The Migration And Transformation Behavior Of Heavy Metals On Pyrolysis And Liquefaction Of Sludge

With the increasing consumption of fossil energy and combustion of air quality,soil quality and adverse climate change,increasingly researchers around the world are paying attention to the development of biomass energy for alternatives to fossil energy.Biomass is a renewable,new energy and also potential material for sustainable development.The sludge is a kind of biomass.In recent years,the increasing of people’s material and cultural needs and sewage factories result in sludge production form municipal,papermill,slaughterhouse increases sharply.In China,the state puts forward higher emission requirements for the urban sewage discharge in order to adapt to the new requirements of the water environment protection(A standard of the first level standard).Therefore,sludge reduction and disposal have been became a growing concern.Several strategies have been taken to solve that problem such as sludge landfill,cropland application,incineration,and ocean dumping.However,these methods have their responding defects.Recently,the use of sludge to produce biochar has become a mainstream,which is widely used.Pyrolysis and liquefaction technologies have been widely used in sludge treatment,which can improve the stability of heavy metals in biomass.In this paper,pyrolysis and liquefaction technologies have been applied in municipal sludge,paper mill sludge and slaughterhouse sludge.The fractionations of Cu,Cr,and Zn in bio-chars from pyrolysis and liquefaction of MSS,PMS,and SS were studied.The environmental risk of bio-chars from pyrolysis and liquefaction of sludges were evaluated,and thus comparing the transformation and migration behavior of HM between pyrolysis and liquefaction,and between different sludges.The results shown that pyrolysis and liquefaction largely affected the redistribution of HM in raw materials.The risk assessment results indicated that the environmental risk levels of Cu and Zn were significantly reduced in bio-char,while risk level of Cr was slightly decreased after pyrolysis or liquefaction.Both pyrolysis and liquefaction are promising detoxification technologies for the sludges in terms of the mitigation of HM toxicity.It was suggested that dewatered sludge could be reduced toxicity/risk before pyrolysis or liquefaction,especially for Cu and Zn in slaughterhouse sludge.