With climate change comes increasing water shortages,
and potentially longer periods of drought. As policymakers look urgently to
wastewater recycling to stem the gap in water resources, the question is -- how
best to reuse water and ensure public safety. New and emerging contaminants
like antibiotic resistant genes (ARGs) pose a potential hazard to public safety
and water security. One concern is the spread of ARGs through the water system
and an increase in development of antibiotic-resistant super bugs.
Researchers from the University of Southern California
studied and compared samples from an advanced groundwater treatment facility in
Southern California and groundwater aquifers to detect differences in ARG
concentrations. While they found that the advanced groundwater treatment
facility reduced nearly all targeted ARGs to below detection limits,
groundwater samples had a ubiquitous presence of ARGs in both control locations
and locations recharged with water from the advanced water treatment facility.
Historically, indirect reuse treatment methods in
which an environmental barrier is an intermediary step in the water cleaning
process have been more popular than the direct "toilet to tap"
process. While indirect methods of water reuse treatment were, from a public
perception and appetite, considered more reliable, it is actually direct reuse
"toilet to tap" approaches which do not introduce an environmental
buffer that produce safer, more pure water for potability. The reason for this
lies in the way ARGs in the environment can contaminate potable reuse water.
While some ARGs are naturally occurring in microbial
communities, antibiotics, ARGs and antibiotic resistant pathogens are on the
rise in water sources as a result of the overuse of antibiotics in general. In
a typical water treatment cycle, wastewater is treated first at a wastewater
treatment facility. The study found that this water remains high in ARGs, as
they persist throughout the treatment process. From here, water intended for
potable reuse is further purified using advanced physical and chemical techniques
including reverse osmosis -- a process that uses a partially permeable membrane
to purify drinking water.
Since wastewater treatment plants are not generally
designed for removal of micropollutants like antibiotics, they tend to persist
in treatment systems, leading to high densities of ARG resistant bacteria at
different stages of treatment. When this water is introduced into an aquifer,
where ARGs are already naturally occurring, it can become contaminated with
ARGs and antibiotic resistant bacteria. To further complicate the issue, ARGs
are easily transferred through horizontal gene transfer, increasing the risk
for antibiotic resistant pathogens.
See:
Posted by Dr. Tim Sandle, Pharmaceutical Microbiology
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