Effect of different surfactants on removal efficiency of heavy metals in sewage sludge treated by a novel method combining bio-acidification with Fenton oxidation

The aim of this work was to investigate the effect of different surfactants on the removal efficiency of heavy metals in sewage sludge treated by a method combining bio-acidification with Fenton oxidation. Four surfactants were adopted such as anionic surfactant(sodium dodecyl benzene sulfonate, SDBS), nonionic surfactants(tween-20 and tween-60) and cationic surfactant(hexadecyl trimethyl ammonium chloride, HTAC), respectively. The indigenous sulfur-oxidizing bacteria in bio-acidification phase were enriched and cultured from fresh activated sludge obtained from a wastewater treatment plant. It is shown that different surfactants exhibited distinct effect on the removal efficiency of heavy metals from sewage sludge. The nonionic surfactants,especially tween-60, promotes the solubilization of heavy metals, while the anionic and cationic surfactants hinder the removal of heavy metals. Copper is efficiently leached. The removal efficiency of cadium is relatively lower than that of Cu due to the demand for rigorous p H value. Lead is leached with a low efficiency as the formation of low soluble Pb SO4 precipitates.

An experimental and thermodynamic equilibrium investigation of the Pb,Zn,Cr,Cu,Mn and Ni partitioning during sewage sludge incineration

The effects of different chlorides and operational conditions on the distribution and speciation of six heavy metals（Pb, Zn, Cr, Cu, Mn and Ni） during sludge incineration were investigated using a simulated laboratory tubular-furnace reactor. A thermodynamic equilibrium investigation using the Fact Sage software was performed to compare the experimental results. The results indicate that the volatility of the target metals was enhanced as the chlorine concentration increased. Inorganic-Cl influenced the volatilization of heavy metals in the order of Pb 〉 Zn 〉 Cr 〉 Cu 〉 Mn 〉 Ni. However, the effects of organic-Cl on the volatility of Mn, Pb and Cu were greater than the effects on Zn, Cr and Ni.With increasing combustion temperature, the presence of organic-Cl（PVC） and inorganic-Cl（NaCl） improved the transfer of Pb and Zn from bottom ash to fly ash or fuse gas. However,the presence of chloride had no obvious influence on Mn, Cu and Ni. Increased retention time could increase the volatilization rate of heavy metals; however, this effect was insignificant. During the incineration process, Pb readily formed Pb SiO4 and remained in the bottom ash. Different Pb compounds, primarily the volatile PbCl2, were found in the gas phase after the addition of NaCl; the dominant Pb compounds in the gas phase after the addition of PVC were PbCl2, Pb（ClO4）2and Pb Cl2O4.

Treatment method of hazardous pickling sludge by reusing as glass–ceramics nucleation agent

Heavy metal containing pickling sludge（PS） is one of the by-products of the stainless-steel-making industry,which has been considered hazardous due to contained chromium and nickel.Traditional methods of PS disposing are landfill and cement solidification.This research is aimed at disposing PS by solidification/stabilization and reusing it as a nucleation agent of glass–ceramics.The crystallization behavior and the properties of a glass in the CaO–MgO–SiO2–Al2O3 system were studied by considering PS as the nucleation agent.Experimental results confirm that introducing 14 wt% PS as the nucleation agent of glass–ceramics can decrease crystallization temperature by 110.8 °C,refine the grain size by forming isometric crystals with size of 2 lm,enhance Vickers hardness by 2690 MPa and decrease water absorption from（1.21 ± 0.10） wt% to（0.04 ± 0.01） wt%.Therefore,it is reasonable to conclude that PS can be utilized as a nucleation agent to improve the crystallization and mechanical properties of the glass–ceramics.The testing results of US EPA toxicity characteristic leaching procedure（TCLP）confirm the safety of this reusing method.