Photo Credit USGS – Wastewater: The Primary Treatment Process
1. Screening 2. Pumping 3. Aerating 4. Removing sludge 5. Removing Scum 6. killing bacteria
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While it may not seem (or even be) glamorous, there are scientists who spend considerable time examining the input and output of wastewater (sewage) treatment plants. Given the potential environmental impact of the discharges from these facilities, it is important work.
The subject of wastewater treatment plants - and the substances that their processes can fail to remove during treatment - has come up before in this blog.
In 2007, with governments around the world stockpiling large quantities of Tamiflu (Oseltamivir) in anticipation of a pandemic, concerns turned to what would happen if millions of doses were dispensed, consumed, and excrete by humans into the waste water system in a short period of time.
In The Law of Unintended Consequences we looked at a report in Environmental Health Perspectives (EHP) called Potential Risks Associated with the Proposed Widespread Use of Tamiflu that found enough of excreted oseltamivir carboxylate (OC) would survive treatment, and be ejected into the environment, to raise concerns.
In October of 2009 and we saw another report (see Everything Old Is News Again), based on studies done the previous year in Kyoto, Japan – that showed elevated levels of the OC Metabolite in wastewater discharge.
In 2011, in Pandemics & The Law Of Unintended Consequences we saw yet another study that looked at potential problems inherent in the massive distribution and consumption of antibiotics and antivirals during a pandemic.
WWTPs (Wastewater Treatment Plants) depend upon microbial activity in order to breakdown or `digest’ sewage.
Antibiotics in the sewage – at elevated levels such as might be seen during a pandemic – could inhibit microbial activity, resulting in the failure of WWTPs and the discharge of under-treated wastewater into the environment.
Today, a new study, this time on MRSA (methicillin-resistant Staphylococcus aureus) and how it fares in the wastewater treatment process. As many WWTPs provide reclaimed water for irrigation use, the concern is that MRSA shed in feces might make it through the plant and into the environment.
The University of Maryland-led study study appears as an open access article that appears in Environmental Health Perspectives.
Methicillin-Resistant Staphylococcus aureus (MRSA) Detected at Four U.S. Wastewater Treatment Plants
November 1, 2012 Research
Rachel E. Rosenberg Goldstein, Shirley A. Micallef, Shawn G. Gibbs, Johnnie A. Davis, Xin He, Ashish George, Lara M. Kleinfelter, Nicole A. Schreiber, Sampa Mukherjee, Amir Sapkota, Sam W. Joseph, and Amy R. Sapkota
Abstract
Background: The incidence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections is increasing in the United States, and it is possible that municipal wastewater could be a reservoir of this microorganism. To date, no U.S. studies have evaluated the occurrence of MRSA in wastewater.
Objective: We examined the occurrence of MRSA and methicillin-susceptible S. aureus (MSSA) at U.S. wastewater treatment plants.
Methods: We collected wastewater samples from two Mid-Atlantic and two Midwest wastewater treatment plants between October 2009 and October 2010. Samples were analyzed for MRSA and MSSA using membrane filtration. Isolates were confirmed using biochemical tests and PCR (polymerase chain reaction). Antimicrobial susceptibility testing was performed by Sensititre® microbroth dilution. Staphylococcal cassette chromosome mec (SCCmec) typing, Panton-Valentine leucocidin (PVL) screening, and pulsed field gel electrophoresis (PFGE) were performed to further characterize the strains. Data were analyzed by two-sample proportion tests and analysis of variance.
Results: We detected MRSA (n = 240) and MSSA (n = 119) in 22 of 44 (50%) and 24 of 44 (55%) wastewater samples, respectively. The odds of samples being MRSA-positive decreased as treatment progressed: 10 of 12 (83%) influent samples were MRSA-positive, while only one of 12 (8%) effluent samples was MRSA-positive. Ninety-three percent and 29% of unique MRSA and MSSA isolates, respectively, were multidrug resistant. SCCmec types II and IV, the pvl gene, and USA types 100, 300, and 700 (PFGE strain types commonly found in the United States) were identified among the MRSA isolates.
Conclusions: Our findings raise potential public health concerns for wastewater treatment plant workers and individuals exposed to reclaimed wastewater. Because of increasing use of reclaimed wastewater, further study is needed to evaluate the risk of exposure to antibiotic-resistant bacteria in treated wastewater.
Environ Health Perspect 120:1551–1558 (2012). http://dx.doi.org/10.1289/ehp.1205436 [Online 6 September 2012]
The full report runs 8 pages, and can be download here.
A summation of this research is available from the University of Maryland’s School of Public Health. I’ve cut to the chase with the excerpts posted below, so follow the link to read the full story.
The School of Public Health News
November 5, 2012
NEWS RELEASE
Contact: Kelly Blake, kellyb@umd.edu, 301-405-9418Superbug MRSA Identified in U.S. Wastewater Treatment Plants
University of Maryland-led study is first to document environmental source of the antibiotic-resistant bacteria in the United States
<SNIP>
They found that MRSA, as well as a related pathogen, methicillin-susceptible Staphylococcus aureus (MSSA),were present at all four WWTPs, with MRSA in half of all samples and MSSA in 55 percent.MRSA was present in 83 percent of the influent-- the raw sewage--at all plants, butthe percentage of MRSA- and MSSA-positive samples decreased as treatment progressed. Only one WWTP had the bacteria in the treated water leaving the plant, and this was at a plant that does not regularly use chlorination, a tertiary step in wastewater treatment.
Ninety-three percent of the MRSA strains that were isolated from the wastewater and 29 percent of MSSA strains were resistant to two or more classes of antibiotics, including several that the U.S. Food and Drug Administration has specifically approved for treating MRSA infections. At two WWTPs, MRSA strains showed resistance to more antibiotics and greater prevalence of a gene associated with virulence at subsequent treatment stages, until tertiary chlorination treatment appeared to eliminate all MRSA. This suggests that while WWTPs effectively reduce MRSA and MSSA from influent to effluent, they may select for increased antibiotic resistance and virulence, particularly at those facilities that do not employ tertiary treatment (via chlorination).
“Our findings raise potential public health concerns for wastewater treatment plant workers and individuals exposed to reclaimed wastewater,” says Rachel Rosenberg Goldstein, environmental health doctoral student in the School of Public Health and the study’s first author. “Because of increasing use of reclaimed wastewater, further research is needed to evaluate the risk of exposure to antibiotic-resistant bacteria in treated wastewater.”
Most WWTPs are designed to efficiently remove solids and to disinfect discharge water, but do less well when it comes to removing chemicals.
Although only four plants were studied in this project, the results suggest that plants that fail to chlorinate routinely may be at greater risk of letting antibiotic resistant bacteria back into the environment.
Whether it is antiviral or antibiotic metabolites, remnants from illicit drug use, or resistant organisms themselves, what comes out of these treatment plants can affect our environment, and our population.
On a planet with 7 billion people, figuring out how to safely dispose of, recycle, or treat human waste has become a major challenge.
Shortcomings in WWTP systems – even seemingly small ones - can pose serious public health risks, including potentially creating and spreading resistant bacterial organisms.
As the authors of this study concluded, more research is now needed to evaluate and quantify the risk.
