Study On The Treatment Of Coking Wastewater By Multi-stage A/O VT-MBR Combined Process

Coking wastewater is a typical refractory organic wastewater.Currently,most of them are treated by biological methods,but there are problems such as poor effluent quality and poor removal of organic pollutants.Membrane Bioreactor(MBR)has the advantages of high volume load,short hydraulic retention time,and low residual sludge,but the shortcomings of membrane fouling and high energy consumption limit the large-scale industrial application of MBR.The Vertical Tubulant Biological Reactor(VTBR)has many advantages,such as high amount of biofilm,good mass transfer effect and not easy to be blocked.The tail gas of VTBR can provide air source for the membrane module,and the residual pressure can also be used as the driving force of the membrane,which can improve the utilization rate of aeration and reduce the energy consumption.The purpose of this thesis was to couple the VTBR process and MBR to form a Vertical Tubulant Membrane Bioreactor(VT-MBR),which used tubular membranes to improve the effluent quality,and used VTBR exhaust gas to generate gas in the tubular membranes.The liquid two-phase flow slowed down the membrane fouling caused by the polarization of the concentration difference and the filter cake layer.The effect of the VT-MBR combined process on coking wastewater treatment under different operating parameters was investigated.The results showed that the optimal operating conditions of the treatment system were:total hydraulic retention time was 60 h,reflux ratio was 3:1,aeration the amount was 30L/h.Under this operating condition,the effluent COD_Cr,NH₃-N,TN and volatile phenol concentrations were 224±20mg/L,16.26±1.07mg/L,34.94±1.60mg/L and 0.22±0.05mg/L,respectively,the removal rates were respectively(95.49±0.41)%,(58.94±2.72)%,(69.54±1.39)%and(99.08±0.21)%.According to the analysis of three-dimensional fluorescence spectrum,the components of dissolved organic pollutants in the coking wastewater increased from 1 to 4 after anaerobic treatment.The microbial community of the inoculated sludge and the stable running sludge was analyzed.The results showed that after inoculated sludge was acclimated,the Chao1 index of microbial Alpha diversity in aerobic and anaerobic sludge decreased by 68.0%and 80.1%,respectively,compared with that in the inoculated sludge.The abundance of the main flora changed significantly.Proteobacteria was the most abundant,with the abundance of 56.37%and 85.99%in anaerobic sludge and aerobic sludge,respectively.The membrane fouling was analyzed.As the aeration rate increased from 20 L/h to 40 L/h,the average membrane fouling cycle increased from 12 d to 16 d,but the irreversible fouling resistance of the membrane increased from 18.82%of the total resistance to 36.05%.It was not conducive to the long-term operation of the membrane module.The concentration of Extracellular Polymeric Substance(EPS)and Soluble Microbial Products(SMP)in the sludge of the membrane module would decrease with the increase of aeration.P/C(Protein/Carbohydrate)decreased with the increase of aeration,and the aeration had a greater impact on the protein in EPS.The P/C in the supernatant SMP and the total SMP increased with the increase of the aeration volume,and the aeration volume had a greater impact on the polysaccharides in the SMP.From the fluorescence spectrum of the supernatant of the membrane module sludge,it was known that aeration could increase the types of dissolved organic matter in the membrane module.The optimal conditions for membrane cleaning were explored,and the results showed that the cleaning efficiency of 2%citric acid+0.1%Na Cl O soaking method was 77%.When the concentration of EDTA-Na₂(C₁₀H₁₄N₂O₈Na₂)in the 0.1%Na Cl O solution is 120 mg/L,the membrane module cleaning efficiency reaches the best,and the membrane cleaning efficiency is 92%.