Study On Biodegradability And Decolorization Of Reactive Black KN-B By Anaerobic Granular Sludge

The decolourization efficiencies of reactive black KN-B were researched by up-flow anaerobic sludge blanket reactor (UASB) using glucose as co-substrate by pilot-scale experiments, the mechanism of dye decolourization were also analyzed by batch adsorption and degradation tests. The degradation kinetics was then discussed by further degradation decolorization tests. The influence of carbon source concentration, dye concentration, pH, temperature, salinity on biodegradation decolorization of KN-B was also investigated. Furthermore, the degradation process of reactive black KN-B and preliminary degradation products were achieved by UV-Vis and IR spectrum.The decolourization of reactive black KN-B was investigated by the UASB reactor using glucose as co-substrate and at various sulfate concentrations. The results showed that the average removal of COD_Cr and color higher than 60% and 72% were achieved, respectively, when COD_Cr and dye concentration of influent was 800-1300mg·L^-1 and 10-40 mg·L^-1, respectively, the conditions were: the tempreture was 20-29°C, hydraulic retention time (HRT) was 24h, the effluent VFA was lower than 200 mg·L^-1, alkalinity was 508-668mgCaCO₃·L^-1. The concentration of sulfate lower than 500 mg·L^-1 had no effect on COD_Cr and dye removal efficiencies, but sulfate concentration higher than 800 mg·L^-1 would result in COD_Cr and color removal efficiencies gradually reducing. When sulfate concentration reached 1500 mg·L^-1, COD_Cr and color removal efficiencies were only 38.3%, 65.8%, respectively; the effluent VFA approached to 400 mg·L^-1, alkalinity was lower than 200mgCaCO₃/L, the reactor was badly affected. Diameter of anaerobic granular sludge was 0.5-5mm in the UASB reactor, microbe was not only dominated by filamentous bacteria, but also some cocci and bacilli.The mechanism of dye decolourization was also reseached by the adsorption and degradation tests. Adsorption of the dye by anaerobic granular sludge fitted well both Freundlich model (R² =0.9824) and Langmuir model (R² =0.9460), however, the adsorption amount of reactive black KN-B was low. By discussing the adsorption mechanism of reactive black KN-B, it indicated that the negatively charged sludge would have certain repulsive interaction to reactive black KN-B existing in form of anionic in solutions, which resulted in the low adsorption amount. The adsorption rate was only 14.3%, and the absorption peak at 600 nm didn't change during the adsorption tests, while the color removal rate was 80.1% and the maximum absorption wavelength almost vanished during degradation, so the decolorization of reactive black was due mainly to degradation, rather than adsorption.Furthermore, the degradation experiment of reactive black KN-B in keeping with time was performed, and degradation kinetics was analyzed at the same time. The conclusion demonstrated that anaerobic granular sludge could decompose reactive black KN-B with or without glucose as a co-substrate (reactive black KN-B was reduced by 43.1% through 24 hours' anaerobic treatment with dye as sole carbon source). The degradation of reactive black KN-B with or without the presence of glucose conformed to the first order reaction and the second order reaction, respectively.The degradation decolorization of reactive black KN-B wastewater by anaerobic granular sludge was then carried out by treating compounding simulated wastewater in the 250mL flasks reactor. The effect of carbon source concentration, dye concentration, pH, temperature, salinity on biodegradation decolorization of KN-B was investigated. Through the orthogonal experiment, the optimal conditions for reactive black KN-B wastewater decolorization were obtained: dye concentration 50 mg·L^-1, temperature 50℃, pH=8, salinity 500 mg·L^-1. The decolorization rate of dye was up to 87.5%.From the UV-Vis and IR spectrum of dye before and after degradation, the absorption peak at 600 nm in the visible region, at 309nm and at 255nm in the ultraviolet region vanished, decreased and increased, respectively. It proved that aromatic amines produced after the cleavage of the azo linkage, most of them could not be metabolized anaerobically, which need be degraded by further aerobic treatment. The results were in accordance with IR spectrum'.