| This experiment is based on two sewage treatment processes,oxidation ditch and membrane filtration.A new type of sewage biological treatment device was designed.Four flat-sheet membrane modules are placed in the circulation trench.Aeration pipes are installed under the membrane module.Four underwater push devices are arranged at an equal distance,so that the whole system formed a circulating flow in the continuous mode with influent and effluent,so it is called Continuous Circulation Flow Membrane Bioreactor(CCF-MBR).Compared with the traditional MBR,it not only combines the high-efficiency retention of the membrane with the simultaneous nitrification and denitrification of the oxidation ditch,but also reduces the energy consumption and membrane pollution.This article focuses on a detailed analysis of the various operating performances of CCF-MBR,including the physical,chemical,and microbial characteristics of mixed liquid sludge,as well as the analysis of influencing factors of membrane pollution under internal changes and external conditions,providing a stronger technical support for the process to be widely used in actual engineering practice in the future.The design,processing,and assembly and debugging period of CCF-MBR lasted for 120 days.At the same time,the pre-experiment for the granulation culture of filamentous bacteria and the preliminary preparations for the formal operation of the reactor were started.Due to external research conditions changing,the reactor was started and stopped twice,the first formal operation lasted for 80 days;the second formal operation was 100 days.These two runs are here referred to as Experiment 1 and Experiment 2.Experiment 1 studied how the physical-chemical characteristics of the mixed liquid and the composition of the microbial community are affected by changes in external conditions(including temperature and water concentration),and the key factors influencing the change of membrane pollutants are obtained.According to the purpose of the experiment,we need to set three kinds of temperature changes: rise,sudden fall,and constant phase.In the meanwhile,a variety of characterization methods were used to analyze the composition of the pollutants on the membrane surface.Combining the change data of the internal and external indicators in the system,it was concluded that the formation of different color cake layers on the membrane surface was mainly the internal sludge concentration,extracellular polymers and microorganism's community composition which caused by external temperature changes.The second experiment mainly studied that by changing the impeller device,adjusting the impeller speed can not only maintain the stability of the operating efficiency of the reactor system,but also effectively change the water flow around the membrane module to increase the difficulty of adhering to the foulant layer with significantly increased membrane flux.In order to maintain a relatively stable F / M ratio,it is necessary to adjust the COD concentration of the influent according to the growth of biomass,and always maintain a carbon: nitrogen: phosphorus ratio of 100: 5: 1.At the same time,in daily microscopic examination and particle size distribution measurement,it was found that the sludge samples near the paddle will gradually intertwined with the increase of running time,Improving the settling performance of the mixed liquid.In summary,this work proved that the independently designed oxidation ditch type membrane bioreactor not only has excellent sewage treatment effect,which maintained a removal that more than 95% COD and 90% total nitrogen under a large influent load condition,and also reduce membrane pollution effectively under the hydraulic conditions of the combination with longitudinal aeration and tangential scour.This technology has important reference value and broad application prospects in the wastewater treatment process. |
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