Wastewater Reclamation And Reuse
WASTEWATER RECLAMATION AND REUSE
In many locations where the
available supply of fresh water has become inadequate to meet water needs, it
is clear that the once-used water collected from communities and municipalities
must be viewed not as a waste to be disposed of but as a resource that must be
reused. The concept of reuse is becoming accepted more widely as other parts of
the country experience water shortages. The use of dual water systems, such as
now used in St. Petersburg in Florida and Rancho Viejo in California, is
expected to increase in the future. In both locations, treated effluent is used
for landscape watering and other non potable uses. Satellite reclamation
systems such as those used in the Los Angeles basin, where wastewater flows are
mined (withdrawn from collection systems) for local treatment and reuse, are
examples where transportation and treatment costs of reclaimed water can be
reduced significantly. Because water reuse is expected to become of even
greater importance in the future.
Current Status
Most of the reuse of wastewater
occurs in the arid and semiarid western and southwestern states of the United
States; however, an increasing number of reuse projects are occurring in the
south including Florida and South Carolina. Because of health and safety
concerns, water reuse applications are mostly restricted to non potable uses
such as landscape and agricultural irrigation. In a report by the National
Research Council (1998), it was concluded that indirect potable reuse of
reclaimed water (introducing reclaimed water to augment a potable water source
before treatment) is viable. The report also stated that direct potable reuse
(introducing reclaimed water directly into a water distribution system) was not
practicable. Because of the concerns about potential health effects associated
with the reclaimed water reuse, plans are proceeding slowly about expanding
reuse beyond agricultural and landscape irrigation, groundwater recharge for
repelling saltwater intrusion, and non potable industrial uses (e.g., boiler
water and cooling water).
New Directions and Concerns
Many of the concerns mentioned in
the National Research Council (NRC, 1998) report regarding potential microbial
and chemical contamination of water supplies also apply to water sources that
receive incidental or unplanned wastewater discharges. A number of communities
use water sources that contain a significant wastewater component. Even though
these sources, after treatment, meet current drinking water standards, the
growing knowledge of the potential impacts of new trace contaminants raises
concern. Conventional technologies for both water and wastewater treatment may
be incapable of reducing the levels of trace contaminants below where they are
not considered as a potential threat to public health. Therefore, new
technologies that offer significantly improved levels of treatment or
constituent reduction need to be tested and evaluated. Where indirect potable
reuse is considered, risk assessment also becomes an important component of a
water reuse investigation. Risk assessment is addressed in Chap. 13.
Future Trends in Technology
Technologies
that are suitable for water reuse applications include membranes
(pressure-driven, electrically driven, and membrane bioreactors), carbon
adsorption, advanced oxidation, ion exchange, and air stripping. Membranes are
most significant develop- ments as new products are now available for a number
of treatment applications. Mem- branes had been limited previously to
desalination, but they are being tested increasingly for wastewater
applications to produce high-quality treated effluent suitable for reclamation.
Increased levels of contaminant removal not only enhance the product for reuse
but also lessen health risks.
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