Study On The Mechanism Of Magnetic Biochar Promoting Anaerobic Methanogenesis Of Phenolic Compounds

Phenolic compounds,as important chemical raw materials or intermediates,are discharged into water with the industrial production process.Phenolic wastewater has the characteristics of poor degradation performance and high biological toxicity.Conventional treatment technology cannot achieve economic and efficient removal,which poses a serious threat to the environment.Anaerobic biological treatment technology has the advantages of high toxicity load,low operation cost,energy saving and high efficiency,which is widely used in industrial wastewater treatment.However,due to the sensitivity to environmental conditions（such as p H,temperature,organic load,toxic substances,etc.）,the efficiency of anaerobic process in the treatment of phenolic wastewater cannot meet the increasingly stringent wastewater treatment standards.Therefore,it is urgent to develop a cost-effective new anaerobic enhancement technology to solve the bottleneck of refractory phenolic wastewater.In this study,nitrogen-doped sewage sludge based activated carbon（N-SBAC）was optimized and prepared by using the excess sludge from wastewater treatment as carbon precursor.Micron-grade high iron-containing fly ash（MHIFA）was loaded on its surface to obtain MHIFA/N-SBAC.The efficiency and mechanism of MHIFA/N-SBAC in enhancing anaerobic degradation of high concentration 2,4,6-trichlorophenol（2,4,6-TCP）were analyzed.MHIFA/N-SBAC was used to enhance anaerobic degradation of coal gasification wastewater by up-flow anaerobic sludge bed（UASB）reactor,and its efficiency and applicability were analyzed.The results were as follows:（1）The prepared magnetic carbon materials were characterized by SEM,BET,XRF,XPS,XRD and FTIR.The SEM results showed that after MHIFA was loaded on the surface of N-SBAC,Fe3O4 particles were clustered and evenly dispersed on the surface and pores.BET results showed that the specific surface area of MHIFA/N-SBAC was 307.45 m2/g,and the pore size belonged to mesoporous.XRF results indicated that the mass fraction of Fe3O4 in MHIFA/N-SBAC reached 21.33%,and XPS data demonstrated that the magnetic conductive metal of the load was Fe3O4.XRD analysis showed that the diffraction peak of MHIFA/N-SBAC at 2θ accorded with the standard XRD pattern of Fe3O4.FTIR results manifested that there was a characteristic peak of Fe-O functional group of MHIFA/N-SBAC at 581 cm^-1.In addition,in the leaching experiment of MHIFA/N-SBAC,the concentration of several main heavy metal ions was far lower than the specified allowable leaching concentration,which met the national emission standard.The above results indicated that the prepared MHIFA/N-SBAC had reliable and safe performance.（2）MHIFA/N-SBAC was used to enhance the anaerobic degradation of high concentration 2,4,6-TCP.The results indicated that with the assistance of MHIFA/N-SBAC,the final removal rates of COD and 2,4,6-TCP reached 75.6%and 75.1%respectively,which was 2.1 times and 1.81 times higher than that of the control group.The maximum methane yield reached 107.25 m L/d,about 1.65 times that of the control group（64.88 m L/d）.The addition of MHIFA/N-SBAC increased the biomass and conductivity in anaerobic activated sludge,and enhanced the concentration of extracellular polymer and coenzyme F₄₂₀.The analysis of microbial community structure demonstrated that the addition of MHIFA/N-SBAC changed the microbial community structure.The relative abundance of Pseudomonas was35.82%,while it accounted for only 26.20%in the control group.The enriched electrogenic bacteria Pseudomonas might conduct direct interspecific electron transfer（DIET）with Methanothrix through the bioelectric connection assisted by MHIFA/N-SBAC,so as to further promote the anaerobic degradation of 2,4,6-TCP.As a functional bacterium induced by MHIFA/N-SBAC,the relative abundance of Azotobacter was 39.06%,while it only accounted for 28.59%in the control group.It played a key role in hydrogen production metabolism by maintaining NADH/NAD⁺balance.COGs functional data showed that under the induction of MHIFA/N-SBAC,the functional abundance of“amino acid transport and metabolism”and“carbon transport and metabolism”of microorganisms increased,which promoted the degradation of phenolic compounds and the transformation to final products.（3）The UASB reactor was used to enhance the anaerobic degradation of coal gasification wastewater.The results manifested that with the assistance of MHIFA/N-SBAC,the COD removal rate of wastewater was increased to 64.4%and the methane yield was 1093.6 m L/d.At the same time,MHIFA/N-SBAC significantly improved the biodegradability of coal gasification wastewater and reduced acute biological toxicity.The results of sludge characteristic analysis showed that MHIFA/N-SBAC facilitated microbial growth and enzyme activity,and increased the concentration of extracellular polymer and coenzyme F₄₂₀.At the same time,MHIFA/N-SBAC also promoted the sludge granulation process in the form of lots of specific signal molecules and low diffusion signal factors.The existence of MHIFA/N-SBAC increased the abundance and diversity of microbial population,especially promoted the growth and aggregation of Geobacter.The bioelectrical connection between Geobacter and Methanothrix might be strengthened through the DIET process.Combined with high pollutant removal rate and methane generation rate,it was speculated that the electron transfer accelerated by DIET might promote the conversion of refractory pollutants in coal gasification wastewater to methane.Under the impact of total phenol and p H,MHIFA/N-SBAC improved the tolerance and stability of UASB reactor.In conclusion,MHIFA/N-SBAC could significantly enhance the anaerobic degradation of high concentration 2,4,6-TCP.More importantly,MHIFA/N-SBAC had great practical application in anaerobic degradation of coal gasification wastewater.This study combined the theoretical research and practical application of anaerobic electron transfer,which not only effectively solved the bottleneck of anaerobic and efficient degradation of phenolic pollutants,but also realized the high resource utilization of waste,which had significant economic,environmental and social benefits.At the same time,it provided theoretical basis and technical support for solving the problem of phenolic wastewater treatment,which had great practical significance and industrial application prospect.