top of page

A new way to dispose of NYC's sewage biosolids can save money and counter the climate crisis at the same time - but needs support from NYC and NY State agencies and legislators

The big picture...

is changing how it processes municipal solid waste, and aims to reduce the amount of waste sent to landfills to zero   About half of the City's total waste, some 12,000 tons a day, is handled by NYC Department of Sanitation. Private haulers take the other half, from commercial waste sources. Altogether, Sanitation reports that NYC generates around 14 million tons of waste per year.

NYC's sewage sludge

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 a small number of contractors about $50 million a year to remove it.  Over the last few decades, the City has gone from dumping it in the ocean to mostly sending it to landfills.  With landfills filling up and becoming more costly to use, the City has been evaluating what to do with the biosolids. 

The NYC Department of Environmental Protection, which manages the City’s water and sewer system, collects sludge from 14 wastewater recovery plants and takes them to centralized facilities for dewatering.  Over the last few years,  they have reported studying what to do with the sludge, looking into direct land application, anaerobic digestion, incineration, and the newer and less well known thermal processing techniques of gasification and pyrolysis.  We'll look at each one in turn.

Until 1992, NYC put its sludge on barges and dumped it in the ocean, when Congress banned ocean dumping.  NYC then sent 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.  

DEP Commissioner Vincent Sapienza recently testified to the NYC Council Environmental Committee that around that time, landfilling was so much cheaper than any more beneficial use that they sent nearly 100% of City biosolids to landfills. 

In 2018, about 85% of NYC biosolids was going to landfills in states across the eastern US including Alabama, Ohio, Georgia, Pennsylvania, and upstate NY. The remaining 15% was composted or used in abandoned mine reclamation. 

Today, said Sapienza, "We are actually up to now about 31% of that material being beneficially used, 69% still going to landfill but the goal over time is to continue to more and more beneficial use.” He cited the City's cost to landfill biosolids was $122 a ton, and for beneficial use, $139 a ton. (NYC Council Environmental Committee hearing, 5/21/21, p. 37 of hearing transcript.)

The vendors who haul the City's biosolids by truck and rail

NYC DEP has four contracts to transport treated sewage biosolids by truck and rail from the city’s wastewater treatment plants to nearby dewatering facilities in the area and elsewhere for final disposal.  The City works with a small number of haulers: Tully Environmental, Action Carting, and EPIC / Synagro. (There is a 5th contract, between NYC DEP and the the Passaic Valley Sewage Commission in Newark, NJ for the processing of NYC DEP liquid sludge (sludge that has not yet been dewatered).  The 3 haulers and PVSC take all of NYC’s biosolids. 

When the vendors pick up the biosolids, it becomes their responsibility, but the City can steer the outcome through the terms of its contracts with the vendors.  The contracts are valid for several years and then expire, to be replaced with new DEP contracts, which the vendors then bid for.   The 2020 rail contract incentivizes haulers to direct biosolids toward “beneficial uses.” The new trucking contracts that were issued in early 2021 specifically bar haulers from landfilling biosolids.

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.

DEP was looking closely at many options for biosolids disposal:

- Direct land application
- Anaerobic digestion
- Incineration
- Pyrolysis / gasification 

(Source: "NYC DEP Biosolids Program: A Review and Update," 10/12/16.)  

The forms of biosolids management now considered beneficial uses are those that reduce greenhouse gas emissions.  The worst is burning biosolids – incineration – which turns all the solid carbon into carbon dioxide gas.  The next worst is landfilling – in which the biosolids decompose anaerobically – they putrefy – and the carbon turns into methane gas, an even more destructive greenhouse gas than CO2. 

Better methods are those with measurably lower carbon emissions, such as drying biosolids into fertilizer pellets, or directly applying biosolids to land.   


Applying biosolids directly to land  

Biosolids made from sludge could be composted, pelletized and / or alkaline treated.  It can then 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 direct land application of sewage biosolids is limited. 

There are many other smaller producers of municipal biosolids in New York State, and it's easy for them to sell their biosolids to geographically nearby customers.
  So, land application is unlikely to suddenly become a viable alternative route for NYC biosolids. 

Anaerobic digestion

Anaerobic digestion (AD) is
a set of processes through which microorganisms digest sewage sludge in the absence of oxygen.   

Wastewater treatment plants generate large amounts of methane gas - as do biosolids buried in landfills.  As biosolids decay in the absence of oxygen, they emit methane.  When methane is released into the atmosphere, it traps heat in the atmosphere much more powerfully than carbon dioxide gas. 

DEP is expanding how much of our biosolids are anaerobically digested before it is sent to elsewhere for disposal.  The goal is to generate methane under controlled circumstances, capture it, and burn it as fuel.  DEP now refers to wastewater treatment plants as wastewater resource recovery facilities to reflect this (
NYC DEP Strategic Plan 2018, p. 23).

Anaerobic digestion (AD) systems already operate at all 14 DEP wastewater treatment plants. While AD reduces biosolids volume, most of the volume of the waste remains and still needs to be disposed of. 

The biogas they produce, mostly methane and CO2, 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.

Again, according to the 2016 report "NYC DEP Biosolids Program: A Review and Update," DEP reported it was weighing the disposal options of direct land application, anaerobic digestion, incineration, and pyrolysis / gasification.  We know that land application is unlikely to have a major role and anaerobic digestion is already a part of the process.  What about incineration?


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, emitting carbon dioxide gas, and 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.

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?  In theory, 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 would 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.

A huge concern about incineration is that the average municipal solid waste mix has changed over the last 50 years, with less paper and yard waste, and more plastic. Plastics often release toxins when incinerated.

However, as time passed, DEP's public positions changed.

NYC DEP documents and commentary in 2021 reveal that incineration has been completely dropped as an option for sewage biosolids.

Now, the DEP page about wastewater treatment says: “Some of the further processing technologies that can be used to qualify biosolids for reuse include composting, drying, and gasification or pyrolysis.”

Gasification  / Pyrolysis

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 as gas, to cause further greenhouse heating.

It's a new approach for cities. 
The city of Stockholm, Sweden opened a biochar plant in 2017, using garden and park wastes as feedstock.  They plan to build four more plants.  The project is one of the winners in the 2014 Mayors Challenge, which is a competition for cities held by Bloomberg Philanthropies. Stockholm created an manual for other cities interested in setting up biochar projects. Ithaca, NY is planning to pyrolyze its biosolids. 

But very close to home, Aries Clean Technologies is
opening a pyrolysis facility in Linden, NJ which will run completely on NJ municipal biosolids. Its capacity of 430 tons per day of biosolids will be reduced to 22 tons per day of ash with 5-10% carbon by weight.  The material falls within the very broad definition of biochar from the International Biochar Initiative as "The solid material obtained from the thermochemical conversion of biomass in an oxygen-limited environment".  The Linden plant is  effectively a pilot project for NYC's biosolids.

The Aries Linden facility will charge charges haulers a fee per ton (known as a tip fee or a gate fee) similar to that of landfills, but because they are close to NYC, haulers have much shorter distances to transport the waste, significantly reducing overall disposal costs – perhaps only 50% of what it would cost to haul biosolids to Pennsylvania.  Aries claims it will be the lowest cost option for biosolids disposal in the NYC metropolitan area. 

100% of the solid byproducts from Linden will be sold to a large NJ concrete manufacturing company. Ash from biosolids would replace coal fly ash in the process of making concrete. They are seeking approval for dry byproduct to be designated as a beneficial use of biosolids from both NYC DEP and NJ DEP.

With incineration off the table, it’s virtually inevitable that NYC will increasingly rely on gasification / pyrolysis to handle its biosolids waste stream. Since NYC cannot fund, site or build any processing facilities on their own within the City, NYC DEP will have to develop partnerships with gasification / pyrolysis vendors like Aries for a growing fraction of the City’s biosolids.

In addition to Aries, several other vendors are in touch with DEP, including
Bioforce Tech and Green Waste Energy.

BioforceTech is currently operating a biosolids gasification and pyrolysis plant near San Francisco, CA that is processing ____ tons of municipal biosolids per day. Its technology was reviewed and approved by the California (State Environmental Agency??) as well as the US EPA.  BioforceTech also operates __ biosolids gasification / pyrolysis plants in the following countries: __________.

Any such vendor that wants to open a plant near NYC will face serious obstacles in getting up and running. 

- Virtually no one knows that gasification / pyrolysis of organic waste are not the same as incineration / combustion (which is widely loathed and often toxic). and are distinct and separate thermal processing methods

- Virtually no one knows that because gasification / pyrolysis captures solid carbon in the ash by-product for permanent sequestration, those methods are not just cost-effective ways to reduce waste disposal volumes and costs, but are a critical part of any climate crisis response.

Our ability to deploy G/P is endangered because so few of the people who should support it – including climate activists, environmental justice advocates, and participants in state agency deliberations – know about it.

Many of these stakeholders in decisions about solid waste disposal projects mistakenly assume that G/P is just another form of incineration / combustion.  When the companies who are promoting G/P projects try to explain the difference, they are easily dismissed as purveyors of greenwashing.  Highly credible, independent, third party advocates for G/P must step up and educate other stakeholders. 

The few officials who do know about G/P, and who are depending on broader availability of G/P to accomplish agency goals, have an obligation to lead in developing public education initiatives.

Without this advocacy for the benefits of thermal processing of organic waste through gasification / pyrolysis, misguided local opposition will arise to block innovative climate-protecting interventions.

When Aries Clean Technologies introduced plans to site a new G/P facility in Newark, NJ, environmental justice group The Ironbound Community Corporation reflexively assumed the plant was an incinerator, and refused to even consider explanations that it was not.  They mounted a campaign to NJ elected officials and State agencies that killed the proposal.  There’s no reason to think that other G/P proposals won’t come under attack from other environmental justice groups and conventional NIMBYs. 

NYC and NY State must recognize the value of gasification / pyrolysis in lowering carbon emissions, and take a public stand, for those technologies to get started.

NYC DEP, despite effectively planning to rely on G/P vendors, has no current plans to support or protect potential G/P projects with the public education efforts. They defer to NY State Department of Environmental Conservation, which is running the waste advisory panel to the Climate Action Council set up under New York State’s Community Leadership and Climate Protection Act.

NYC DEP is assuming that the City will be able to depend on private gasification / pyrolysis system developers to handle the City's 1,400 tons per day of sewage biosolids. However there is no guarantee that those 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.

DEP assumes it's the role of NY State government agencies and stakeholders in State lawmaking processes to take a position on these technologies.  Yet now, NY State's recently passed Climate Act erroneously lumps gasification / pyrolysis in with incineration.

Both NYC DEP and the stakeholders for the NY State Climate Act need to affirmatively recognize how gasification / pyrolysis, which enable carbon sequestration, are a crucial part of the City and State's climate response. 

Next Steps in NYC and NY State.




bottom of page