The assessment of phosphorus recovery potential in sewage sludge incineration ashes — a case study

Abstract

A sewage sludge incineration ash contains large amounts of phosphorus, which are considered as a novel anthropogenic waste–based substitute for phosphorus natural resources. Phosphorus is accumulated at most in phosphate minerals of whitlockite structure, that contain Fe, Ca, and Mg and in the matrix composed of Si, Al, Fe, Ca, P, Mg, K, Na in various proportions. The goal of this study was to estimate phosphorus recovery potential. A four-stage sequential extraction, following the modified Golterman procedure, was applied. Separation of four independent fractions enabled to understand better the manner of phosphorus occurrence in the studied ash. The results of the extraction indicated the greatest release of phosphorus combined with organic matter using sulfuric acid. The release was on average at the level of 64%. The chelating Na-EDTA compound indicated lower ability to extract phosphorus (at the level of 35%), and the highest ability to extract heavy metals and potentially toxic elements (As, Zn, Mo). The sequential extraction led to the total recovery of phosphorus of around 40–60%

Characteristic of phosphorus rich compounds in the incinerated sewage sludge ashes: a case for sustainable waste management

“…Additionally, Fe is characterized by low solubility especially in basic pH 40 . Kasina 21 indicated using sequential extraction method based on Golterman procedure 41 the total recovery of phosphorus of around 40–60%, which compared to other described in the literature ISSA was very low. The recovery rates from ISSA can reach up to 90% 42 depending on the ash composition.…”

“…From the environmental point of view precipitation of sulphide minerals would be advantageous, since it is responsible for bonding and immobilization of metals considered as toxic 35 such as As, Zn, Cu, Cd and which presence may also negatively influence the phosphorus recovery 32 . From our previous study 21 , 36 we learned that the chelating Na-EDTA compound indicated low ability to extract phosphorus (at the level of only 35%), and the highest ability to extract heavy metals and potentially toxic elements (As, Zn, Mo) whereas the greatest release of phosphorus was obtained using sulphuric acid at the level of 64% however obtained fraction is considered non-bioavailable 37 .…”

“…Phosphorus recovery from ISSA has been a topic of growing scientific interest however, less research is focused on the characterization of phosphorus rich compounds which usually are present as complex aggregates, difficult to distinguish or present as amorphous phases whereas phosphate minerals are not common 4 . This makes the recovery of phosphorus difficult and often inefficient 21 , which is why the detailed characterization of phosphorus rich compounds is so important and of a big relevance in waste management and sustainability. The development of recovery methods, which are still not fully efficient even for the natural phosphorus resources, starts with good understanding of its occurrence and composition.…”