Wastewater treatment plant processes affect P-phases in sewage sludge ashes

Phosphorus is a vital component of fertilisers – and a growing global population relies on a stable supply of agricultural produce. Endeavours to recycle phosphates from sewage sludge ash (SSA) have so far been limited by lacking understanding of material associations and the actual phosphate compounds in SSA. Owed to the high amorphous content of ashes, unlike X-ray diffractometry (XRD), automated mineralogy systems (MLA here) allow for a deeper study of phosphate-bearing phase associations in ashes. An intricate knowledge of target resource association is crucial for efficient recycling: this applies to all target products, elemental P, phosphoric acid or recycled fertiliser. Failing to understand these morphologies and target associations will inevitably lead to inefficient processes – perhaps even close off this resource completely. Thus, phase studies add to all P-recovery approaches from sewage sludge ashes. Sludge of three German cities has been incinerated under the same conditions and sampled, thus enabling an analysis of ash characteristics.