Study On Biodegradability And Color Removal Of Dyestuffs And FABR/O Treatment Of Textile Dyeing Wastewater

Printing and dyeing wastewater(PDW)has been the main source of water pollutants in the textile industry.It has large amount of discharge,high level of color,complicated components,non-biodegradability and high contamination,what is more that some dyestuffs are also toxic.With the development of synthetic fiber and improvement of printing and dyeing and post finishing technology,difficult to biodegrade organics such as sizes,dyes,detergents and chemical auxiliaries and finishing agents are discharged into PDW in large quantity,increasing the difficulty of wastewater treatment.There are some problems such as low treatment efficiency,massive residual sludge,large volumes of water treatment chemicals and high operating cost in existing biological treatment.Therefore an effective and economical treatment for PDW increasingly becomes a difficult problem of environmental protection.Because of the increasing shortage and severely pollution of water resources,disposal of PDW has drawn high attention.Thus the study of biodegradability of dyes and auxiliaries under different conditions,and the development of high efficiency and low cost system of wastewater bio-treatment have momentous significance,great social and environmental benefits.In this research,two groups of typical and structurally different common cationic dyes (Cationic Red 2GL,Cationic Red GTL,Cationic Red 6B,Cationic Brilliant Blue 2RL, Basic Green)and reactive dyes(Reactive Red 6BN,Reactive Yellow 2GR,Reactive Blue BRF,Reactive Black B)were chosen as research objects.Through analyzing water pollutants in the dyeing wastewater of these dyes,their biodegradability under aerobic, facultative anaerobic(FA)and anaerobic conditions was determined,analyzed and evaluated using respiration measurement and substrate removal.A new bio-treatment process—Facultative Anaerobic Baffled Reactor/Oxic(FABR/O)for PDW was established and studied.The main operating parameters such as dyes concentration,sulfate concentration,soda concentration and hydraulic retention time(HRT)of the process were optimized through experiments.The kinetic parameters of the process were also studied. Finally,the biodegradation approaches of Cationic Red 2GL and Reactive Yellow 2GR were preliminarily explored using UV-Visible spectrophotometer,infrared spectrum and high performance liquid chromatography/mass spectrometer.The results after comprehensive analyses include the followings.1.This study analyzed the water pollutants in the PDW.Among the 21 types of dyes and auxiliaries measured,only two auxiliaries of chelating dispersant C-5000 and leveling agents 1227,and cationic red 6B are poorly biodegradable and the others are hardly biodegradable organics.The COD_Crof the effluent are mainly composed of that of the natural organic impurities in the raw cotton,difficult to biodegrade auxiliaries in the bleaching and dyeing while the high level of color is mainly caused by residual dyes in the effluent.The softeners have the greatest contribution to the total COD_Cr,about 57.5%.In the effluent of acrylic textile dyeing,the difficult to biodegrade auxiliaries such as oil-stained removing agent,leveling agents and softener are the main contributors to about 70% of the total COD_Cr.The level of color of the effluent is mainly caused by residual dyes.2.The bio-adsorption of cationic dyes and reactive dyes studied here to activated sludge from municipal sewage treatment plant conforms to Freundlich type isotherm.The adsorbability of cationic dyes to activated sludge is outstanding.As the adsorption time increases,the residual dye concentration reduces and the percentage of adsorption also increases.The adsorption is mainly in the form of ionic absorption.The adsorption of reactive dyes to activated sludge is the combined results of physical and chemical adsorptions and the quantity of absorption is low.There is hardly any absorption of reactive Black B to activated sludge.3.The percentage of color removal of the studied cationic dyes is high under aerobic conditions.Increasing the sludge concentration has no prominent effect on percentage of color removal of the cationic dyes.Increasing the acetic acid concentration and dye concentration has little effect on the percentage of color removal of cationic red 2GL, cationic red GTL,cationic blue 2RL and basic blue.It reveals that the biological de-colorization of these cationic dyes seems to be the combined results of biological absorption and subsequent biodegradation.The acetic acid concentration could enhance the color removal percentage of cationic red 6B.It could be that the co-metabolism takes place between 6B and acetic acid.The percentage of color removal of reactive dyes under aerobic condition increases as the degradation time,sludge concentration and glucose concentration increase.As the dye concentration increase,however,the color removal of the dyes reduces.The aerobic activated sludge has poor biodegradability to Black B which has disazo structure.It can be deduced that the biological color removal is mainly the results of micro bio-degradation based on the conclusion that activated sludge has very little adsorption potential of reactive dyes.In the range of sulfate concentration(<2%)studied sulfate does not exert a negative effect on the biological color removal of reactive red 6BN.It helps the biological color removal of reactive dyes effluent by adding the right amount of sulfate.Under anaerobic condition,the cationic dyes and reactive dyes can be treated using anaerobic activated sludge from municipal sewage plant when the dyes concentration is less than 200 mg/L.Their anaerobic biodegradability is excellent and de-colorization was highly visible during anaerobic reaction.There is no obvious re-colorization after anaerobic de-colorization of cationic dyes.Only the color of disazo reactive dye Black B re-appears when the samples were taken from the reactor for testing.The biodegradation and color removal of high strength of reactive dyes(500 mg/L)are restrained to some extend when glucose is not added.The cationic dyes tested have good de-colorization under FA condition.The FA de-colorization of reactive dyes differs greatly.The azo dyes are more easily decolorized than disazo dyes.The FA de-colorization of cationic dyes is much higher than that of reactive dyes with high percentage of color removal and short time required,but COD_Cr removal of cationic dyes is lower than that of reactive dyes.The two groups of dyes all have good FA biodegradablity within a large temperature range of 15～30℃.The results of facultative anaerobic-oxic tests show that the FA de-colorization of cationic dyes is much higher than that of reactive dyes while the aerobic de-colorization of reactive dyes is higher than that of cationic dyes.The de-colorization of both types of dyes is all greater than 96.2%.The aerobic COD_Crof removal of both groups of dyes is higher than that of the FA COD_Crremoval.The B/C of FA effluent is much higher than that of influent.The biodegradability is greatly enhanced and the total COD_Crremoval is greatly increased.4.The anaerobic baffled reactor was modified into facultative anaerobic reactor in the improved FABR/O system reported here and a new type of pile materials were attached to the insides of the reactor.The system combined biofilm with aerobic activated sludge,more effectively blocking the FA activated sludge in the reactor,overcoming the disadvantages of strict anaerobic operating requirement and realizing quick start-up.The residual sludge of aerobic reactor can be flowed back into the FABR,which set to function as sludge reducing. The improved FABR/O system was applied to PDW treatment process.FABR/O system is very effective in treating PDW.The highly effective color removal takes place in the FABR and the COD_Crlargely reduces.The total COD_Crand color removal percentages reach over 85% and 90% respectively during the 24h-HRT,for 1000～1200 mg COD/L and 100 mg dye/L of the influent.The percentage of COD_Crremoval reduces with increasing dye concentration.The sulfate concentration(100～2500 mg/L)has little influence on the treatment efficiency of FABR.The COD_Crremoval of reactive dyes stabilizes over 70%,and the percentage of color removal above 91.8%.The soda concentration impacts greatly on the treatment efficiency of FABR.Increase of the soda concentration results in decrease of the COD_Crremoval and color removal.When the soda concentration increases to 2000 mg/L, the percentage of COD_Crremoval and color removal drop to 33.5% and 68%,respectively. Therefore,particular attention should be paid to monitoring and controlling the soda concentration in actual engineering.The kinetic study of FABR/O system shows that the biodegradability of difficult to biodegrade wastewater has greatly been improved and the saturated constant decreases after the wastewater is treated by FABR.5.The structures of Cationic Red 2GL and Reactive Yellow 2GR before and after FABR/O process were preliminarily analyzed using UV-Visible spectrophotometer,infrared spectrum and high performance liquid chromatography/mass spectrometer.The spectrograms show that the two dyes are well biodegraded in the FABR.There is no absorption in the visible zone and the de-colorization is excellent.The effluent tends to be no color or less color.There appear some small molecular substances such as hydrocarbons, amines and aethers.Under the function of facultative anaerobes,the azo bond of dyes cleaves and the structures of dyes break down from large molecules into medium molecules and finally tiny molecules.The peaks of benzene ring in the spectrograms disappear at the end.The improved FABR/O system presented in this study includes the many advantages. The biochemical reaction conditions are very loose.The new pile materials attached to the baffled plates inside of the FABR.The FA biofilm combines with aerobic sludge supplementing each other,which has much better treatment efficiency than general anaerobic-aerobic process.The improved FABR/O system also has the features of simple construction,stable operation,high processing efficiency,low operating cost and low residual sludge.