Automated underground waste disposal
Imagine not being woken up at the crack of dawn by the sounds of dustbin collectors outside your home, or not having to put up with bulky and foul smelling refuse containers in the street, outside your offices, or even at your local science park? Many cities around the world have already adopted an automated underground waste system that could soon be heading to the UK. Developed by Swedish company Envac Centralsug, the system was first introduced at a hospital in Sweden in 1961, and the company has now completed about 600 installations worldwide. But it is only recently that Envac's approach to handling waste appears to be gaining ground in the UK. ‘To our understanding, waste handling issues weren't top priority in the UK until very recently,' explains Jonas Törnblom of Envac.
The company is currently in talks with UK-based property investment and development company Quintain, who controls 70 acres of land surrounding the new Wembley Stadium in London and intends to regenerate the area with the refurbishment of Wembley Arena, and through the development of cafes, restaurants, an entertainment complex and about 4,000 homes. ‘A final decision is expected early May,' says Törnblom.
But how does Envac's ‘invisible solution' for waste operate? Working on the principle of under pressure suction, it comprises several collection points that are linked together by steel piping to a central collection station. Refuse is deposited, either indoors or outdoors, into an inlet and temporarily stored in a chute on top of a discharge valve. There is a level indicator in each inlet that tells the system when it is full and locks it.
When full, the inlets are emptied one by one using a computer control system that switches on the fans - an air inlet valve is also opened to allow transport air to enter the system. The bags fall by gravity into the network of pipes and are sucked to the collection stations at a speed varying between 20-25m/s, depending on the density of the waste. The refuse enters the station via a cyclone, whereby the transport air passes through dust and deodorant filters before it is released, and the refuse falls into a compactor that packs it into a sealed container.
The process also caters for recycling, as there can be separate inlets for each fraction of waste, be it paper, organic waste, or plastic. Once pre-sorted and deposited in the inlets by individuals, all fractions are transported in the same pipes. But to avoid any mix up, only waste from full inlets of the same fraction is emptied and transported at any one time, before moving on to another category of refuse. The control system directs a diverter valve to convey each category of waste into the correct container.
Flexibility appears to be a key feature of the technology, with each installation varying from the next. Törnblom says, ‘We decide together with the developer and the council which fractions should be collected in each individual installation. We have no influence on whether the waste goes to recycling, landfill or incineration. The decision must be taken by the council'. The collection station, however, is usually located away from the city, preventing the disruption caused by truckloads of rubbish being transported through polluted and congested urban areas.
Business parks, warehouses and factories usually have larger inlets for their increased volumes of waste. These are normally only possible to open with use of a key, transponder or card. ‘The technology saves valuable space inside or outside buildings, that otherwise would been occupied by bins, transport paths/ access roads and turning points. This also makes the technology economically attractive for the developers,' adds Törnblom.
One of the drawbacks is that only very small amounts of glass can be processed due to its abrasive property, thus requiring a separate collection scheme for this material. Moreover, there is the high level of investment required to build the infrastructure. ‘The investment will differ depending on if it is a new construction or in an [existing] built up area,' explains Törnblom. ‘Also, density of buildings will have an effect on the cost.' He says that in a new development the average cost will be about £1,000 per flat.
There are also maintenance costs, with service inspections twice a year. After the initial 10-year-period, containers are normally replaced - although, the steel piping usually lasts for over 30 years. The pipes, 400mm in diameter for residential operators and 500mm for commercial, are coated on the outside with PE-coating for corrosion protection, but not on the inside, describes Törnblom. ‘We don't use stainless steels unless we expect very corrosive materials to be dumped into the system. We use pipes with different thicknesses and hardnesses depending on the type of waste that we expect to be transported and the exposure [to abrasion]. For example, the closer to the terminal, the more waste will travel in the pipe.'
Blockages occasionally occur and are identified and cleared by the control system by opening and closing the discharge valves or restarting the fans. How is this investment offset by the reduction of manual collection costs? Envac estimates a reduction by about 30-40% (residential) and 60-80% (commercial). Quintain envisages that it would recoup its costs in about 15 years. But only time will tell. If the Wembley project goes ahead, its effectiveness may well determine the viability of other installations in London and elsewhere in the UK.
Perhaps the potential is far greater for new developments in the UK than existing urban areas, not simply due to the cost, but also the inconvenience of overhauling a city's infrastruture. According to Envac, undertaking the construction alongside other roadworks or the installation of gas and water pipes might be a solution. It remains to be seen how well the system is received in the UK when indviduals no longer have their trusty bins on their doorsteps. ‘We try to put the inlets as close to the households/commercial operators as possible. A maximum walking distance of 50m should not be exceeded. We can have up to 100 flats per inlet, but are normally less than that,' says Törnblom.
There may well be areas for refinement, but examples in Sweden, Spain, The Netherlands and Korea, suggest cleanliness and hygiene is improved. Envac certainly has its eye on London. ‘The boom in construction and real estate makes this technology much more affordable. We believe many of the projects in the London area [Olympics 2012] would be ideal for this technology,' adds Törnblom.