Study On Treatment Of Refractory Organic Wastewater By Persulfate Activated By Iron Based Sludge-derived Biochar

In this effort,we aim to synthesize high performance persulfate?PS?activator with feedstock of municipal sewage sludge and employ it for refractory organic wastewater treatment to realize the strategy of "treat waste by waste".PS based Advanced Oxidation Processes?AOPs?have been intensely studied for refractory organic wastewater treatment because of the low biodegrability of these wastewater.Sludge-derived biochar?SDBC?,the solid residue after pyrolysis process of municipal sewage sludge,was widely employed as efficient adsorbent of organic pollutants.Sewage sludge always contain a certain amount of iron,which hints the potential of SDBC to be an economical PS activator.In this strategy,organic pollutants can be degraded in SDBC/PS system and sewage sludge can be utilized.We firstly employed SDBC as PS activator to remove aqueous 4-chlorophenol?4-CP?in this study.Then,we firstly synthesized SDBC supported zerovalent iron?ZVI-SDBC?by reducing the indigenous iron ions in municipal sewage sludge with NaBH₄ to improve the activity of SDBC for PS activation.To facilitate phase separation,we firstly synthesized magnetic SDBC?MSDBC-1?by a novel "one-pot" method that pyrolyzing sludge after co-precipitation of Fe3O4 particle.The two abovementioned catalysts were employed as PS activator to remove aqueous acidic orange 7?A07?.In addition,seven kinds of inorganic anions were chosen to study the influences of common anions on 4-CP removal efficiency by SDBC/PS system.Lastly,we employed municipal landfill leachate?MLL?effluent through Membrane Bio-Reactor?MBR?system?labeled as MBR effluent below?as real wastewater to confirm or disprove the implications of SDBC/PS system in industrial application.By the aforementioned efforts,we obtained the following results and conclusions.?1?SDBC successfully activated PS,and 4-CP was enriched on the surface of SDBC by the high adsorption capacity of SDBC on 4-CP,which improved the degradation of 4-CP.Amorphous Fe???on the surface of SDBC rather than persistent free radicals should be considered as main active components in PS activation.Heterogeneous active components contributed mostly to the activation of PS.SDBC showed high stability in 3 times reuse experiments and neglectable iron leached from it.The performance of SDBC/PS system was nearly independent on initial pH values.The dominant oxidative radicals of SDBC/PS system was identified as sulfate radicals.?2?Characterization results of ZVI-SDBC confirmed the suscessful reduction of a part of iron into Fe⁰.ZVI-SDBC was more reactive than SDBC in PS activation.Distinguished with SDBC,ZVI-SDBC active PS mainly by sustainable and slow releasing of Fe²⁺,and Fe²⁺ played an important role in A07 removal.Acidic medium favored A07 removal.ZVI-SDBC showed lower stability than SDBC in the reuse experiments,but showed higher one than most of the previous reported ZVI catalysts.?3?We compared the novel MSDBC-1 with MSDBC-2 which was synthesized by traditional co-precipitation method.Results showed the successful loading of Fe₃O₄ particle on the surface of the two aforesaid MSDBCs,and the magnetic properties were satisfactory.However,Fe₃O₄ particle on the surface of MSDBC-2 obviously aggregated and blocked some holes on the surface of SDBC.Fe species distributed uniformly not only on the surface but also in the interior of MSDBC-1,and formed Fe-O-C chemical bond on the surface,indicating strong interfacial interactions between Fe3O4 and carbon components that benetted the stability of MSDBC-1.Results of BCR sequential extraction procedure digestion and iron leaching tests further confirmed the stability of MSDBC-1 and high reuse performance was obtained in reuse experiments.In addition,MSDBC-1 showed higher efficiency on PS activation than MSDBC-2 did.?4?NO₃-and SO₄^2-showed very limited influences on 4-CP removal by SDBC/PS system.However,HCO₃-,CO₃^2-and H₂PO₄-inhibited 4-CP removal obviously.The order of inhibition levels is H2PO4-<HCO₃-<CO₃^2-.Two halide irons,Cl' and Br-,at low concentration of 1.85-18.5 mM,showed slightly promotion effects on 4-CP removal.However,high concentration of halide irons inhibited 4-CP removal.Although most anions showed inhibition effects on 4-CP removal,4-CP could be degraded even when anion concentration was as high as 370 mM,which was 200 times of the initial concentration of PS.This result suggested the resistivity of SDBC/PS system to the inhibition effects of common anions.?5?In the treatment of MBR effluent,SDBC/PS showed high performance on removal of not only TOC but also ammonia nitrogen.In addition,biodegrability of MBR effluent was also improved obviously.Acidic medium slightly favored TOC removal and slightly inhibited ammonia nitrogen removal.In summary,the findings from this thesis have significant implications for persulfate based AOPs which have been intensively studied and applied for a remediation of water,soils and etc.,and the utilization of municipal sewage sludge.