Co-pyrolysis Of Municipal Sewage Sludge And Biomass For Producing Bio-chars And Mechanism Study

In this study,municipal sewage sludge(MSS)and hazelnut shell were used to produce bio-char by co-pyrolysis with chemical activation,and characteristics of thermal decomposition and kinetics were analyzed during co-pyrolysis.Hazelnut shell,as a kind of biomass,has abundant organic content to improve surface area and porosity of the bio-char,and decreases content of heavy metals in raw materials.Co-pyrolysis technology will achieve stabilization,decrement,harmless and reclamation in sludge disposal,and solve the problem of sludge disposal fundamentally.In single factor experiments,activating agent variety,final pyrolysis temperature,pyrolysis time,concentration of activation reagent and additive percentage of hazelnut shell were analyzed to impact trend and mechanism action by the yield and iodine absorption number of the bio-chars.The iodine absorption number of bio-char had achieved 1068.22 mg/g after co-pyrolysis with 850?,45 min,4 mol/L K2CO3,30%hazelnut shell.However,higher temperature and longer pyrolysis time might widen the micropore to mesopore or macropore because of the further etching effect,which will not increase but decrease the iodine absorption number,even the specific surface area of bio-chars.SEM images presented visual understanding of micromorphology.The Langmuir surface area was 874.61-1990.23 m2/g,and the area of micropore was 585.58-1354.30 m2/g.The pore volume was 0.41-0.59cm3/g,and the average pore size was 3.05-4.10 nm.FTIR spectrometry was used to qualitatively determine the changes of surface functional groups and deduce chemical reactions.It was shown that there were abundant functional groups on the surface of bio-chars,such as alcohol hydroxy,phenolic hydroxy,carboxyl,aldehyde and ether.The abundant crystal types appeared in bio-char,and graphitized structure existed after 850?.The Langmuir model was fitting well to the isotherm data.The Cu(?)theoretical maximum monolayer adsorption capacity of the bio-char was 43.54 mg/g.The pseudo-second-order-model can describe process of Cu(?)adsorption well.For co-pyrolysis process,it can be divided into four stages during co-pyrolysis of MSS and hazelnut shell by TG-DTG-MS plots.The comprehensive index D of the first,second,third stage were 2.23,9.83,18.89,112.55*10·%2/K3·min2respectively.Gaseous productions evolved by a series of thermal decomposition reactions were divided into three forms,small molecules of gas,alkanes with different carbon numbers and aromatic hydrocarbons.During co-pyrolysis,there were some interactive effects of thermal decomposition between MSS and hazelnut shell.The inhibitive interaction occurred between 260?-400?.The accelerative interaction occurred between 450?-900?.For kinetics of co-pyrolysis,FWO,KAS and Starink methods were used to analyze activation energy.?=0.2-0.4 was the second stage of co-pyrolysis,which had the activation energy of 123.10-174.43 kJ/mol.?=0.5-0.8 was the third stage of co-pyrolysis,which had the activation energy of 201.54-614.84 kJ/mol.The correlation coefficient R2 were above 0.9385,and the standard deviation of activation energy was less than 2.02%.By Satava-Sestak method,No.13 mechanism function was in accordance with the thermal decomposition condition of co-pyrolysis of MSS and hazelnut shell.The activation energy was 140.56 kJ/mol,the pre-exponential factor InA was 39.60.The reaction mechanism was Avrami-Erofeev equation(n=4),which means random nucleation and nuclei growth.The co-pyrolysis process was an overlapping thermal decomposition process and the curve of d?/dT can be divided into five fitting curves with Lorentzian function.The mechanism function of five peaks was No.13,and the reaction mechanism was random nucleation and nuclei growth.It was been deduced that the peaks were from decomposition and release of bound water and light organics,fat hydrocarbons,protein,cellulose and hemicellulose,lignin.For heavy metals,BCR-three step sequential extraction procedure and software simulation of HSC Chemistry 6.0 were used to analyze the immobilization,migration and transformation mechanism of heavy metals.The potential ecological risk of heavy metals was low risk all the time from pyrolysis at 600?-1000? after K2CO3 activation.The bio-char produced by co-pyrolysis of MSS and hazelnut shell has significant surface area,pore structure and functional group structure.The bio-char also has well adsorptive property of Cu(?).The heavy metals in the bio-char are oxidizable and residual fractions,and has low risk of the potential ecological risk.In further analysis,the bio-char can be used in sewage adsorption and soil remediation of environmental protection management.Sludge harmless disposal and keeping ecological balance can be achieved in the meantime to solve problems fundamentally.