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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015
Design Report
Water Quality Improvement using Floating Treatment
Constructed Wetlands
in Beira Lake
Designed and prepared by:
Eng. Mrs. Chandanie Jayatilake (Senior Engineer – PMU/ MCUDP)
L. Arct. Ms. Wasana Dharmadasa (Landscape Architect-PMU/ MCUDP)
Metro Colombo Urban Development Project, PMU
Ministry of Megapolis and Western Development
12th
floor, Wing A, Sethsiripaya, Battaramulla.
Sri Lanka
05th
October 2015

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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015
Contents
1. Introduction to Beira Lake 2
2. Environmental Aspects and Water quality of the lake 3
3. Water Quality assessment 3
4. Necessity to Improve the Water Quality 6
5. Water Quality Issues 6
6. Action of Floating Treatment Wetlands (FTW) 6
7. Removal of nutrients from the water 7
8. Green Movement Against Green Water 8
9. Floating Treatment Wetlands 8
10. How does FTW work? 8
11. Floating Wetland Principles 10
12. Benefits of Floating Wetlands 10
13. Plant Species for FTW 11
14. Design Methodology 13
15. After care 15
16. References 15
17. Annex – 1: Location map for sewer diversion locations

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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015
Water Quality Improvement using Floating Treatment Constructed
Wetlands in Beira Lake
Design Report
1. Introduction to Beira Lake:
The Beira Lake is located in the heart of the city of Colombo, and has a highly urbanized
catchment of 448 ha that is mostly flat, with ground levels ranging from less than 1m to 6m
above mean sea level. The lake covers 65.4 hectares and has a mean depth of 2.0m. It
comprises four main basins: the East Lake, the Galle Face Lake, the West Lake and the South
West Lake. The East Lake is the largest and deepest basin (43.2 ha, max.depth of 5.6m),
while the other three basins are much smaller and shallower (total of 22.2 ha, max. depth of
3.4m).
EAST BEIRA LAKE
SOUTH WEST LAKE
WEST LAKE
GALLE FACE LAKE
The lake catchment is densely populated with hotels, industries, colonies etc. which release
waste water to the lake directly or indirectly.
Past studies in environmental screening showed that the lake water has high levels of
phosphorus and nitrogen compounds that lead to dense bloom of toxic bacteria causing
eutrophication, or depletion of oxygen in lake water, and killing of aquatic organisms.
Pollution in the lake has already identified as the inflows from the polluted canals and
storm-water inlets.

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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015
The Colombo Municipal Council has identified drainage inlets to the Beira lake and they
have already taken action to divert 08 contaminated inlets under MCUDP, out of 19 locations
(continually adding the number of inlets, illegally) and also they have plans to divert the
other locations in future with the sewer rehabilitation programme (location map in Annex -
1).
Another reason for the lake pollution is underserved settlers by the side of the lake bank. In
these locations, sewers are directly discharged into the lake. This problem is already
addressed in Urban Development Authority plans to resettle these communities.
Presently, cleaning services have undertaken by Sri Lanka Land Reclamation Development
Corporation. Under this cleaning process removal of solid waste coming to the lake and
aquatic plants like ‘water hiesenth’ are carried out.
2. Environmental Aspects and Water quality of the lake:
The water coming to the lake is contaminated with garbage, sewers, industrial wast etc.
Water quality of the lake is assessed by several studies during past and found to be high
levels of pollutants. Some results of the Environmental study under MCUDP is given below
(Water Quality Assessment).
The bad quality water continuously emit polluted gases making the surrounding area
unhealthy.
The pollution in the lake has resulted in the eutrophication of the lake and encouraged
periodic unrestrictive growth of algae, fish kills, bad odours and discolouration of the water
which caused public nuisance besides being a health hazard.
3. Water Quality assessment:
According to the ‘Environmental Screening Report for Construction of bank protection walls
of Beira Lake and rehabilitation of McCullum lock gates – Final report, December 2011 by
Uni-Consultancy Services, Moratuwa, water quality of the Beira lake is as in the table given
below.

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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015
Table 2 of the report. Water quality fluctuations of Beira lake
Parameter Water Quality
(during 1997-
2009)
pH 5.6 – 7.3
Conductivity (dS/m) 0.17-3.3
Turbidity (NTU) 2-7
Ammonia (mg/l) 0.8-4.2
Nitrates (mg/l) 0.3-3.1
Phosphates (mg/l) 0.4-3.4
DO (mg/l) 1.2-4.5
BOD (mg/l) 10-38
COD (mg/l) 23-75
Reference :Greentech.(2011).
The comments on the above table is:
COD, BOD, turbidity and total suspended solid content are high in the water. Dissolved
oxygen is low which indicates organic pollution. Phosphate concentrations are relatively
high which indicate nutrient enrichment due to disposal of domestic and industrial
wastewater into the lake over time.
Study by the Uni-Consultancy Services, University of Moratuwa. In July 2013
This study shows the heavy metal content in the selected locations.

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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015
Table A54: Heavy metal contents in S18 (Beira Lake – location 2)
Ref: Report on sediment & water quality analyses at selected locations Final
Report July 2013
Uni-Consultancy Services, University of Moratuwa.
With this results it is shown that the water quality in Beira lake is below maximum cronic
toxic level other than Fe, Al, Mn, Ca, Mg.

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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015
4. Necessity to Improve the Water Quality:
In accordance with the above studies it is evident that the water quality is not in a healthy
conditions and require improvement.
The functions of newly coming up Parks and recreational spaces surrounding the lake will
deeply affect with the lake water quality. It is not only the water but the air quality also has
affected.
5. Water Quality Issues
High nutrient levels in natural water bodies contribute to algal blooms and uncontrolled
aquatic plant growth that eventually rots and robs its dissolved oxygen in the lake water. If
a water body reaches a state known as eutrophic, it is devoid of oxygen and no living
creatures can survive. Clean and healthy water bodies provide habitat for fauna such as frogs,
fish and yabbies, as well as beneficial uses such as water recycling and recreational use.
6. Action of Floating Treatment Wetlands (FTW)
Literature Review:
The technology of Constructed floating islands mimics how natural wetlands purify water.
Through the sheer enormous surface area of both the root systems and the floating matrix,

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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015
together they provide habitat for biofilm growth (habitat of microscopic bacteria) that do the
valuable work of purifying water. These floating treatment wetlands remove nutrients (TN,
TP), suspended solids (TSS), metals (Zn, Cu) and excess ammonia (NH3), increasing the
availability of oxygen for other processes. FTW have now been approved as a Stormwater
Best Management Practice (BMP) in several U.S. jurisdictions. Used in conjunction with
lake-bottom aeration below the islands, the floating wetland treatment effect improves
dramatically.
One of the biggest risks involved in environmental clean-up tasks is the threat of unintended
consequences. Often, the addition of synthetic chemicals intended to neutralize or prevent
the spread of contaminants results in crucial elements of the biological web being negatively
affected, sometimes severely. In almost every case, natural clean-up processes provide a
practical way to eliminate the threat of negative side effects.
Floating Treatment Islands utilize nature to deal with contamination. Biological activity and
plant uptake clean the water instead of chemicals.
The biofilm and microbes that colonize on the island matrix and phytoremediation plants
improve water quality naturally without the need for additional human intervention.
As a total solution floating reed-beds provide a cost effective passive system that mops up
pollutants and prevents further degradation of the water body and banks, slowly restoring
ecosystem functionality.
7. Removal of nutrients from the water:
1. Incorporation into biomass in the FTW – removal of biomass periodically/ part will
be sink into the bottom to absorb by the sediment
2. Incorporation into the food chain, via bacteria, algae, zooplankton, insects and
minnows. Phosphorous would be permanently removed by harvesting fish.
3. Research shows that up to 80% of the nutrient removal from a typical FTW system
is attributed to bacterial activity and approximately 20% to plant growth (Gersberg
et al., 1986).
(Ref: Report Prepared by: Floating Island International, Inc. P.O. Box 252 Shepherd, MT
59079
and

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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015
Apex Engineering, PLLC 4050 Fieldstone Crossing Missoula, MT 59802 , June 2015
Prepared for: Chandanie Jayatilake Metro Colombo Urban Development Project Ministry
of Urban Development, Water Supply & Drainage Sri Lanka.)
8. Green Movement Against Green Water
Floating Constructed Wetlands are floating platforms where suitable shrubs/plants can be
grown on and thus floating on the water surface.
Due to the plant growth on the FTW, it will contribute to a significant reduction in
greenhouse gas emissions and also, by encouraging aerobic digestion, the amount of
methane produced, which is nearly 23 times more damaging than CO2, will be “greatly
reduced”.
The plant growth will consume CO2 and absorb the sunlight during the day time reducing
the urban heat as well. Thus FTW will help to reduce the Global Warming action.
Over the past two decades, artificially created floating wetlands have been studied in various
parts of the world for a range of applications, such as water quality improvement, habitat
creation, and aesthetic enhancement in the following treatment applications.
• Combined stormwater-sewer overflow
• Sewage
• Acid mine drainage
• Piggery effluent
9. Floating Treatment Wetlands:
A floating wetland is a man-made raft that floats on the water’s surface and houses native
wetland plants. These floating wetlands have plant, and root interactions similar to a natural
wetland and provide homes to beneficial water-cleaning microorganisms. Floating wetland
islands are anchored to stay in one area of the pond but can rise and fall as the water level in
the basin changes. These islands can be installed in an existing wet basin without re-grading
the side slopes or other costly retrofits.
10. How does FTW work?
The planting medium of choice which is spread over the surface of the Floating Island and
in the planting holes. Selected plants are planted in the planting holes. Plant roots grow

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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015
through the island into the water column below. The older the island, the longer the roots,
which equates to a greater surface area for bacterial habitat. Biofilm bacteria colonies grow
on the roots and begin to clean the water of nutrients, suspended solids and some heavy
metals. The roots provide a biological haven for the development of biofilms that contain
diverse communities of microorganisms, which aid in various treatment processes. These
same nutrients provide the food source that the plants need for growth. The result is a
“concentrated wetland” effect. In the presence of oxygen from an aeration system below the
islands, the aerobic bacteria living in the root bio-film, thrive, reproduce and create an even
greater wetland treatment effect, than when aeration is not present.
Plant roots are believed to play a key role in the treatment processes within FTWs by virtue
of the contact that is afforded as the water passes directly through the network of hanging
roots that develops beneath the floating mat. Plant roots provide a living surface area for
development of biofilms containing communities of attached-growth micro-organisms
responsible for a number of important treatment processes.
A symbiotic relationship forms between the biofilm and the plants. This cooperation,
which awards fixed nitrogen to the plants and an abundant carbon source to the microbes,
boosts the efficiency of the cleaning by both participants. This partnership is what makes the
phytoremediation method used in islands so effective.
As these excess nutrients transition into the food chain via biofilm/periphyton, both
water quality and fish growth rates can be dramatically improved.
 Beneath the water surface Dynamic Media columns and suspended roots promote
the establishment of beneficial aquatic biofilms, which cleanse the water through
the breakdown, sorption and metabolic transformation of nutrients and impurities.
 Full spectrum waterway ecosystems absorb excess nutrients incorporating them
productively in healthy and attractive enhanced aquatic food chains, while reducing
their availability to algae, lemna and other aquatic weeds.

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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015
11. Floating Wetland Principles
Floating vegetation provides a biological filtration system for the removal of nutrients and
other pollutants from water bodies.
The combination of plants and bacteria provide the means of converting contaminants to
forms that are benign in terms of water quality effects. This is achieved by plant absorption
and the action of various types of bacteria that inhabit the panel and plant structure. The
floating structure itself and the root mass in the water column provide the range of micro-
environments that allow these processes to operate.
A square metre of Floating Wetland has the capacity to process about 5 kg on Nitrogen
(N) and 2 kg of Phosphorus (P) based nutrients per year. This is a typical nutrient loading in
one megalitre of polluted water. In practical situations about 3-5% coverage of the water
surface is normally recommended.
12. Benefits and Advantages of Floating Wetlands
The following are the benifits in Floating Constructed Wetlands:
 Suppression of algal blooms and eutrophication through high efficiency stripping
of nutrients.
 Absorption of dissolved heavy metals
 Clarification of water through the flocculating effect of bacteria

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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015
 Removal of dissolved organic matter
 Reduction of odours
 Suppression of waves
 Provision of habitat for aquatic fauna and birds
 Aesthetically pleasing effect of floating gardens
 Reduced evaporation through the shading effect on water
Following are the advantages of Floating Constructed Wetlands:
 No evidence of sludge, without clogging of beds and without the costs of transport
and deposition;
 No emission of unpleasant odors;
 Low energy costs and low consumption;
 Low cost of installation;
 Low maintenance cost, reduced maintenance;
 Low cost of operation
 Compliance with applicable laws;
 Possibility of water reuse
 Operation constant 24 hours a day, 365 days a year
 Ability to withstand variations of flow.
13. Plant Species for FTW:
Varieties of plants are capable of reducing different contaminants in the surface water.
Varieties of Bulrush are used for nitrate reduction.
Vetiver plant is studied and found to be useful in removing nutrients as well as heavy metals
in water.
These plant species can be selected based on factors such as their ability to absorb or break
down the contaminants of concern, adaptation to local climates, biomass, root structure, rate
of growth, and their roots’ ability to take up large quantities of water.
This diversity of phytoremediation plants means that they can be implemented to address
specific contamination needs. Poplar trees are commonly used to clean up volatile organic
compounds (VOCs) such as ethanol and formaldehyde, while colonial bent grass uptakes
toxic heavy metals such as cadmium and mercury. Sunflower plants can uptake arsenic and
store it in the vacuole.
Bulrush are popular for floating wetlands because they are good for absorbing nitrates.

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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015
All plants need phosphorus to grow but native plants which grow fast and have long roots
are good choices.
Vetiver Zezonoids – shows to be grow in very adverse conditions and absorb nutrients. The
nutrients deposits in the root system. And also it gets occasional flowering and non-invasive.
Vetiver grass uptakes significant amounts of nutrient preventing algal blooms
The contestant uptake of available nutrient in the water, reduced nutrient concentrations to
the point where algal blooms and aquatic weeds could not grow, which eliminated costly
management of troublesome weeds and algal blooms
Nutrient reduction rates with reference to Vetiver
Highly tolerant to heavy metal toxities
Ref: Vetiver System for Prevention and Treatment of Polluted Water and Contaminated
Land
Paul Truong, The Vetiver Network East Asia and South Pacific Representative Veticon
Consulting, Brisbane, Australia.
The vetiver plant however, is a very versatile plant as it can withstand extreme conditions.
It can be cultivated in most countries, and thrives in tropical conditions. There are many
features which renders this plant suitable for this application.
 Long living.

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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015
 Covers a wide range of temperatures
(-14ºC to greater than 55ºC).
 Can grow in different soil pH levels.
 Can withstand rainfall levels from 300mm to greater than 5000mm.
 Tolerant to all heavy metals.
 Saline tolerant.
 Fire tolerant.
 Impervious to pests and diseases.
 Powerful and deep root system.
 Non competitive and non invasive.
 Stiff stems which are resistant to high velocity flows.
The vetiver grass is a low cost, environmentally friendly method that is exceptional for the
treatment of water. It only requires little pest management and has already been taken
advantage of in many countries.
14. Design Methodology:
14.1 Coverage by the FTW
Total surface area of the Beira lake : 432,000 m2
Coverage percentage by FTW : 3% to 5%
Total FTW area required : 17,280 m2
(4% of the lake surface area)
No of plants to be used (plant concentration): 5 plants per m2
Total no. of plants required : 86, 400 numbers plant.

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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015
Fig. example of floating treatment wetland
14.2 FTW Construction:
Construction material – pvc pipes/ bamboo
The individual FTW will be limited to small units to ease the handling manually. And the
small units will be used in combination to get irregular shape FTWs as required.
14.3 Removal of Nutrients from water:
- Periodic removal of leaves from the plants
- By the action of FTW plant roots; bacterial activity
- Fish harvesting
14.4 Water Quality Monitoring:
Water quality monitoring will be carried out for a period of one (01) year with a planned
frequency and thereafter as required. A series of tests will be carried out for various
parameters concerned for the water quality.
14.5 Selection of Plants:
Non invasive native plants will be selected to grow in the FTW.
Main composition will be Vetiver plants and other suitable species (flowering and
ornamental plants) also will be mixed to create a design aesthetically pleasing waterscape
environment.

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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015
Preferable plant species:
Vetiver
Flowering plants- Heliconia/ lilies/ calathea species/ maranta species /
peperomia species / cannas.
Foliage plants: alocasia species/ colacasia species
Vetiver was planted in Beira and it has given very good growth in the lake water and this plant is
sustainable.
15. After care:
 Depending on nutrient loading in basin, after several years islands may require a
severe “trimming” of shoot and root biomass, above and below the matrix to
improve longevity and buoyancy of the island.
 The removed leaves could be used in handicraft work, thus providing income
generation to the needful.
16. References:
1. vetiver.org. - internet
2. Report by Commander Eng. Chaminda Ariyadasa, MCUDP
3. Colombo Urban Wetland Planning Review – for MCUDP, by Wildfowl & wetland
trust (consulting) Ltd. 2013.
4. Restoring ‘Beira Lake’ An Integrated Urban Environmental Planning Experience in
Colombo, Sri Lanka, by Metropolitan Environmental Improvement Programme.
5. Floating Treatment Wetland Island :
http://www.superfloats.com/Products/vetiver.shtml

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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015
Annex – 1

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Design Report: Water Quality improvement using FTW_MCUDP, Oct.2015