FUCTIONALITY OF GEOTEXTILE MEMBRANES WITHIN PERMEABLE PAVEMENTS FOR BIOGEGRADATION, INFILTATION AND WATER DETENTION OF CONCENTRATION URBAN STORMWATER RUNOFF Kiran Tota-Maharaj 1*, Stephen John Coupe 2 & Piotr Grabowiecki 3 1* University of Salford Manchester, Civil Engineering Research Centre, Newton Building, Salford, Greater Manchester, M5 4WT, United Kingdom 2 Sustainable Drainage Applied Research Group, Coventry University Priory Street, Coventry, CV1 5FB, United Kingdom 3 Institute 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 Upper Geotextile Upper Geotextile Pea Gravel & Gravel Sub-base Pea Gravel & Gravel Sub-base Sample pipes Pea Gravel & Gravel Sub-base Lower Geotextile
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 July, 2011 176 73.6 51.2 45.7 August, 2011 179 51.1 45 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 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 Dec, 2011 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
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 July, 2011 110 15 12 16 August, 2011 160 10 4 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
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.