Drug resistant infections were first identified in 1960 in
hospitals and called hospital-acquired MRSA (Methicillin-resistant S. aureus). MRSA
causes difficult-to-treat and potentially fatal bacterial infections in
hospital patients, and is sometimes referred to as a “superbug.” However, in the late 1990s, MRSA infections began
to appear outside the hospital setting in the greater community in otherwise
healthy people who had not been in a hospital and had no other known risks for
these kinds of infections. The incidence of these so called “community-acquired”
MRSA infections has been increasing in the United States.
Peopled infected with MRSA shed the bacteria from the nose,
feces, and skin; therefore, MRSA can end up in municipal wastewater streams
after being washed down the drain or flushed down the toilet and spread in ways
beyond direct contact. Several scientists led by researchers at the University Of Maryland School Of Public Health, have performed a study that was published last November showing that it
is possible that municipal wastewater could be a reservoir of this micro-organism.
The scientists tested water entering and leaving four unnamed waste water treatment
plants, WWTPs. The mid Atlantic ones were probably Back River in Baltimore and possibly Sykesville based on their descriptions.
They found that MRSA, as well as a related pathogen,
methicillin-susceptible Staphylococcus aureus, MSSA, were present in the waste
water inflow at all four WWTPs. MRSA was found to be present in 83% of the raw
sewage samples taken at the plants. The percentage of MRSA and MSSA positive samples decreased as treatment within the WWTP progressed.
Only one WWTP was found to have MRSA 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.
In WWTPs Primary Treatment consists of sedimentation and
screening of large debris using screens and large settling tanks. Until 1960’s
primary treatment was the only form of sewage treatment in most sewage plants.
Secondary treatments usually include biological and/or chemical treatment. One
of the most common biological treatments is the activated sludge process; in
which primary wastewater is mixed with bacteria that break down organic matter
and cleans the water. Oxygen is pumped into the mixture. A clarifying tank allows
sludge to settle to the bottom and then the treated wastewater moves on for
tertiary treatment. Coagulation, filtration and disinfection take place in
tertiary treatment. A coagulant is added, the commonly used high-lime process can
reduce phosphorus to below 0.10 mg/L. This process also serves as a barrier to
viruses, captures organics leaving secondary treatment, and precipitates heavy
metals and other suspended particles. Coagulation is followed by filtration which
removes organic matter, microorganisms, minerals and excess nutrients. The finalbarrier to pathogens is a chlorination and dechlorination process.
As the University of Maryland scientists showed, plants that
do not use the chlorination process could potentially be releasing disease
causing bacteria into the environment. As waste water is recycled more and more this
raises concerns for the safety of the greater community being exposed to
undertreated recycled water or bio solids. 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. This study makes clear the need to upgrade all waste water
treatment plants to advanced waste water treatment plants that use disinfection
with chlorine and to eliminate the storm related untreated releases of dilute sewage by our older cities combined sewer systems. Not addressed in the study was the survival of MRSA in bio-solids, it can only be inferred to be a possibility. Our WWTPs must also be upgraded to advanced treatment of the residual sludge to Class A to
ensure all bacteria is killed before the sludge is released to the greater environment
and human exposure. Not all WWTP treat all their bio solids to that level, but it
is possible and should be done. The city of Alexandria is an example of a plant
that treats all Biosolids to Class A Exceptional Quality with even higher
standards and is safe for use in community settings.
It is possible to reuse and recycle waste water safely. Since 1978, the upper Occoquan Sewage Authority in
Northern Virginia has been discharging recycled water into a stream above
Occoquan Reservoir, one of the two potable water supply sources for Fairfax
County, Virginia. Recycled water has been part of the Occoquan supply for 34
years and chances are if you are in Fairfax, parts of Prince William and
Loudoun counties you have been regularly drinking recycled water. However, this
water is always treated with tertiary treatment that includes chlorination and
dechlorination before it is released back into the Occoquan and Fairfax Water fully treats and tests all water delivered as potable. The Occoquan Watershed Policy not only specified the type of
waste treatment practices that would have to be adopted on a basin-wide scale,
but provided for an on-going program of water quality monitoring to measure the
success (or failure) of the waste water treatment. The Occoquan Watershed
Laboratory (OWL), operated by the Virginia Polytechnic Institute Department of
Civil Engineering conducts comprehensive studies of the Occoquan water quality,
and effects of the waste water treatment effluents.
Noman M. Cole, Jr. Pollution Control Plant in Fairfax,Virginia is now engaged in a direct water recycling program, reusing treatedwastewater for landscape irrigation and industrial processes. The Noman Cole
plant is engaged in the Water Reuse Project also known as the Purple Pipe
Project, to directly reuse some of the water. (The pipes are colored purple to
designate the water as non-potable, but have undergone chlorination to ensure
water safety.) The Purple Pipe project has completed the first phase of the
project and is delivering 1.4-1.6 million gallons of fully treated waste water
to the Covanta Fairfax, Inc. Resource Recovery Plant and Laurel Hill Golf Course.
The paper Methicillin-Resistant
Staphylococcus aureus (MRSA) Detected at Four U.S.
Wastewater Treatment Plants was written by 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 and published in the November 2012 issue of Environmental Health Perspectives
No comments:
Post a Comment