| Membrane extraction is a new separation technology which combines membrane process with liquid-liquid extraction. It has advantages in high efficiency, low energy consumption, simple process, stable running, and so on. Biological process is the most widely used and economical technology in the treatment of wastewater. It has advantages in high efficiency, simpleness and conveniency in operation and management, low cost in maintenance. It has been to the most widely used technology in the treatment and control of environmental pollution. But for the hyper-saline organic wastewater, it is hard for microorganisms to survive under the conditions of high salinity and extreme environment. The application of biological process is limited. Based on the respective advantages of membrane extraction and biological process in the field of wastewater treatment, high efficiency in membrane separation and economics in biological process, an extractive membrane bioreactor was constructed. Salicylic acid (SA) was chosen to be the target compound. The research on a new treatment process that a membrane separation combined with biodegradation was carried out. The characteristics of membrane mass transfer and biodegradation were investigated. The following studies were carried out:(1) The research on biodegradation of SA. SA-degrading bacteria were acclimated by serial batch culture. The effects of salinity on biodegradation of SA were investigated. The results showed that:If the salinity came to 60 g/L, the SA-degrading bacteria can not survive.(2) The research on membrane extraction of hyper-saline SA simulation wastewater. In the membrane extraction reactor, the effects of influent flow rate, system temperature, pH in the stripping solution and initial SA concentration in the influence on mass transfer process, the SA removal efficiency, and the SA recovery efficiency were investigated. The results showed that:The Kov is exponentially related to influent flow rate. And Kov increased as the influent flow rate, system temperature, pH in the stripping solution or initial SA concentration increased. Membrane resistance was determined to be the major factors affecting mass transfer process. The order of magnitude of Kov was 10-7 m/s. Around 97% SA removal was obtained under conditions of influent SA concentration of 854.2±19.7 mg/L, flow rate of 3 L/d, system temperature of 323 K, pH of 11.5±0.2 in the stripping solution and membrane length of 50 m. In the membrane extraction process, different amounts of SA residues were left in the membrane under different operating conditions. The SA recovery efficiency was basically between 40～145%.(3) The research on treatment of hyper-saline SA simulation wastewater in an extractive membrane bioreactor. Under appropriate conditions for microorganisms to grow, influent SA concentration was changed to investigate the characteristics of membrane transfer and biodegradation. The results showed that:With the continuous decrease of influent SA concentration, the mass transfer driving force decreased, and Kov mainly showed a downward trend. After 27 d of cultivation in the biological zone in the reactor, the biofilm gradually formed on the outside of membrane tube. SA extracted through the membrane was effectively utilized by microorganisms in the biological zone under appropriate environmental conditions. The SA concentration in the biological zone was basically maintained at 18.7±6.0 mg/L.(4) The research on contrast of the characteristics of membrane transfer between the extractive membrane bioreactor and the membrane extraction reactor. Compared with the membrane extraction reactor, under the same system temperature and influent flow rate, but different pH conditions, Kov in the extractive membrane bioreactor increased in different degrees as different influent SA concentration. The mass transfer process in the extractive membrane bioreactor was better than that in the membrane extraction reactor. |
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