Phosphorus is an essential element for all living organisms and has no substitute. For decades, phosphate rocks have been the primary source for fertilizers production. Israel is one of the significant producers of phosphate fertilizers. However, over the last decades, phosphorus reserves in Israel have significantly diminished, mainly leaving low-quality phosphate reserves accessible. In recent decades, there has been a growing global trend to recycle phosphate from waste, aiming to promote the replacement of phosphorus natural resources and mitigate environmental damage caused by eutrophication. Sewage sludge is one of the sustainable sources of phosphate recycling. In Europe, recycling phosphate from sewage sludge is supported by EU legislation and is already mandatory in several EU countries.
Our ongoing project, funded by the Ministry of Energy, aims to evaluate the potential reuse of phosphate extracted from sewage sludge, both with and without incineration. Our study showed that non-incinerated sludge from WWTPs in Israel may contain up to 2.5% phosphorus (P), whereas, after incineration, the P content increases up to 12%. An upper estimate of the P recovery potential from all Israeli domestic WWTPs is 12,800 tons of P as P₂O₅ per year. To put this into perspective, this amount represents 2% of the phosphorus produced by Rotem Amfert Ltd.
Laboratory experiments demonstrated that phosphate can be quantitatively extracted from both incinerated and non-incinerated sludge using acid, with higher extraction efficiency observed in incinerated sludge. Under alkaline conditions, calcium phosphate salt is formed, which can potentially serve as a starting material for the industrial production of P-containing fertilizers. Assessments have been made on phosphorus bioavailability and trace elements' mobility from precipitated phosphate salts and incinerated sludge materials, which is crucial for determining the recovered phosphorus products' environmental safety and agricultural efficiency.