beiralakewaterqualityimprove with ftw_design report

0 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


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


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.


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.


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.


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.


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,


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


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


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.


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


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.


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.


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.


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.


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

http://www.superfloats.com/Products/vetiver.shtml


Annex – 1

beiralakewaterqualityimprove with ftw_design report

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