Removal of Heavy Metals From Sewage Sludge by Acid Treatment

Abstract

Sludge samples were found to contain significant amounts of heavy metals (Cr, Cu, Ni, Pb and Zn) and were subjected to acid treatment using either hydrochloric, sulfuric, nitric or phosphoric acid. The optimum combination, in terms of metal removal efficiency and environmental impacts was sought through a variety of tests by applying a ratio of 1:5 of sludge quantity (g) per volume of acid (ml). The concentrations of the different acids used, were in the range of 5%-20% and the contact times ranged between 15 and 60 minutes. The optimum combination was achieved when the sludge samples were in contact with H2SO4 20% v/v for 60 minutes. In order to estimate the metal leachability, the heavy metal content as well as the metal distribution in the residue were investigated and it was found that most of the heavy metal content was extracted while the remaining was removed from the initial mobile phases to the more stable ones.

Removal of copper from industrial sludge by traditional and microwave acid extraction

“…The metals are accordingly removed from the industrial sludge. Several investigations have shown the effectiveness of strong acids in extracting metals from sludge and slag [1,2,4,19] and that higher concentrations of acid leaching correspond to greater heavy metal content from slag and sludge [4,5,[19][20][21]. However, Fig.…”

Extraction of heavy metal from sewage sludge using ultrasound-assisted nitric acid

“…Previous studies showed that low pH, high temperature, and long contact time can improve heavy metal extraction [3]. Various inorganic acids (HNO 3 , HCl and H 2 SO 4 ) [10], organic acids (oxalic and citric acid) [3], and strong complexing agents (NTA and EDTA) [11] have been proposed as effective extracting agents. Nevertheless, high extraction efficiency requires a large number of dosages, which results in high processing costs and difficulty in pH adjustment of the sludge compost.…”

Simultaneous heavy metals removal and municipal sewage sludge dewaterability improvement in bioleaching processes by various inoculums

“…Various pretreatment approaches including ultrasonic (Na et al 2007), thermal hydrolysis (Neyens and Baeyens 2003), microwave (Yu et al 2009), and chemical conditioning such as adding FeCl 3 into sewage sludge (Krishnamurthy and Viraraghavan 2005) have been used to improve dewaterability of sewage sludge. Other attempts such as chelating (Mosekiemang and Dikinya 2012), ion exchange (Elektorowicz and Muslat 2008) and using organic or inorganic acids (Naoum et al 2001) have been devoted to extracting heavy metals from sewage sludge. However, high consumption of energy or chemicals, operational difficulties and organic matter loss restrict their practical application (Kumar and Nagendran 2008;Liu et al 2012b).…”