As a consequence of the efforts by EPA and state environmental authorities throughout New England and beyond to update wastewater treatment requirements, including management of the sludge produced, significant questions and concerns about the direction and impacts of the regulatory changes have emerged. Today, wastewater treatment plants (“WWTPs) face particularly onerous challenges in the decades-long process of removing nutrients and other contaminants of concern in wastewater before it is discharged to inland rivers or coastal waters.
WWTPs were initially built as early as the 1890s to address primary treatment (removal of solids), later upgraded to secondary treatment (for bacterial decomposition), and, since the 1980s, for tertiary treatment (for nutrient removal). Large regional and small municipal facilities were improved at each step to meet the challenge. In the 1990s and early 2000s, EPA and state regulatory authorities established necessary but aggressively low concentrations for these elements (nitrogen for coastal waters, phosphorous for inland rivers) before treated wastewater may be discharged. In answering these challenges, WWTPs have relied largely on chemical, sometimes biological, treatment to take up and absorb the nutrients into sewage sludge solids.
In every aspect of our lives, we rely daily on the proper treatment of wastewater from our homes, businesses, and industries to protect our rivers and coastal estuaries, as well as our health. Historically, New England’s responsibility for properly treating wastewater and managing and disposing of sludge fell to large and small urban industrial cities. Since the 1970s, intrastate regional authorities have emerged to serve many large cities and adjacent communities. Established in the late 1800s and early 1900s, WWTPs have been repeatedly modified, enlarged, and improved to treat contaminants in wastewater with increasingly sophisticated treatment technologies. In the 1960s through the 1970s, the federal Construction Grants Program covered as much as 90% of the cost to construct new or substantially upgrade existing wastewater treatment plants throughout New England, recognizing the importance of this critical infrastructure to protect public health and the environment.
The crucial primary stage in the wastewater treatment process is the removal of solids contained in the wastewater collected from the community and entering the WWTP. For much of that history, the collected solids (sludge) were dumped in landfills or the ocean offshore. Currently, offshore disposal of sludge is prohibited to avoid degradation of the coastal environment. Landfill disposal is now often restricted to “cake,” a regrettable euphemism for 90% dewatered sludge.
Both sludge and cake contain high concentrations of the nutrients removed in the wastewater treatment process, which cause eutrophication, stimulating aquatic plant and algae growth, which die off to consume oxygen in the waters, particularly in slow-flowing rivers and coastal ponds. Today in New England, the nutrient-rich sludge produced by WWTPs is landfilled (preferably as cake), incinerated in specialized facilities, or used for agricultural land application to enhance crop growth. In some areas of the country, sludge is disposed of in man-made vegetated lagoons to extract nutrients from the sludge.
In New England, the growing challenge for WWTPs, particularly those which also have on-site sludge incinerators and are located along rivers with restricted flow, is caused by nutrients being effectively recycled between the WWTP and sludge dewatering and incineration, requiring more chemical treatment for its removal and producing more and more sludge for incineration in each cycle. Essentially, the nutrients, which are not “destroyed” by incineration, remain trapped and recycled in a virtually closed loop.
Adding to this challenge for WWTPs is the shrinking availability of incinerator capacity in New England and growing limitations on the agricultural use of sludge. This results from two factors: more stringent federal regulation of sludge incineration and local and state prohibitions on agricultural land application of sludge. Available sludge incinerator capacity has dropped in response to enhanced air pollution control regulations adopted in the last decade, leading to the closure of smaller incinerators and adding to the already daunting challenge of siting new incinerators.
In addition, the current focus on the so-called “forever chemicals,” such as PFAS (per – and polyfluorinated substances) used in coatings and consumer products to resist heat or stains, is impacting the use of sludge in agriculture. The growing concern about the potential health impacts of PFAS uptake into the food chain has resulted in Maine recently banning the application of nutrient-rich sludge in agriculture, while farm communities in Western Massachusetts are grappling with similar concerns.
These challenges facing municipal and regional WWTPs, sludge incinerators, farm communities, and even consumers require thorough consideration by regulators, regulated facilities, and all of us. While these challenges may be daunting, the current framework and efficacy of wastewater treatment and sludge management in New England, which has responded to the ever-changing regulatory requirements, cannot be left to the rule of unintended consequences.
