Biodecolorization Of AZO Dye And Aerobic Degradation Of Typical Product From Decolorization

Reactive black5(RB5) which is widely used in textile industry is a typical disazo dye. Wastewater containing RB5should be treated before being discharged into environment as it has the features of deep color, high COD and poor biodegradability. Furthermore, sulfanilic acid is a common aromatic amine produced from decolorization of azo dyes. The negatively charged sulfonyl and amino groups of SA molecule are known to its high water solubility, high toxicity and structural stability. Due to environmental and health concerns, SA contained wastewaters need to be treated prior to its discharged into the environment.An Enterobacter strain (GY-1) was isolated from textile wastewater treating sludge. The kinetic of decolorization of RB5was studied. Whilst aerobic degradation of sulfanilic acid (SA) using activated sludge and the effect of ammonium-oxidizing bacteria on SA were investigated. Furthermore, degradation of SA using microbial fuel cells (MFC) was conducted. The main contents of this study are as follows.1,An Enterobacter strain (GY-1) with high activity of decolorization of Reactive Black5(RB5) was isolated from textile wastewater treating sludge. The optimal growth conditions are pH10, temperature30℃, inoculum5%and liquid volume50mL.2,Decolorization of RB5must be controlled under anaerobic condition. The optimal decolorizing conditions were35C, pH6, inoculum8mL and liquid volume100mL. The decolorization of RB5was attributed to extracellular enzymes. In addition, the strain GY-1exhibited widely decolorization as indicated by19kinds of dye decolorized by the strain GY-1.3,The mechanism in which bacteria GY-1decolorize RB5is cometabolism. Cometabolic substrate can be glucose, starch, sucrose, fructose, galactose, oxalic acid and citric acid, among which glucose is the best substrate of this study and the optimal concentration of substrate is4g/L. Organic compounds such as beef extract and peptone can facilitate decolorization of RB5, while inorganic compounds such as sodium nitrate had inhibitory effect on decolorization of RB5.4,Various metal compounds have different effects on activity of decolorization of RB5. MgSO4and MnSO4can increase the activity of decolorization of RB5. While some other compounds have inhibitory effects on the activity of decolorization of RB5. The sequence of the inhibitory effect of metal compounds on RB5decolorization is as follows: Ag2SO4> COSO4> Pb(NO3)2> HgSO4> CuSO4> FeCl3> ZnSO4> CaSO45,Effects of different operation parameters (temperature and dye concentration) and various electron donors/co-substrates on decolorization of RB5by GY-1were systematically investigated to reveal the key factors that determine the performance of the azo dye decolorization. A kinetic model was established giving the dependence of decolorization rate on cell mass concentration (first-order). The rate increased with increasing temperature from20to35℃, which can be predicted by Arrhenius equation with the activation energy (Ea) of8.50kcal mol-1and the frequency factor of6.28×107mg1g-MLSS-1h-1. Michaelis-Menten kinetics and Eadie-Hofstee plot were used to determine Vmax,1.05mg l-1h-1and Km,24.06mg l-16,Aerobic SA biodegradation could be monitored by real-time DO measurement. The sludge was enriched for over three months with SA (>500mg/L) as the sole carbon and energy source and dissolved oxygen (DO,>5mg/L) as the primary electron acceptor. Effects of aeration rate (0-1.74L/min), DO concentration (0-7mg/L) and initial SA concentration (104-1085mg/L) on SA biodegradation were quantified. A modified Haldane substrate inhibition model was used to obtain kinetic parameters of SA biodegradation and oxygen uptake rate (OUR). Positive linear correlations were obtained between OUR and SA degradation rate (R2>0.91). The concomitant release of near stoichiometric quantity of sulphate (3.2mmole SO42-released from3.3mmole SA) and the high chemical oxygen demand (COD) removal efficacy (97.1%) indicated that the enriched microbial consortia could drive the overall SA oxidation close to a complete mineralization. In contrast to other pure-culture systems, the ammonium released from the SA oxidation was predominately converted into nitrate, revealing the presence of ammonium-oxidizing bacteria (AOB) in the mixed culture. No apparent inhibitory effect of SA on the AOB activity (i.e. nitrification) was noted.7,A series of batch kinetic experiments were conducted to evaluate the effect of AOB on aerobic SA degradation in a SA-enriched activated sludge culture capable of oxidizing SA and ammonium simultaneously. To account for the effect of AOB on SA degradation, allylthiourea (ATU) was used to suppress AOB activity in the culture. The results indicated that specific SA degradation rate of the mixed culture was negatively correlated with the initial ammonium concentration (0-93mM-N, R2=0.99). The presence of AOB could accelerate SA degradation by reducing the inhibitory effect of ammonium (>10mM-N).8,Effects of biocathode of MFC on degradation of SA with pH3by continuous experiments were studied. The result indicated that the biocathode of MFC could facilitate degradation of SA. Furthermore, the effects of external resistance and aeration rate on degradation of SA and characteristics of biocathode were also investigated. SA degradation rate with low external resistance (0.5Ω and1Ω) was higher than that with high external resistance (100Ω). Overall, RB5and SA which are tipical azo dye and aromatic aimine, separately were studied in this work. The strain GY-1with high efficient decolorization of RB5was isolated from activated sludge treating dye wastewater. Decolorization of RB5by GY-1through cometabolism was investigated systimaticaly. Decolorizing characterization and kinetic were further investigated. Furthermore, activated sludge with ability of degrading SA efficiently was obtained by acclimatizing using SA as the sole carbon and energy source. The effect of dissolve oxygen (DO) on decolorization of SA by activated sludge was studied. The concentration of SA could be indicated indirectly through in-stu DO measurement. In addition, on the use of MFC to facilitate biocathodic degradation of SA under acidic condition was also carried out. This study not only provided theoretical basis for treatment of wastewater containing azo dyes,but also estabilised foundation and experimental basis for mineralization of products from decolorization of azo dyes and treatment of acidic wastewater using electrochemical method.