Sow a seed and next year harvest it as a plant. Take a seed from that plant and re-sow it and you have a new plant. Recycling is the very nature of farming. The problem has been that some of the inputs being used; fertiliser for one, are not as sustainable – and that is something that the Swedish group EkoBalans has focused on when developing a sustainable full-bodied NPK fertiliser from recycled wastewater.
The fertiliser not only contains nitrogen and phosphorous but also organic matter to build up the humus content in the soil. The nutrient goldmine in urban wastewater has been long-known and many attempts have – and are – being made to harvest it. And EkoBalans thinks it has found a formula that will work.
Recycling plants instead of water-treatment plants
“The problem with today´s water-treatment plants is that they are not constructed to recycle nutrients; just to clean the water so the nutrients become too diluted,” says Phd biologist Gunnar Thelin, founder and owner of EkoBalans. “There is no economic value in extracting the nutrients and transporting masses of water long distances.”
A further problem is that chemicals are used to remove phosphate from the wastewater making the nutrient unusable for farmers. The EkoBalans solution is to remove water to produce a solid fertiliser. “If you instead use a biological method for extracting the phosphate, and that is not difficult, it would be reusable for us,” says Linnéa Kollberg, process engineer at EkoBalans.
Despite the low concentration of nutrients in the enormous flows of wastewater, its process, which builds on separating much of the water from the nutrients, is able to pick up some 20-25% of the phosphate (if it has been cleaned biologically) and about 15 % of the nitrogen in current wastewater plants. That is acceptable but would be so much higher if the plants were remodelled.
“We´ve made the assumption that today´s water-treatment plants will have to be re-modelled into nutrient recycling plants,” says Mr Thelin. “And extracting just phosphate wouldn´t be enough to make us relevant.” Focusing on capturing nitrogen from the wastewater has therefore become the base for further development.
Plastic carriers in the stripper chamber. Their function is to spread the ammonium-rich fluid on an as large surface as possible in order to maximise the transformation of the ammonium from liquid to gas form.
Struvite from the phosphor extracting step.
The ready-to-use NPK pellets boosted with organic matter.
At his 640ha Östergård farm Peter Knutsson have tested EkoBalans fertiliser for two years with good results.
Being tested in Helsingborg
The firm’s production method is now being used in a full-size, state-of-the-art water-treatment – or recycling – plant being set up in the city of Helsingborg, in the south-west of Sweden. The facility is connected to a newly constructed part of the city where houses have three waste outlet pipes going to the plant; one from toilets, one from bath, clothe-washing and dish water and one with milled food waste as a biomass component.
In such a plant, the production parameters rise sharply. It lifts the nitrogen extraction levels to around 1,000mg/litre instead of a mere 40-50mg/litre in conventional facilities. “Instead of extracting 20% and 15% of the phosphate and nitrogen, we can now extract 75-80% and 75% respectively,” says Mr Thelin. Using a gas separation unit also means that the end products are cleaned from contaminations.
Up and running, the Helsingborg plant will be able to produce 29t of nitrogen as ammonium sulphate and 5.9t of phosphate as struvite crystals annually.
Creating sustainable farming
Though plants like the one in Helsingborg are still rare, there are others around Scandinavia which are constructed much in the way EkoBalans would want it. “We need new types of fertilisers that work in a circular system,” says Mr Thelin. “We have to find ways to take care of the increasing nutrient flows produced in the urban environment.” He can see plants like the one in Helsingborg being built in the next five to seven years.
In the meantime, while existing water-treatment plants get modified and new flow-separating plants are being built, Ekobalans plans to produce some 2,000t of its fertiliser this year, sourcing its nitrogen from a steel plant by-product, and phosphate and biomass from a biogas plant.
This recycling process is of course not only of national interest; the knowledge EkoBalans and Mr Thelin have accumulated during the six years of developing this product will now be exported to Murcia, Spain together with the first pilot plant, where they will oversee the plant being set up and tried out.
Preserving soil health
But just making a conventional fertiliser out of wastewater is not enough, according to Mr Thelin. “You have to apply it in the right context, with a green matter component, so over time you build up the humus content in the soil.” His fertiliser thus also contains magnesium, sulphur, micronutrients and calcium.
The nitrogen content – at 21% compared to 34% in conventional fertilisers – worries farmers but Mr Thelin claims it is not relevant to compare his product with a conventional NPK mineral fertiliser.
“We see our product as part of a circular economy, a new way of thinking. We move plant nutrients from wastewater to the fields. We cannot go on with the conventional way of putting on as much as possible with the plants only able to absorb 30% of it and the rest going out in nature as run-off.”
Farmers happy with test results
For the second year running, arable farmer Peter Knutsson and his son Johan are taking part in a trial of the EkoBalans fertiliser, and so far they are impressed.
At their 640ha Östergård farm some 20km east of Helsingborg, they grow a variety of crops including wheat, rapeseed, barley, potatoes, sugar beet, beans and peas. The NPK pellets have been used in different brands of fertilizer spreaders and worked well after being cut a bit shorter. “This year we tried it out on malting barley and last year on oats, and it has performed better than expected, really,” says Johan.
The pair are concerned about the lower nitrogen content, but if the fertiliser benefits the financial bottom line it would make it more attractive. “We like the idea of making use of nutrients that otherwise would go to waste, and I believe we farmers have to do our share in making food production more sustainable,” says Peter.
We like the idea of making use of nutrients that otherwise would go to waste
Field trial supervisor Ulrika Dyrlund Martinsson, at the Rural Economy and Agricultural Societies, is so far equally impressed by the results. “In a visual inspection you could not see any difference in yields when using EkoBalans versus conventional fertiliser, and we saw only a small difference in the protein content,” she says.
And she agrees with the idea of producing alternatives to today´s input products. “We will have to start looking around for alternatives and take care of what we are producing in a recycling system. Phosphate is a finite product and it will only become more difficult and more expensive to get hold of in the future.”
Although the world sources of phosphate has been revised upwards, Mr Thelin reckons we still need to reduce our burden on nature: “Whether the mined phosphate will last us 80 or 400 years is irrelevant, it´s just arithmetic. Regardless, we have to recycle phosphate, nitrogen and other nutrients that are already in the system.”