| Sludge activated carbon was prepared from digested and undigested sludge from Songjiang wastewater treatment plant using a chemical activating agent(ZnCl2) and pyrolysis in a muffle furnace,in which the sludge was covered with aluminum foil. The influence of the concentration of ZnCl2,pyrolysis temperature,pyrolysis time and dipping temperature were studied based on orthogonal experiments and single factor experiments.According to the iodine adsorption value,the optimal preparation conditions for the adsorbent were found to be:pyrolysis temperature 550℃,ZnCl2 concentration 3 mol/L,dipping temperature 40℃and pyrolysis time 25 min.A thermal analytical balance was used to analyse the pyrolysis characteristics of the sewage sludge with or without ZnCl2 under N2 atmosphere.Simultaneously,the differential equations were established and applied to question the pyrolysis reaction functions as well as pyrolysis parameters.Three stage of pyrolysis reactions were identified according to the weight loss for sewage sludge without ZnCl2,four stages for sewage sludge with ZnCl2ZnCl2 influenced the dehydration of the sludge and fixed more carbon.It is considered that ZnCl2 penetrated to the interior of sewage sludge and accelerated the swell and dissolution of the mucus.The sludge activated carbon was characterised using elemental analyses,SEM photography,FTIR,thermal analysis and BET-N2 adsorption.It was found that the surface of sludge activated carbon(with ZnCl2) exhibited more small pores compared with the sludge carbon(without ZnCl2).According to the pore diameter distribution curve,the pores of activated carbon from sewage sludge were mainly mesporous.The average pore diameter,the pore volume and the SBET area were 2.48 nm,0.13 cm3·g-1 and 418.79 m2·g-1,respectively.Leaching experiments showed that the heavy metal concentrations in the leachate of the activated carbon from sewage sludge reached the Chinese standards.The activated carbon prepared was used to the treatment of heavy metal solutions. The adsorption experiments were conducted to investigate the removal efficiency of metals at different conditions such as adsorption time,pH value,adsorbent dose and. initial metal concentrations.The experiment showed that the sludge activated carbon had a good capacity for removing Cr(Ⅵ),Cu(Ⅱ) from aqueous solutions.The adsorption isotherms were fitted with Langmuir model better than Freundlich model and the adsorption type is chemisorption with single molecule.The calculated adsorption capacities of Cr(Ⅵ),Cu(Ⅱ) were 26.53 mg·g-1 and 16.48 mg·g-1, respectively.The kinetic data of the adsorption can be fitted with the pseudo-second order model and intra-particle model,indicating that the adsorption was affected by diffusion and adsorption reactions.The regeneration of used sludge activated carbon was also studied in this work. Based on the iodine value,TG and adsorption isotherms,the solvent regeneration efficiency was evaluated.It can be concluded that the sludge activated carbon prepared from municipal sewage sludge may be applied to the removal of heavy metal -bearing wastewater.
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