The Portland Water District (PWD) is exploring options for an advanced regional facility to treat biosolids contaminated with per- and polyfluoroalkyl substances (PFAS), according to a press release by Brown and Caldwell.
PWD is working with the environmental consulting firm Brown and Caldwell, which is developing a conceptual plan and vetting prospective technologies. One such solution under consideration is pyrolysis and gasification, the chemical decomposition of organic materials via heat application to produce fuel-rich off-gas and valuable, environmentally-safe biochar. By using thermal oxidation, the off-gas can be reused as the heat source or to generate power. In tandem, these processes can potentially destroy PFAS to alleviate concerns with biochar reuse or air emissions.
At its four wastewater treatment facilities (WWTFs), PWD treats wastewater to produce clean water and biosolids. The clean water is released into receiving waters and the biosolids are treated, then transported to landfills.
In the past, biosolids were used as a fertilizer and soil amendment as they contain essential nutrients and organic matter for plant growth. Under Maine law LD 1911, the state banned the spread of biosolids due to the presence of PFAS, a complex group of manufactured chemicals found in everyday consumer and industrial products, including cleaning and personal care products.
Deemed “forever chemicals” for their ability to remain intact in the environment over time, PFAS have been detected in soil, air, and discharges to wastewater systems. Scientific research is ongoing to determine adverse health outcomes resulting from high levels of PFAS exposure.
Banning biosolids from being used as a fertilizer created a disposal challenge. It made landfills the primary disposal option. However, biosolids need to be mixed with another bulking material in a 5-to-1 or greater ratio to make them suitable for landfills. And, only certain landfills in Maine have the capacity to accept this type of waste.
The major disposal landfill, the state-owned Juniper Ridge Landfill, has reduced the amount of biosolids it receives from Maine’s WWTFs. Subsequently, Maine’s biosolids are now being trucked to landfills outside the state, and often to Canada.
To sustainably and safely manage biosolids, PWD is finding solutions to reduce quantities produced, lower hauling and disposal costs, and explore beneficial use options. A solution under consideration is constructing a regional facility using advanced thermal destruction technologies, such as pyrolysis and gasification, to safely and economically reduce or eliminate PFAS.
“The safe disposal of biosolids is critical to safeguarding the environment and protecting public health,” said Scott Firmin, PWD’s director of wastewater services. “We are leaving no stone unturned as we seek innovative and economical solutions to tackling the nationwide threat of PFAS.”