Your Technical Questions Answered: SAF Café Insights

A few weeks ago, we participated in Innovate UK Business Connect’s SAF Café webinar, which aims to share expertise and insights into the Sustainable Aviation Fuel (SAF) market. Our Chief Strategic Development Officer, Dr Stephen Wise, took to the microphone to explain how our biotechnology is opening different parts of the waste sector to SAF production and turning traditionally hard-to-handle waste streams into a valuable commodity.

During the webinar, the audience asked numerous technical questions, spanning issues such as waste composition, how our technology works, GHG emissions, and the biggest challenges facing a business like ours. We covered a lot of ground, so we thought it would be helpful to share all those questions and Dr Stephen’s answers in this blog.

You can read them all below.

If SAF contains plastic particles, it can lead to several negative consequences, including damage to engine components and fuel seals. How do you ensure the elimination of all plastic particles in accordance with ASTM D7, 566 specification?

Our technology converts waste into feedstock for use in the SAF process.

This feedstock may undergo a gasification process, for example, to generate synthetic gas. This gas is treated to extract the SAF.

Does producing floc create a biomass water byproduct, and if so, what happens to it?

Our biotechnology does not create a water byproduct, as it’s evaporated as part of the accelerated composting process. When you compost waste, it generates heat, which drives moisture off the waste.

What is the hydrogen percentage content of the waste?

The answer to this depends on the composition of the waste going into our technology. Mixed Residual Waste will vary depending on its source and make-up, unlike washroom waste and AD de-packaging rejects, which tend to be much more consistent.

We’ve been working with some offtakers to examine the hydrogen and oil content of the floc produced by our technology, and we would be happy to share those findings once they are available. Just email [email protected]

How do you contain and treat leachate from this process?

There is no leachate from our process. Our technology operates within a sealed unit with four chambers. The only way anything can come out of the unit is either as a solid when it’s discharged at the end of the process as floc or as moisture, which evaporates into the atmosphere.

What is the capex required for a plant? What does it cost to operate? And is there a gate fee?

Every operator has different needs, so we tailor our solution to meet them. Consequently, it’s impossible to give ‘off the shelf’ prices.

Operating costs are fixed and cover the bio-stimulants needed to facilitate the process, as well as electricity for heating at the start of the process and to turn the shafts. Other factors are less well-known and individual to each customer – such as the number of units they require, the specific needs of their sites, how they plan to load waste into the technology, and how it will be handled, stored, and sent for offtake, post-treatment.

At Advetec, we typically work with smaller operators. Each of our units can process up to 10 tonnes per day or 3,650 tonnes per year, depending on the material input and factors such as bulk density, all of which impact the process itself.

Clients can deploy our technology via a lease model, incurring a standard monthly cost, or through a sale. There is no gate fee, as our technology lives on customers’ sites.

Can you guarantee the quality of the SRF produced based on the composition of the incoming material?

The more consistent the input waste the more consistent the output floc. Consistency enables us to provide greater certainty around the quality of the floc. We undertake waste composition testing and run trials in our XO1 to determine the expected quality of the floc. We would look to provide certainty of quality or guarantees around specific parameters such as moisture, CV, ash, and chlorine based on the waste composition.

Could biotechnology also be used to separate more of the organics from the packaging for addition to solid digestate or input to the AD, as well as producing floc for SAF?

Further separation of the organics from the plastic stream is possible. However, it requires additional equipment to screen out any loose organic material (the non-loose organics are attached to the plastics as a thin film, giving it a slightly brown tinged look). Whilst this is technically possible, it is unlikely to make commercial sense. The quantity of organics extracted and fed back into the AD system to generate biogas will be small and will not create enough value to cover the cost of the required equipment.

Does the process create Greenhouse Gas emissions (GHGs)?

Food waste creates biogenic carbon only, which does not contribute to GHGs. Our technology is a composting process; therefore, the only thing it breaks down is organic material.

Does the calorific value of waste change during the process?

The Calorific Value (CV) of approximately 100 tonnes of waste is approximately 12 or 13 megajoules. By the time the biotechnology has removed the moisture and degraded the organic matter, CV is reduced. Some of the ad plant rejects and washroom waste achieve CVs of approximately 20 megajoules.

We will always do waste composition analysis to understand what’s going into a unit, and based on that, make broad guarantees about its performance, including the CVs. This process can also help identify typical chlorine and ash content levels – although we don’t make guarantees about those, as we can’t guarantee what customers will put into the unit. Some of the more consistent waste streams, such as ad packaging rejects, make it easier to make guarantees.

How do you remove ash from the flock?

Density separation is an effective method for removing ash – which is the non-combustible element such as stones and glass. Mixed Residual Waste (MRW) can have a higher ash content of approximately 22%, which is typically composed of glass, sand, and ceramic. When density separation is used, the heavy fractions can be separated, leaving a low-ash material ready for further processing. Streams like washroom waste and ad packaging rejects already have a very low ash content (5-10%) because they comprise predominantly combustible materials.

How does the energy efficiency of this process compare to conventional time-based processes, for example, by burning a fraction of the downstream syngas to preheat the waste?

If you used the downstream syngas to preheat the waste, it would remove the need for electricity. However, if you look at the whole life cycle of doing that, i.e., moving that material, you quickly identify problems. It would involve more vehicles on the road and a bigger treatment plant, which in turn creates more emissions than you’re saving.

One of our units doesn’t require a significant amount of electricity to run, and these costs are factored into our economic modelling for each customer. This approach highlights all costs upfront to make the financial case and prove viability.

We are transparent with customers when we produce our economic models. If it doesn’t work, we’re quick to identify that. However, as more legislation comes into effect, the economic argument for biotechnology continues to grow. Our technology is becoming increasingly cost-effective every day, as the costs of other disposal routes are rising significantly.

Energy from Waste (EfW) plants and landfill disposal currently cost over £120 per ton, and in some places, we know of smaller operators paying as much as £160 per tonne for EfW. So, it’s easy to see why alternatives like ours, which dramatically reduce those costs, are so well received.

What’s the maximum size of a single unit?

A single XO22 unit will process between 10 and 15 tons of waste per day, or approximately 3,500 tonnes per year, which is typical for a smaller waste operator. The more units used, the more waste capacity is unlocked. The XO22 unit has a physical footprint of 8.9 x 11.4 x 38 (ft).

How many biotechnology plants are currently in operation?

Some of our smaller XO units are in operation in the United States in theme parks and shopping centres. We also have an XO22 deployed on a cruise line operator’s island in the Caribbean and recently installed one in the Western Isles in Scotland for a local authority, as well as couple of waste handlers around the country and one organisation processing fines using an XO. Our pipeline of orders includes sending units to AD plants and washroom waste handlers, as well as a number to UK waste handlers dealing with residual waste.

What are the biggest challenges facing Advetec?

The biggest non-technical challenge we face is related to the time it takes to liaise with the regulator and navigate the permitting process. From application through to getting the full permit for the operators, it’s a lengthy process. It initially took 18-24 months because the Environment Agency (EA) had a backlog of permit applications and finite resources. Now, we’re at less than 6 months for a permit, which is testament to the relationship we’ve built with the Environment Agency.

Most of the operators we’re working with need a variation to their existing permit to take our technology. The EA often takes this as an opportunity to update everything else on the permit, which creates more work for the operator. It’s one of the areas where we add the most value to our customers, helping them ensure they have all the necessary information to support their application.

Another key challenge is understanding the various waste streams. Initially, our technology focused on MRW, but we now also handle more specialised waste streams. From a technical perspective, this requires us to develop a highly detailed and technical understanding of each waste stream and its performance in terms of processing times, quantities, and the quality of the floc output. It’s a time-consuming but fascinating task, and one that allows us to apply our technology more broadly and support a greater number of waste businesses.

What are biostimulants, and how are they used?

Our process involves accelerated composting, where bacteria break down the waste. The best way to explain biostimulants is to liken them to giving bacteria a sugar rush. It’s essentially food.

The bacteria occur naturally within the waste. Subject to the waste stream, we add a higher quantity of those specific bacteria and then provide it with a superfood to allow it to work more rapidly.

Customers receive the biostimulant in a dry form, for use in a container attached to the side of the machine. Once wet, it goes into the machine. This process is automatic.

Does Advetec have any offtake agreements in place?

We do. In terms of the SAF market, it’s still relatively early, as there are no plants yet; however, we have a head of terms with one SAF project through a partner.

We are working with an offtaker for plastics and are currently exploring oil offtakers. We also have an offtake agreement with a cement kiln, with more of those in the pipeline.

We work closely with our customers. If they want to send their floc somewhere else, they can, but we are always keen to highlight the opportunities our contacts and offtake partners provide.

To watch the full SAF Café webinar, visit the Innovate UK Business Connect Website.