Synergistic effect of rice husk addition on hydrothermal treatment of sewage sludge: Fate and environmental risk of heavy metals

Abstract

Hydrothermal treatment (HTT) at 200°C was applied to immobilize heavy metals (HMs) and the effect of rice husk (RH) addition was investigated based on total HMs concentration, fractionation and leaching tests. The results indicated that a synergistic effect of RH addition and HTT could be achieved on reducing the risk of HMs from medium and low risk to no risk. Metals were redistributed and transformed from weakly bounded state to stable state during the HTT process under RH addition. Notably at a RH/sludge ratio of 1/1.75 (d.w.), all the HMs showed no eco-toxicity and no leaching toxicity, with the concentrations of leachable Cr, Ni, Cu and Cd decreased by 17%, 89%, 95% and 93%, respectively. This synergistic effect of RH addition and HTT on the risk reduction of HMs implies that HTT process with RH addition could be a promising and safe disposal technology for sewage sludge treatment in practice.

Effect of the Amount of Sludge on Physicochemical Properties and Chemical Structure of Low‐rank Coal under Hydrothermal Conditions

“…found that there were synergistic positive effects on the fuel properties and air pollutant emissions in the thermal conversion process of both biomass and low‐rank coal because of the similar chemical molecular structure. Shi et al . demonstrated that heavy metals in SS may be stabilized during the HT process when rice husk is added to SS.…”

Novel treatment and value-added utilization of oily sludge using ionic liquid and pyrolysis

“…It was observed that the mobile and bioavailable heavy metal ion fractions were transformed into relatively stable fractions after pyrolysis and most of the heavy metal ions were found to exist in the residual form in the biochar pyrolyzed at 700 °C (Devi and Saroha, 2014). Similarly, Islam and Park, (2017) Shi et al (2013b) reported that the addition of rice husk during the hydrothermal treatment of sewage sludge exhibited a reduction effect on the leaching toxicity of heavy metals in sludge residues. It was observed that at the rice husk/sludge ratio of 1/1.75, the concentrations of leachable Cr, Ni, Cu, and Cd decreased by 17%, 89%, 95%, and 93% respectively.…”

“…Some of the oil properties such as HHV and carbon content were found to be improved by co-pyrolysis (Q. . Some efforts have been made to investigate the cumulative effect of biomass addition on lowering the contamination risk of heavy metals in sewage sludge residues (H. Jin et al, 2017;Shi et al, 2013b). However, there has been limited research investigating co-pyrolysis effect of oily sludge and sawdust on heavy metal immobilization.…”

“…Cd, while the Cd leaching was further reduced with the addition of 5, 10, and 15% biomass in the soil. Shi et al (2013b) also reported that the addition of rice husk during the hydrothermal carbonization of sewage sludge resulted in a synergistic effect on reducing the risk of heavy metals (Cr, Ni, Cu, and Cd) in the solid residues. However, many previous studies on the thermal treatment of waste focused on the total heavy metal contents and the leaching behavior of residues after treatment (Jin et al, 2014;Thurnau, 1996).…”

“…(Shie et al, 2003;Wang et al, 2007). It was reported that the co-pyrolysis with other waste materials could even enhance the treatment performance (Debela et al, 2012;Shi et al, 2013b). For example, Debela et al (2012) found that the pyrolysis of contaminated soil immobilized some heavy metals such as Pb and…”