Study On The Degradation Of Phenolic Pollutants In Coal Chemical Wastewater By Fenton-like And Anaerobic Digestion Methods

Coal chemical wastewater is a typical refractory organic industrial wastewater that occurs in large quantities,has complex qualities,and contains a significant number of refractory organic pollutants.After pretreatment and biochemical treatment,wastewater still contains many toxic and harmful substances,mainly phenolic pollutants.Improving the treatment of pollutants in coal chemical wastewater is necessary to ensure environmental safety and human health.Therefore,the effective removal of phenols is the key to the effective treatment of coal chemical wastewater and sustainable green development.In this study,considering the common phenolic compounds in coal chemical wastewater as target pollutants,the degradation mechanism and removal effect of phenolic pollutants were discussed based on the homogeneous Fenton-like method,heterogeneous Fenton-like method,and anaerobic microorganism method,respectively.P-cresol degradation in the Fe（III）-EDDS/H₂O₂ Fenton-like system modified by Mn²⁺was studied.The optimum reaction conditions were determined,the effect of p H on the reaction system was investigated,and the reaction mechanism under different p H conditions was discussed.The results show that Mn²⁺-EDDS complex was highly stable under neutral or weakly alkaline environments,which could reduce Mn²⁺leaching.Meanwhile,the produced O₂^·-could enhance the reduction of Fe（III）-EDDS to Fe（II）-EDDS and accelerate the production of·OH.Thus,the efficiency of p-cresol degradation through the Fenton-like reaction catalyzed by the Fe（III）-EDDS complex was significantly improved.However,under acidic conditions（p H 3.5）,Mn²⁺and EDDS failed to form an effective complex,thereby inhibiting Fe（II）reduction.The optimal dosage and molar ratios for reaction were determined experimentally,as follows:Fe（III）ion,0.7 m M;Mn²⁺:Fe（III）=1:1;EDDS:Fe（III）=1:1;and H₂O₂:Fe（III）=15:1.Considering phenol as the target pollutant,EDDS was grafted onto hydroxylated carbon nanotubes and chelated with Fe（III）to form a chelate（CNTs-EDDS-Fe）;the catalytic effect of CNTs-EDDS-Fe composites in heterogeneous Fenton-like reaction under neutral condition（p H=7）was studied.The presence of key groups and key elements in the catalyst was determined by the characterization of the material.Reaction conditions,such as catalyst addition,H₂O₂ addition,and p H value,were studied in detail through experiments.The recyclability of EDDS on hydroxyl carbon nanotubes was confirmed by cycle experiments.The results show that at 25°C,the applicable range of the p H value of the material in the heterogeneous Fenton-like reaction is 3–9,and the optimum dosage of the material is 0.36 g/L.The optimum amount of H₂O₂ was 13.75m M.After five recycling experiments,the degradation rate of phenol was maintained above 90%,indicating that the CNTs-EDDS-Fe composite has suitable recyclability.Considering phenol as the target pollutant,the effect of conductive carbon nanotube/nano-iron oxide composite（CNTs-Fe₃O₄）on the degradation of phenol in an anaerobic digestion system was studied.Water quality indices,such as the chemical oxygen demand（COD）and ammonia nitrogen,were monitored,and the microbial community was analyzed.The experimental results show that the removal rate of COD is the highest in the group with the CNTs-Fe₃O₄ complex.Analysis of the micro community showed that the diversity in the group with conductive material composite was lower;however,but the abundance of degrading bacteria（Raineyella,Corynebacterium,Hydrogenibacillus,Thermicanus,Clostridium＿sensu＿stricto etc.）was higher,indicating that the addition of conductive material CNTs-Fe₃O₄ to the anaerobic digestion system could promote the direct interspecific electron transfer（DIET）among functional microorganisms.Simultaneously,Fe（III）can be used as the final electron acceptor to promote the anaerobic process,increase the substrate utilization,and finally improve the phenol removal rate.