top of page

A new way to dispose of NYC's sewage biosolids can save money and counter the climate crisis - but won't be implemented without support from NY City and State agencies and legislators

NYC produces about 1,400 tons per day of biosolids - treated sewage sludge. NYC's Department of Environmental Protection (DEP) is responsible for its disposal, and currently sends most of it to faraway landfills by truck and rail, which is not sustainable.  Not only can sludge buried in landfills produce methane, a greenhouse gas much more powerful than carbon dioxide, but as landfills across the country fill up, the costs to send biosolids to landfills will only get higher.  NYC has a goal of ending landfill disposal by 2030. So what will NYC do with its sewage sludge?

NYC DEP has been studying that question for the last few years.  (For more details, see
the full article on this site.) Ocean dumping was banned a long time ago.  Spreading it on land as a soil amendment is impractical.  The two leading contenders were both forms of heat treatment: incineration and gasification / pyrolysis.  After ruling out incineration, DEP sees it as virtually inevitable they'll have to partner with private companies that will set up treatment facilities in or near NYC, using the processes of gasification and pyrolysis. 

The distinction between incineration and pyrolysis is crucially important. Incineration is correctly associated with carbon dioxide gas emissions, and a high risk of pollution - and is widely known and hated.  On the other hand, pyrolysis, which is virtually unknown, not only minimizes carbon dioxide emissions, but enables capture of the carbon in the waste as a solid, permanently keeping it out of the atmosphere.   It's carbon negative.  Although pyrolysis of organic waste is an important new response to the climate crisis, hardly anyone knows that it exists.  Efforts to pyrolyze organic waste are often confused with incineration and attacked, preventing the technology from being implemented.

The difference between the two thermal approaches is crucial, so it must be reviewed carefully.  When organic wastes are heated in the presence of oxygen - as in incineration - they catch fire, and the carbon is released into the atmosphere as carbon dioxide gas.

Pyrolysis is the chemical decomposition of materials subjected to extreme heat in an oxygen-free environment.  It usually refers to carbon-containing, organic materials.  Without oxygen, the heated materials in a closed, airtight system can't catch fire.  Instead of bursting into flame, it chars.  Pyrolysis is accompanied by gasification: the wastes give off gases that can be captured and burned to fuel the process or used to produce energy. 

The carbon content of the waste, often referred to as biochar, remains as part of the ash.   About 5% of ash from pyrolyzed sewage biosolids is stable carbon. It's easier to visualize charcoal, which is the pure form of solid carbon that results when very high carbon materials, such as wood, are carefully pyrolyzed.

Whether the biochar is in its pure form or a percentage of an ash, the capture of carbon as a solid compound stable over the long term is called carbon sequestration.  The solid materials left as end products can be used for a variety of industrial purposes.  The Drawdown Project praises biochar production as
one of the top 100 top climate crisis initiatives.

However, there is a major obstacle to NYC moving toward gasification / pyrolysis of its biosolids.  New plants using these technologies are very likely to be opposed by environmentalists who don't recognize that these technologies are crucial parts of the climate change response. NYC DEP has kept its review completely to itself.  That has to change, to defuse opposition to the new facilities that NYC will have to rely on very soon.

Aries Clean Energy built a gasification / pyrolysis facility nearby in Linden, NJ that can take 400 tons per day of NJ municipal biosolids.  All of the ash will be taken for use by a concrete manufacturer. A plan by Aries to build a second plant in Newark was killed by an environmental justice group that mistakenly assumed gasification/pyrolysis was the same as incineration, and that refused to engage in discussion or consider evidence that the proposed plant would not be polluting, including approvals from NJ DEP and US EPA.

There is no guarantee that Aries or other developers will be able to site NY metro area projects in what is potentially a hostile environment.  NYC DEP has not shown any interest in advocating for these mostly unknown and often misunderstood technologies - making it less likely that NYC will be able stop landfilling biosolids by the 2030 deadline.

NYC government - including NYC DEP - needs to take a proactive approach, acknowledging the benefits, safety and importance of gasification / pyrolysis - to ensure that the facilities they anticipate partnering with can actually be built.

So far, NYC DEP shows no interest in taking this role, saying it's the responsibility of the NY State Department of Environmental Conservation, and the committees filling out the details of the new NY State climate law.

At the state level,
New York State’s new climate law erroneously lumps both incineration and pyrolysis.  The law prevents gasification / pyrolysis from being considered an alternative compliance mechanism - not the most important thing itself - but reflecting an unjustified bias against those technologies.


In 2019, NY State passed the Community Leadership and Climate Protection Act (CLCPA) It sets goals of sharply reducing greenhouse gas emissions, and quickly increasing the amount of electricity generated from renewable sources.  The law set up a Climate Action Council and a set of advisory panels to develop scoping plans and fill out details on how parts of the Act will be implemented. 

Currently, the Act lumps pyrolysis together with incineration and excludes both, as ‘waste to energy’ technologies, from participating in ‘alternative compliance mechanisms.’

In the Act, alternative compliance mechanisms, or ACMs, will be used to achieve net zero carbon in those situations where fossil fuels are not able to be completely eliminated (estimated at 15% of 1990 levels).  
Clauses G and I of § 75-0109, Promulgation of Regulations to Achieve Statewide Greenhouse Gas Emissions Reductions, read that: “G. The following types of projects shall be prohibited: I. Waste-to-Energy projects, including incineration and pyrolysis;…”

Many of the advocacy groups pushing the bill were operating on the mistaken assumption that both processes are equally harmful producers of greenhouse gases, and this premise guided the drafting of the bill. 

There is a long history of opposition to incineration by coalitions of environmentalists and environmental justice advocates.  The pollution from incineration is real, as are the disproportionate impacts of waste disposal facilities on disadvantaged communities.  Not all forms of thermal processing are the same.  Unfortunately, in previous years, vendors have proposed projects using some forms of gasification / pyrolysis that still had serious pollution impacts, or otherwise were found to be untrustworthy, causing permanent skepticism toward innovative waste management technologies. 

What's needed is broader awareness raising about the distinction between incineration, which increases greenhouse gas emissions, and gasification / pyrolysis, that reduce greenhouse gas emissions, and by producing biochar, go carbon negative by sequestering carbon in solid form.  If NYC DEP really wants private partners to set up gasification / pyrolysis projects to process NYC's sewage biosolids, they should take proactive steps to educate the environmental activist community, as well as other City and State officials, about the benefits of these technologies.

See on this website:

- Introduction to biochar
- short version of NYC biosolids and biochar article
- full article: NYC biosolids and biochar
- Disposing of NYC wood waste
- New uses for biochar

“What is biochar and how is it made?” is a great recent review of biochar, organic waste and thermal treatment from RIT Golisano Institute for Sustainability.

For a wide range of resources and reports, visit the US Biochar Initiative's
Biochar Learning Center.




Rendering of the Aries plant in Linden, NJ.

bottom of page