International trials have proven that what we assume to be “residual” waste actually still includes high levels of recyclate, even in areas with high recycling rates. The evolution of sensor-based sorting processes is proving that recyclables can be extracted from construction waste and that black bag waste is an important additional revenue stream.
by Jonathan ClarkeMore Waste Management World Articles
The recovery and recycling of materials from the municipal waste stream has largely been pursued on the assumption of a Western-style waste infrastructure. Developed countries like the US, Germany and the UK have educated their audiences to understand how to separate out recyclables. Materials Recovery Facilities (MRFs) have been developed to further separate out these recyclables into different types – cardboard and white paper, or HDPE and PET polymers being good examples.
We can go further: where once the quality of recyclates relied largely on hand-picking, we have now developed automated techniques to achieve greater reliability while processing and recovering higher volumes of recyclable materials. Mechanical screens – such as trommels and ballistic separators – play their part, but perhaps the most important addition to the automated materials recovery arsenal is sensor-based sorting.Boosting the waste management arsenal: sensor-based sorting has become a valuable addition to material recycling facilities
Sensor-based sorting technology makes it possible to fully automate separation of recyclable materials. Essentially, the input stream is analysed by a fast-moving scanning sensor installed over a conveyor belt. It 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. Sensor-based sorting produces much higher recovery rates and more consistent product than mechanical or hand sorting alone.
Systems are also being adapted for the negative targeting of materials - i.e. removing a material that is not wanted because it is a potential contaminant. This might include the extraction of coloured flake from clear flake in plastics reprocessing, for example.Changing attitudes
As other niche applications emerge, it would be very easy to continue to develop specific solutions for increasingly specialist projects. However, two years ago sensor-based sorting specialist TITECH assessed exactly what its systems could be used for and where the industry was going. It was realised that separation at source was not necessary, and that sensor-based sorting systems could recover high quality, high volume recyclates from mixed black bag waste.
Professionals from around the world were invited to attend a trial that would demonstrate that recyclates could be recovered to commercial quality and quantity using black bag waste as the input material. The trial took place at the WeSoTech MRF in Germany. It used municipal waste generated from Freising, a small town near Munich, where residents have separate collections for light packaging, glass, paper and organics. The town already had a stronger than average recycling record.Sensor-based equipment plays it part along with screens and conveyors
Around 180 tonnes of residual municipal waste from the area was sorted using WeSoTech’s special combination of mechanical screens and optical sorters. The plant layout was specially designed to process waste with a high organic content and significant quantities of recyclable material were retrieved. The recovered materials were sent to commercial reprocessors and independent laboratories to verify that they were of acceptable quality.
From the results, TITECH calculated that almost 900,000 additional tonnes of materials like paper, plastics, glass and metals could potentially be recovered from Germany’s municipal waste stream. That’s about three times the amount currently being recovered through kerbside sorting alone.
This trial clearly demonstrated that what we assume to be ‘residual’ waste actually continues to include high levels of recyclate – even in areas with a good recycling record. Of course, there are a number of reasons why the levels of recyclates in the residual municipal waste stream appear to be so high. Among these are confusion regarding what can be recycled. Furthermore, automated sorting of residual waste can extract additional recyclable materials like wood and metals. While this trial was in no way intended to diminish the vast improvements that have been made in introducing kerbside recycling schemes in developed countries, its results did give the waste industry pause for thought.
For example, it demonstrated that black bag waste is an important additional revenue stream and that processing this waste to recover recyclates could lead to a dramatic reduction in materials being sent to landfill.
On a more global scale, the WeSoTech trial also demonstrated that it might be possible for developing countries, or those that had not traditionally embraced the concept of separate collections for recycling, to introduce facilities that could extract valuable recyclables from black bag waste. If it could be achieved in practice, the ability to process black bag waste would remove many intangible barriers to recycling, such as levels of education and cultural desire for change, as well as issues such as the ability to finance and develop the necessary infrastructure.
Over the last two years, the trial results have been built upon to identify and overcome the barriers to black bag waste sorting using sensor-based systems. The company has now developed a unique approach that will recover recyclables from black bag waste on a commercial scale.
One major issue that needs to be overcome is the mixed nature of the materials in black bag waste. More specifically, it is the high content of organic material – typically in excess of 40% of the total volume – that can spell disaster for quality recyclables. The recovery process must therefore ensure that the organic fraction does not become a major contaminant. This can be achieved through effective plant design.A Spanish AD facility is recovering around 90% of all inert material from the organic stream before it enters the digester
The design process must be considered as a whole, from the input material and how it is first introduced into the plant to the final desired outcomes – in this case high quality, high volume recyclables. One key factor when designing for black bag waste is not to shred the infeed material at all. This will only spread the organic matter more evenly through the mix, increasing contamination and making recovery of target materials like plastics and paper more difficult. It is far better to use bag breakers, which release the materials without mixing them further and allow them to be presented well on the conveyor.
The vast majority of the organic matter in black bag waste is contained in the ‘70mm or less’ fraction, so this fraction should be targeted and eliminated early on.
The next stage involves a unique approach that splits the remaining materials into two concentrations; one of which is paper-rich, the other plastics rich. These two fractions are then separately processed through a combination of optical sorters and mechanical screens to yield final end products such as mixed paper, film, PET, HDPE and metals. The advantage of this approach is a greater recovery of recyclates.
It always takes time for new ideas and new approaches to filter through into the marketplace, but there are now various facilities coming on-stream that are based on the lessons learned from the WeSoTech trial, including an innovative AD plant in Spain and a municipal waste plant in Cyprus (see case studies). Another industry trial has been also in Germany to demonstrate the ability of sensor-based sorting systems to pull recyclables from construction waste. Although the full results are not available yet, the trial did prove that this is another area where recyclables can be recovered reliably in significant quantities.
The Western approach to source separation is not foolproof. Large quantities of recyclables are still finding their way into black bag municipal waste, and it would be foolish to ignore this – particularly as sensor-based sorting has now been proven to work as a means of recovering these materials.
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From a global perspective, the fact that recyclables can be extracted in sufficient quantity and quality from mixed municipal waste means that countries no longer need to wait for major infrastructure or education programmes – they can begin recycling now.
Countries within Eastern Europe, South America and the Middle East will soon be able to produce recyclables that can compete in international secondary materials markets.
Jonathan Clarke is managing director of TITECH UK
CASE STUDY – Spain
Although Spain does have a policy of separate recyclables collection, levels of recyclables in black bag waste are high. Commissioned in summer 2009, the materials recovery facility in Rioja can handle up to 130,000 tonnes of black bag waste per year. Equipped with two lines and capable of processing 40 tonnes per hour, this facility is focussed on the recovery of HDPE, PET and mixed plastics from the municipal waste stream. It also features a major innovation in the processing of organic waste: front-end processing of the infeed for its anaerobic digester.
Essentially, the facility realised that it had a serious potential problem. The organic matter for the anaerobic digester contained relatively high levels of contamination from inert materials such as ceramics, stone and glass. As a result, the digestion tank became less efficient as the inert material built up and regular shutdowns were required to clean out the system. This cost time and money.
The decontamination process for the infeed material took around 18 months to perfect and relies on a TITECH Xtract system. The facility is now recovering around 90% of all inert material from the organic stream before it enters the digester. According to the operator, this has increased the period between maintenance shutdowns by a factor of nine. The inert materials are sent for further recovery and are currently used as secondary aggregate or landfill cover. Other markets are also under investigation.
CASE STUDY – Cyprus
Cyprus has not traditionally had any separate collection system for recyclable materials. The cost of developing a twin approach for recyclables and residual waste respectively is not a practical option for the island.
A revolutionary new facility that opened in Larnaca early this year has made Cyprus one of the first countries to recover and recycle materials from black bag waste on a commercial scale. Representing a major step forward for the global recycling industry, this new facility is capable of processing up to 180,000 tonnes of municipal black bag waste per year. It uses a number of TITECH optical sorting systems to target film, mixed paper, PET, HDPE and mixed plastics, as well as ferrous and non ferrous metals. The fully automated facility greatly reduces the number of pickers required; just 10 pickers are used in the Cyprus plant and their task is specifically for quality control purposes.
Working with the existing, single source collection system, the new black bag waste sorting facility enables Cyprus to recover valuable recyclables without having to invest in a new collection system or undertake a major public re-education campaign.