Distribution behavior and risk assessment of metals in bio-oils produced by liquefaction/pyrolysis of sewage sludge

Abstract

The distribution behaviors of metals in bio-oils derived from sewage sludge (SS) by liquefaction with different solvents (ethanol, methanol, or acetone) and by pyrolysis at different temperatures (550-850 °C) were investigated. The concentrations of crust metals (K, Na, Ca, Mg, Fe, and Al) in bio-oils were much higher than those of the anthropogenic metals (Cu, Zn, Pb, Cd, Cr, Ni, V, Mn, Ba, Co, Ti, Sn, As, and Hg), but the anthropogenic metals were more inclined to distribute in bio-oil phase compared with crust metals. The anthropogenic metals in bio-oils can be divided in three groups in terms of the distribution similarities according to Cluster analysis: (A) Cu, Co, Ni, V, and Sn; (B) Cr, Ti, Mn, and Ba; (C) Pb, Cd, As, Hg, and Zn. Cu, Cr, Hg, Cd, V, Co, and Sn distributed in the liquefaction/pyrolysis bio-oils accounted for as high as 5-20% of the metals in SS and were evaluated "moderate enrichment" by the enrichment factors method. According to the potential ecological risk index (PERI) method, Hg presented very high risk, Cu presented moderate risk, and Cd presented low to moderate risk; and the overall risk levels of these bio-oils were very high risk (except P550, presented considerable risk).

Pyrolysis of wastewater sludge and composted organic fines from municipal solid waste: laboratory reactor characterisation and product distribution

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Machine-learning-aided thermochemical treatment of biomass: a review

“…It is worth mentioning that biomass inorganics, such as K and Na, are distributed predominantly in the aqueous phase. In addition, only small fractions of phosphate and heavy metals are distributed in the aqueous phase (Leng et al, 2020d and, large fractions are in biochar (Leng et al, 2014 and, and trace amounts are in bio-oil (Leng et al, 2015;. The yields, compositions, and properties of oil/char/gas/aqueous phases have been reported in recent ML studies using descriptors for biomass and thermochemical processes introduced in Sections 2.1-2.3 (Fig.…”

Inhibitory effects of CaO/Fe2O3 on arsenic emission during sewage sludge pyrolysis

“…Pyrolysis of sewage sludge attracted lots of attentions of researchers , because it is one of the most effective and clean ways to recover energy and nutrients from sewage sludge (Fytili and Zabaniotou, 2008;Park et al, 2010;Song et al, 2014) and also the first and fundamental step in gasification, combustion . However, arsenic concentrated in sewage sludge volatizes easily (Yao et al, 2004) and usually transforms from organic forms into more toxic inorganic forms (Jomova and Valko, 2011) during the process of pyrolysis, affecting the quality of bio-oil or bio-gas (Leng et al, 2015), and threatening human health for its carcinogenic characteristics (Ito et al, 2001;Mohan and Pittman, 2007). A deep understanding of the arsenic release behaviors during sewage sludge pyrolysis is essential.…”