This month a news post appeared on internet that the Michigan State University developed a new method to recover phosphate from waste water. It was based on a new technology to adsorb phosphate on iron-based phosphate nanoparticles. This technique is not very new, but nevertheless it is an interesting technique that still gets too little attention.

The principle behind the technology is that very small iron particles with a size of a few nanometers are fixed on a carrier. This may be granular activated carbon, an ion exchanger resin or any other suitable substrate. The high active surface area of these particles makes it possible to get really high adsorption capacities for phosphate, up to 50-100 g/kg adsorption material. This approach has been demonstrated by various research groups. A somewhat different approach is followed by the Dutch company Biaqua that uses ferritin to stabilize the nano sized iron particles. Ferritin is a protein that also plays a role in the natural metabolism of many organisms.

The question is how this technology could be used in practice. A first interesting application could be polishing of wastewater flows with low phosphate concentrations. This could, for example, be the effluent of a sewage treatment, but also other streams with low phosphate concentrations (order 1-20 mg/l) like polluted surface water run off could be of interest. The adsorbent makes it possible to accumulate the phosphate in high concentrations while achieving very low effluent concentrations at the same time. Regeneration of the adsorbent can take place on site or on a central location, depending on the scale of the chosen application. With the regeneration the phosphate is released and can then be precipitated as calcium phosphate that can serve as raw material for the fertilizer industry.

A different approach might be possible for more concentrated flows. Here the adsorbent could be used to selectively adsorb the phosphate. Of special interest for this case could be the dilute fraction of manure after a traditional solids separation. One of the most promising technologies in The Netherlands for the treatment of this stream is to concentrate this stream into a liquid mineral concentrate. This concentrate contains high concentrations of N and K, with some additional phosphate. Because of the high N and K concentrations, the P adds little value to the concentrate. Adsorbents could be used to remove the P and market is as a separate stream, thus increasing the value of the recovery process.

Adsorption technologies for phosphates could therefore be a new development that opens up new options for phosphate recovery. It is therefore a topic that should be taken into account more often in addition to the classical solutions.

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