landfill capacity is shrinking, and costs will keep going up. Landfilling sludge contributes to climate change in two steps: the use of fuel needed to transport it, and the release of methane as sludge degrades anaerobically in landfills.
To reflect changing best practices, NYC DEP is transitioning how it talks about wastewater treatment plants. It will consider them wastewater resource recovery facilities (NYC DEP Strategic Plan 2018, p. 23).
DEP is looking closely at many options for biosolids disposal:
- Direct land application
- Anaerobic digestion
- Pyrolysis / gasification
(Source: "NYC DEP Biosolids Program: A Review and Update," 10/12/16.)
Applying biosolids directly to land
Biosolids made from sudge could be composted, pelletized and / or alkaline treated. It could be used as a fertilizer, spread directly on parks, lawns and golf courses, or used in mine reclamation. According to anecdotal reports from DEP staff, NYC biosolids are within the regulatory limits for heavy metals and are treated to reduce biological pathogens. They're safe to use as fertilizer for growing food for human consumption when used properly. In practice, that hasn't convinced potential customers. Because of negative public perceptions, and the availability of other inexpensive fertilizers, the market for sewage biosolids is limited. There are many other smaller producers of municipal biosolids in New York State, and some of them may be successfully selling their biosolids to geographically nearby customers.
What we know is that recently about 85% of NYC's biosolids has been hauled to distant landfills, and the remaining 15% is composted or spread on top of old mines. It could be the market for land application of biosolids can easily be supplied by nearby smaller municipalities. Unless there's a new development, land application is unlikely to suddenly become a viable alternative.
Anaerobic digestion is a set of processes through which microorganisms digest sewage sludge in the absence of oxygen. AD systems operate at all 14 DEP wastewater treatment plants, where the process significantly reduces the volume of biosolids. AD is already a central part of DEP's biosolids handling approach.
AD systems produce biogas, mostly methane and CO2, The biogas is burned to heat the plant's boilers and produce some of its electricity.
The Newtown Wastewater Treatment Plant in Greenpoint, Brooklyn is pioneering the next step in biogas-fueled electric generation - feeding the power directly into the electric grid. This will be expanded to other city plants where it makes sense.
With land application unlikely to have a major role and anaerobic digestion already a part of the process, the real choices will be between a variety of incineration and gasification / pyrolysis options. A detailed review of these options would depend on information that's not available to the public. Here are some considerations.
Since it would take a long time for NYC to site, permit, and build its own facility, as well as train staff to operate it, it would probably be easier and faster for the City to partner with a vendor who would own, operate and staff a facility.
Incineration is the combustion of waste in the presence of oxygen. According to the US EPA, after the water evaporates, the heated waste catches on fire, and 65-75% of the solids burn off, leaving behind a smaller volume of ashes. Incinerators must comply with Federal regulations to ensure their exhaust gases are carefully treated to remove pollutants.
Incinerators are usually combined with systems that recover metals and use steam to generate electricity, in what are called waste to energy facilities. About 12% of the national waste stream is burned for energy in 86 incinerator-based facilities across 25 states.
There are already existing WTE facilities near NYC that take mixed municipal solid waste: Newark, Rahway and Camden, NJ; Westbury, Babylon, East Northport, and Peekskill,NY; Bridgeport, Hartford, and Bristol, CT; Peekskill, NY; and Chester, PA.
NYC now disposes of some of its mixed municipal solid waste at the Covanta WTE facility in Newark, NJ.
Could a vendor build and operate a new incinerator for sewage biosolids in NYC? Yes. However, an incinerator dedicated to biosolids instead of MSW would be more expensive to comply with Federal emissions rules, and finding a site and getting permits might be difficult.
Could NYC dispose of biosolids at any of the existing WTE facilities in the area? Maybe - if their permits could be modified to take sewage sludge biosolids. And depending on the price.
Some concerns about incineration:
- As cities strive to recycle or compost more of their municipal solid waste, there's less to be incinerated.
- The average MSW mix has changed over the last 50 years, with less paper and yard waste, and more plastic.
- Plastics often release toxins when incinerated.
- Many states classify municipal solid waste incineration as a renewable source of energy, allowing incinerators to compete for subsidies intended for wind and solar.
Pyrolysis / Gasification
When organic waste is heated in a low or no oxygen environment, there's a similar sharp reduction in waste volume. Gases are produced that are burned up within the pyrolysis process chamber and help to heat the waste. The solid residue that's left is a mixture of ashes and carbon. The proportion of carbon varies with the waste material used as feedstock, and the times and temperatures used in the pyrolysis process. Whatever the proportion of solid carbon that remains, it is carbon that will not be evaporating into the atmosphere. The climate benefit of producing solid carbon is explained on the previous page.
It's a new approach for cities. Stockholm, Sweden has been turning municipal green waste into biochar. Ithaca, NY is planning to pyrolyze its biosolids. But very close to home, a pyrolysis facility to run completely on municipal biosolids is set to open in 2020 in Linden, NJ, taking biosolids from around NJ.
Both incineration and pyrolysis / gasification methods will capture heat energy from the process that can run a steam boiler and generate electricity. Ideally, a process will yield more heat energy than what is needed to dewater and heat the waste.
Conferences of the Northeast Biosolids and Residuals Association sometimes address how other city agencies and utilities have weighed the two general approaches. Apparently, Buffalo decided to revitalize its biosolids incinerator, while Albany decided to close theirs.
What are next steps for NYC DEP?
DEP staff has been researching how to address NYC's biosolids waste stream for some time. While a DEP biosolids specialist has generously provided background and reviewed this material, it's important to point out that the state of DEP's process and its timeline are proprietary and cannot be released to the public. We can only speculate on how far their research has gone, and what they've discovered.
One of DEP's next steps is to put out a request for proposals for pilot projects that would demonstrate beneficial uses of biosolids. The RFP process has already been in the works for several years, and as of summer 2019, there is no set date for its release. DEP also has an RFP out for a consultant to develop an agency-wide carbon neutrality plan.
Meanwhile, in June 2019, NYC Council passed legislation declaring a climate emergency, following San Francisco and Hoboken.
Since the NYC Council has already declared a state of climate emergency, shouldn't we be an early adopter of pyrolysis too? We can be a model for other governments, nationally and globally.
We don't know which vendors and facility operators DEP has been in touch with, what proposals they have already made to the City, and what the comparative costs of incineration and pyrolysis might be. But since a pyrolysis process is potentially a new, important climate crisis response, it shouldn't be evaluated just on the basis of its costs to the City. We have to educate our elected officials about how carbonizing waste streams supports the City's climate plans. Then, we have to get them to push DEP for updates - and a faster process.
NYC Council should schedule a hearing with NYC DEP on the status of research into biosolids disposal options. They should ask DEP to speed up its research, and report back regularly - not just on disposal costs per ton of each option being considered, but on how much climate-protecting solid carbon the City could produce through each option. Also, officials should consider how the City could use that carbon internally or encourage development of commercial and industrial uses for it.
Please review the other biochar pages on this site, including the request to NYC Council.