Study On The Properties And Mechanism Of Phenolic Wastewater Treatment In Anaerobic Fluidized Bed Microbial Fuel Cell

The composition of coal chemical wastewater is complicated,which has caused serious damage to human health and ecological environment.As a typical bio-refractory and high strength industrial organic wastewater,coking wastewater contains complicated contaminants such as cyanide,ammonia,phenols,polycyclic aromatic hydrocarbons and heterocyclic compounds.According to the latest institutional survey,most domestic coal chemical companies do not have satisfactory treatment of phenol-containing wastewater.The concentration of chemical oxygen demand?COD?and priority control pollutants in biochemical effluents is often difficult to meet the national industrial wastewater discharge standard.Microbial fuel cell?MFC?has been received extensive attention as a novel biotechnology for wastewater treatment with concomitant electricity generation by microorganisms.Moreover,the wastewater treatment efficiency is much better under the combination of microorganism and electrochemistry.In this study,the anaerobic fluidized bed?AFB?process was combined with microbial fuel cell technology to treat coking wastewater.An integrated system termed single chambered air cathode anaerobic fluidized bed microbial fuel cell?AFB-MFC?was constructed for treating coking wastewater?CWW?.The properties of generation electricity and treating wastewater were investigated.The changing and transferring,degradation mechanism and reaction kinetics of organics in coking wastewater during the treatment process were analyzed.And the problem of the difficult removal of phenols,benzenes,heterocyclic compound and polycyclic aromatic hydrocarbon in coking wastewater was solved.Firstly,the structure and operating parameters of fluidized bed reactors were optimizated by calculations and simulations.The liquid-solid model in the AFB-MFC reactor was established by the Fluent simulation software,simplifying the reactor as a two-dimensional model by the Gambit pre-processing software.The fluid-bed distribution board opening rate and sewage inlet velocity were simulated to investigate fluidized state of the activated carbon in the fluid-bed,when the sewage inlet velocity of 2 mm/s,5 mm/s,7 mm/s and 9 mm/s.The objectives of this simulation were to find out the best fluidizing velocity;starting speed of reducing the microbial fuel cell;velocity of improving the producing electricity and sewage processing.The results showed that the fluidization was the best when the opening rate of distribution board was 8%and the inlet speed was 5 mm/s.Secondly,MFC performance was improved by optimizing biological carriers and electrode materials.The effects of biocarriers kind on the electricity generation and wastewater treatment efficency were investigated used active carbon and graphite as biocarriers respectively.The results show that the starting time decreased when biocarriers was added,and the starting time of active carbon MFC was the shortest..At the same time,the output voltage and power increased greatly,and internal resistance decreased.Nano-Fe₃O₄ was prepared by the chemical co-precipitation method and used for modifying the graphite rod anode of an AFB-MFC.The electrochemical properties were described by cyclic voltammetry and electrochemical impedance spectroscopy,the results showed that Nano-Fe₃O₄promoted the electron transfer and electrochemical activity on the surface of anode.When the modified anode was used in MFC,the maximum power density and output voltage were up to 9.81 mW/m² and 243 mV,respectively,which were 114%and 23.4%higher than those of the unmodified anode.Thirdly,it is proved that the anaerobic fluidized bed microbial fuel cell is effective in treating coking wastewater.On the basis of optimizing the process conditions and electrode materials,the effects of initial COD of raw wastewater,the microorganism acclimatization ways,the operational ways and external resistances on electricity generation and wastewater treatment of the AFB-MFC utilizing coal pyrolysis wastewater were investigated.The results show that electricity could be generated by AFB-MFC with the different initial COD of wastewater influent concentrations?952 mg/L,1528 mg/L,223 mg/L 8 and 3419 mg/L?,the output voltage and electricity generation increased with increasing initial COD.When the initial COD of the raw wastewater was 2238 mg/L,the maximum output voltage and maximum power density of MFC were 284.5 mV and 14.69 mW/m²,respectively.The properties of electricity generation and wastewater treatment in AFB-MFC were best under gradient acclimatization with the maximum power density?10.95 mW/m²?and COD removal efficiency?86.28%?.Besides,the electricity generation and COD removal of series of three stage MFCs and single MFC were compared.The maximum output voltage of series MFCs was more than 100%higher than that of the single MFC,and COD removal efficiency increased significantly.Fourthly,the degradation mechanism and reaction kinetics of main organics were revealed.The composition and migration of organic matter in coking wastewater treatment were analyzed by liquid-liquid extraction and GC-MS.The degradation mechanism and reaction kinetics of the main organic matter were studied.After a cycle of treatment in AFB-MFC,the removal of phenols,benzenes,alcohol,heterocyclic compound and polycyclic aromatic hydrocarbon were 99.28%?96.32%?99.21%?95.91%and 92.85%,respectively.The mass concentrations of main five phenol pollutants were measured.The detection limits of phenol pollutants were 2.48⁵.50?g/L,and the linear correlation coefficients?R²?were higher than 0.993 and the average recoveries values ranged from 72.6%to 115.8%.From the intermediate dimethyl succinic acid,it was deduced that in anaerobic fluidized bed microbial fuel cells,m-cresol was first carboxylated to dimethyl succinic acid and then further decomposed to small molecule compounds.The degradation reaction of phenol,o-cresol and 2,4-Dimethylphenol follow the first-order kinetics in AFB-MFC,and the rate constants of kinetics equations are 0.06989 h^-1,0.07641 h^-1 and 0.08783 h^-1,respectively.Moreover,the degradation reaction of 2,4-di-tert-butylphenol can satisfy first-order kinetics equation,but which rate constant is 0.0179 h^-1.The concentration of decyl alcohol is the highest of all alcohols in the coking wastewater,and the degradation reaction kinetic equation of decyl alcohol in the AFB-MFC is-ln?C C₀??28?-1.1142?10?3.1325t-0.3430t².Finally,the changing and transferring regulation of sulfur element in the wastewater treatment process were investigated.And the effects of sulfur ion on electricity generation and sewage treatment performance were studied.Moreover,the inhibition mechanism of sulfide on m-cresol degradation was proposed.The degradation of phenols and electricity generation were affected by sulfur ion.When the concentration of sulfur ion was low,the change of degradation rate was little.But,when the concentration of sulfur ion was higher,the degradation rate of phenol was very slow.At lower sulfur ion concentration,the entrance of sulfur ion resulted in an increase of electrolyte,and thus,the conductivity strengthen and the electricity generation of MFC enhanced.However,with increasing of sulfur ion concentration,toxicity appeared little by little,thus breeding of microorganism was restrained and degradation rate of organics decreased,and the power generation capacity decreased.The effect of sulfur ion on microbial degradation of m-cresol was significant.This mechanism of inhibition can be described by the Michaelis-Menten equation included a correction constant when competitive inhibition exists.Sulfur ion as an anti-competitive inhibitor,sulfur ion can combine with an enzyme-substrate complex to form an inactive complex that prevents the enzyme from catalyzing the reaction,thereby inhibiting the degradation reaction of the substrate m-cresol.