Permeable pavements have the potential to control urbanisation impacts, ...
presence of geo-textile membranes within the permeable pavement structure in.
FUCTIONALITY OF GEOTEXTILE MEMBRANES WITHIN PERMEABLE PAVEMENTS FOR BIOGEGRADATION, INFILTATION AND WATER DETENTION OF CONCENTRATION URBAN STORMWATER RUNOFF
Kiran Tota-Maharaj1*, Stephen John Coupe2 & Piotr Grabowiecki3 1*University
of Salford Manchester, Civil Engineering Research Centre, Newton Building, Salford, Greater Manchester, M5 4WT, United Kingdom 2Sustainable Drainage Applied Research Group, Coventry University Priory Street, Coventry, CV1 5FB, United Kingdom 3Institute of Geophysics, Polish Academy of Sciences, Warsaw, Poland
Permeable pavements have the potential to control urbanisation impacts, which have been recognised over many years. Due to an increase in numbers of vehicles and machines being operated by the public, this is causing the potential of more pollutants being produced, especially hydrocarbons and heavy metals, that are consequently being released into the environment. With impermeable surfaces, these pollutants are being carried by run-off water into the sewers and natural watercourses, where unfortunately they can inevitably cause significant and costly damage to treatment plants, or devastate the fauna and flora of our streams and rivers.
Sustainable Urban Drainage Systems (SUDS) Sustainable urban drainage systems are a concept that embraces varying types of storm water management solutions (DEFRA, 2007). SUDs are characterised by the natural response of: •Catchment •Infiltration •Evaporation •Attenuation •Surface storage •Reduced runoff (CIRIA, 2007). SUDS can be described as an approach to managing storm water events and rainfall practically, which replicates natural drainage.
The use of Sustainable urban drainage systems is to apply different drainage techniques in catchment areas depending on the use of land and its characteristics (CIRIA, 2007). The application of SUDS provides an advantage as it will help to reduce to the volume of urban runoff into drainage and sewer systems.
Furthermore this will also reduce the runoff load at combined sewer overflows (CSO) and sewage treatment plants whereby due to urban creep, the design capacity would be not be able to bear the excessive storm water.
Permeable pavement systems are made of layers. These are a surface layer, and a sub base layer which rests on existing soil. Furthermore one or more intermediate layers are also present, which are gravel and crushed stone. Also course fine sand may be included between the surface layer and the sub-base.
The permeable pavement system must provide sufficient strength in order to withstand and support vehicle loads without any deformation from occurring and to allow storm water infiltration to the pavement’s subbase. The sub-base has a very important role in order to structurally distribute the load of the pavement to the underlying layers of gravel and soil, but also acts as a water storage layer The storm water which is filtered through the pavement structure is then further infiltrated to the underlying soil or it is collected in a formal drainage system beneath the pavement surface.
• • • •
Permeable systems enable pollutants to be trapped by the sub-base or by a geo-textile. At the lower surface of the sub-base a pervious geotextile is present, in order to provide infiltration to the ground if intended, or an impervious geo-membrane if there is no need for infiltration . A permeable pavement system (PPS) is able to provide a structural pavement for the public and road traffic whilst allowing water to filter through the gaps of the pavement. This water can be retained for: Temporary storage Storm attenuation Dispersal to the ground Collection for storm water reuse. Permeable pavements are also known as pervious pavements that can be constructed from materials such as asphalt, concrete, ceramic or plastic cells. However, the research focuses on permeable pavements created with concrete block paving systems
The main aim of this research study is to assess and quantify the performance of permeable pavements in reducing storm water pollution loads for UK conditions. Furthermore this research project assesses the effectiveness of permeable pavement systems as a sustainable urban drainage system (SuDS) in treating concentrated urban runoff for water reuse and recycling. The key objectives are to assess the presence of geo-textile membranes within the permeable pavement structure in terms of its efficiencies in removing water pollutants. The overall aim of this project is to enhance understanding of the pollutant removal processes for laboratory based PPS and the effectiveness of PPS systems. The design variation of the pavements includes: No geotextile membranes, (ii) One upper layer geotextile and (iii) an upper and lower geotextile membrane
Geotextiles Geotextiles are a permeable manufactured fabric and are sometimes referred to as filter fabrics. Geotextiles are placed between two layers, or they are placed between a layer and the sub-grade to provide segregation. Furthermore geotextiles add tensile strength to the pavement. Geotextiles are a form of pervious polymeric materials such as: •Geo-grids •Geo-membranes •And geo-composite Geotextiles have openings or pores that vary in size usually between 0.02 to 0.002 inches. In order to distribute the traffic load over soft sub-grade a woven geo-textile is placed under the base course. Geo-membranes are an impermeable manufactured fabric used to line the excavated site
Experimental Layout Permeable pavement blocks
No Geotextile Pea Gravel & Gravel Sub-base
Upper Geotextile
Pea Gravel & Gravel Sub-base
Upper Geotextile Pea Gravel & Gravel Sub-base Lower Geotextile
Sample pipes
No geotextile
One upper geotextile
A upper and lower geotextile membrane
The influent mixture consisted of wastewater and de-chlorinated tap water and glyphosate applied to the top surface of the pavement rigs. Glyphosate is a broad spectrum, non-selective systemic herbicide. After 5 days the initial 5 litres of inflow is released and a sample is taken out from each container to be tested for water quality parameters. The experiment includes analysis of these relevant parameters:
Phosphate PO₄ - P Nitrate NO₃-N Ammonium NH₄⁺ - N Chemical Oxygen Demand (COD) Ortho-Phosphate Biological Oxygen Demand (BOD) Nitrate NO₂-N Suspended solids
COD (mg/l) Mean Monthly Concentrations Inflow
Outflow 1
Outflow 2
Outflow 3
August, 2011
176 179
73.6 51.1
51.2 45
45.7 31.3
Sept, 2011
147
35.1
32.5
27.5
Oct, 2011
122
33
34.1
31.8
Nov, 2011
118
33.8
37.8
20.2
Dec, 2011
73.4
59.9
54
35.8
Jan, 2012
99.4
50.3
52.9
40.5
Feb, 2012
98.3
81
60
53
July, 2011
Ammonium (NH3-N, mg/l) (Mean Monthly Concentrations) Inflow
Outflow 1
Outflow 2
Outflow 3
July, 2011
33.9
1.43
2.32
1.92
August, 2011
24.3
2.44
3.08
1.17
Sept, 2011
25.6
2.47
2.97
0.651
Oct, 2011
26.8
3.25
3.59
1.99
Nov, 2011
22.1
6.37
6.86
3.97
28.9
0.314
0.869
0.864
Jan, 2012
27.5
5.56
5.92
2.83
Feb, 2012
28.6
8.8
7.74
5.98
Dec, 2011
Nitrate (NO-N, mg/L) Mean Monthly Concentrations Inflow
Outflow 1
Outflow 2
Outflow 3
July, 2011
0.351
11.2
11.6
13.9
August, 2011
0.123
1.89
2.75
6.91
Sept, 2011
0.208
3.81
3.64
5.48
Oct, 2011
0.205
2.93
1.76
5.22
Nov, 2011
0.216
3.82
3.01
3.34
Dec, 2011
0.219
8.37
7.02
7.78
Jan, 2012
0.703
2.2
2.18
4.84
Feb, 2012
0.690
5.65
6.23
11.1
BOD (mg/L) Mean Monthly Concentrations Inflow
Outflow 1
Outflow 2
Outflow 3
August, 2011
110 160
15 10
12 4
16 2
Sept, 2011
120
4
7
8
Oct, 2011
80
8
42
23
Nov, 2011
60
3
5
4
Dec, 2011
120
1
3
2
Jan, 2012
40
3
2
5
Feb, 2012
38
2
3
1
July, 2011
Mean monthly Inflow and outflow concentrations of orthophosphate- phosphorous (PO4-P mg/l); from June to January 2012, Sample number n = 35.
For SOME VARIABLES the geotextile membrane made significant differences in pavement rig no.2 and no.3 over pavement rig no.1
But by applying two geotextile membranes one in the upper layer and another in the bottom layer for pavement rig no.3 this made a difference to the results obtained especially for COD, Ammonium and Suspended Solids .
CONCLUSIONS The experimental results showed the effectiveness of geotextile membranes present within a permeable pavement structure and made significant differences in water quality for the removal of key parameters. The geotextile membranes retained most of the waste and pollutants within the pavements rig no.2 (upper geotextile) and no.3 (upper and lower geotextile) unlike pavement rig no.1. The outflow from pavement rig no.2 and no.3 was much cleaner, transparent and contained very low concentrations of pollutants in the outflow when compared to the effluent produced by pavement rig no.1.
