Specialized bacteria can remove rogue drugs during sewage treatment

UPDATE, March 10, 2016
I’ve added links for three previous reports related to the degradation of pharmaceuticals and personal care products.
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Concerns are growing about medications and person-care products that pass through sewage-treatment plants and into Puget Sound, where the chemicals can alter the physiology and behavior of fish and other organisms.

Almost everywhere scientists have looked, they have found drugs that people have either flushed down the drain or passed through their bodies. Either way, many active pharmaceutical compounds are ending up in the sewage at low levels. Conventional sewage-treatment plants can break down up to 90 percent or more of some compounds, but others pass through unaltered.

Now, researchers are working on a process that would use specialized bacteria to break down pharmaceutical compounds at existing sewage-treatment plants. The idea, developed by researchers at the University of Washington, is ready for a limited pilot project at one of the treatment plants in the Puget Sound region.

Heidi Gough, left, and Nicolette Zhou with a table-top treatment plant in the lab. UW photo
Heidi Gough, left, and Nicolette Zhou with a table-top sewage-treatment plant in the lab.
UW photo

Studies into this issue began more than 20 years ago, when it became clear that all sorts of compounds were passing through sewage-treatment plants and getting into the environment. Among the early findings was that male fish exposed to artificial birth-control hormones were changing into female fish. Later studies showed that common antidepressant medications seemed to be changing the behavior of fish, making them easier targets for predators.

In addition to estrogens and antidepressants, researchers have found blood thinners, cholesterol-reducing drugs, various heart medications, several hormones and painkillers, along with caffeine, cocaine and various cosmetic and cleansing chemicals.

A study funded by the Environmental Protection Agency looked for 56 active pharmaceutical compounds in sewage effluent from 50 major treatment plants around the country, finding significant levels of many compounds.

A new study by NOAA’s Northwest Fisheries Science Center and the University of Washington looked at 150 compounds coming from two sewage treatment plants in Puget Sound. They were Bremerton’s plant on Sinclair Inlet and Tacoma’s plant on Commencement Bay. They also tested the local waters along with juvenile chinook salmon and Pacific staghorn sculpin to see if the fish were picking up the compounds.

According to a NOAA news release, the study “found some of the nation’s highest concentrations of these chemical compounds and detected many in fish at concentrations that may affect their growth or behavior.” For additional reporting on that study, check out the Kitsap Sun story by Tristan Baurick and the Seattle Times story by Lynda Mapes.

These chemicals could be having effects on various animals in the food web — from benthic organisms that live in the sediments to marine mammals — but more study is needed. Complicating the situation is that multiple pharmaceutical chemicals may work together to create different effects, depending on their concentrations and the affected organism.

Many people would argue that we have enough information to dramatically increase our efforts to remove these compounds from wastewater going into Puget Sound. Drug take-back programs have been started in many cities and counties throughout Puget Sound to encourage people not to flush unused pills down the toilet or drain. See the Take Back Your Meds website. Still, Washington state has yet to develop a comprehensive statewide program that would cover everyone.

Meanwhile, nobody can say what percentage of the drugs going into the treatment plants were dumped down the drain versus being excreted from the human body. But it wouldn’t matter as much if the chemicals could be eliminated at the sewage-treatment plant.

More than a decade ago, Heidi Gough of the UW’s Department of Civil & Environmental Engineering began working on the development of bacteria that could break down these chemicals of concern. She and her colleagues have isolated cultures of bacteria that can break down triclosan, an antimicrobial; bisphenol A, a plasticizer; ibuprofen, an anti-inflammatory drug; 17β-estradiol, a natural hormone; and gemifibrozil, a cholesterol-lowering drug.

The process of isolating helpful bacteria and boosting their numbers could theoretically be used to break down almost any chemical of concern. To be suitable, the bacteria must 1) break down the target chemical to a very low level, 2) grow well in common growth media without the target chemical, 3) break down the chemical even when other nutrient sources are abundant, and 4) work quickly within the normal rate of sewage treatment.

Nicolette Zhou, a former UW graduate student, worked with Heidi to successfully develop a bench-top treatment plant to test the process. Nicolette also produced a computer model of how the operation would perform at a large-scale treatment plant. She completed her analysis and received her doctorate degree last fall. Her latest findings are now awaiting publication in a scientific journal.

Previous reports:

  • Genes involved in Bisphenol A degradation, Environmental Science and Technology.
  • Degradation of triclosan and bisphenol A by five bacteria, Pub Med.
  • Cultivation and characterization of bacteria capable of degrading pharmaceutical and personal care products, Pub Med.

Other systems have been proposed for breaking down complex pharmaceuticals, such as advanced oxidation or other chemical or physical treatment. But biological breakdown offers the most hope in the short term, because it is how most sewage-treatment plants work can be implemented quickly without major modifications and appears to be economical on a large scale, Nocolette told me.

In a large-scale system, the first step would be to identify the specific contaminants to be reduced and then select the bacteria. Some bacteria will break down multiple chemicals, she said.

The bacteria would be grown in a tank and be fed into the sewage digesters reactors, preferably in a continual flow. Multiple chemicals of concern might require several tanks for growing different bactieria.

If the process is successful and adopted by many treatment plants, an alternative process could be developed. Instead of growing the bacteria onsite, where conditions could be difficult to control, all sorts of bacteria could be grown in an industrial facility. The industrial plant would isolate the actual enzymes needed to break down the chemicals and ship them to the treatment plants. The enzymes could be stored and fed into the treatment process as needed.

The research into this treatment process has progressed to where the next step is a small-scale pilot project at a sewage-treatment plant in the Puget Sound area, Nicolette said. A portion of the actual wastewater would be diverted to the pilot plant, where sewage would be subjected to the specialized bacteria and tested for the level of treatment.

Ultimately, more studies are needed to establish a safe concentration for the various chemicals that come from pharmaceuticals and personal-care products. That way, one could culture the appropriate bacteria and establish a reasonable effluent limit for chemicals going into Puget Sound.

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