Chlorine Sewage Treatment Plant Seen as Risky
by Erica Gies
Ever since the advent of modern plumbing, people have embraced a practice of flush and forget. Unfortunately, public works employees and clean-water advocates rarely enjoy such a luxury, and recent debate has focused on the final step in sewage processing, chlorine disinfection, which is no longer the foregone conclusion it once was.
Chlorine disinfection kills pathogenic bacteria so people swimming or fishing near treatment plants’ discharge locations don’t contract cholera, E. coli infection, Legionnaires’ disease or other illnesses. The practice is still widespread, and chlorine remains the most widely used disinfectant at 16,000 wastewater treatment plants nationwide, according to John Millett, a spokesman for the U.S. Environmental Protection Agency.
However, the toxicity of chlorine that kills harmful bacteria also hurts other life. And while the EPA says treatment plants must dechlorinate before spewing out treated wastewater, that effluent is not pure. It contains dechlorinated byproducts, colloquially referred to as DBPs, which are considered to be carcinogenic.
“The chemical process might cause more problems in the environment than if you didn’t do it at all,” said Tom Franza, assistant general manager of wastewater enterprise for the San Francisco Public Utilities Commission, or SFPUC. “Scientifically it’s controversial, but the regulators take the approach that, since we’re not real sure, let’s chlorinate.”
In 1988, SFPUC successfully petitioned the San Francisco Bay Regional Water Quality Control Board to eliminate requirements to disinfect water released from a pipe four miles offshore. SFPUC conducted a study with the EPA and the National Oceanic and Atmospheric Administration that tracked effluent currents and demonstrated that the bacteria died quickly in the cold, salty water and that the stream never made it shoreward, where surfers or bathers might get sick. Effluent released in the bay, closer to where people swim and fish, is still disinfected through chlorination.
Sejal Choksi, San Francisco chapter director of Baykeeper, a nonprofit environmental organization, cited a study by the National Resources Defense Council showing that DBPs called trihalomethanes, or THMs, are potentially carcinogenic and correlate to an increased risk of miscarriage and birth defects.
“Although this information pertains to drinking water, it would apply to wastewater too because dechlorination doesn’t get rid of TTHMs (total trihalomethanes) and other DBPs associated with chlorination,” Choksi said. “And so if it’s being discharged into the water along with all the other stuff being discharged, it seems it would have an impact on aquatic species and reproduction.”
According to one study, Choski said, the levels of TTHMs in San Francisco Bay were above the legal limit in 2000.
Chlorine disinfection is even more of a problem when chlorine leaks into the receiving bodies of water before dechlorination is completed.
“It burns the fish tissues, especially in the gills,” Choksi said. “In order to protect itself, (the fish) secretes a mucus which builds up and ends up clogging its respiratory system. It could have an impact on the nervous system, too. At really low concentrations, chlorine can kill aquatic invertebrates. And that can affect the food web, the whole ecosystem. Chlorine is definitely not a good thing to have in the water.”
Bruce Wolfe, executive officer of the San Francisco Bay water board, concurred, saying, “It’s important to get the right quantity of chlorine. It’s a balance. And that’s been the source of quite a number of violations of effluents limits over the years…. So a number of them have used that rationale to say, ‘Let’s get out of the chlorine business.'”
Wolfe said he recognizes that changing disinfection systems requires an upfront capital cost for municipalities. However, he said he has seen operators use chlorine spill fines to make the argument to budget planners that it’s time for a change.
“It’s just another piece of the puzzle that the plant operators use to say that using chlorine is basically an old technology,” he said.
In the short term, some municipalities such as San Francisco have succeeded in reducing their chemical use by improving chemical-delivery methods and developing more sensitive instruments to take measurements, according to Arleen Navarret, regulatory manager for SFPUC Wastewater Enterprise.
Still, Navarret would like to see chemical residues in the effluent reduced even further.
“The fewer chemicals we can put into the environment the better off we are,” she said. “I am not sure that we really understand the fate of bacteria in our receiving waters, and regulations are created by the EPA that often are designed for a particular area, and then those regulations are administered to the entire nation.”
A treatment used in five plants around the San Francisco Bay Area as well as in municipalities in Ohio, Pennsylvania and elsewhere around the country that doesn’t impart DBPs utilizes ultraviolet light, which kills bacteria by changing their genetic structures. Other promising technologies not yet in widespread use for wastewater management include ozonation, the use of membranes, peracetic acid or bromine, and even a diamond electrode-based system.
Still, there is resistance to adopting the new waste-treatment technologies. Regional boards don’t want to backslide. And some wastewater-treatment experts also are uncertain whether the effectiveness of new technologies has been proven.
“The technology might look very good on paper, but you need to make sure they’re going to work in practice,” said Domenec Jolis, senior engineer at SFPUC Wastewater Enterprise. “The consequences could be very severe.”