Parameters Optimization And Membrane Fouling Mechanism Of A~2/O-MBR Process

A2/O-MBR process as a combined process type in application of membrane bioreacetors(MBR)in urban sewage treatment,has been recognized by most of the urban sewage treatment plant.It has been one of familiar processes in the upgrading and reconstruction of wastewater treatment plant.This study used two sets of A2/O-MBR small pilot plant to simulate the actual A2/O-MBR project in a long time.Optimization of parameters,the critical flux,membrane cleaning and pretreatment of wastewater,were carried out.Combining with the actual situation of the project process,a stable operation and optimization management strategy was proposed.This study can provide technical support to the large scale application of MBR technology in the reconstruction of the city sewage treatment plant and,has high value.The results showed that the critical flux was affected by temperature and aeration intensity,in the long run of A2/O-MBR.When the temperature and aeration intensity were lower,there was an obvious drop.Critical flux increased gradually with the increase of temperature and aeration intensity.And when the temperature was more than 26 ℃,the increase of temperature and aeration intensity didn’t affect the critical flux,critical flux tends to be stable.In addition,when the sludge concentration was between 4 and 10 g/L,the critical flux was not obviously affected.During the optimization A2/O-MBR process parameterst,it was found that the change of COD and ammonia nitrogen was no affected by the change of sludge age.COD of effluent was less than 10 mg/L and ammonia nitrogen was less than 0.1 mg/L;when the sludge age was 22 d,reflux ratio was 200%,the proportion of the influent anaerobic tank and anoxic tank was 5:5,the best removal effect on the total nitrogen of the system,and the effluent total nitrogen was 8.1 mg/L(average removal rate was 51%).It can be speculated that the low carbon source,was major factor to limit the total nitrogen removal.The average total phosphorus concentration in effluent of A2/O-MBR was 1 mg/L,which can not meet the first level A of(GB18918-2002),auxiliary chemical phosphorus removal was need.On-line cleaning membrane cleaning experiment found that dosing 6 min(200 mg/L NaCIO),purging 9 min,and dosing 6 min(200 mg/L NaClO+NaOH),9 min purging cleaning effect was best;Restorative cleaning results showed that the membrane fouling was mainly composed of cake layer,gel layer had less contribution to membrane pollution,and membrane fouling was dominated by inorganic pollution.The pretreatment results showed that the proportion of impurities in the range of particle diameter>1 mm、0.4～1 mm、0.2～0.4 mm、0.1～0.2 mm were 40.0%,15.6%,28.0%and 16.4%,respectively.With the decrease of particle size,the impurities of VSS/SS value also decreases.After 1 mm to 0.1 mm sieve,the removal rate of SS and COD increased.And the higher the mesh accuracy,the better the removal rate of SS and COD can be achieved.However,the removal rate of ammonia,total nitrogen and phosphorus did not be affected.In addition,in the entanglement simulation of impurities,it was found that there was no entanglement of 0.1～0.2 mm impurities,and the impurities of 0.1～1 mm and 0.1～0.4 mm,appeared winding phenomenon,and the membrane wound of impurities(diameter of 0.1～1 mm)was most serious.