Clean, phosphate-free water and recovering valuable nutrients
Since the eighties, clean water plants in the Netherlands, remove phosphate and nitrogen from wastewater.
It’s a win-win situation.
- the nutrients can be used in fertilizers and bring money in
- it’s cleaner, phosphate-free water
- and it’s important to recover useful materials
The phosphate is found in the human (and animal) urine.
The fertilizers cause rampant bloom of algae, dying it is forming a smelly and not harmless ‘green soup’.
Initially, the phosphate removal was done with chemicals. Afterwards the phosphate-rich remains of the sewage sludge was landfilled or incinerated. The new proces saves the city of Amsterdam up to 600,000 euros per year, plus 21,000 euros from the struvite.
The city reports a strong business case: phosphate and fertilizer are formed int useful fertilizers pellets in a separate reactor. “The granules will be redirected to the farmers.
Struvite is a slow-release fertilizer, which slowly releases the fertilizer to the crop and fits easily in precision agriculture,” says Veltman. “Fertilizer producer ICL, is interested. Struvite can be sold for 35 euros per tonne. The city of Amsterdam can produce 900 tonnes per year.
Above a container with three compartments the process employee demonstrates how simple the phosphate recovery works.
1. The first tray receives the phosphate-rich water from the sludge centrifuge
2. Oxygen is blown into the second compartment, the acidity is increased
3. In the third bin, magnesium is added
Now, the desired precipitation of phosphate crystals is a fact.
Fewer chemicals for phosphate removal is important. Also: cleaner, phosphate-free water is important for us to recover useful materials.
About half of the phosphates in wastewater are reused as struvite. The other remains in the solid sludge. “That sludge is burned for electricity. But companies have started new experiments to recover more phosphates from the sludge.
Optimization in order to recover phosphate and nitrogen is increasingly important. Phosphate is interesting because of the shortage of the mineral. And the mineral is only found in Morocco, China, Russia and Tunisia. Geopolitical problems, such as with oil and gas, are not excluded.
There are tests with nutrients, separation the urine in toilets.
Kampschreur “If struvite is accepted by the law, the waste water industry will be providing a quarter of the phosphate use of Dutch agriculture.”
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