Extraction of heavy metals and phosphorus from sewage sludge with elimination of antibiotics and biological risks

[Display omitted] •Sewage sludge ash contains a significant amount of phosphorus.•The extraction of heavy metals from sewage sludge must eliminate other risks.•The incineration of the sewage sludge allows the reduction of its mass up to 14 times.•Extremely acidic environment allows the extraction of > 80% of P from sludge ash.•P precipitation from sludge extract takes place at a lower pH than Cu, Ni, Zn, Cd, Co. The sewage sludge generated by the wastewater treatment plants is quite a hazardous waste. It may contain heavy metals, pathogenic bacteria (including those resistant to antibiotics due to their interaction with them) and viruses, helminths, acrylamide and drugs, including antibiotics. The selective elimination of certain risks does not make the sewage sludge safe for the environment. The purpose of this article is to implement a common sludge processing methodology with the elimination of biological risks, antibiotics and heavy metals. Incineration can eliminate most of the risks associated with sludge, leaving only heavy metals. Although the content of heavy metals in the ash increases (due to the destruction of organic matter and water vaporization), at the same time it is a prospective source of phosphorus (20.59 ± 0,00 % P2O5). The extraction of phosphorus from the ash sludge has a very good yield in the extremely acidic environment of 83.57%, using nitric acid. Extraction yield for most heavy metals investigated has a yield of over 50% (Cu – 66.54 %, Mn – 66.28 %, Zr – 61.33 %, Zn – 60.59 %, Cr – 57.47 %), less Ni with 29.94 %. Si and Ti migrate very slightly (0 % and 0,48 %, respectively). By treating the extract solution with a basic agent (eg KOH), most of the components studied (Al, Ni, P, Cu, Cl, Cd, Co, Zn, Fe, Pb and S in form of SO42-) decant with a yield > 90%, only Cr has a precipitation yield