Study On A/O/A/O Process For The Treatment Of Textile Dyeing Auxiliaries Wastewater

As a kind of fine chemical products, textile dyeing auxiliaries differ from each other. The wastewater released when producing these products belongs to hardly-degradable industrial wastewater which is characterized as great fluctuation in COD and contains complex composition. At present, there are very limited references about the degradation of surfactants which are raw materials for producing textile dyeing auxiliaries. Focusing on the wastewater treatment plant of textile dyeing auxiliaries, this research has monitored the organics treatment situation of each treatment process, and analyzed the exited problems of A/O/A/O process. Concerning these problems, it has conducted pilot test simulating the A/O process treating textile dyeing auxiliaries wastewater and investigated biodegradation mechanism of these organics in this wastewater under A/O/A/O process. It also put forward relative optimum proposals on operation parameters of A/O/A/O process. The main conclusion are as follows.1. Coagulation-double A/O-coagulation-sand filtration and activated carbon adsorption process has been applied for the treatment of textile dyeing auxiliaries wastewater, the average COD, ammonia nitrogen and Linear Alkylbenzene Sulphonic Acid (LAS) treatments of effluent are97.4%,96.8%and99.2%, respectively, which satisfied the " standard of wastewater reusing for industrial water ". In each wastewater treatment unit, A/O/A/O process made the most contribution on COD removal which reached74.1%. Though the effluent COD of biotreatment process was at a stable position which maintained around200mg/L, the average COD removal rates of latter A/O process only accounted for30%of the whole process removal rates. The average ammonia nitrogen removal rate of A/O/A/O process reached97.2%, however, the ammonia nitrogen removal rate of O1was only58.3%, which indicates there is a great potential for the former A/O process to improve its pollutants removal efficiency.2. The pilot test simulating A/O process has been operating well throughout the experiment, the average COD, ammonia nitrogen and LAS in the effluent reached 190mg/L,4.4mg/L and0.6mg/L, and the removal rate of these pollutants were91.6%,92.4%and97.3%, respectively, which had improved32.8%and34.1%of the COD and ammonia nitrogen removal rate, respectively, comparing the former A/O process in the wastewater treatment plant. This paper also compared the effect of different mixed liquor suspended solids(MLSS) and Hydraulic Retention Times (HRTs) on the pollutants removal efficiency in Sequencing Batch Reactor (SBR), and it has been proved that the best pollutants removal efficiency could be reached when the MLSS and HRT of the SBR were5000mg/L and36h, respectively, the corresponding improved COD and ammonia nitrogen removal rate were27.2%and29.7%comparing with the former A/O process’. The biodegradation mechanism of textile dyeing auxiliaries wastewater treated by A/O/A/O process was investigated, which demonstrated macromolecular organics of the influent were broken down into relative smaller organics whose average molecular weight was500. In addition, it has been proven that most of the organics from the effluent were long-chain alkanes, which demonstrates that the pollutants in the effluent of A/O process whose COD is below200mg/L could not be easily biodegradable. Through pilot test as well as research on biodegradation mechanism of textile dyeing auxiliaries wastewater, this paper has put forward optimum proposals on operation parameters of A/O/A/O process, which indicates that in order to upgrade the exited wastewater treatment process, the dissolved oxygen(DO) and MLSS in O1tank should maintain about2mg/L and3500-5000mg/L, respectively, and the HRT of O1tank could be shortened from42h to36h. When the pollutants removal efficiency of the former A/O process reaches certain level similar to the pilot test’s, the aeration in O2tank could be reduced or even stopped.