“…However, biological treatments (i.e., bioleaching, aerobic, and anaerobic composting processes) require a longer period of operation and inevitable energy consumption, compared to physical and/or chemical treatments, including membrane separation, chlorination, and thermal treatments, which limit their practical applications for the treatment and disposal of sewage sludge (Chaudry et al 1998;Zorpas et al 2001;Fraissler et al 2009;Zhu et al 2013). Chemical treatments (i.e., chemical extraction and chemical precipitation) has several advantages, including a shorter reaction time, easy operating procedures, and higher removal efficiencies of heavy metals, compared to biological treatments (i.e., bioleaching, aerobic and anaerobic composting processes) (Babel & del Mundo Dacera 2006;Ren et al 2015). Various types of chelating reagents (e.g., ethylenediaminetetraacetic acid [EDTA]), organic acids (e.g., citric acid), and inorganic acids (e.g., hydrofluoric acid) are available for the removal and stabilisation of heavy metals from sewage sludge (Amir et al 2005;Babel & del Mundo Dacera 2006;Ren et al 2015).…”