general introduction of natural and constructed wetland its function and removal mechanism for treatment of wastewater.

1. CREDIT SEMINAR REPORT
ON
CONSTRUCTED WETLAND FOR
WASTE WATER TREATMENT
Prepared By
Anudeep Nema
(D16CE001)
2016-2017
CIVIL ENGINEERING DEPARTMENT
SARDAR VALLABHBHAI NATIONAL INSTITUTE OF TECHNOLOGY
SURAT- 395007
THESIS SUPERVISIOR
Dr. K. D. YADAV
(Asst. Professor, CED,
SVNIT, Surat)
THESIS SUPERVISIOR
Dr. R. A. Christian
(Associate Professor, CED,
SVNIT, Surat)

2. Introduction
Constructed Wetland
Functions & Values
Classifications
Removal Mechanism
Considerations For Deigns
Summary
CONTENT

3. Water
Vital for sustaining the natural
systems on and under the earth's
surface
 We depend on its good quality
and quantity for drinking,
recreation, use in industry and
growing crops.

4. Scarcity Of Water
 Most of the developing countries will face water shortages
in the near future.
 The existing water sources are contaminated due to direct
disposal of untreated sewage and industrial wastewater into
surface water, which degrades the water quality.
 Wastewater treatment is a way to solve this scarcity.
 Wastewater has always fascinated researchers and holds
intuitive application to the general public as well.
 It can treated by:
 Natural system , and
 Artificial system
INTRODUCTION

5. The natural treatment systems are available under three
major categories:
 Aquatic or pond/ lagoon systems;
 Terrestrial or land application systems;
 Wetland systems.
Wastewater treatment is accomplished by physical,
chemical and biological processes.
Plants play major role in natural treatment system.
Natural Systems

6. Natural Wetlands
Natural wetlands have been
used to treat waste water for
hundreds of years
Typically occurs in low lying
areas where surface and
groundwater accumulates
nutrients and their
transformations
Also good for removing
metals and organic pollutants

7. These systems are deigned artificially as per the desired
degree of treatment to be achieved.
 Eg. Activated sludge, Aerated lagoon, Agricultural treatment,
filtration, Chemical addition, Capacitive deionization etc.
Centralized approach of water-based sewer systems was
applied to attain considerable public health improvement in
urban areas of industrialized countries.
Constructed Wetland (CW) is one of the efficient treatment
system, used in many parts of the world.
Artificial Systems

8. Specifically constructed for the
purpose of treating anthropogenic
discharge such as municipal or
industrial wastewater, at a location
other than existing natural wetlands.
They are a semi natural, cost
effective , biological wastewater
treatment technology designed to
mimic processes found in natural
wetland ecosystems
Constructed Wetland

9.  Water quality improvement
 Flood storage; de-synchronisation of
storm & surface water
 Cycling of nutrients
 Wildlife & fish habitat
 Utilization of natural processes
 Aesthetics & landscape enhance merit
9
FUNCTIONS

10. Advantages and Disadvantages
Advantages:
Site location flexibility
(compared to natural
wetlands)
Simple operation and
maintenance
Can be integrated attractively
into landscaping
High removal of contaminants
Disadvantages:
× Mosquitoes (in Free Water
Surface Systems)
× Start-up problems
× Space requirement
× Variable performance
possible
× Designs still largely
empirical (till date)

11. Classification Based On Water Flow Regime:
 Free water surface flow (FWS) CWs
 Subsurface flow CWs,
The sub-surface flow systems are further classified as:
 Systems with horizontal subsurface flow (SFS-h or HF)
 Systems with vertical subsurface flow (SFS-v or VF)
 Hybrid systems (combinations of a, b)
CLASIFICATION OF
CONSTRUCTED WETLAND

12. Classification of constructed wetland (modified from Vymazal and Kroepfelová, 2008)
CLASSIFICATION OF
CONSTRUCTED WETLAND

13. Horizontal flow (HF) wetland
 During this passage the wastewater will come into contact with
a network of aerobic, anoxic and anaerobic zones.
 The entry of wastewater through the rhizosphere, the
wastewater is cleaned by microbiological degradation and by
physical and synthetic procedures.

14. Vertical flow (VF) Wetland
 This type of system has oxygen transfer capacity bringing
about great nitrification.
 They can efficiently reduce BOD.

15. Hybrid Wetland(Combination of
Horizontal and Vertical)
 Nitrification doesn’t occurs in HF wetland because of the
restricted oxygen exchange capacity, whereas VF wetland has
much more oxygen exchange capacity.
 VF wetlands additionally have some confinements like less
efficient in solids removal and can be clogged.

16. Classification Based On Macrophyte Plants:
 Floating macrophyte-based system (i.e. Lemnaspp or Eichornia
crassipes)
 Submerged macrophyte –based system (i.e. Elodea
canadiensis)
 Rooted emergent macrophyte –based system (i.e. Phragmites
australis, Tipha spp)
 Floating leaved macrophyte –based system
Classification OF CONSTRUCTED
WETLAND

17. VEGETATION
17
Plants Properties
Arrow Arum (peltandra virginica) High wildlife value, Slow grower.
Common 3-square rush(Scirpus
punger)
Fast coloniser, high metal removal,
tolerates dryness.
Softstem bulrush (scirpus validus)
Aggressive coloniser, high pollutant
removal, provides food for species.
Broad leaved cattail (typha latifolia) Aggressive, high pollutant removal
Common reed (phragmites australis)
Highly invasive, pest species, poor
wildlife value

18. Removal mechanism
Of Construction Wetlands

19. Biological Mechanisms
Following Biological mechanisms pertains in constructed
wetlands :
 Bacterial metabolism - Helps in the removal of colloidal solids
and soluble organic by suspended, benthic and plant
supported bacteria. Bacterial nitrification and de-nitrification.
 Plant metabolism - Uptake and metabolism of organics by
plants. Root excretion may be toxic to organisms of enteric
origin.
 Plant absorption - Under proper conditions significant
quantities of these contaminants will be taken up plants.
 Natural die-off - Natural decay of organisms in an unfavorable
environment.

20.  The main role in the transformation and mineralization of
nutrients and organic contaminants is played by microorganisms.
These contaminants or nutrients are metabolized in different
ways.
 Oxygen removal from the wetland system is done by Biofilm
decomposition of compost, and it promotes the formation of
hydrogen sulphide.
 Nitrification-denitrification is the fundamental microbial nitrogen
expulsion component.
 Nitrogen compounds are continually transformed from inorganic
to organic compounds and vice versa.
 The most receptive zones of the plant in constructed wetland are
in the rhizosphere.
 seasonal variations affecting nutrient uptake by the plants and
microbial activities should be considered.
Microbial Biofilms mechanism of
Contaminant removal

21. Following non-biological mechanisms pertains in constructed
wetlands :
Sedimentation – Gravitational settling of solids.
Filtration – Particulates filtered mechanically as water passes
through substrate , root masses or fish.
Adsorption – Van der Waals force. Adsorption on substrate and
plant surface.
Precipitation – formation of co-precipitation with insoluble
compounds.
Decomposition – Decomposition of less stable compounds by
phenomena such as UV irradiation , oxidation and reduction.
Non-Biological Mechanisms

22. Wastewater
Constituent
Removal Mechanism
Suspended solids  Sedimentation, Filtration
Soluble organics
 Aerobic microbial degradation, Anaerobic microbial
degradation
Phosphorus  Matrix sorption, Plant uptake
Pathogens
 Sedimentation, Filtration, Natural die-off, Predation,
UV irradiation, Excretion of antibiotics from
macrophyte
Wastewater Constituent and There
Removal Mechanism

23. Wastewater
Constituent
Removal Mechanism
Nitrogen • Ammonification followed by microbial nitrification,
Denitrification, Plant uptake Matrix sorption, Ammonia
volatilization
Metals • Adsorption and cation exchange, Complexation Plant uptake
Precipitation, Microbial oxidation/reduction
• Metals were demonstrated to accumulate in the leaves,
shoots, rhizomes with roots and lateral roots having the
highest content, while the lowest concentrations were
found inside the shoots.
BOD removal • particulate BOD by settling and filtration, then converted to
soluble BOD by hydrolysis
• soluble BOD due to degradation by attached microbial
growth (biofilms on stems, roots, gravel particles etc)
Ammonia • Ammonia might be adsorbed from arrangement through
cationic trade response with inorganic silt or soil when it is
ionized. volatilization as ammonia (at pH > 8.5)

24. physical (filtration, sedimentation, adsorption and
aggregation),
Biological (consumed by protozoa, lytic bacteria,
bacteriophages, natural death) and
chemical (oxidative damage, influence of toxins from other
microorganisms and plants) processes.
Sedimentation of total coliforms, fecal coliforms and
Salmonella trapped in sediments of tainted surface water is
mainly responsible for pathogen expulsion from wetland
system .
Human pathogenic viruses were also found to be removed
from wetland systems.
Removal of Pathogens from
Constructed Wetland System

25. Aerobic patches around roots due to oxygen release
Upper layers of biofilms can be aerobic whereas deeper layers
can be anoxic/anaerobic
Redox conditions
Free Water Surface (FWS)
• Aerobic in upper layers and
• Anaerobic in sediment
Horizontal Sub-surface Flow (HSSF) • Anaerobic
Vertical Flow (VF)
• Aerobic due to intermittent
loading

26. Preliminaries
 geographic (Site selection)
 economic (system area, depth , width )
Compartments
 for resting (liners, media selection )
 maintenance
Unexpected events(floods)
Plant selection
 Typha, Scirpus, Phragmites
Inlet and Outlet considerations
Design features

27. Natural systems
Sun
Wind Land
Seeds
Soils
Plants
Microbes
Basic Design Question: How Much Area
Needed?
 Basic assumption 2-10 m2/PE Area and 0.1- 1.0m Depth
 Since wetlands are low-rate systems which are completely
depending on solar energy, they need a much larger surface
area than conventional systems with electrical energy input.

28. Source: Wood (1995) for FWS and SSF; Ridderstolpe (2004) for VSSF
Design parameter FWS
(free water surface)
HSSF
(horizontal sub-surface
flow)
VSSF
(vertical sub-
surface flow)
Wastewater type
Domestic
wastewater
domestic
wastewater
greywater
Detention time (days) 5 - 14 2 - 7 N/A
Max. BOD loading rate (g/m2/day) 8 7.5 4-6
Water or substrate depth (m) 0.1 – 0.5 0.1 – 1.0 N/A
Hydraulic loading rate (mm/d) 7 - 60 2 - 30 40 - 80
Area requirement (ha/m³/day) 0.002 – 0.014 0.001 – 0.007 N/A
Aspect ratio – length/width 2:1 to 10:1 0.25:1 to 5:1 N/A
Mosquito control Required Not required Not required
Harvest frequency (years) 3-5 3-5 N/A
Design Criteria For Different
Types Of Constructed Wetlands

29. General Constructed Wetland
Considerations (Mitsh, 1992)
Keep the design simple
Design according to the natural
topography of the site.
Design for the extremes of weather
and climate conditions.
Should work well in cold climates
Plantation should be done after
construction
 may take some time, up to a year, to
become fully developed
 Vegetation management required

30. Selecting an appropriate location can save significant costs.
A site that is well suited for a constructed wetland is one
that:
 Is conveniently located to the source of the wastewater
 Is gently sloping,
 Contains soils that can be sufficiently compacted to
minimize seepage to groundwater
 Is above the water table
 Does not contain threatened or endangered species
 Does not contain archaeological or historic resources.
Site Selection

31. The wetland might be sized based on the equation
proposed by Kickuth:
𝑨 𝒉 = 𝑸 𝒅 𝐥𝐧 𝑪𝒊 − 𝐥𝐧 𝑪 𝒆 /𝑲 𝑩
KBOD is determined from the expression KT, where,
KT = K20 (1.06)(T-20)
where A = area
Qd= ave flow (m3/day)
Co & Ct = influent & effluent BOD (mg/L)
KBOD = 0.10
Sizing based on specific area requirement per Population
Equivalent (PE)
System Sizing

32. For subsurface flow constructed wetland depth of substrate
is restricted to approximately the rooting depth of plants.
For horizontal flow it is recommended to use an average
depth of 40cm taking into considerations of the precipitation.
(Garcia et al., 2004)
For vertical flow it is recommended to use substrate depth of
70 cm, which can provide adequate nitrification in addition to
the organic pollutants removal.
Depth Of Wetland

33. Hydraulic gradient can be used in place of slope, and
The hydraulic conductivity will stabilize at 10-3 m/s in the
established wetland.
Ac = Qs / Kf (dH/ds)
Ac = Cross sectional area of the bed (m2)
Qs = average flow (m3/s)
Kf = hydraulic conductivity of the fully developed bed (m/s)
dH/ds = slope of bottom of the bed (m/m)
For graded gravels a value of Kf of 1 x 10-3 to 3 x 10-3 m/s is normally
chosen.
dH/ds of 1% are used.
Bed Cross Section Area (Only For
HF Wetland)

34. Slope of 0.5 to 1% is recommended for ease of construction and
proper draining.
 0.5%or less for FWS systems
 2%or less for HSSF systems
The soil could be mixed with ordinary Portland cement to
decrease the soil permeability and compacted to seal the
wetlands. Liners use for sealing
 Bentonite
 Polyvinyl chloride (PVC)
 Polyethylene (PE)
 Polypropylene
Bed slop and sealing of the bed

35. To control flow, flow path & water depth in wetlands.
Weir boxes, inlet manifold, cleanout, shutoff devices & debris
screens are installed for efficient working of wetlands.
Multiple inlets and outlets are provided for a single wetland for
better working.
Inlet and Outlet Structures

36.  The selection of the filling medium of a constructed wetland is
based on:
 hydraulic conductivity - high enough to allow easy water flow
 local availability - reduced transport costs
 phosphate sorption capacity - more P-binding sites available
(depending on Fe, Al and Ca content), the longer and the
more P can be adsorbed;
 Diameter size of media used in HF wetlands varies from 0.2 mm to
30 mm.
 Effective grain size (d10) should be 0.2 to 1.2 mm, uniformity
coefficient(d60/d10) should be 3 to 6. (Reedet al., 1990, Vymazal
et al., 1998, GFA, 1998, Liénard et al., 2000, Brix, H., 2004)
Media Selection

37. Prerequisites for being able to
use constructed wetlands
Wastewater not be too toxic for bacteria and plants
Sufficient incident light to allow photosynthesis
Temperature should not be too low
Adequate quantities of nutrients to support growth
Detention time should be long enough.
Organic loading should not be too high (expressed as g
BOD/m2/day)
Enough space, because it is a low-rate system

38. Basic maintenance
Natural, low-tech systems (require low but still adequate
maintenance)
Vymazal et al. (1998) recommends checking larger systems (>
500 PE) on a daily basis, including:
 pretreatment units
 inlet structures
 outlet structures
If maintenance is ignored:
 uneven flow distribution
 local overloading
 deterioration of treatment efficiency in the long term

39. Economical alternative over conventional methods
Application of constructed wetland technology for
commercial wastewater treatment signifies a step towards
“green technology”.
They provide a wide range of benefits in wastewater
treatment and represent economic benefits in terms of
energy consumption
They should be investigated and given a chance for use as an
alternative technology in wastewater treatment by local
municipalities and industries.
SUMMARY

40. Removal of major pollutant like organic matter, nutrients and
heay metals.
If constructed wetlands are appropriately designed and
operated, they could be used for secondary and tertiary
wastewater treatment under local conditions, successfully.
Hence constructed wetlands can be used in the treatment
train to upgrade the existing malfunctioning wastewater
treatment plants, especially in developing countries.
SUMMARY

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