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Water reuse, i.e., the use of treated municipal
wastewater for beneficial purposes, is well-established in the United States. It
is now recognized as an important integral component of water resources
management in many parts of the country. As droughts and population increases
continue to stress the availability of fresh water supplies, reuse of treated
municipal wastewater will play an ever-increasing role in helping to meet water
demands.
Historically, reclaimed water was first used for agricultural applications that
do not require high quality water, e.g., pasture irrigation or nonfood crop
irrigation, and were often perceived as a method of wastewater disposal. In the
last 30 years, there has been a dramatic increase in both the types of reclaimed
water applications and quantities of water used, and the trend has shifted
toward higher level uses such as urban irrigation, toilet and urinal flushing,
commercial and industrial uses, and indirect potable reuse. Current treatment
process trends include membranes in lieu of media filtration and UV for
disinfection.
Making reclaimed water safe for reuse is achieved by eliminating or reducing the
concentrations of constituents of concern through source control, wastewater
treatment, and/or by limiting human exposure via design or operational controls.
Health-related concerns and issues pertaining to nonpotable applications are
more easily resolved than those pertaining to indirect potable reuse, although
some questions remain regarding microbial pathogens. The assessment of health
risks associated with indirect potable reuse must consider both microbiological
and chemical contaminants and is less definitive due to limited chemical and
toxicological data and inherent limitations in available toxicological and
epidemiological methods.
While the U.S. Environmental Protection Agency has published guidelines, there
are no federal regulations governing water reclamation and reuse in the U.S.;
hence, the regulatory burden rests with the individual states. Water reuse
criteria vary considerably among states, although there is some degree of
consistency in the states that have extensive reuse experience, such as Arizona,
Florida, and California. While it would be incorrect to state that all reuse
criteria are lacking a sound scientific basis, it is true that there are
significant information gaps and issues that need to be resolved to aid
regulatory agencies in the development of rational criteria.
This lecture will review the current state-of-the-art of water reuse, including
reclaimed water applications, water quality requirements, treatment technology,
monitoring needs, and use controls. Water reuse criteria and their supporting
rationale will be presented. Current issues, including those related to
selection of indicator organisms, microbial risk assessment, disinfection/removal
of protozoan parasites, and means to monitor the integrity of membrane processes
will be described as well as research efforts directed at resolving those
issues. Case studies will be included to illustrate some of these topics.
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