How a new add-on makes phosphorus recovery more circular

Last year, EasyMining began a new stage of development for an add-on to its Ash2Phos process, aimed at expanding beyond the technology’s core focus. Now, it’s ready to be integrated into future facilities and help recover more value from sewage sludge ash.

17 Jan 2024

According to Cristian Tunsu, EasyMining’s R&D Lead for the project, development of the add-on originally began as a way to improve one of Ash2Phos's co-products. Along with high-grade phosphorus, the company’s renowned circular solution also extracts iron as ferric chloride, aluminium chemicals, silicates in the form of sand fraction, and a concentrate of heavy metals – all from incinerated sewage sludge. The goal of the project, which was eventually codenamed “Sahara,” was to find a more efficient way to produce the ferric chloride, but it ended up creating a process that did more.

– We realised we could bring in the add-on and recover the iron that isn’t reclaimed in Ash2Phos. And while doing that, we realised this module – with some additional steps to the process – had other advantages, explains Tunsu.

On its own, the Ash2Phos process recovers roughly 15% of the iron in sewage sludge ash. With the new add-on, it increases to more than 90%. That produces much more ferric chloride at a much higher level of purity while removing the reddish hue from the sand (hence why the development project was named after a famous desert). The add-on process also doubles the amount of aluminium and even increases the phosphorus recovered from just over 90% to nearly 100%.

A key aspect of development has been a grant from the Swedish Energy Agency, Energimyndigheten under the innovation programme Re:Source. In October 2022, the agency announced it was awarding EasyMining, together with its project partners FeralcoThomas ConcreteSydvatten and Ragn-Sells, just over 3.5 MSEK (million Swedish Krona) to further investigate the new add-on. The funding has been essential in speeding up the project’s transition from the R&D phase to engineering and in kicking off extensive business case analyses and product validation tests with partner organisations.

– We’ve made quite a lot of progress. I would say a lot has happened in the last year, says Tunsu.

Collaboration with leaders in water treatment & concrete

The ferric chloride produced within the Re:Source programme with the add-on process is currently being validated by two of Sweden's biggest names for water treatment: chemical manufacturer Feralco and drinking water producer Sydvatten.

As a coagulant, ferric chloride is vital in large-scale operations to make water drinkable. And because this ferric chloride comes from a waste stream created through water treatment, it’s an ideal circular solution. What's more, it can be ready for application immediately. So, an Ash2Phos facility with the add-on that's in close proximity to a water treatment plant would have an even lower environmental impact due to shorter transport.

Meanwhile, the iron-free sand from the new add-on is being validated by Thomas Concrete, a global provider of concrete mix. The grey colouring seems to make the sand much more suitable as cement replacement in concrete manufacturing, and it’s considered to have great potential as a method for lowering overall carbon emissions from concrete production.

For Tunsu, such partnerships have not only been vital for proving the market applications of the upgraded outputs but also for providing invaluable input on adjusting to create a better product.

– Collaboration is always important, but it’s great to have this insight from the other stakeholder businesses because then you can design the best process by knowing what your users want and need. It’s much faster and better when you’re actually working together, he explains.  

The potential to recover everything

The first commercial implementation of the new add-on process is evaluated for an Ash2Phos plant in the southern Swedish city of Helsingborg. It recently received local approval, and there’s great potential for it to become a sustainable provider of a necessary and often imported resource to the country’s water treatment industry. When operational, if the  Helsingborg plant includes this add-on; it could recover enough ferric chloride to meet most of Sweden’s needs.

Yet Tunsu says there’s another advantage to consider. Sure, the new add-on can produce a necessary element for a more circular method of creating drinking water.. And, certainly, it optimises the original Ash2Phos technology. But the combination of the add-on and Ash2Phos does more than any other method of phosphorus recovery on the market.

– Ash2Phos with the new add-on is the only solution out there that can recover all macrofractions in the ash as clean commercial compounds, he says.