Where do the contents of bins end up? Diligent recyclers may feel irked at neighbours who are too lazy or mean to segregate rubbish, but the reality is waste is carefully screened to maximise its potential
Green bin
GARY BRADY, managing director of Thornton’s Recycling, stands watching a conveyor belt in the company’s mixed dry recyclables facility in west Dublin. “It’s like the Generation Game,” he jokes.
Well yes, there’s the cuddly toy, and another one, sadly decapitated, then a garden parasol, a leather football, some video cassettes and nappies – lots of nappies.
Not exactly the best game show prizes, but the waste pickers standing on each side of the conveyor belt scoop them up with impressive speed.
Clearly this material is not what’s meant to be in a household green bin, but if left in the system these items can block the machinery, shutting down production completely until they’re prised out.
“You get all sorts; I saw a car bumper in there one day, but nappies are the biggest offenders,” Brady says.
The pickers at the conveyor belt are in fact the second stage of the filtering process. The first sight on entering the green bin recycling facility is a mountain of what looks like rubbish, but there’s gold in them there hills. Or if not actual gold, a least a chance to reduce landfill costs by taking out as much recyclable material as possible.
The mountain is gradually demolished by a giant “grab” machine which loads the material on to a metering drum with rotating teeth to rip open any bin bags. Then the material reaches the “quality control station”: the pickers.
Once the really unpleasant or inappropriate items have been manually removed, the material travels on to another conveyor set on an incline, interspersed with gaps. This captures large cardboard items, while the remaining material drops through and moves towards a machine called a ballistic separator.
This separates the lightest material, mixed paper and plastic films and packaging, from the rest, which should now consist mainly of “rollies” – plastic bottles and cans.
The light stuff moves on to an optical sorter, a particularly impressive looking machine with a camera which scans the waste and uses jets of air to collect the plastic film.
Another optical separator sorts out the clear and opaque bottles and the tetra packs. More waste pickers help this process along, ensuring everything goes into the correct pile.
A magnet removes steel tins while an eddy current shakes out the aluminium.
What remains is a sorry-looking mess. There’s a toilet seat in there, the odd shoe, rotting food and proportionately even more nappies – but it is a considerably smaller pile than the mountain sitting at the door.
This stuff accounts for about 10 to 13 per cent of what arrived in the green bins collected from Thorntons’ 40,000 customers in Dublin, Meath and Kildare.
This might sound like a reasonable result, but, along with the failure of householders to rinse out cartons and tins, it makes life very unpleasant for the 15 or so workers in the building.
In addition to the stench there are swarms of flies – particularly those tiny fruit flies which seem to have a particular fondness for eyes and mouths.
“It’s a horrible job. The workers are all medically screened every six months, and their tetanus shots are always up to date, but it’s a very tough job. If I could get people to separate their waste, and especially to not put nappies and food waste in the green bin, I’d be a lot happier,” Brady says.
Diligent recyclers might feel aggrieved that the contents of their green bin are mixed in the back of the bin lorry with those of neighbours who misuse the free bin because they are too lazy or mean to segregate their waste. However, Brady says, there isn’t a free pass for those abusing the recycling bin.
If a load comes in with a considerable level of contamination, the next time the route is serviced the collectors will look in each bin and a warning sticker will be placed on any bins containing general waste.
If the same customer continues to misuse the bin it will not be collected until they remove the offending waste. Failure to do so will result in withdrawal of service.
“It’s three strikes and you’re out. If someone isn’t going to play by the rules, I don’t want their business.”
Black bin
The residual waste from the green bins makes its way to the nearby materials recovery facility, or black bin depot, to join the rest of the material from the general waste bins.
The perception that the contents of the black bin make their way straight to landfill is very wide of the mark. There is still potential to recover resources from general waste.
Like those of green bins, the contents of black bins wait in large piles. It is then shredded to open out any bin bags and transferred into a machine called a trommel, like a giant washing machine drum, 10ft high and 60ft long, set at an angle. The rotating trommel shakes out “organic finds”, mainly food waste. Because it has come from the black bin it cannot be composted, but it can be processed to make it inert and used as a top layer to cover landfill sites.
What’s left in the trommel is a mixture of plastics, papers and metals, which then goes through an “air classifier” which separates heavy and light material. As with the green bin, metals are removed, as are textiles such as clothing and footwear. The remaining waste, largely paper and plastic, is gradually separated and shredded and brought back together through a number of processes until it has the appearance of dirty confetti.
This material, at this stage a usable product called solid recovered fuel (SRF), is typically used by the cement industry as a substitute for coal in their kilns. Cement firms charge to take this material, but the cost of producing it and the charge still works out at about 20 per cent less than the landfill gate fee. Some 70 per cent of black bin material ends its life as SRF. The organic finds make up about 20 per cent of the bin material. Metals account for about 2 per cent, with just 7-8 per cent going to landfill.
Brown bin
Just a few kilometres away from the Cavan border is the Thorntons compost facility at Kilmainhamwood, Co Meath. The contents of the brown bin, which should contain just food and garden waste, is taken here and over an eight- to nine-week period is turned into a product which looks exactly like what would be sold at a garden centre.
As with what goes in the green bin, contamination is the biggest problem, facility manager Tom McDonnell says.
“Wine and beer bottles and sauce jars. Plastic bags as well. You couldn’t make a mistake and think glass was allowed in the bin, but some people do buy biodegradable plastic bags to line the bin and they can’t be used – it’s only compostable bags that will break down.”
The lorries come in and are weighed and each load is given a unique tracking number. The load is then transferred in the indoor reception hall, where the glass bottles have to be picked out.
The material is shredded and mixed with wood chips and “seed material” – compost which has already been partially through the system. This mix, 60 per cent of which is the new material and 40 per cent is woodchip and seed compost, is loaded into aerated bays where an optimum temperature is maintained for three weeks.
A trommel is then used to screen the material into three types: particles under 12mm in size, which account for about 55 per cent of the mix, are retained to make compost; those between 12mm and 40mm, about 35 per cent, go back to the start for use as seed material, and the remaining 8-9 per cent is residual waste such as the non-compostable bags.
The sub-12mm compost is bulked up for a further three weeks before being transferred into a pasteurisation tunnel.
Here the temperature is brought above 70 degrees for one hour to sanitise the compost, in line with Department of Agriculture requirements, and samples are sent for laboratory analysis to ensure they meet this standard, as well as meeting the European pasteurisation standards.
After three weeks the finished compost is delivered and spread on local farms at a cost of about €10 per tonne to the farmer.
WHERE IT GOES AND WHAT IT'S WORTH
Plastic bottles: PET (polyethylene terephthalate). These clear soft drink bottles are sold for about €350 per tonne. Thorntons supply them to a Monaghan-based company, were they are flaked. The flake is typically turned into textiles, often ending life as fleece jackets.
Opaque plastic: HDPE (high density polyethylene). This opaque plastic, such as milk containers, is sold at about €400 per tonne. Thorntons supply it to a Galway company which makes it into granules used eventually to make products such as drainage pipes for agricultural use.
Cardboard: The board, costing about €125 per tonne, is sent to mills in the Netherlands.
Plastic film: (High grade about €300 per tonne; low grade about €50) This goes to the Netherlands, where it is shredded and reused for plastic bags.
Aluminium cans and packaging: (about €850 per tonne) This goes to metal processors in Europe, where it is melted and rerolled into new aluminium product.
Steel: (about €150 per tonne) This goes to Britain and other locations in Europe, where it is melted and cast into ingots for reuse.
Mixed paper: (about €90 per tonne) This is sent to paper mills mainly in the Netherlands.
Cost of processing a tonne of waste at the Thorntons green bin facility: €60
Cost of sending a tonne of waste to landfill:€100-€120
