Constructed wetlands are small artificial wastewater treatment systems consisting of one or more shallow treatment cells, with herbaceous vegetation that flourish in saturated or flooded cells.
4. Wetland
■ A wetland is a land area that is
saturated with water, either
permanently or seasonally, such that
it takes on the characteristics of a
distinct ecosystem.
■ The primary factor that distinguishes
wetlands from other land forms or
water bodies is the characteristic
vegetation of aquatic plants, adapted
to the unique hydric soil.
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5. Wetland Function and
Values:
Under appropriate circumstances. wetlands can provide:
■ water quality improvement
■ flood storage and the desynchronization of storm rainfall and
surface runoff
■ cycling of nutrients and other materials
■ habitat for fish- and wildlife
■ passive recreation, such as bird watching and photography
■ active recreation, such as hunting
■ education and research
■ aesthetics and landscape enhance merit.
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6.
7. What are Constructed wetlands
Constructed wetlands are small artificial
wastewater treatment systems consisting
of one or more shallow treatment cells,
with herbaceous vegetation that flourish
in saturated or flooded cells. They are
usually more suitable to warmer climates.
In these systems wastewater is treated by
the processes of sedimentation, filtration,
digestion, oxidation, reduction,
adsorption and precipitation.
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8. Components of Constructed Wetlands:
These components can be manipulated in
constructing a wetland.
■ Water
■ Substrates, Sediments and Litter
■ Vegetation
■ Aesthetics and landscape enhancement
■ Microorganisms
■ Animals
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9. Mechanism to Improve water quality
■ Settling of suspended particulate matter.
■ Filtration and chemical precipitation through contact of the water with the substrate and
litter Chemical transformation.
■ Adsorption and ion exchange on the surfaces of plants,
substrate, sediment, and litter.
■ Breakdown and transformation of pollutants by microorganisms
and plants.
■ Uptake and transformation of nutrients by microorganisms and
plants.
■ Predation and natural die-off of pathogens.
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11. Advantages of constructed wetlands:
■ Wetlands can be less expensive to build than other treatment options.
■ Operation and maintenance expenses (energy and supplies) are low.
■ Operation and maintenance require only periodic, rather than continuous, on-site labor.
■ Wetlands are able to tolerate fluctuations in flow.
■ They facilitate water reuse and recycling.
■ They provide habitat for many wetland organisms.
■ They can be built to fit harmoniously into the landscape..
■ They are an environmentally-sensitive approach that is viewed with favor by the general
public.
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12. Limitations of constructed wetlands:
■ Wetland treatment may be economical relative to other options only where land is available
and affordable.
■ Performance may be less consistent than in conventional treatment.
■ The biological components are sensitive to toxic chemicals,
such as ammonia and pesticides
■ wetlands can tolerate temporary drawdowns, they cannot withstand
■ There is yet no consensus on the optimal design of wetland systems
nor is there much information on their long-term performance.
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14. Subsurface flow wetland
■ Subsurface flow wetlands can treat a variety of different wastewaters,
such as household wastewater, agricultural, paper mill wastewater,
mining runoff, tannery or meat processing wastes, storm water.
■ The quality of the effluent is determined by the design and should be
customized for the intended reuse application (like irrigation or toilet
flushing) or the disposal method.
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15. Subsurface flow wetland
■ Subsurface flow wetlands can be further classified as horizontal flow and
vertical flow constructed wetlands.
■ In the vertical flow constructed wetland, the effluent moves vertically
from the planted layer down through the substrate and out (requiring air
pumps to aerate the bed).
■ In the horizontal flow CW the effluent moves horizontally via gravity,
parallel to the surface, with no surface water thus avoiding mosquito
breeding.
■ Subsurface flow systems have the advantage of requiring less land area
for water treatment than surface flow.
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17. Surface flow wetland:
■ Surface flow wetlands, also known as free water surface constructed
wetlands, can be used for tertiary treatment or polishing of effluent from
wastewater treatment plants. They are also suitable to treat storm water
drainage.
■ Surface flow CWs are characterized by the horizontal flow of wastewater
across the roots of the plants. They require a relatively large area to purify
water compared to subsurface flow CWs and may have increased smell
and lower performance in winter.
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19. Horizontal Flow Constructed Wetland
■ In hybrid or multistage systems,
different cells are designed for
different types of reactions. Effective
wetland treatment of mine drainage
may require a sequence of different
wetland cells to promote aerobic and
anaerobic reactions. as may the re-
moral of ammonia from agricultural
wastewater
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22. Reference's:
■ Abdel-Hady, M., (Ph.D. thesis) 2014. “Hydraulic Study of Drainage System”
Constructed Subsurface Wetlands. Mansoura Faculty of Engineering.
■ Nilsson, E., Sha, L., Qian, W., Leedo, M., 2012. Constructed Wetlands “Wastewater
Treatment”. VVA No. 1 Decentralized Water and Wastewater Treatment.
■ Powell, J., Homer, J., Glassmeyer, C., Sauer, N., 2009. Alternative wastewater treatment:
on-site biotreatment wetlands at the Fernald Preserve Visitors Center. In: WM
Conference, Phoenix, Arizona.
■ Xing, A., (M.Sc. thesis) 2012. Recent Developments in Wetland Technology for
Wastewater Treatment. Applied Environmental Science, School of Business and
Engineering, Halmstad University.
■ Zidan, A.A., El-Gamal, M.A., Rashed, A.A., Abd El-Hady, M.A., 2013. BOD treatment
in HSSF constructed wetlands using different media (set-up stage). Mansoura Eng. J. 38
(3.).
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