The Portland Water District (PWD) says it is taking proactive steps to tackle PFAS-contaminated wastewater biosolids with the construction of a regional treatment facility under consideration. Solutions being explored include advanced thermal destruction technologies, such as pyrolysis and gasification, to safely and economically reduce or eliminate PFAS from biosolids.
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; however, under Maine law L.D. 1911, the state banned the spread of biosolids due to the presence of PFAS. Banning biosolids from being used as a fertilizer created a disposal challenge, making landfills the primary disposal option.
However, biosolids need to be mixed with another bulking material in a five-to-one or greater raio 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.
“The safe disposal of biosolids is critical to safeguarding the environment and protecting public health,” says PWD Director of Wastewater Services Scott Firmin. “We are leaving no stone unturned as we seek innovative and economical solutions to tackling the nationwide threat of PFAS.”
PWD is working with the environmental consulting firm Brown and Caldwell, Walnut Creek, California, which is developing a conceptual plan and vetting prospective technologis. 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, Brown and Caldwell says the off-gas can be reused as a heat source or to generate power. In tandem, these processes can potentially destroy PFAS to alleviate concerns about biochar reuse or air emissions.