Study On Reduction Technology Of Nitroaromatic Compounds By Anaerobic Microorganisms And Zero Valent Iron And Its Application

In addition to 2,4-dinitrochlorobenzene(DNCB),2,4-dinitrophenol(DNP)and 2,4-dinitroanisole(DNAN)were also the major constituents of DNAN producing wastewater,which was characterized by high salinity,high nitroaromatic compounds(NACs)concentration and poor biodegradability.In this study,a combined zero-valent iron(ZVI)-Fenton-anaerobic baffled reactor(ABR)-movingbed biofilm reactor(MBBR)process was developed for DNAN producing wastewater treatment.The role of functional group on NACs reduction was comprehensively investigated in the ZVI system.A ZVI coupled anaerobic system was developed to enhance NACs reduction,and the underlying role of ZVI in this process was elucidated.Based on the ZVI coupled anaerobic system,a combined ZVI-ZVI coupled anaerobic system-MBBR-Fenton process was deveploed in the aim of optimizing the DNAN producing wastewater treatment process.A combined ZVI-ABR-MBBR process was tested for the treatment of DNAN producing wastewater.For ZVI process,almost complete reduction of NACs was observed at hydraulic retention time(HRT)8 h and the copper plating ratio is 0.2%.For Fenton process,the optimal pH,H2O2 to Fe(II)molar ratio,H2O2 dosage and HRT were found to be 3.0,15,0.216 mol L"1 and 5 h,respectively.The results of both technical-scale pilot plant and pilot plant test revealed that under the optimal operational conditions,the indexes of effluent,such as COD and aromatic compounds concentration were lower than the discharge standard for water pollutants from ordnance industry(GB 14470.2-2002).The role of functional group on DNCB,DNAN and DNP reduction was comprehensively investigated in the ZVI system.The results showed that pseudo first-order kinetics could well describe the reduction process of the three NACs by ZVI,and the reduction rates of the three NACs follow the order of DNCB>DNAN>DNP.In addition,DNCB was firstly reduced at para-NO2 position,while,the reduction of DNAN and DNP preferentially occurred at ortho-NO2 position firstly.According to the density function theory computations analysis,the charge densities of nitrogen atoms followed the order of para>ortho for DNCB,ortho>para for DNAN and DNP.Additionally,the N-O mayer bond order(MBO)at para and ortho positions followed the order of ortho>para for DNCB,ortho<para for DNAN and DNP.This theoretical calculation analysis was consistent with the results of the ZVI reduction experiment.Based on above analyses,it can be inferred that the electron-withdrawing functional group(-Cl)might strongly deactivate the ortho-NO2 for ZVI reduction,while,the existence of the electron-donating functional groups(-OCH3 and-OH)might result into higher charge density of the N atom at ortho position on DNAN and DNP.A ZVI coupled anaerobic system was developed for the enhanced reduction of DNAN.The results showed that both DNAN reduction and 2,4-diaminoanisole(DAAN)formation were notably improved in the ZVI coupled biosystem.In the ZVI coupled biosystem and biotic control system,complete removal of 40 mg L-1 DNAN could be achieved within 4 h and 20 h,respectively.However,only 28.71±5.06%of DNAN could be removed in the ZVI control system after 20 h.Correspondingly,the DAAN concnentration in the ZVI coupled biosystem,biotic control system and ZVI control system were 27.79±0.69 mg L-1,4.74±0.48 mg L-1 and 0.00±0.00 mg L-1,respectively.The high performance of the ZVI coupled biosystem could be attributed to the high accumulation of formate,low oxidationreduction potential(ORP)and great pH self-buffering capability at presence of ZVI.In addition,the methanogens activity was also accelerated by addition of ZVI.Especially,the ZVI coupled biosystem displayed a more stable performance in terms of DNAN reduction with the coexistence of the competitive electron acceptors,such as nitrate and sulfate.Iron shavings were adopted for optimizing the ZVI coupled anaerobic system,with system stability emphasized.The results showed that the ability to resist environmental stress,such as low HRT,high DNAN concentration and high salinity was strengthened through the addition of iron shavings in the anaerobic reactor.Compared with a loose and rough surface of the sludge in the control reactor,the sludge in the coupled system presented a compact,rigid and granular appearance under iron shavings simulation.Furthermore,the diversity of microbial community in the coupled system was significantly higher than that of the control anaerobic reactor.Additionally,species related to DNAN reduction and methane production were enriched in the coupled system.Based on the ZVI coupled anaerobic system,a combined ZVI-ZVI coupled UASB system-MBBR-Fenton process was deveploed in the aim of optimizing the DNAN producing wastewater treatment process.The observed stable performance and low cost highlights the full-scale application potential of ZVI-ZVI coupled UASB system-MBBR-Fenton process for the treatment of recalcitrant industry wastewater.