Enhanced Degradation Of Dye Wastewater By Coimmobilization System Of Nano Valence Iron And Electricigens

With the large-scale production and use of dyes,a large number of dye wastewater is discharged,which not only causes serious water environmental pollution,but also has potential harm to human health.Biological method has attracted much attention because it is environment-friendly,especially electromicrobial method,which has more prominent advantages than conventional biological method because of its broad-spectrum degradation of environmental pollutants.However,most of the current researches focus on suspended electricigens,which is difficult to reuse and poor-tolerable to toxic dye wastewater.These would weaken the pollution control advantage and decontamination efficiency of electricigens.The conductivity of common embedding agent is poor,so applying immobilization to electricigens will hinder electron transfer between electricigens and electron acceptors,resulting in decrease of degradation efficiency of dyes.Therefore,this paper intends to consider adding conductive materials into embedding agent to construct an efficient-dye-degradation co-immobilized system of electricigens and conductive material.In order to complete this target,the model electricigens Shewanella oneidensis MR-1 and nano zero valence iron(nZVI)with low price and excellent performance were selected.Firstly,we optimized the immobilization conditions to construct co-immobilization system of nZVI and Shewanella oneidensis MR-1.Secondly,the main factors affecting the dye degradation effects of the system were systematically studied,and the operation stability of the system was investigated.Finally,the anaerobic degradation mechanism of dyes in the system was deeply studied.The main conclusions are as follow:(1)The dye degradation effects of co-immobilized system of nZVI and S.oneidensis MR-1 was significantly better than immobilized system of pure S.oneidensis MR-1,that is the addition of nZVI enhanced the contaminant degradation ability of immobilized of electricigens.In addition,the system retained the advantage of electricigens that broad-spectrum degradation ability and could degrade azo dyes(strong polarity,medium polarity and weak polarity),triphenylmethane dyes and metal-complex dyes.(2)The immobilization condition(sodium alginate concentration,CaCl₂concentration and cuing time),nZVI and bacterial concentration had a significant impact on the construction of efficient co-immobilized system.Among them,the immobilization conditions affected the physical properties(such as sphericity,diameter,weight,mechanical strength and mass transfer performance).The type and concentration of conductive materials and bacterial concentration influenced the dye degradation ability of the system.For the selected conductive materials(nano carbon powder,Fe₂O₃,nZVI),nZVI has the best effect on improving the dye degradation ability of immobilized S.oneidensis MR-1.(3)The dye-degradation effects of co-immobilized system of nZVI and S.oneidensis MR-1 were influenced by the initial dye concentration,the number of co-immobilized beads,temperature,p H,salinity and rotate speed.The specific performance was as follow:the system dye degradation efficiency decreased with the increase of initial dye concentration and increased with the increase of the number of co-immobilized beads and rotate speed;temperature(25?40?)and p H(4.5?8.0)affected the dye degradation efficiency of the system slightly,that is,the system has a wide application range of temperature and p H;salinity(0?30 g/L)had little effects on the dye degradation efficiency,that is,the system has good applicability to high-salt dye wastewater.(4)The co-immobilized system of nZVI and S.oneidensis MR-1 performed good mechanical strength and dye degradation activity stability.The specific performance was as follow:after four consecutive cycles(144 hours)of dye degradation,the dye degradation activity decreased only 4.92%,and the mechanical strength of co-immobilized beads decreased about 10%(the surface was still intact).(5)Extracellular electron transport mediated the anaerobic degradation of dyes in the co-immobilization system of nZVI and S.oneidensis MR-1.The specific performance was as follow:the dye-degradation ability of S.oneidensis MR-1 was inhibited by knockout of Mtr gene,and exogenous addition of different electron mediator(riboflavin,AQS,AQDS)could promote the degradation of dyes by S.oneidensis MR-1.(6)In the co-immobilization system of nZVI and S.oneidensis MR-1,nZVI promoted the extracellular electron transfer efficiency by enhancing the conductivity of immobilized beads.What's more,in the dye degradation,nZVI was oxided to Fe(OH)₃and Fe₂O₃,which improved the growth,ATP production and EPS secretion ability of S.oneidensis MR-1,so as to strengthen the dye-degradation ability of immobilized S.oneidensis MR-1.