Preparation Of Sludge-based Micro-electrolysis Filler And Its Effect On The Degradation Characteristics Of Pharmaceutical Wastewater

Pyrolysis can be used as a sustainable technology for sewage sludge（SS）disposal as its advantage in reduction,decontamination and reclamation of SS.The main products obtained from SS pyrolysis are char,tar and pyrolysis gas.In this thesis,a new kind of iron-carbon micro-electrolysis fillers was envisaged to be prepared using SS char for wastewater treatment to improve its biogradability.Firstly,the pyrolysis characteristics of SS were studied,and the evolution of C,N,S and other elements in the pyrolysis process was discussed.Then,a new type of sludge-based micro-electrolytic filler（SMEF）was prepared by pyrolysis using SS as the main raw material,and the preparation condition was optimized using using tetracycline hydrochloride（TC）as the simulated pollutant.Finally,the performance of SMEF on the pollutants removal in TC and real pharmaceutical wastewater（PW）was systematically studied.The main conclusions of this study are as follows:（1）The pyrolysis characteristics of SS at 30-800°C were studied by TG-FTIR.The TG results showed that 185–613°C was the main weight loss area during SS pyrolysis process,and organics degradation mainly occurred at this stage.Carbon-containing gas compounds such as CO,CO₂,CH₄ and benzene are mainly produced at 200–800°C,and derived from the decomposition of organic matter in SS and the secondary decomposition of pyrolysis products（tar）.FTIR results showed that NH₃ was dominant nitrogen containing compounds and mainly generated at 200–550°C,and it is mainly derived from the decomposition of the proteins in SS.Sulfur containing gas H₂S was mainly formed at 200-550°C,which is mainly produced by the decomposition of fat sulfur compounds in SS.（2）Sewage sludge-based micro-electrolysis filler was successfully prepared using SS,attapulgite clay and high purity iron powder as raw materials.The raw material ratio（Fe:SS）and preparation conditions were optimized by single factor experiment.The optimal Fe:SS and preparation conditions were:Fe/SS mass ratio was 1:2,calcination temperature was 1050°C,calcination time was 30 min,and sludge-based biochar filler without iron powder（SBF）was prepared under this condition.（3）SMEF and SBF were characterized by specific surface area analysis,infrared absorption spectroscopy（FTIR）,scanning electron microscopy（SEM）,X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）.The results showed that the surface of SMEF is rough,which can remove pollutants from water by adsorption.The addition of iron powder reduced the BET specific surface area of the filler,and the specific surface area of SMEF was only 8.6%of that of SBF.FTIR and SEM analysis showed that SMEF had abundant surface functional groups and developed porous structure,which could remove pollutants by adsorption.XRD analysis showed that SMEF had zero-valent iron（Fe⁰）and iron oxide Fe₃O₄,as well as metal oxides such as K₂O and Co O.XPS analysis shows that the filler has zero-valent iron,bivalent and trivalent iron elements and Fe²⁺:Fe³⁺is 1:2,indicating that there is Fe₃O₄ in SMEF,which was consistent with XRD results.SMEF contains metal oxides such as K₂O,which makes it alkaline.In aqueous solution,SMEF can slowly release alkaline substances and increase the p H of the solution.（4）The degradation performance of SMEF and SBF on 100 mg/L TC was studied.The results showed that when the initial p H was 3 and the filler dosage was 100 g/L,the removal rate of TC by SMEF and SBF were 89.42%and 78.83%,respectively,when the reaction equilibrium was reached,and the equilibrium time was 90 min and 120 min,respectively.The removal efficiency of TC by SMEF was obviously higher than that by SBF.Combined with the pseudo-first-order Lagergren kinetic model,the removal kinetics of TC by SMEF showed that there were other ways to promote the degradation of TC besides adsorption.The degradation products of TC were identified by LC-MS technology and the degradation mechanism of TC was analyzed.The results showed that TC molecules were gradually degraded into small molecular substances through demethylation,ring opening and carbon-carbon bond cleavage.The degradation performance of TC by SMEF was analyzed by five-round continuous reaction.The results showed that the adsorption of TC by SMEF gradually reached saturation with the increase of reaction times.The removal efficiency of TC decreased and the chemical degradation began to play a major role.The degradation efficiency of TC by five-round reaction was still 61.34%.（5）The degradation performance of SMEF for actual pharmaceutical wastewater was further investigated.The results showed that under the operating parameters of initial p H=5,filler dosage 500 g/L and reaction time 3 h,the removal rates of TOC and TN in pharmaceutical wastewater reached 17.90%and 35.28%,respectively.The long-term operation performance of SMEF was investigated by five-round continuous reaction.In the first run operation,the degradation of pharmaceutical wastewater by SMEF was stable.After five runs operation,the effect was still stable and the five-day biochemical oxygen demand（BOD₅）of wastewater was 2.24 times higher than that before reaction,which effectively improved the biodegradability of wastewater.