| The study investigated the effects of a baffle on the hydrodynamic characteristics of a pilot-scale hybrid growth membrane bioreactor(HG-MBR)and two kinds of typical suspended carriers on the oxygen mass transfer in the HG-MBR using clean water,based on theoretical analysis and experimental measurement.The influences of the area and location of the baffle on the hydrodynamic characteristics of the reactor,the mobility of the carriers,as well as the aeration intensity and mode,the filling ratio and type of the carriers on the microporous aeration oxygen mass transfer were discussed.The fluidization state of the carriers in water was described.The area and location of the baffle and the filling ratio of the carriers were optimized.The mechanisms of oxygen mass transfer in the reactor were also discussed.The results may provide theoretical reference and data support for optimizing the structural design,improving the oxygen transfer efficiency of the reactor and reducing the energy consumption.The main conclusions are as follows:(1)The structural design of the separation mesh in a HG-MBR is an important concern to the hydrodynamic characteristics of the reactor.An optimal design of the separation mesh will promote the recirculation of the carriers in the reactor,reduce the aeration intensity for driving the carriers movement,therefore reduce the energy consumption.The upper part of the separation mesh should be closed,while the lower part should have a suitable channel for the mass exchange between the membrane area and carriers’ area.(2)The combined aeration by A+C tubes is more advantageous in the HG-MBR,which is beneficial to drive the recirculation of the carriers.The optimal operation condition with the baffle at an area of 0.71 m2(0.84 m×0.84 m)and located at the upside of the separation mesh could reach a reduced aeration more than 15%for driving the carriers at the filling ratio of 50%.It is of significance for an energy saving to design a HG-MBR.(3)The hydrodynamic characteristics of the reactor can be changed by adding the carriers.The carriers in the reactor help to prolong the contact time and increase the contact area between gas and liquid.The carriers also aggravate the turbulence of the water,accelerate the mass renewal on the gas-liquid interface,and promote the mass transfer process between gas and liquid phases effectively.Thus,the oxygen transfer efficiency is improved.(4)The aeration intensity plays an important role in the oxygen transfer process with a linear increase tendency.However,it is not as great as possible,it is necessary to consider comprehensive factors of oxygen transfer performance and energy consumption to find an economic aeration intensity.(5)The carriers with different filling ratio can promote oxygen transfer process.The type Ⅱ carrier with the filling ratio of 30%is the best for oxygen transfer at the single aeration of C tube,while the type Ⅱ carrier with the filling ratio of 20～30%is the most suitable at the combined aeration of A+C tubes.(6)To confirm a filling ratio of the carriers in a HG-MBR,the factors such as the size,shape and other characteristics of the carriers,the energy consumption for driving force and the fluidization state of the carriers should be fully taken into account.In real application,the carriers should be fluidized smoothly in the reactor,and a high filling ratio to increase the attached biomass may be not good.It should consider both the needs of biochemical oxygen demand and membrane fouling tendency.(7)Different types of the carriers have important influence on the effect of oxygen transfer.Suitable biological carriers with good hydrodynamic characteristics can enhance the oxygen transfer performance. |
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