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

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 < 80%. As the pH increases, P, Cl, Fe, SO(4)(2-)decant similarly to Al in the solution. Heavy metals Cu, Zn, Cr, Ni tend to settle at a higher pH than P, while Pb and Cr under the same conditions as P.

Automated summary

The sewage sludge generated by wastewater treatment plants is a hazardous waste containing heavy metals, pathogenic bacteria, and drugs. This article explores a sludge processing method that aims to eliminate biological risks, antibiotics, and heavy metals. Incineration is an effective way to reduce the risks associated with sludge and to convert heavy metals into a prospective source of phosphorus.