PERFORMANCE OF GEOSYNTHETIC

FILTERS IN TREATMENT OF URBAN

STORM WATER RUNOFF

Anchit Agrawal AP14012

Kamlesh Chaudhary AP14024

Ashutosh kumar AP14045

Anshul Sharma AP14049

Mohd. Amir Khan AP14073

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INTRODUCTION

Current urban infrastructure is highly reliant on impervious

surfaces, including roadways, parking lots, and building

rooftops.

Rainfall that strikes these surfaces cannot infiltrate into the

soil and subsurface and rapidly becomes surface runoff.

They mobilize and transport particulate matter and other

pollutants.

Storm water control measures (SCMs) currently in use for

storm water treatment are retention ponds, detention basins,

wetland ponds, and grass swales, which requires large land

area.

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Sand filters are common subsurface storm water runoff

treatment systems used in urban areas.

Sand filters clog, all or a portion of the sand must be replaced

to ensure adequate drainage through the treatment system.

A geotextile was hypothesized to be as effective as a sand

filter at capturing suspended solids in storm water runoff

while maintaining adequate drainage during solids

accumulation.

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GEOTEXTILEGeotextiles are any permeable, synthetic, textile material used

with foundation, soil, rock, earth, or any other geotechnical

engineering related as an integral part of a man made project ,

structure or system. The purpose of geotextiles are as follows,

In separation

In drainage

For reinforcement

In filtration

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GEOTEXTILE TYPES

They generally fall in to two categories,

Woven

Woven geotextiles consist of fibers or yarns of a

polymer that are oriented in two perpendicular

directions, one over other

Non woven

Non woven geotextiles consist of discrete fibers which

may be oriented or randomly distributed

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Geotextiles are mainly differentiated by the

Polymer type

Fiber type

Manufacturing process

DIFFERENTIATION BASED ON TYPES6

POLYMER TYPE

Geotextiles are generally made from synthetic fibers rather

than natural fibers.

The synthetic materials or polymers are made in chemical

processing plants from the polymerization of thermoplastics.

Geotextiles are commonly made from the polymers of

Polypropylene (PP)

Polyester (PET)

Polyamide (nylon)

Polyethylene (PE)

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FIBER TYPE

There are 4 main fiber types which are used to manufacture woven

geotextiles

Monofilament fibers

Multifilament fibers

Silt film fibers

Fibrillated fibers

fiber types used to manufacture nonwoven geotextiles are

Continuous filament fibers

Staple fibers

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Typical geotextile fiber types: (a) monofilament; (b) multifilament; (c) slit-film;

(d) fibrillated; (e) continuous filament; (f) staple; (g) multifilament yarn; (h) staple

yarn; (i)silt film yarn

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MANUFACTURING PROCESSWOVEN GEOTEXTILES

The weaving technique is performed in four steps:

• Shedding

• Picking

• Battening and taking up

• Letting off

NONWOVEN GEOTEXTILES

Nonwoven geotextiles are generally made from a spun bonding process.There are 4 major steps in the spun bonding process. That are:•fiber preparation• web formation•web bonding•winding into rolls

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The fibers may be bounded together by one of three techniques.

Mechanical bonding

Thermal bonding

Chemical bonding

MECHANICAL BONDING

• Needle punching is the mechanical process used to bond

nonwoven geotextiles.

• In this process the web is passed under a needle board, which is

made up of thousands of barbed needles.

• The needle design, punch density and depth of punch are the

variables which may affect the pore size distribution of a

geotextile

BONDING11

THERMAL BONDING

•It is a bonding process which melts the web together at fiber

cross over points.

•The web is passed through a source of heat, such as pressurized

steam or hot air which causes fusion at fiber cross over points.

•Strong, flexible bonds may be formed at cross-over points.

CHEMICAL BONDING

•A chemical binder, such as an acrylic resin, may be applied by total immersion or by spraying. •After the binder is applied, the web is passed through an oven or hot rollers to cure the chemical binder.•Another chemical bonding technique uses hydrogen chloride gas.

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WOVEN GEOTEXTILE NON WOVEN GEOTEXTILE

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MECHANISM OF FILTRATION

A filter should prevent excessive migration of soil particles, while

at the same time allowing liquid to flow freely through the filter

layer. Filtration is therefore summarized by two seemingly

conflicting requirements.

A filter must retain soil, implying that the filter pore spaces or

openings should be smaller than a specified maximum value; and

The filter must be permeable enough to allow a relatively free flow

through it, implying that the size of filter pore spaces and number of

openings should be larger than a specified minimum value.

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GEOTEXTILE FILTER REQUIREMENTS

For better performance of filter, it should satisfy some criteria, that

are

Retention : Ensures that the geotextile openings are small enough to

prevent excessive migration of soil particles.

Anti clogging : Ensures that the geotextile has adequate openings,

preventing trapped soil from clogging openings and affecting

permeability

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Permeability : Ensures that the geotextile is permeable enough

to allow liquids to pass through without causing significant

upstream pressure buildup.

Survivability: Ensures that the geotextile is strong enough to

resist damage during installation due to stress applied on it.

Durability: Ensures that geotextile is resilient to adverse

chemical, biological, and ultraviolet (UV) light exposure for the

design life of the project

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IMPACT OF URBAN STORM WATER

RUNOFF ON WATER QUALITY Storm water runoff from urban areas contains significant

concentrations of harmful pollutants.

It affects water quality, water quantity, habitat and biological

resources, public health, and the aesthetic appearance of urban

waterways.

Solids are one of the most common contaminants found in urban

storm water.

Stream bank erosion and erosion at construction sites are the

major sources of solids.

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Elevated levels of solids increase turbidity, reduce the penetration

of light at depth within the water column, and limit the growth of

desirable aquatic plants.

destroy habitat for fish and bottom-dwelling organisms.

Solids also provide a medium for the accumulation, transport

and storage of other pollutants including nutrients and metals.

Impaired navigation due to sedimentation represents another

impact affecting recreation and commerce.

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TREATMENT METHODS

Retention ponds, detention basins, wetland ponds, grass swales.

By passing it through porous medias like sand, anthracite,

activated carbon, asphalt etc.

These technologies require significant land area and are difficult to

retrofit in highly urbanized areas.

Sand filters are common subsurface storm water runoff treatment

systems used in urban area.

Sand filters clog, all or a portion of the sand must be replaced to

ensure adequate drainage through the treatment system.

Removal of filtration media such as sand is highly labor-intensive.

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ADVANTAGES OF GEOSYNTHETIC FILTERS

Minimum maintenance cost

Light weight

Easiness in transportation, folding, rolling, installation,

removal etc

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DESIGN PARAMETERS FOR GEOTEXTILE

FILTRATION Permittivity played a greater role in affecting TSS

removal than the AOS.

Knowing one pore size (such as AOS) is not enough to

determine the capability of a geotextile to retain TSS.

Using permittivity or more than one geotextile pore size

should provide greater accuracy .

The PSD played a large role in affecting TSS removal.

Knowing one particle size, such as D50, of a soil is not

to enough to choose the appropriate geotextile to retain

that soil.

A range of particle sizes, or at least more than one size,

would enhance the design parameter selection .

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Applicability of existing geotextile filtration and

retention criteria

The general formula of the criteria can be written as follows.

(OX/DX) < A

(OY/DY) > B

Where , A= retention ratio (constant)

B=clogging ratio (constant)

OX= characteristic retention pore size (µm)

OY = characteristic clogging pore size (µm)

DX =characteristic clogging soil (TSS) grain size (µm)

DY=characteristic retention grain size (µm).

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The established criteria may not be appropriate for storm water data.

A more effective criteria is to take the ratio O95/D95 to O30/D30

Plot of solids captured in and on geotextile filter as a function

of ratio O95/D95 to O30/D30.

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In only one test condition, the suspended solids mass removal

was less than 75%

NW1, was not able to reduce the solids concentration to the

target value

This occurs as a result of its larger AOS (180 μm), permittivity

(1.2 s−1), and porosity (87%) .

New criteria such as (O95/D95)/(O30/D30) ≥ 0.5 are proposed

in this study.

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Conclusion

Geotextiles are very effective in removing suspended solids

from urban storm water runoff.

While selecting the type we have to consider lots of things

such as AOS, permittivity, porosity etc.

Nonwoven polypropylene type geotextiles are considered as

the most effective in filter performance .

The geotextile which satisfies the 5 criteria and with smaller

apparent opening sizes, permittivities, and porosities are best

suitable for filtration of urban storm water runoff.

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Thank You…

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