Automatic for the people
Many councils are failing to show their public what is happening to their waste. But automated sorting systems can address this problem, says Jonathan ClarkeA more environmentally aware public is putting increasing pressure on local authorities to know what happens to the waste they generate. The need to be accountable has been a long-held tenet of public service, but many LAs are struggling to keep pace with the demand for better waste facilities and better traceability of recovered materials.
The UK is only just beginning to address this issue by investing in more automation, particularly in materials recovery facilities (MRFs), which have traditionally relied on labour-intensive sorting methods. Essentially, with an automated sorting system, the input stream is analysed by a fast-moving scanning sensor installed over a conveyor belt.
The sensor rapidly identifies materials, shapes, textures and colours as well as the object position. The defined sorting fraction is blown onto a second transport system using high-power air jets, while the residual fraction is brought to a third belt for further sorting or disposal. Automated sorting systems can sort most common materials types found in household and commercial waste streams, including:
- newspapers and magazines
- brown cardboard
- white paper and mixed paper
- coloured and clear types of plastic such as PET, HDPE and other polymers such as polypropylene, polystyrene and PVC
- mixed plastics polymers and beverage cartons
- metals packaging
Firstly, it removes the human element from materials recovery. Manual separation is time-consuming, inconsistent and cost-intensive. It is also a highly monotonous and unpleasant task. Replacing humans with machines in this context is therefore beneficial from an economical and welfare point of view.
Secondly, automated sorting produces high levels of consistent product - a purer sorted fraction and higher yields, which in turn spells higher profit per tonne of input and higher diversion from landfill rates. In other words, automation could mean avoidance of a LATS fine, plus a welcome additional revenue stream.
Efficiency starts at the design stage
To get the most out of automated sorting, it is important to involve plant designers familiar with the technology at the discussion stage so that the MRF can be designed around the technology, and around the predicted materials input and output. The cost of installing an automated sorting system can be offset against the following savings: less personnel tied up in sorting; no extra night shift costs; ease of operation as no specialist training required; quick and easy installation; low maintenance and operating costs. Typical payback periods range from six to 36 months.
Automation has an essential role to play in enabling LAs and their waste contractors to meet their obligations - not only to divert more from landfill, but to be more accountable about what happens to the country's waste. It also helps them to contribute to the wider need to recover and reuse as many valuable materials as possible in order to reduce climate change and preserve precious global resources.
A MRF based at Alton in Hampshire is a prime example of automated sorting at its best. Operated by Veolia Environmental Services and installed by Okay Engineering, the Alton MRF forms part of the integrated waste management infrastructure that supports Project Integra, the 28-year agreement between Veolia, Hampshire County Council, the unitary authorities of Portsmouth and Southampton and 11 LAs in the area.
Optical technology sorts it out
Under this agreement, the co-mingled recyclables collected by the LAs are taken to a MRF for sorting. Key to its success in recovering high levels of paper and plastics from the waste stream is TiTech optical sorting technology. The site currently operates five days per week, 16 hours per day on a two-shift basis and processes 90,000 tonnes of co-mingled recyclables per year.
The materials pass through a pre-sort cabin and onto a pair of trommels working in parallel. Initial separation is by size, with cans and plastics continuing on one line and paper and cardboard being diverted onto another line.
The paper line is equipped with an extra-wide conveyor belt, which enables the materials to be more evenly spread on the line. Two TiTech VisionSort systems are used to sort this stream, both by material and by colour. These optical sorters are so accurate that they can differentiate between cardboard and magazines, with the conveyor operating at almost 3m/s.
The cans and plastics stream meanwhile is passed under an electro-magnet and over an eddy current separator to remove metallic objects before being passed through two TiTech VisionSort systems. On this line, the first TiTech PolySort unit separates plastics leaving mixed paper which then passes under a final PolySort.
Jonathan Clarke is country manager (UK) at Titech Visionsort
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