Constructed wetlands for wastewater treatment

1. Constructed Wetlands for Wastewater
Treatment:
Presented by – Konark prakash
M.tech(environmental engineering)

2. Index
1 What are constructed wetlands
2 Advantages of constructed wetlands
3 Types of constructed wetlands
4 Waste water treatment through wetlands
5 Advantages of subsurface over surface wetlands
6 Reference

3. 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
• The constructed wetlands generally
consist of six chambers
• Each chamber consists of four cells:
Within each cell are water hyacinth
plants
• The constructed wetland removes
solids, dissolved solids, nutrients,
and pathogens.

4. Advantages of constructed wetlands
• Wetlands are less expensive to build and operate than
mechanical systems.
• There is no energy required to operate a wetland.
• Wetlands are passive systems requiring little maintenance.
Normally, the only maintenance required is monitoring of the
water level and rinsing the media every few years to remove
solids and restore adsorption capacity.
• Wetlands can also provide wildlife habitat and be more
aesthetically pleasing than other water treatment options.
• Subsurface wetlands produce no biosolids or sludge that
requires disposal.

5. CONSTRUCTION & INSTALLATION
1. Excavation and Forming 2. Waterproofing
3. Distribution piping 4. Perforated drains

6. Types of constructed wetlands

7. Surface flow
• Free water surface
Wetlands, like most natural wetlands are those where the water
surface is exposed to the atmosphere. Water flows over soil media.
A channel (flow bed) is dug and lined with
an impermeable barrier such as clay or
geo-textile. The flow bed is then covered
with rocks, gravel and soil. Vegetation is
also planted. It is better to have plants that
are native to the area. After that the
wastewater is let into the flow bed by an
inlet pipe. The usual depth of the
wastewater is 10 to 45cm above ground
level. As the water slowly flows through
the wetland, simultaneous processes clean
the wastewater and the cleaned water is
released through the outlet pipe.

8. Surfaceflowwetlands

9. Subsurface wetlands
• The water surface is below ground level.
• In this, water flows below media.
• No water on soil surface but subsurface is saturated.
Vertical flow wetland -

10. Horizontalflow wetland

11. • Liner
• Inlet structure
• Bed (including media and plants)
• Outlet structure
• Slope
Systems have been designed with bed slopes of as much 8 percent to
achieve the hydraulic gradient. Newer systems have used a flat bottom
or slight slope and have employed an adjustable outlet to achieve the
hydraulic gradient.
• Aspect Ratio
The aspect ratio (length/width) is also important. Ratios of around 4:1
are preferable. Longer beds have an inadequate hydraulic gradient and
tend to result in water above the bed surface.
Typical Subsurface Wetland System consists of :

12. Wetlands treat water in the following ways
• Filtration and sedimentation – Larger particles are trapped in
the media or settle to the bottom of the bed as water flows
through. Because these systems are normally used with a
pretreatment system, such as a septic tank or detention pond,
this is a small part of the treatment.
The main treatment processes are :-
• The breakdown and transformation by the microbial
population clinging to the surface of the media and plant roots
• The adsorption of materials and ion exchange at the media
and plant surfaces.
The plants in the bed also provide oxygen and nutrients to
promote microbial growth. The rest of the bed is assumed to be
anaerobic

13. TheSubsurfaceWetlandshaveprovedtobeeffectiveatgreatly
reducingconcentrationsof followingparameters
• 5-day biochemical oxygen demand (BOD5)
• Total suspended solids (TSS)
• Nitrogen
• Phosphorus
• Fecal Coliforms
Wetlands have also shown the ability for reductions in metals
and organic pollutants.
Biochemical oxygen demand is a measure of the quantity of organic
compounds in the wastewater that tie up oxygen. BOD5 is removed by the
microbial growth on the media and the plant roots. BOD5 is the basis for
determining the area of wetland required using a first order plug flow (first
in, first out) model.

14. • TSS
The results for TSS removal have been similar to BOD5 in that the majority
is removed in the first few feet of the bed (or first couple of days) and a
system properly sized for BOD5 removal would be properly sized for TSS
removal.
• Nitrogen
The removal of nitrogen in the form of ammonia and organic nitrogen
requires a supply of oxygen for nitrification. This oxygen usually comes
from the plant roots. Nitrate removal in a wetland takes place by plant
uptake, de-nitrification and microbial processes. A number of factors
affect the rate of nitrate removal, including hydraulic loading
rate/hydraulic retention time, concentration of nitrate in the inflow water,
temperature of the water, soil conditions, vegetation processes, and flow
characteristics in the wetland.
• Phosphorus
For significant phosphorus removal, sand or fine river gravel with iron or
aluminum oxides is needed. These finer materials with their lower
hydraulic conductivity require larger areas and may not be feasible if that
is not a major goal.
• Fecal Coliforms
This is usually not enough to satisfy local regulations, however, so some
sort of after treatment is needed.
The reduction is enough to significantly reduce the scope of the after
treatment process.

15. Advantagesof SubsurfaceWetland(SSW)overFree
WaterSurfacewetland(FWS)
• No exposed water surface to attract mosquitoes or for people
to come in contact with.
• Fewer odors.
• Due to the greater surface area in contact with the water and
greater root penetration of the plants, subsurface systems can
be significantly smaller. Although the media cost can be
expensive, it is usually offset by the smaller land area
required, resulting in a lower cost for the subsurface system.
• Better performance in colder climates due to the insulating
effect of the upper media layer.

16. Reference
• J. Vymazal ENKI, o.p.s. and Institute of Systems Biology and
Ecology, Czech Academy of Sciences, Dukelská 145, 379 01
Třeboň, Czech Republic