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On the road to recovery

At least two average-sized landfill sites could be filled with just the road and gully waste alone that we dispose of each year - material that could be recovered, treated and used instead as aggregate. Roadside and gully waste typically consists of sand and gravel (70%), leaves, twigs and other organics (8%), larger aggregates (10-12%), fines (8-10%) and litter (2%). But waste collected by road sweepers and gully suckers varies in content and consistency, depending on the vehicle design, cleansing method, location, weather and time of year. Identifying a cost-effective and sustainable treatment method for this material has proved difficult.

Industry has, to a large extent, buried its head in the sand when it comes to gully waste treatment, often leaving it for ‘someone else to deal with’, paying high rates to have the waste and water taken away and treated or, occasionally, illegally dumping it.

But recent environmental and legislative developments mean that those responsible for the treatment of this material are having to re-evaluate their current practices - or face the consequences. Following recent changes in the Landfill Directive, liquid wastes are banned from landfill; waste must be pre-treated before it can be landfilled and hazardous waste with a total organic carbon (TOC) content of more than 6% is no longer accepted for landfill.

“Sending road sweeper and gully waste to landfill incurs significant disposal and landfill tax costs”

So the disposal of roadside and gully arisings straight to landfill, with little or no pre-treatment, potentially contravenes current legislation. And adhering to this legislation is not the only driver to waste recovery. There are a number of persuasive commercial and environmental reasons why local authorities and their contractors should be addressing their management of this material.

Sending road sweeper and gully waste to landfill incurs significant disposal and landfill tax costs. Landfill tax currently stands at £48 per tonne but is set to increase to more than £70 per tonne by 2013. The cost associated with transporting this waste to landfill sites also needs to be taken into consideration. Road sweepings and gully arisings typically contain 60 to 75% of gravel and sand-sized particles which, once treated, are inert and can potentially be put to beneficial use. But if landfilling is the only viable option, it is possible to re-categorise the material as inert/inactive waste by reducing its organic content to less than 3% TOC. The result of this process is a reduction in the landfill tax to £2.50 per tonne.

Further commercial opportunities lie in the potential to put the reclaimed material to beneficial reuse. There are many options for using the recovered grit as a recycled aggregate including backfill, pipe bedding, road underlay and brick making. Recycled aggregate from gully waste offers the added benefit of being exempt from the aggregates levy, which currently stands at £2 per tonne.

The Department for Environment, Food and Rural Affairs has considered this waste stream in the context of local authority recycling targets and associated Best Value Performance Indicators. Where a council is responsible for waste collection and street cleansing, under Section 89 (2) (a) of the Environmental Protection Act 1990, gully waste can be included as part of an authority’s recycling targets.

So it is clear there are many compelling reasons for addressing the treatment of this often overlooked, but potentially extremely valuable, waste stream. While increased landfill taxes are acting as the stick to move industry forward, the carrots of reduced cost and pressure to improve environmental best practice should be driving local authorities and their contractors to re-appraise what they are doing with their roadside and gully waste.
George Anderson is director of Siltbuster

CASE STUDY: ROAD WASTE TO RESOURCE

The client: ADMEC Municipal Services, a road sweeper hire company in the north east of England. It has 35 staff and an operational fleet of around 20 mechanical road sweepers. From its base in Birtley, it provides mechanical sweeping services for customers such as construction sites, house builders, local authorities, industrial sites and facilities management contractors.

Conscious of increasingly stringent legislation relating to the disposal of liquid waste to landfill and the realisation that most of the material it collected was going to landfill, ADMEC identified the need to better manage its waste process.

Managing director George Tweddle explains: “We could see the need for and the opportunity to provide our customers with something different. Rather than the common practice of leaving the arisings on the client’s site for them to deal with, we wanted to develop a complete service which would enable us to sweep, gather and remove the liquid and solids waste from site and bring it back to our depot for full treatment.”

ADMEC processes on average 50 to 75 tonnes of material a day, and the Gritbuster system can process 10 to 15 tonnes an hour of a range of feed consistencies. ADMEC’s aim is to recover and recycle as much of the recovered material as possible, including the water, with a target recycling rate of 95%.

Its new system sees road sweepings and gully arisings returned from sites, tipped straight from trucks or by loading shovel from stockpiles, into the purpose-built main reception hopper. The material is transferred by bucket wheel into a rotating trommel screen to be washed, and is then separated into an oversize (+10mm) and smaller (-10mm) fraction.

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 clay-like material falls through the trommel holes for further washing. It is then processed to further separate 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 produced by passing the material through an adjacent Siltbuster hydrocyclone and dewatering screen.

Sand material forms most of the road waste, and this recyclable sand - coarse and fine grades - is now sold locally by ADMEC for a range of uses including block paving, pipe bedding and concrete. Fine organics are taken off-site for composting, filter cake is used for landfill restoration and even the oversize goes for further treatment to recover the gravel for recycling.

After processing the larger particulates, all that remains is the silt and fine solids-laden water. This is treated in one of Siltbuster’s water treatment plants, resulting in clean water for recycling and pressed fine solids filter cake.

The handling of water is key to the operation. Tweddle explains: “The Gritbuster system accepts everything collected on-site and it just eats the water we bring back, so we can process everything we gather. We recycle the treated water back into the trucks, which is especially useful for dry weather sweeping operations.”

From a commercial and operational perspective, Tweddle says the results of new system are clear: “We don’t dispose of any material to landfill any more and, compared with 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. Some drivers return to the yard up to three times a day to tip, and the feedback has been very positive. Now we don’t have to worry about when landfill sites are open or not and we have full control of our overall operations. All of these are major incentives for having the Gritbuster system in place.”

 

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