21st January 2021
continued from Part 1
They have dropped levels of regulated disinfection by-products by up to as much as 90%.
However, there is one major drawback to this shift: the creation of potentially more harmful by-products. "It might push down on regulated disinfection by-products, but then other things pop up that are even more toxic," says Richardson, whose research team discovered previously unknown disinfection by-products in chloraminated drinking water. One of those finds, iodoacetic acid, is the most DNA-damaging disinfection by-product known to date.
Prasse underscored the concern: "From a regulatory perspective, we could say we're fine. But it's a false sense of security."
Rather than continuing on the toxic treadmill of replacing one potentially toxic chemical for another, a more effective solution may be to focus upstream in the treatment process — such as keeping organics out of the system in the first place. "That requires engineers, chemists, toxicologists and regulators to come together and figure something out," says Prasse. the method of forcing water through a semipermeable membrane is growing in popularity for systems that want to reuse wastewater for drinking water purposes.
Remucal notes that some treatment technologies may be good at removing a particular type of contaminant while being ineffective at removing another. "We need to think about the whole soup when we think about treatment," she says. What's more, Remucal explains, the mixture of contaminants may impact the body differently than any one chemical on its own.
Richardson's preferred treatment method is filtering the water with granulated activated carbon, followed by a low dose of chlorine.
Granulated activated carbon is essentially the same stuff that's in a household filter. (EWG recommends that consumers use a countertop carbon filter to reduce levels of disinfection by-products.) While such a filter "would remove disinfection by-products after they're formed, in the plant they remove precursors before they form by-products," explains Richardson. She coauthored a 2019 paper that concluded the treatment method is effective in reducing a wide range of regulated and unregulated disinfection by-products.
Despite the technology and its benefits being known for decades, relatively few full-scale plants use granulated active carbon. They often cite its high cost, Richardson says. "They say that, but the city of Cincinnati [Ohio] has not gone bankrupt using it," she says. "So, I'm not buying that argument anymore."
Greater Cincinnati Water Works installed a granulated activated carbon system in 1992. On a video call in December, Jeff Swertfeger, the superintendent of Greater Cincinnati Water Works, poured grains of what looks like black sand out of a glass tube and into his hand. It was actually crushed coal that has been baked in a furnace. Under a microscope, each grain looks like a sponge, said Swertfeger. When water passes over the carbon grains, he explained, open tunnels and pores provide extensive surface area to absorb contaminants.
While the granulated activated carbon initially was installed to address chemical spills and other industrial contamination concerns in the Ohio River, Cincinnati's main drinking water source, Swertfeger notes that the substance has turned out to "remove a lot of other stuff, too," including PFAS and disinfection by-product precursors.
"We use about one-third the amount of chlorine as we did before. It smells and tastes a lot better," he says. "The use of granulated activated carbon has resulted in lower disinfection by-products across the board."
Richardson is optimistic about being able to reduce risks from disinfection by-products in the future. "If we're smart, we can still kill those pathogens and lower our chemical disinfection by-product exposure at the same time," she says.
Reposted with permission from Ensia