Recycling Road Sweeper Waste Turns Cost into Opportunity

01 March 2011 Every year in the UK it is estimated that more than one million tonnes - approximately half a million cubic metres - of roadside and gully waste is sent to landfill - equivalent to filling at least two average-sized landfill sites every year. Most of this material, if recovered and treated, could be used as aggregate and diverted from landfill. However, treatment of this potentially valuable waste stream has to a large extent been brushed under the carpet - with companies leaving it for someone else to deal with, paying high rates to have the waste and water taken away and treated, or even illegally dumping it. Recent environmental and legislative developments such as the Landfill Directive, however, mean that those responsible for the treatment of this material must re-evaluate their current practices - or face the consequences. Adhering to this legislation is not the only driver to recovering roadside and gully waste; there are a number of extremely persuasive commercial and environmental reasons why companies should be addressing their management of this material. Commercially, sending waste to landfill is extremely costly; landfill tax rates currently stand at £48 per tonne but are set to increase to over £70 per tonne by 2013 and possibly even higher in the future. As 60% - 70% of gully waste is inert once treated, significant tax savings are made possible by simply not sending this material to landfill. Furthermore, once treated, even if landfill is the only option, it is taxed at just £2.50 per tonne. From an environmental perspective, putting treated highway residue to alternative reuses means that waste and landfill reliance are both minimised. Putting theory into practice ADMEC, an independent road sweeper hire company based in the north east of England, provides mechanical sweeping services for local authorities, construction sites, house builders, industrial sites and facilities management contractors. Established in 1993, ADMEC claims to offer a complete road sweeping solution - from the hire of sweepers through to handling the road waste itself. Conscious of the increasingly stringent legislation relating to the disposal of liquid waste to landfill, and the fact that even the Environment Agency's NetRegs lists water as the first constituent of road sweepings, ADMEC realised that things needed to change. The company says that it first ventured into the handling of road waste a number of years ago, and relied on the use of a tipping area - as seen on many sites across the UK - to allow water to drain out of solids naturally before using a basic form of water treatment. However, the majority of the material still ended up in landfill, often at extortionate disposal rates. George Tweddle, managing director at ADMEC explains: "We could see the need for and the opportunity to provide our customers with something different. We wanted to develop a complete service, which would enable us to sweep, gather and remove both the liquid and solid waste from the site and bring it back to our depot for full treatment." Identifying a more sustainable solution In its search for a solution, ADMEC focused its attention on Gritbuster, a new road sweeping and gully waste treatment and recycling system developed by silt management specialists, Siltbuster Limited. Having seen the Gritbuster system at work on a Highways Agency contractor in Somerset, the company purchased a similar unit in January 2010, locating it at its Birtley depot. To keep costs down as much of the existing treatment equipment as possible was utilised in the project, and operations using the new system commenced in late January, with full treatment and recycling quickly being established. This has resulted in more than 4500 tonnes of road sweepings being processed to date, initially all ADMEC's own sweeper waste, but increasingly the company says that it is also processing third party waste from local authorities in the region. According to the company, on average the system is processing 50 to 75 tonnes of material per day, with higher volumes during particularly busy periods. The system is capable of processing up to 10 to 15 tonnes per hour. ADMEC says that the key to its approach is its aim to recover and recycle as much of the material as possible, including the water, to achieve a 95% recycling rate. The process Material is transferred by bucket wheel into a rotating trommel screen to be washed. It is then separated into an oversize (+10 mm) material and smaller (minus 10mm) fraction. The oversize material typically contains the larger gravel-like material and the usual road debris e.g. bottles, coke cans, broken number plates, leaves, etc. Once separated, it is conveyed out of the machine for further handling and processing. The remaining material, containing the sand, fine organics, silt and any claylike material falls through the trommel holes for washing. Further processing separates the fine organic matter from the coarse sand/gravel fraction, before each is separately dewatered and conveyed out of the unit as separate products. A second finer grade of sand is also produced by passing the material through an adjacent Siltbuster hydrocyclone and dewatering screen. Sand material forms the bulk of the road waste and it is this recyclable sand, both coarse and fine grades, which ADMEC now sells locally for a range of uses including block paving, pipebedding, concrete etc, ensuring that, wherever possible, it returns to the construction sector for re-use. Fine organics are taken off-site for composting, filter cake is used for landfill restoration and even the oversize now heads for further treatment to recover the gravel for recycling. After processing all the larger particulates, all that remains is the silt and fine solids laden water, which is treated in a Siltbuster water treatment plant situated alongside. The result is claimed to be clean water for recycling, and pressed fine solids filter cake. align="left" hspace="5" vspace="1">The company is also now using the treated water to fill its road tankers ,which are used to fill motorway barriers and for other grey water applications, and recycling of the recovered sand other materials such as the organics and the filter cake is underway. In addition to the coarse washed sand, the additional hydrocyclone and dewatering screen has enabled the recovery of the fine sand as another product. As the company does a lot of house building sites, it says it has seen a lot of recyclable fine bricklaying type sand coming. According to Tweddle, from a commercial and operational perspective, the results are clear: "We don't dispose of any material to landfill anymore and compared to our previous approach we're seeing significant savings in our operations and the generation of a new revenue stream with the sale of the recycled material." "Our sweeper drivers always have a place to tip throughout the day or night if required, which means that when the trucks are full, they can return to the yard, tip and get back out working again." he concludes.