Characterization of heavy metals and oil components in the products of oily sludge after hydrothermal treatment

• Published in: Journal of hazardous materials 2022-02, Vol.424 (Pt A), p.127293-127293, Article 127293
• Main Authors: Duan, Yihang, Gao, Ningbo, Sipra, Ayesha Tariq, Tong, Kun, Quan, Cui
• Format: Article
• Language: English
• Subjects: Biological Availability; environmental risk; heavy metals; hydrothermal treatment; Metals, Heavy; oil; Oils; oily sludge; Sewage; Spectroscopy, Fourier Transform Infrared
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2021.127293

In this study, the method combining hydrothermal treatment (HT) and in-situ mechanical compression (MC) is used to treat oily sludge. The possible transfer and reaction pathways of different oil components during the process of HT&MC were investigated. In addition, the leaching toxicity, distribution, and risk of heavy metals in oily sludge treated in different temperatures and residence times were evaluated. The results revealed that siloxane and heavy oil components are left in the solid residue, and the light oils and oils with hydrophilic groups are transferred to hydrothermal fluids. The content of Cd, Cr, Pb, and Zn in form of F4 (residual) in the solid residue obtained at a hydrothermal temperature of 240 °C and residence time of 60 min increased by 7.37%, 1.21%, 3.06%, and 9.97%. This reduced the biological availability and environmental risk of heavy metals in the treated oily sludge. Meanwhile, the result of FT-IR illustrated an increase in hydroxyl groups of alcohols, phenols and organic acids, which have a beneficial effect on the adsorption of heavy metals and other pollutants. All results indicated that HT&MC might be a suitable pretreatment method for the stabilization of heavy metals in oily sludge. [Display omitted] •The possible transfer pathways of different oil components are discussed.•The characteristics of heavy metals under different reaction conditions are studied.•Heavy metals are concentrated but stabilized in the solid residue.•Leaching concentration and ecological risk of heavy metals are remarkably reduced.