Study On Characteristic Of Oxygen-enriched Aeration With Membrane-Recirculated Membrane Bioreactor

Enhancement of oxygen solubility and transfer coefficient in waste water is one of important tools for increasing aerobic bio-treatment efficiency. This paper describes a method of generating 28.8% O₂ using a membrane as an aeration source. It has been studied in this paper that, the transfer characteristic of the enriched oxygen in the water, the effect of enriched oxygen aeration on the biodegradation of organics, and the effect of sewage concentration and aeration rate on the efficiency of bio-reactor. It has been shown from the result that, the efficiency of enriched oxygen aeration on the biodegradation of organics is much higher than that in conventional oxygenic aeration, and there is an optimal aeration rate. In this study, the oxygen transfer coefficient of the enriched oxygen aeration is 1.3 times higher than that in the conventional oxygenic aeration. The efficiency reaches the maximum when reaction time is about 40⁶0 mins. The advantage is more obvious at a higher sewage concentration. In a 10 days running of re-circulating the sewage water via the membrane bioreactor, the hydraulic retention time has been shorten to approximately 1/3 of that if using conventional oxygenic aeration; when inlet COD is around 450～700 mg·L^-1 and the outlet COD is less than 20 mg·L^-1, the removal of COD was up to 95%; when inlet ammonia nitrogen is around 18 mg·L^-1 and outlet ammonia nitrogen is less than 2 mg·L^-1, the removal of ammonia nitrogen was up to 90%. The effluent has a low turbidity and un-detectable SS. It has been shown from the experimental result that the bioreactor efficiency is greatly increased by this method; the system was stable in a scheduled time without plug-up by using 2 mm diameter PES hollow fiber membranes. Increasing trans-membrane pressure (TMP) resulted in an increase in flux, and the flux was independent of TMP above a critical value. Increasing flow velocity degrades the formation of a fouling layer, which was independent of flow velocity once it reached a critical value. For different MLSS, there were a suitable TMP and a suitable flow velocity. At the MLSS of 2.2 ,3.1, and 4.6 g·L^-1,the suitable TMPs were 100 ,80 , and 60 kPa respectively, and the suitable velocity was between 0.6 and 0.9 m·s^-1。The optimal back-flush period was 40 min, and the optimal back-flush procedure was to back-flush for 60s then forward-flush for 15 s with the inlet valve open. The flux was restored to about 78% and 89% of its original flux when back-flush or chemical cleaning were applied respectively.