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PERFORMANCE OF GEOSYNTHETIC
FILTERS IN TREATMENT OF URBAN
STORM WATER RUNOFF
HARITHA.P.A
ROLL NO : 35
S8CA
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.
 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.
GEOTEXTILE
Geotextiles 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
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
Geotextiles are mainly differentiated by the

Polymer type

Fiber type

Manufacturing process
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)
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
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
MANUFACTURING PROCESS
WOVEN 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
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
•
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.
•
WOVEN GEOTEXTILE
NON WOVEN GEOTEXTILE
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.
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

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
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.

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.
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.

ADVANTAGES OF GEOSYNTHETIC FILTERS

Minimum maintenance cost

Light weight

Easiness in transportation, folding, rolling, installation,
removal etc
EXPERIMENT SETUP
Silty soil collected from a landfill cover in Polson County,

Montana, was used to prepare a suspended solids material.
A hydrometer test was conducted on the soil to determine the

particle sizes of the fine-grained soil passing through U.S. standard
sieve number 200 (75 μm).
Particle size distribution of suspended particles used in this study

was P1 & P2.
P1 with PSD of 0-180μm and with a D50 of 106μm.


P2 with PSD of 0–106μm and with a D50 of 50 μm.

Cu for P1 and P2 are 12 and 35, respectively.

Cc forP1 and P2 are 2.1 and 4.8, respectively.
Physical and hydraulic properties of geotextiles used in this study


Influent TSS concentration = 200 mg/L.
Influent flow rate = 6 mL/S.

Samples of effluent were collected in plastic containers every 8 min.

TSS concentration measurements were conducted.

Each test was run for 75 min.

Nine effluent samples were collected during each test.

Then calculated the effluent TSS EMC value for each test.
Tests were stopped at 75 min or whenever the water level reached

the top of the column (30 cm) or until the filter clogged.

Each complete set of tests addressed in this work is labeled as Test
A.B, where A is the geotextile indicator and B is the particle size
distribution of the influent suspension .
RESULTS AND ANALYSIS
TSS Removal
Influent concentration=200mg/L.

Target concentration for TSS in water is 30mg/L.

Effect of total solids loaded to each filter on TSS
concentration for particle size distribution P1
Effect of total solids loaded to each filter on TSS
concentration for particle size distribution P2
Total solids captured by NW2 filter as function of solids
loaded to filter for TSS concentration of 200 mg/L
Total solids captured by NW3 filter as function of solids
loaded to filter for TSS concentration of 200 mg/L.
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 .

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).

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.
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.
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.
Thank You…