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Comment Separation Processes

This P-recovery process is market-ready

By Gerald Ondrey |

At PowTech 2019 this month (Nuremberg, Germany), Glatt Ingenieurtechnik GmbH (Weimar, Germany; www.glatt.com) introduced a waste-free process that recycles the phosphorus from sewage-sludge ash to produce ready-to-use, high-quality fertilizers. The market-ready process fulfills the legal obligation of the German fertilizer ordinance (DüMV), which requires waste-disposal companies to recover phosphorus, and can recover virtually all of the phosphorus from the ash of incinerated sewage sludge.

In the first step of the two-stage PHOS4green process (diagram), a suspension is produced from the phosphate-containing ash, a mineral acid (for example, phosphoric acid) and, depending on the objective, other components. This acid treatment macerates the ash, and converts insoluble phosphates into a form that can be absorbed by plants. In the second step, the suspension is sprayed into a fluidized-bed granulator, which is blown with hot air. As the water evaporates, the granules grow in size before being discharged. Product is screened to separate granules of the desired size from over- and undersized solids, which are recirculated to the granulator.


“The process recycles 100% of the ash,” says Jan Kirchhof, senior sales manager Process and Plant Engineering at Glatt. “By flexibly adapting the recipes, a wide variety of fertilizers, including complex varieties (NP, PK, NPK), can be produced, which can be placed on the market as new products,” he says.

The process has been tested on various sludge ashes, from mono-incineration plants, in a pilot plant at Glatt’s Technology Center in Weimar. The pilot unit can produce approximately 60 kg/h of standard fertilizer. Several engineering phases have already been completed for the first large-scale commercial plant, which is now in the approval phase. Groundbreaking for this project is anticipated in the next few weeks. The modular system can be configured for the desired capacity, with various configurations handling a capacity of 10,000–40,000 ton/yr of sludge ash. Nevertheless, smaller and larger plant set-ups are possible.

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