The Preparation Of Pyrolytic Biochar From Organic Solid Waste And Its Removal Mechanism For Organic Pollutants From Water

Pyrolysis treatment of organic solid waste is a win-win strategy.On the one hand,it can realize its resource disposal,and on the other hand,the obtained biochar can be used as an environmental functional material to deal with the current crisis of organic pollution in water bodies.However,the removal performance(including adsorption and catalysis)of biochar prepared from different raw materia ls and methods for organic pollutants is significantly different,but the specific structure-activity relationship is not clear,which cannot effectively guide the preparation of high-efficiency biochar functional materials.Therefore,this thesis used dif ferent organic solid wastes as raw materials to prepare biochar.Then their microstructures were regulated by means of series structure control methods.The modified biochars achieved the removal of typical organic pollutants by two different ways,includi ng adsorption removal,and combine persulfate to build advanced oxidation process system to achieve their oxidative degradation.The main focus was on the structure-activity relationship between the structural characteristics of biochar functional materials and their performance(adsorption and catalysis),and the specific mechanisms were discussed in depth.The specific research content and results are as follows:(1)Using municipal sewage sludge as raw material,a series of porous magnetic sludge biochars were prepared by alkali-acid combined modification,which were used as adsorbents to remove tetracycline hydrochloride(TC)from water.Compared with the single alkali or acid modification,the alkali-acid combined modification had more advantages in increasing pores numbers,enriching surface functional grou ps,and reducing the risk of secondary pollution.Structure-activity relationship showed that the specific surface area(BET)of porous sludge biochar was linearly correlated with its adsorption capacity.Among them,the alkali-acid modified SNMS-800(202.5m²/g)showed the best adsorption capacity toward TC(286.91 mg/g),and the adsorption was mainly achieved through?-?stacking and pore filling interaction.In addition,the good adsorption stabilit y,good regeneration performance and magnetic separation ability of SNMS-800 further manifested its good application prospects.This study reveals the structure-activity relationship between the pore numbers of biochar and its adsorption capacity,which pr ovides a basis for the preparation of advanced biochar adsorbent materials.(2)Using waste shrimp shells as raw materials with the acid modification,the hierarchical porous(macropores,mesopores and micropores co-existed)shrimp shell biochar(HPB)was prepared for 2,4-dichlorophenol(2,4-DCP),TC and rhodamine B(RHB)removal.Adsorption experiments manifested that,HPB exhibited excellent adsorption capacity(Q_m>300 mg/g)and ultra-fast adsorption equilibrium ability(<10 min)for all of them.The adsorptive forms by HPB depended on whether the pollutants owned obvious charges.In the single-layer system,the charged point of the pollutant contributed the most to the adsorption,which was 5.13 times the contribution of the benzene ring site.While in the multilayer adsorption system,the contribution of the benzene ring site was greatest.The structure-activity relationship showed that,the hierarchical pore structure was the decisive factor for HPB to achieve rapid adsorption equilibrium,and the high ly graphitization of HPB helped to increase its adsorption capacity.In addition,the effective application ways of“HPB column”and“HPB tea bag”,and the treatment of pharmaceutical wastewater further demonstrated its great application potential.This st udy further reveals the relationship between the pore structure of biochar materials and its adsorption rate,and further provides a basis for further preparation of advanced biochar materials.(3)Using municipal sewage sludge as raw material,the magneti c nitrogen-doped sludge biochar(MS-biochar)was synthesized through a one-step method.Then used as a catalyst,MS-biochar/persulfate advanced oxidation system was constructed to achieve the oxidative degradation of TC.Experiments showed that,MS-biochar could activate persulfate(PDS)effectively and further degrade TC.And its catalytic effect was better than typical sp²-hybrid carbon materials(including graphite powder,graphene oxide and multi-walled carbon nanotubes).Component peeling experiment showed that,the acid-soluble component contributed the most in MS-400/600 for PDS activation,which mainly promoted the generation of SO₄^·-.The carbon framework was the main contributor to the catalytic performance of MS-800,and mainly promoted the generation of·OH.The Fe species,doped N species and sp²-C structures in MS-biochar were three important catalytic sites for PDS activation.Metal leaching test,repetitive experiments,and treating of actual pharmaceutical wastewater further proved its application potential.This research proposes a method for resource disposal of surplus sludge,and provides a research basis to construct an efficient biochar/PDS system.(4)Using waste shrimp shells as raw materials,a series of hierarchical porous shell biochar materials(PSS-biochar)were prepared by adjusting the pyrolysis temperature and supplemented by acid modification.The PSS-biochar/PDS system was constructed to degrade 2,4-DCP.Experiments showed that,the pyrolysis temperature was crucial for the micro-structure of PSS-biochar.PSS-800 had the best catalytic performance,and its degradation rate toward 2,4-DCP was 29 times that of PSS-400.The hierarchical pore structure and carbon configuration were two key factors affecting the catalytic performance of PSS-biochar.Moreover,temperature-induced differences in carbon configuration could further change the activation mechanism of PSS-biochar for PDS.Specifically,PSS-400/PDS system induced a free radical pathway,while the PSS-800/PDS system induced a novel non-free radical one.In addition,the non-radical activation path of PSS-800 had strong anti-interference ability,and showed good application potential of organic polluted water with high-salt or interferences.This study further reveals the structure-activity relationship between the structural characteristics of biochar and its catalytic efficiency,and also reveals a new mechani sm in biochar/PDS system.(5)Using waste shrimp shells,4,4'-dihydroxydiphenyl sulfone and triphenylphosphine as raw materials,S source and P source,respectively,the effects of S doping and P doping on N,S-doped shrimp shell biochar(NSC-biochar)was investigated.Results demonstrated that,the post-source P doping could induce the macropores in an orderly trend,increase its BET,enrich the surface functional grou ps,and promote the degree of graphitization,thereby improving the activating performance for PDS to degrade 2,4-DCP.However,excessive S doping could reduce the pore abundance,change the surface zeta potential,and reduce the adsorption capacity,thereby reducing its effectiveness for PDS activation.In addition,post-source P doping could enrich the surface catalytic sites,enhance its electronic conductivity and induce efficient electron transfer mechanisms(non-radical path).This study clarified the influence of post-source S-doping and P-doping on the structure of N,S-doped biochar and the effect of PDS activation,and provided basic and theoretical guidance for constructing an efficient biochar/PDS oxidation system.