Toxic metals carried in surface water runoff from roads and other heavy-traffic locations threaten the health of rivers and streams through persistent and bio-accumulative pollution. Incapable of being broken down biologically, they become attached to silts and sediments and dissolve in the runoff washed off hard surfaces during heavy rain.
This pollution is the result of tyre erosion, dust from brake and clutch pads, fuel and lubricants from engine wear and exhaust emissions. The pollutants attach to silts and sediments in surface water when it rains, and some are dissolved in the water.
As a result, persistent, toxic and bio-accumulative pollutants are carried into rivers, streams and groundwater. Copper and zinc, in particular, are directly toxic, so can affect aquatic species as soon as they enter the watercourse.
When a risk assessment, conducted according to Highways England's Design Manual for Roads & Bridges, identifies unacceptably high levels of soluble copper and zinc, then action must be taken to treat the pollution.
So, SDS worked with scientists at the University of Chester to develop a versatile, cost-effective engineered treatment media that could capture copper and zinc in surface water runoff from motorways, trunk roads and other high-traffic areas and can be used in regulatory-compliant Sustainable Drainage Systems (SuDS).
We perfected a unique combination of naturally-occurring materials and conducted testing to reflect a range of rainfall conditions under the observation of an independent representative from a UKAS-accredited laboratory in accordance with the British Water protocol. We called the new material SDS Aqua-XchangeTM.
So how does it work? Because of its granular composition, SDS Aqua-XchangeTM has a large active surface area, enabling high-performance pollutant removal in a small space. The highly-efficient granular material uses the processes of adsorption and ionic exchange to form unbreakable bonds with the heavy metals, including copper and zinc, capturing and retaining them even in heavy storms.
The breakthrough of SDS Aqua-XchangeTM is that it is both affordable and truly versatile. It gives highway drainage designers unprecedented flexibility, because the material can be incorporated into a range of SuDS components to boost their treatment performance.
It can be used in both existing and new drainage schemes and requires minimal maintenance. In a typical application, a layer of SDS Aqua-XchangeTM can be added as an additional component to a linear filter drain. Installed at a shallow depth, contractors avoid costly excavation or use of heavy cranes.
Delivered to site in lightweight, one cubic metre bags, SDS Aqua-XchangeTM is now available for consulting engineers and infrastructure contractors to deploy as stormwater treatment in highways drainage, as well as on other higher risk locations such as retail car parks, freight and logistics hubs.
SDS Aqua-XchangeTM can also be combined effectively with other proprietary SuDS devices. As it can filter out finer silts and sediments, it can be deployed downstream of a hydrodynamic vortex separator such as SDS Aqua-SwirlTM that targets larger particles. It can also be combined with geocellular storage, such as SDS GEOlight®, when additional attenuation is needed as part of the roadside treatment system.
It can also be used to deliver pre-treatment as part of a vegetative SuDS scheme, enabling smaller SuDS ponds or wetlands to be designed where otherwise there would have been no room for them. Compliant with guidelines in CIRIA C753 The SuDS Manual, SDS Aqua-XchangeTM can be included as a component in vegetative SuDS devices such as dry swales, raingardens or bio-remediation zones, so that robust retention of copper and zinc is completely assured while plants can continue to thrive as part of the landscaped design.
In a typical application on a linear development, such as a road scheme, a 250mm layer of Aqua-XchangeTM is introduced into a filter drain, beneath a layer of standard aggregate.
The use of a linear filter drain allows a flexible design system, removing the need for large areas of additional land take. Solids suspended in the runoff are filtered and collected in the aggregate whilst the soluble pollutants are captured by the layer of Aqua-XchangeTM beneath. This linear design offers a huge treatment capacity which can be more than eight times greater than in an end-of-pipe treatment device.