Study On A/O~4-MBR For The Treatment Of Fluorescent Dyes Production Wastewater

Wastewater from fluorescent dye production, a typical industrial wastewater with high concentration of organic matter, is hardly biodegradable. Its high salinity and toxicity would cause severely pollution to the environment when it was discharged directly to waters without a proper treatment. Conventional biological processing to this kind of wastewater can hardly reach a desired water quality in effluent due to its poor biodegradability. It was reported that membrane bioreactor (MBR) overmatches the conventional process in treating refractory organic wastewater, indicating a possibility that MBR could be applied in the treatment of this kind of wastewater. The purpose of this research was to systematically study the long-term performance of an A/O4-MBR system in the treatment of wastewater from fluorescent whitening agent production. The removal effect of various kinds of pollutants in different treatment units was estimated. Trans-membrane pressure (TMP) combined with other parameters was used to indicate the degree of membrane fouling with time profile, and diverse membrane cleaning methods were investigated. The main results were as follows:The average removal efficiency of fluorescence intensity indicating the pollutant concentration, CODcr and NH3-N were 37.05%,75.23% and 75.23%, respectively, when the wastewater was treated by using this technology with a stable water quality in the effluent and a good resistance to shock-loading. The effluent quality can meet the standards of wastewater quality discharged to municipal sewers (CJ343—2010). Membrane pool had also a great contribution to NH3-N removal with the removal rate up to 44%. The average Cl- concentration in influent was 5890mg/L, with a maximum of 10397 mg/L, whereas 5572mg/L in effluent in average. High Cl-concentration resulted in an inhibition of active sludge, leading to low sludge concentration and removal efficiency, which, however, had little impact on the stability of the whole system in operation.The membrane fouling was developed slowly in the initial stage while speeded up in the later period of steady running. The critical filtration pressure of the system was 0.016～0.020MPa. Wall thickness of membrane was increased and the fouled membrane was covered with gel layer or slime cake layer which is dense and nonporous. It was observed that pollutants were accumulated in the inner part of membrane and most of the membrane pores were seriously blocked. The foulant substances contained some proteins and carbohydrates, and polysaccharides could be the main component for membrane fouling. Comparison of several chemical cleaning methods revealed that chemical cleaning was more effective than physical cleaning. NaClO and NaOH solution could greatly recover the membrane permeability, and moderately high concentration of NaClO could reach the best result in terms of cleaning.