90
T. Gichamo et al.
11.2 Natural WWT Methods
11.2.1 Waste Stabilization Pond
The waste stabilization pond is a shallow earthen basin that can store wastewater and
form a sequence of aerobic, anaerobic, and facultative ponds. Constructed wetland is
planted with a combination of floating, submerged, and emergent vegetation (Dubey
and Sahu 2014). The combination of the vegetation could regulate and preserve the
physical, chemical, and biological properties of wastewater. Stabilization pond is
very suitable for warm-climate and developing nations because of the availability of
sunlight and high temperature, land availability, and simplicity of operation. Waste
stabilization pond is appropriate in areas where land is cheap, its operation and
maintenance cost is very competitive and it could produce high-quality effluent with
less cost.
11.2.2 Constructed Wetland
Constructed wetlands are artificial marshy areas constructed by earthmoving, land
leveling, and grading which contains wetland vegetation as filtration structures such
as cattail, canary grass, and reeds. The vegetation has certain filtration structures and
different paths of wastewater flow that could reduce pollutants as the water flows
from path to path. When the sewage passed through the media, the impurities remain
behind, and more pure water passed over, where composite chemical, biological
and physical wastewater treatments are taken place (Rozkosny et al. 2014). Unlike
natural marshland, the constructed wetland has a good hydraulic regime which could
improve effluent quality and increase the treatment efficiency of the system (Crites
et al. 2014b). The most common types of constructed wetland treatment methods are
sub-surface flow, free surface water flow, and vertical flow types. In the sub-surface
flow type, the water level should be below the top of the wetland, and wastewater
allowed passing through permeable media to increase purification of water. Vertical
flow wetland consists of sand and gravel as filters; wastewater is sprayed over the
filters and facilitated pure water to pass vertically. In vertical flow wetlands, the
vertical flow of water through filtration substrate is very slow, hence it is nutrient
removal efficiency is high (Dubey and Sahu 2014) however, temperature fluctuations
could decrease the efficiency. In the constructed wetland treatment system, the plant
root zone symbiotic relationship between plants and microorganisms plays a major
role in removing pollutants. The oxygen released during respiration of leaves is very
crucial for metabolic processes of microorganisms thus speed up absorbing essential
nutrients and breaking-down of contaminants (Kuschk et al. 2003). In the symbiotic
relation between plants and microorganisms, wastewater could be treated through the
uptake of organic and inorganic compounds, the release of carbon by vegetation, and
breakdown of pollutants. Constructed wetland, well-vegetated with water hyacinth
T. Gichamo et al.
11.2 Natural WWT Methods
11.2.1 Waste Stabilization Pond
The waste stabilization pond is a shallow earthen basin that can store wastewater and
form a sequence of aerobic, anaerobic, and facultative ponds. Constructed wetland is
planted with a combination of floating, submerged, and emergent vegetation (Dubey
and Sahu 2014). The combination of the vegetation could regulate and preserve the
physical, chemical, and biological properties of wastewater. Stabilization pond is
very suitable for warm-climate and developing nations because of the availability of
sunlight and high temperature, land availability, and simplicity of operation. Waste
stabilization pond is appropriate in areas where land is cheap, its operation and
maintenance cost is very competitive and it could produce high-quality effluent with
less cost.
11.2.2 Constructed Wetland
Constructed wetlands are artificial marshy areas constructed by earthmoving, land
leveling, and grading which contains wetland vegetation as filtration structures such
as cattail, canary grass, and reeds. The vegetation has certain filtration structures and
different paths of wastewater flow that could reduce pollutants as the water flows
from path to path. When the sewage passed through the media, the impurities remain
behind, and more pure water passed over, where composite chemical, biological
and physical wastewater treatments are taken place (Rozkosny et al. 2014). Unlike
natural marshland, the constructed wetland has a good hydraulic regime which could
improve effluent quality and increase the treatment efficiency of the system (Crites
et al. 2014b). The most common types of constructed wetland treatment methods are
sub-surface flow, free surface water flow, and vertical flow types. In the sub-surface
flow type, the water level should be below the top of the wetland, and wastewater
allowed passing through permeable media to increase purification of water. Vertical
flow wetland consists of sand and gravel as filters; wastewater is sprayed over the
filters and facilitated pure water to pass vertically. In vertical flow wetlands, the
vertical flow of water through filtration substrate is very slow, hence it is nutrient
removal efficiency is high (Dubey and Sahu 2014) however, temperature fluctuations
could decrease the efficiency. In the constructed wetland treatment system, the plant
root zone symbiotic relationship between plants and microorganisms plays a major
role in removing pollutants. The oxygen released during respiration of leaves is very
crucial for metabolic processes of microorganisms thus speed up absorbing essential
nutrients and breaking-down of contaminants (Kuschk et al. 2003). In the symbiotic
relation between plants and microorganisms, wastewater could be treated through the
uptake of organic and inorganic compounds, the release of carbon by vegetation, and
breakdown of pollutants. Constructed wetland, well-vegetated with water hyacinth