Preparation Of Functional Sludge-based Carbons Through Chemical Conditioning-Dehydration Coupled To Pyrolysis Strategy

Activated sludge process played an irreplaceable role in biological wastewater treatment,a large amount of excess sludge was produced during the wastewater treatment.Conversing waste sludge into functional carbon materials through pyrolysis strategy is one of the important technologies to achieve sludge resource reutilization in eco-friendly and harmless way,which has broad application prospect in sludge management.However,a large amount of energies was involved during the pyrolysis process because of high moisture content(over 90%)in sludge.Mechanical dehydration can reduce sludge moisture and enhance sludge resource reutilization.The major component in sludge,extracellular polymeric substances(EPS)always bind firmly to water molecules due to its special characteristic of gelatinous structure,leading to sludge deep dewatering difficulties.Thus,chemical conditioning is vital to realize sludge dewatering enhancement.In addition,traditional sludge-based carbon(SBC)has some drawbacks since its low specific surface and limited functional adsorption capacity,there has some limitations for its practical use.The thesis aims to the problems of difficulty in sludge deep dewatering and limited water purification abilities of SBC,proposed "Investigation on preparation of carbon-based functional materials based on sludge conditioning coupled pyrolysis and its water purification mechanism".Detailed research content for the thesis is as following:1)For the problems of high content of bound water in sludge and its dehydration difficulties.We employed integration of Fe(?)-sulfite oxidation and polyacrylamide flocculation(Fe/S-PAM)treatment for removing the bound water and improving sludge dewaterability under aerobic condition.Meanwhile,the multiple spectroscopies(including 2D/FTIR,2D/UV and XPS)to unravel the transformation of organic substances(especially for proteins,polysaccharides,nucleic acids)during the Fe/S-PAM treatment,to clarify sludge conditioning mechanism.Fe/S produced SO3·-radicals which could decompose the EPS in sludge,releasing bound water into free water.In addition,the formed Fe(III)from Fe/S led to re-coagulation of decomposed EPS,and C=O groups of tryptophan played the leading role in Fe-EPS association binding,causing transformation of the secondary structure of proteins(especially ?-sheets and ?-helices).Then,the introduction of PAM caused re-flocculation of disintegrated sludge flocs,enhancing the sludge filterability.This work provides a novel and cost-effective method for efficient removal of bound water in sludge,and subsequence improvement in sludge dewaterability.The above results also provide scientific guidance for oxidation process coupled to flocculation technology in sludge dewatering enhancement.2)A multistage WAS utilization process for preparing the carbon-based Fenton-like catalysis materials is proposed.More specifically,WAS is firstly used as an biological adsorbent for heavy metals(Cu and Ni)removal,and complexes of sludge-metals are converted into heterogeneous Fenton-like carbon-based catalysts under anaerobic condition through pyrolysis strategy.The mechanisms of interaction between extracellular polymeric substances(EPS)and metals are investigated,and the physicochemical properties of sludge-based carbons(SBC)are comprehensively characterized using varies techniques(including XRD,FT-IR,BET,TGA,SEM and TEM).Then,combined with ESR,XPS and free radical quenching experiment to unravel mechanisms of E2 degradation by Cu/Ni-SBC.The results showed that WAS can remove Cu/Ni from aqueous system via coordination and electrostatic interactions between EPS and heavy metals,and the maximum adsorption capacities of WAS for Cu and Ni are 116.16 mg·g-1 and 108.29 mg·g-1,respectively.In addition,the existence of Cu/Ni in WAS can catalyze the sludge pyrolysis process to improve por-structure of SBC,and exhibited excellence oxidation-degradation capacity towards E2 in real wastewater.The mechanistic of E2 degradation is explored using electron-spin resonance spectroscopy(ESR)analysis,both O2·-and ·OH radicals are responsible for E2 degradation in Cu(?)-SBC-H2O2,while O2·-radicals contributes to E2 degradation in Ni(?)-SBC-H2O2 system,and the former performed better degradation capacity towards E2.In addition to this,Cu(?)and Cu(?)are both formed in Cu(?)-SBC during the oxidation process,while only Ni(?)is found in the Ni(?)-SBC-H2O2 process,confirming that different catalytic oxidation reactions are occurred,leading to different E2 degradation efficiencies in Cu(?)-SBC-H2O2(100%)and Ni(?)-SBC-H2O2(79%)systems.The study facilitates a great strategy to multi-stage circulating utilization for sludge,and also provide a scientific guidance for mechanistic studies towards organic pollutants degradation by heavy metal-SBC.3)Based on problems of low specific surface and limited adsorption capacity of traditional sludge-based carbon(SBC).KMnO4-Fe(?)was used as chemical conditioners to synchronously to improve sludge dewatering performance,and to catalyze the biomass pyrolysis of WAS for preparing multi-functional material to remedy arsenic containing wastewater.The activated sludge is firstly conditioned by KMnO4-Fe(?),and a series of physical processes such as drying,high temperature pyrolysis and grinding are used to prepare Mn-Fe-SBC,which is then applied to the treatment of arsenic-containing groundwater.The results showed that the sludge dewaterability was significantly improved due to the moderate pre-oxidation of EPS by KMnO4,and the sludge particles were re-flocculated by in-situ generated Fe(?)from KMnO4-Fe(?).The conditioned sludge cake was then utilized for preparing Fe-Mn-SBC,and the high surface area(100.08 m2/g)characteristic of Fe-Mn-SBC had a great adsorption capacity towards arsenic.In addition,Fe-Mn-SBC could effectively oxidize As(?)to As(?),the addition of low dose of H2O2 can further improve total arsenic removal due to catalytic peroxidation of Fe-Mn-SBC towards As(?).The co-existing HA could also be removed through adsorption by Fe-Mn-SBC,but HA inhibited the formation of hydroxy iron(Fe(OOH))and competed the active adsorption sites,leading to a reduction in arsenic removal efficiency.