Simultaneous phosphorus and amorphous silica recovery from incinerated sewage sludge ash

In the Italian and European context, sewage sludge (SS) production and disposal from urban wastewater is a very current problem, with environmental and economic repercussions. The large amount of waste to be treated makes landfill disposal no longer viable. Alternative methods have been proposed: agricultural use, compost and incineration. In particular, mono-incineration is an option that allows the recovery of both energy and matter, minimizing waste. Incinerated sewage sludge ashes (ISSA) from different European plants were studied to evaluate the recovery of their most interesting components: phosphorus (P) and silicon (Si). A procedure for the simultaneous P and Si recovery was proposed, starting from the ISSA acid leaching. P dissolved in solution after the leaching, is selectively precipitated, to create a calcium phosphate product for fertilizer applications. Si is recovered in subsequent steps as amorphous silica (SiO2) and proposed as adsorbent for the removal of drugs from wastewater.