After watching developments in the anaerobic digestion (AD) sector – and noting the nature of changing arisings in the marketplace, the struggles that some AD plants had with their front-end processing and the challenges with ensuring efficient transport logistics – waste management company Levenseat decided to develop an organic waste pre-treatment process.
As managing director Angus Hamilton explains, many AD plants do not have the best or most advanced front-end processing, and there were clearly a number of plants that had issues with contaminants in their system. So Levenseat saw an opportunity to create a pretreated AD feedstock. Hamilton says it also became apparent that there was demand for feedstock which would be flexible enough to fill capacity gaps.
At the same time, the company faced demand from its customers for food waste collections. But Levenseat operated only an in-vessel composting (IVC) facility, not an AD plant.
“With the market the way it was, we saw it as a risk to develop [an AD plant] ourselves and secure the feedstock, especially as there was excess capacity elsewhere in the country,” he says. “We felt that rather than build more capacity in an uncertain market, it was better to utilise the capacity at other plants where there is a demand for the material. So that is what led us down this path.”
Around two years ago, the company started trialling different technologies and working on the process to produce a pre-treated organic material, optimise that material, and leave it with two streams with improved characteristics for AD and IVC treatment respectively. So, for example, the fraction for composting is a de-watered solid more suited to the composting process, while the fraction for AD is like a liquid soup designed to give high gas yields.
Its pre-treatment operation – which can take in organic waste from both commercial and industrial sources and households – has also allowed it to process more food waste and expand its services to customers without having to change its IVC process, which is located next to the pre-treatment plant.
Hamilton believes the efficiency of the IVC operation has improved due to the liquid element being removed, which means the composting process can start faster when the material is not waterlogged.
Around 10 months ago, the pre-treatment plant was significantly upgraded and its processing capacity boosted, which is effectively when it started operating commercially.
Hamilton explains that the process has provided a synergy in the business that enhances its existing IVC process, while also broadening the range of services it can offer. He says: “We are now providing a service to AD plant operators and waste producers where we are able to provide both with exactly what they require, changing a waste into a fuel for the AD industry. Ultimately, this helps to optimise the use of existing AD capacity effectively, allowing operators to maximise their gas yields and power production while maintaining product quality.”
Levenseat has been working with a couple of AD plants, effectively forming a partnership, and helping to fulfil the specific requirements of the plants, be it a shortage of feedstock or the need to boost the yield from the plant.
He adds: “We do see a lot of potential here in terms of having the flexibility of moving that material around and also potentially supporting smaller scale AD plants that do not have the ability – or where it does not make sense for them to invest in front-end treatment of food waste – but where they need high gas yield material such as food waste.”
But Hamilton says that without many small-scale AD plants in the marketplace, it will be a case of waiting to see if Government policy supports more localised plants or large-scale facilities: “It is something that is a potential development, given the right circumstances.”
The AD plants it is supplying currently do have their own front-end processing but, either due to logistics or circumstances, it suits them to take pre-processed material.
Hamilton explains: “It may be that they do not have enough capacity at their own frontend processing for food waste, and that helps with their capacity planning. The other aspect is down to logistics, and it makes more sense for us to move the material in bulk by tanker to the AD plant because they are not in the same capture area as we are for the food waste.”
At the moment, the AD plants it works with are charging Levenseat a significantly reduced gate fee for the organic waste. “But we are seeing demand for this material growing and I think that, in the short term, we are likely to be in a position where we are at a zero gate fee position. I foresee that, given potential demand, we could end up in the position where we are able to charge for the feedstock going into the AD plant.
“I think it will be a gradual change as the industry changes its view on this from a waste to a fuel,” Hamilton adds.
He reports good engagement from the AD sector to the process “because it is a useful source of feedstock for them in a form they know is to guaranteed parameters, so they can put it straight into their tanks and get the benefit from it without the hassle factor”.
At the other end of the system, Levenseat has also had positive feedback from its waste customers because it means another outlet for their waste, and puts a lot more flexibility into the market.
Hamilton sees the process as a way of allowing the company to sit between energy production and waste, and provide each sector with what it needs: “It allows AD plants to focus on energy production because we are providing that fuel resource to them from the waste. So we are dealing with that dirty, difficult waste element and providing them with guaranteed feedstock for the energy plant.”
Currently it is not creating specific blends for specific operators but this could happen in the future. “We do see potential in doing that if we find ourselves in a position where we have certain operators looking for different characteristics from others,” says Hamilton.
“What we could do in the next phase of development is to do more of a custom blending for specific characteristics. We do see a number of opportunities to take this to the next step. It will maximise the resource from the waste coming in and [us] acting as a blender – not a broker as such, but a middleman between the energy generation and the waste market. We would do that physical blending and then send the product on to the AD plants.”
Levenseat is still on a learning curve with the project, and is monitoring and reacting to how the market develops. Hamilton concedes that getting the physical processing right has been challenging and it is still trying to refine the process, improve capacity, improve the efficiency of separation and so on. Contamination of feedstock is another challenge: “It is something anyone operating in the organics market learns, and it is a question of constantly trying to educate customers and identify sources of contamination.”
While the short-term benefits the pre-treatment plant has brought to the business include added flexibility and the ability to take in more food waste, in the long term Hamilton believes it will create additional opportunities.
“I would say the organics market is in a huge state of flux at the moment, and that creates a number of opportunities and also significant risks. This is the approach we felt fits us best in terms of managing those risks while still trying to take advantage of the opportunities.”
The Levenseat organics pre-treatment process
The three-step process combines a front-end de-packaging system with further processing through blending, attrition and separation of the original food waste feedstock into two fractions.
Step 1: Packaged and raw food waste is accepted at the reception area where it is assessed prior to de-packaging.
Step 2: De-packaged food waste is transferred to a blending tank and pre-preparation stage, where it is further broken down helping to tackle the fibrous and variable nature of food waste.
Step 3: The resulting product is then pumped into a separation press, where the food waste is split into two fractions: a thick liquid fraction which becomes a liquid anaerobic digestion feedstock and a solid fraction that is ideal for the in-vessel composting (IVC) process.
The liquid AD feedstock is fed straight into a storage tank ready for export by tanker, offering AD plants a tailor-made feedstock.
The solid fraction is passed to Levenseat’s IVC process. Having extracted a high degree of moisture to make the AD feedstock, the consistency of the resulting compost is improved, making it easier to handle, reducing the need for amendment materials and ensuring a good nutrient balance.