groundworks 59


Removing hydrocarbon pollutants from surface water run-off


By Graham Martin-Loat, Smart Sponge Products Ltd A


s the demand for oil grows – and its cost soars – so the problems of its damaging environmental effects also increase. As far


as the media are concerned, chief of these is seen to be the main product of combustion, namely CO2


, which is destroying the ozone layer


and accelerating the greenhouse effect. However CO2


is not the only problem, certainly as far as


local authorities are concerned. During rainfall, and particularly during heavy


downpours, the run-off water from roads can contain large quantities of hydrocarbon pollutants resulting from oil leaks and exhaust emissions from the non-stop vehicular traffic. Indeed, the limitations of current stormwater drainage systems, in terms of protecting the environment from escaping pollutants, have become distress- ingly evident. With the increasing frequency of major flooding more and more pollutants are escaping into the natural surroundings and water table – a problem that will become worse within the next 50 years if rainfall volumes increase by the predicted 40 per cent. Partly as a result of this, the latest European Water Framework Directive requires more sustainable management of water resources and better stormwater protection. Among the pollutants pre-sent in stormwater


are: hydrocarbons; heavy metals such as lead, chromium, copper, nickel and zinc; road de-icing salts (sodium and calcium chloride); and sulphur- bearing smog compounds. Run-off in rural areas, or where gardens are near roadways and parking areas, can also contain nitrates, phosphates and pesticides. Of these hydrocarbons and oil deriva- tives, the concentrations of which are steadily increasing as a result of the growth in numbers of cars and lorries, are arguably one of the worst offenders and historically one of the hardest to deal with. However, today there is a new weapon in the engineer’s armoury that is rapidly proving its worth and gaining acceptance: a unique molecular structure based on innovative polymer technolo- gies that are chemically selective to hydrocarbons. Developed initially to deal with the aftermath


of oil spills and the damage they cause to coastal environments, this technology fully encapsulates recovered oil, resulting in a substantially more effective response that prevents absorbed oil from leaching. It can also remove low levels of oil


from water, eliminating sheen. As hydrocarbons are absorbed into its struc- ture, the sponge swells and maintains porosity and filter- ing capabilities and the pollu- tants are transformed into a stable solid for easy recycling, providing a closed-loop solution to water pollution. It is also capable of destroying disease-causing micro- organisms from surface water such as E-coli, streptococcus and legionella bacteria. The anti- microbial mechanism is based on the patented agent’s interaction with the micro-organism cell membrane, destroying the micro-organism inac- tivation without any chemical or physical change in the agent. The technology is currently on test with


Wiltshire County Council (WCC). We were asked to demonstrate its ability to deal with gully waste, particularly in the light of the Water Framework Directive that requires authorities to clean up storm water that makes its way to river basins. Currently WCC gullies are emptied by a gully sucker and taken to depots for ‘drying out’ and dis- posal of the waste, which is highly contaminated with hydrocarbons and other material. The ideal would be to remove the hydrocarbons to accept- able levels so that the dry waste could be recycled as a fertiliser. During discussions with WRAP – the Waste Resources and Action Programme for the UK – it was decided that an acceptable level of hydrocarbons in a storm water gully of <100 ppm was unrealistic and the initial target should be 200, working towards 100 in due course. We suggested that the technology could help


with this and deployed the product in three sepa- rate areas – a roundabout site, adjacent highway and the disposal depot itself – embracing 17 locations within both gullies and an oil separator. Hampshire CC agreed to carry out independent testing with lab tests carried out by a third party. Initial analysis before deploying SST revealed average levels of hydrocarbon contamination of over 8,500ppm with some readings above 24,000ppm, so urgent action was required. After deployment, samples taken at intervals of three and six months revealed average hydrocarbon contaminations of 0.96ppm and 0.68ppm respectively. This was an excellent result, particularly for the areas within the depot where the 24,000ppm contamination had been brought down to under 100ppm after the first three months. In Wiltshire Council’s own trials, water quality


samples and weight of petro- leum hydrocarbons (PAH) were taken every three months from each gully along a stretch of highway. Initial PAH levels aver- aging 8500ppm decreased to 0.200ppm at six months, 0.045ppm at nine months and 0.009ppm after a year, a truly remarkable result. The trial has clearly proved that the product reduces the level of PAH in contaminated surface water runoff, far exceeding EU legislation criteria. In the future, Wiltshire Council is aiming to recycle the spent material as a waste-to-fuel energy, which gener- ates 10,000–18,000 BTU/lb. Commenting on the tests, Wiltshire reported:


“In the immediate future we are installing this technology in all of the depots we use to tip out gully waste. This will mean our disposal costs will be reduced considerably because of the unique way the material works and of course its longevity. We regularly clean out the gullies that collect water from roads – at least once a year, more often in problem areas. It is hoped that by installing the sponge in strategic areas in the near future, our disposal costs will be reduced ever further.” As a result of this success, Wiltshire have


‘With the increasing frequency of major flooding more and more pollutants are escaping into the natural surroundings and water


table – a problem that will become worse within the next 50 years’


been instrumental in helping us with the devel- opment of a more effective Smart Gully solution devised to fit within both new and existing gullies to remove hydrocarbons. This new product will be used in strategic areas around Wiltshire for that purpose and to permit simpler annual maintenance. The implications for these


tests are wide-ranging in that it is now possible to exceed oil separator stan- dards of oil removal at a local level through the use


of a simple gully adaptation. What’s more, this same process could be applied to any area where hydrocarbon contamination could be a problem either from traffic or refuelling areas on sites and the solution is both economic and efficient. In fact, if the system were to be used across a county, the annual volume of waste produced by this system could be used within the waste-to- energy scheme and burnt as fuel, saving many thousands of tonnes of contaminated waste.


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