Phosphorus Recovery from Sewage Sludge

Phosphorus is an essential element for all living organisms and therefore irreplaceable. It is a key ingredient of our food and plays an important role in the fertilizer industry. Furthermore, phosphorus compounds are also used in the animal feed production, the pharmaceutical industry, in high-performance rechargeable batteries (Lithium Iron Phosphate electrodes) and in surface treatment.

Since the economic minable and less polluted stocks of phosphorus are running out and the commodities are allocated in only a few countries, serious shortages of the element in the coming decades should be taken into consideration. This trend has already become noticeable in recent years when the phosphate rock prices raised on the market, resulting in a 10-fold increase.

After a brief price decline to a fifth of the maximum price, following the economic crisis in 2008/2009, the prices are significantly increasing again. To make it worse, Germany and the majority of European countries lack their own phosphate mineral resources, making them dependent on imports. In the light of these circumstances research activities for phosphorus recovery have been undertaken worldwide. Most active countries contributing to the research are, next to Germany, Japan, Canada, Sweden, the USA and Switzerland.

Most important material flows associated with phosphorus recovery are primarily wastewater, sewage sludge or sewage sludge ash and meat-and-bone meal (MBM). Additional flows might include manure, biomass ash, compost, digestate from biogas plants or residues from the food industry, which are already partially in use for fertilization purposes.

Substances considered to have the largest single potential for phosphorous recovery are sewage sludge and sewage sludge ash. In previous years, much of the phosphorus was fed back into the food chain by a direct sludge application on agricultural land. However, due to sewage sludge’s main function as a wastewater pollutant sink and due to uncertainties regarding the amounts of the plant available phosphorus in the sludge, such utilization has become questionable and should be avoided in the future. As a possible alternative, sewage sludge can be treated thermally. Thus, the development of phosphorous recovery methods from sludge ashes is of utmost importance.

 

 

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