What is sewage sludge and how do we dispose of it?
Sewage sludge is a disgusting but essential part of the Narragansett Bay Commission’s (NBC) work to manage wastewater and keep Narragansett Bay and Providence clean. After wastewater is cleaned at NBC’s Fields Point Facility in Providence, sewage sludge is left, and it’s getting increasingly tough to figure out what to do with it.
Wastewater, which includes human waste, food residue, environmental waste, rainwater, and even garbage, is first filtered through screens at the NBC, which block large items like sticks and bottles from moving through the water treatment process. Those larger items are removed and landfilled. In the next phase of treatment, dense matter (like human waste), sinks to the bottom of a tank at the treatment facility, while lighter waste and fats float to the top. The water, now separated from most of the solid, dense, waste, moves on for further treatment and is eventually sent back, clean, into Narragansett Bay. The waste that sank to the bottom is thickened using a chemical polymer, and the resulting sewage sludge must be dewatered and discarded.
Sewage sludge could be dumped into the ocean but the Ocean Dumping Ban Act of 1988 prohibited that. Today, there are three primary outlets for the disposal of sewage sludge: landfilling, incineration, and land application. Landfilling, uncommon in this region, is not a sustainable option because of the greenhouse gases released once the sewage sludge enters the landfill. Plus, there simply isn’t enough room at Rhode Island’s only landfill. Land application is a more sustainable way to recycle sewage sludge and benefit the soil, at the same time, but it’s not commonly used here, simply because there is not enough land to apply significant quantities of sludge, (referred to more delicately, after treatment, as ‘biosolids’). The land application of biosolids has come under recent scrutiny for the potential human health impacts–but more on that later. The other primary outlet, on which the NBC relies, is incineration.
Managing Providence’s sewage
The NBC is unique in New England as it’s one of only a few wastewater treatment facilities that manages its own dewatering, creating sludge that can be transported to the incineration facility and burned. Other wastewater treatment facilities create liquid sludge, and rely on outside vendors to dewater the sludge so that it can be incinerated. Rhode Island has two incinerators–one in Woonsocket operated by Synagro, and another in Cranston, operated by Veolia. 25-30 municipalities in the region send their solid and liquid sludge to Woonsocket.
The Wastewater Treatment Facility in Woonsocket is owned by the City, and maintained by Jacobs, a Texas-based consulting and engineering firm, with incineration managed by Synagro, a biosolid recycler based in Baltimore (RI DEM). The incinerator can accept about 105 tons of dewatered sludge per day, based on their current air permit, and collects about 22 dry tons of biosolids from the NBC alone. Working with Synagro since 2006, the NBC pays the company about $5.8 million annually to transport and incinerate its sewage sludge.
While incineration is relatively cost-effective, according to Janine Burke-Wells, the Executive Director at the North East Biosolids & Residuals Association (NEBRA), it’s an option with serious problems. Outages are common due to the age of many incinerators, and vendors must keep up with changing environmental regulations. According to a recent Massachusetts Department of Environmental Protection Study conducted by consulting firm Tighe & Bond that analyzed sewage sludge management solutions, the Woonsocket incinerator needs about 2 weeks of downtime annually for maintenance. An outage or delay in the incineration process can have compounding effects on wastewater treatment facilities throughout the region that have to treat and move sludge out of their facilities on a daily basis.
While generally, sewage sludge management strategies must diversify, there is one immediate threat to incineration in Rhode Island. Synagro faces a class action lawsuit filed by Woonsocket residents due to the odors emitted from the facility. This comes after the treatment facility was sued in 2023 for releasing partially untreated sewage into the Blackstone River. Amidst these challenges, Woonsocket’s City Council decided in May of last year that Synagro must phase out its acceptance of liquid sludge. There has been no timeline communicated for this phase-out, but once they do, there will be a huge impact on wastewater treatment facilities throughout the state and region that rely on Synagro to manage their liquid sludge. The study by Tighe & Bond revealed, through a market risk analysis, that Rhode Island’s incineration is at high risk of disruption in the next five years. We have increasing quantities of sludge, but do not have enough management capacity for it.
As the largest wastewater treatment facility in Rhode Island and one of the largest in New England, the Narragansett Bay Commission will need to step up as a leader in exploring alternative sludge management solutions. Jim McCaughey, Deputy Director of the NBC, says that the exploration of alternative solutions is an ongoing exercise. The NBC’s contract with Synagro ends in May 2026, and although the looming shift to stop liquid sludge acceptance won’t have direct implications for the NBC, because they de-water their own, they’re worried about how the shutdown may impact treatment facilities throughout the region. One potential solution McCaughey noted was the development of a centralized dewatering facility at Fields Point. This would allow the NBC to accept liquid sludge from other facilities, dewater it, and send it along to an incinerator.
Beyond incineration, the NBC is considering another long-term disposal solution: pyrolysis. This involves a high-heat process, devoid of oxygen, that would turn sludge into biochar, a carbon-rich solid, which could eventually be used as a soil amendment. While this technology has been used on a small scale for decades, wastewater treatment facilities are still years away from adopting this as a widespread solution for sludge management. Janine Burke-Wells from NEBRA thinks we need to turn our attention back to land application as a primary outlet.
The struggles with land application
The Environmental Protection Agency (EPA) released a risk assessment in January, acknowledging what many experts already knew–sewage sludge contains at least two types of per- and poly-fluoroalkyl substances (PFAs), known as ‘forever chemicals’ that pose risks to human health. Maine, recognizing the potential health risks of applying sewage sludge to land, banned the practice in 2022. Connecticut has followed suit, with other states considering similar bans on the land application of biosolids. The EPA has not implemented any significant measures to stop the land application of sewage sludge in the United States.
PFAs are indeed a concerning component of sludge, among many other harmful materials, as anything that’s flushed down the toilet can end up in our sewage sludge. The key action needed to reduce the concentration of PFAs in sewage sludge is source reduction, limiting the forever chemicals in products we use on a day-to-day basis. “The frustrating thing with PFAs is that we’re finding them in our sludge in the parts per billion, but if you go to McDonald’s and buy a sandwich, the packaging has it in the parts per million (1000x more). That’s a lot,” said Jim McCaughey.
Janine Burke-Wells clarified that the known human health implications of PFAs are limited to farm families, not the general public. She argues that the benefits of land application should outweigh the drawbacks if sludge is being tested and monitored regularly to gauge the level of harmful chemicals. “The land application end use for biosolids is not always the cheapest or the easiest but it is the most sustainable. The benefits are many and include enhancing soil health, recycling nutrients, reducing fertilizer/pesticide use, strengthening farm economies, and providing micronutrients like zinc, iron, manganese, and copper that healthy soils need and that you will not find in other products, and it has been shown to increase soil carbon content.” On the flip side, “the concerns about recycling [biosolids] are also real and include odors, over-applying of nutrients, and trace contaminants like PFAS, pharmaceuticals, etc.” So, while the existence of forever chemicals in PFAs is concerning, it’s nothing new, and they’re not going anywhere until the sources of the PFAs are more strictly regulated.
Until recently, there was some hope that steps would be taken to address PFAs in wastewater. The EPA proposed enacting surface water quality standards under the Clean Water Act, but this proposal was withdrawn following President Trump’s Executive Order for a Regulatory
Freeze Pending Review.
A murky path forward
Wastewater treatment facilities around the region and organizations like NEBRA are working together to brainstorm solutions. One effort has been led by NEIWPCC (formerly called the New England Interstate Water Pollution Control Commission), which created a BioHub to match wastewater treatment facilities with vendors working to find innovative sludge management solutions. Burke-Wells refers to the hub as a ‘dating app’, allowing service vendors and representatives from treatment facilities to collaborate and share solutions on an ongoing basis.
The source reduction of PFAs is key, but in the meantime, finding alternatives to incineration, landfilling, and land application is critical. For Providence residents who would rather not think about their sewage once it leaves their toilet, think again. Limited solutions to sewage sludge management will eventually lead to a higher demand for management services and a higher price tag. Those higher prices will be passed along to the NBC’s ratepayers.
Janine Burke-Wells has one clear call to action: “Pooping and flushing is something we all doo. We all play a part in the ‘quality’ of the wastewater and resulting sludges. If people knew the benefits of recycling these valuable organic materials, maybe they would be a little more careful with what they flush. Only the three Ps (pee, poop, (toilet) paper, please!)”. The next time you flush, think about the journey those solids take to arrive at the Wastewater Treatment Facility, and what would happen if we had nowhere to put that sludge.
TAKE ACTION:
If you’re interested in learning more, join the Providence Eye at its upcoming Port Day on Saturday, May 17. One of the tours that day will feature a tour of the Fields Point wastewater treatment facility. There will be workshop sessions on all different aspects of the Port of Providence, as well. Mark your calendar: registration begins in April.
Also, the RI Clean Water Association will have free tours of waste water treatment plants as part of this year’s Clean Water Week. There will be a free tour of the Narragansett Bay Commission’s water treatment facility coming up. The tour takes about 45 minutes and tour participants need to wear closed, toed shoes:
April 12
Free Tour of Water Treatment Facility as part of Clean Water Week
2 Ernest Street
Providence/Narragansett Bay Commission
10 AM – 2 PM
www.ricwa.org
Emily Smith moved to Providence in 2022 and wanted to contribute to the Providence Eye to learn more about her new community. Emily works in international development, facilitating grants to all parts of the world. She lives in Federal Hill.
