Botkin Environmental Science Earth as Living Planet 8th txtbk

19.11 Land Application of Wastewater 419
the city of Arcata, in northern California, makes use of
a wetland as part of its wastewater treatment system. The
wastewater comes mostly from homes, with minor inputs
from the numerous lumber and plywood plants in Arcata.
It is treated by standard primary and secondary methods,
then chlorinated and dechlorinated before being discharged
into Humboldt Bay. 33
Louisiana Coastal Wetlands
The state of Louisiana, with its abundant coastal wetlands,
is a leader in the development of advanced treatment using
wetlands after secondary treatment (Figure 19.18).
Wastewater rich in nitrogen and phosphorus, applied
to coastal wetlands, increases the production of wetland
plants, thereby improving water quality as these nutrients
are used by the plants. When the plants die, their organic
material (stems, leaves, roots) causes the wetland to grow
vertically (or accrete), partially offsetting wetland loss due
to sea-level rise. 36 There are also significant economic savings
in applying treated wastewater to wetlands, because
the financial investment is small compared with the cost
of advanced treatment at conventional treatment plants.
Over a 25-year period, a savings of about $40,000 per
year is likely. 35
In sum, the use of isolated wetlands, such as those in
coastal Louisiana, is a practical way to improve water quality
in small, widely dispersed communities in the coastal zone.
As water-quality standards are tightened, wetland wastewater
treatment will become a viable, effective alternative that
36, 37
is less costly than traditional treatment.
Phoenix, Arizona:
Constructed Wetlands
Wetlands can be constructed in arid regions to treat poorquality
water. For example, at Avondale, Arizona, near
Phoenix, a wetland treatment facility for agricultural
wastewater is sited in a residential community
(Figure 19.19). The facility is designed to eventually treat
about 17,000 m 3 /day (4.5 million gal/day) of water. Water
entering the facility has nitrate (NO 3 ) concentrations as
high as 20 mg/l. The artificial wetlands contain naturally
occurring bacteria that reduce the nitrate to below the
maximum contaminant level of 10 mg/l. Following
treatment, the water flows by pipe to a recharge basin
on the nearby Agua Fria River, where it seeps into the
ground to become a groundwater resource. The cost of
the wetland treatment facility was about $11 million,
about half the cost of a more traditional treatment facility.
(a)
(b)
(c)
FIGURE 19.18 (a) Wetland Pointe au Chene
Swamp, three miles south of Thibodaux, Louisiana,
receives wastewater; (b) one of the outfall pipes
delivering wastewater; and (c) ecologists doing
field work at the Pointe au Chene Swamp to
evaluate the wetland.