Experimental Study On Treatment Of Municipal Wastewater By The Segmented MBBR Process

A hot area of research has been done in using Moving Bed Biofilm Reactor(MBBR)to treat municipal wastewater in recent years.In this study,segmented cylindrical MBBR reactor(segmented MBBR)and non-segmented cylindrical MBBR reactor(non-segmented MBBR)were selected.The segmented MBBR reactor was divided into four reaction zones from the bottom to the top.Each two adjoining reaction zones were separated by a baffle with small holes.Biofilm was cultivated in the non-segmented MBBR by using synthetic municipal wastewater,which had good performance of nitrogen removal.By analyzing and comparing the process of segmented and non-segmented MBBR treating municipal wastewater,a better reactor was to be selected for good operating mode.During the experiment,watching the operation of the reactor,summarizing the influence factors that affecting the operation of the reactor,and then,each factor had been studied in deepth.At the same time,the corresponding measures should be taken to ensure operation stability and denitrification efficiency in low C/N ratio urban sewage treatment,which was in order to provide a theoretical reference for the practical application of MBBR in low C/N ratio urban sewage.Through these studies,some main conclusions were drawn as follows:(1)AQUAPOROUSGEL,was used as a biomembrane carrier,and the non-segmented MBBR could obtain fairly good effect under these conditions that the DO concentration was about 5.3 mg/L and pH value was 6.5 by means of interval influent and continued aeration.The biofilm in the reactor grew well when the removal rate of COD,ammonia-nitrogen and TN was steady at around 87%,65%and 20%,respectively.While,the surface color of the carrier had changed from white to brown and microbial microscopy revealed a large number of aerobic bacteria,nitrifying bacteria and partial anoxic bacteria.(2)Experiments were done to research the factors that could affect the operation of the system including MBBR reactor being segmented or no,the DO concentration,fill rate and C/N ratio,or so,with the flow pattern of continuous inlet and outlet and continued aeration.With the DO concentration,about 5.3 mg/L and pH value,about 6.5,two experiments were done when the ammonium concentration of the inlet being 35 mg/L and 50 mg/L,respectively.The results indicated that the COD removal efficiency of the segmented MBBR was more or less as that of the non-segmented MBBR,the removal efficiency of ammonia-nitrogen,TN and TP within the segmented MBBR was better than that within the non-segmented MBBR.The conclusion also was underpinned by the theoretical analysis of dynamic load Ud,hydraulic retention time(HRT)and design volume V.At the same time,the number of microorganisms and the removal efficiency of pollutants in the four reaction zones of the segmented MBBR were found to be different from each other.With the pH value was about 6.5,the experiment was carried out in the segmented MBBR at different DO concentrations.When about 4.5 mg/L of the DO concentration,the removal efficiency of COD,ammonia nitrogen,TN and TP was about 87%,85%,68%and 37%,respectively,which was better than the removal efficiency with about 5.3 mg/L of the DO concentration.With the DO concentration,about 5.3 mg/L and pH value,about 6.5,the experiment was carried out in the segmented MBBR at different filling rate of the packing,which was 40%,50%and 60%,respectively.Test results show that when the filling rate was 50%,the fluidization of the packing was good,the collision between the packing was appropriate,and the removal of pollutants was the best,the removal rate of COD,ammonia nitrogen,TN and TP was about 85%,76%,57%and 24%,respectively.With the DO concentration,about 5.3 mg/L and pH value,about 6.5,urban sewage was treated in the segmented MBBR with different C/N ratio,which was 7.1,5.1,3.4 and 2.3,respectively.The results showed with the C/N ratio from big to small,the removal rate of COD would be decreased,but the outlet concentration of COD of each C/N ratio was similar,and the removal effect of ammonia nitrogen,TN and TP was the best when C/N ratio was 5.1.It shows that the segmented MBBR had strong adaptability facing the change of water quality,but the concentration of C/N ratio would affect the system's removing contaminants.(3)With the flow pattern of continuous inlet and outlet and continued aeration,the urban sewage of low C/N rate was treated in the segmented MBBR using two kinds of operation mode of two-point flooding and additional carbon source.Better denitrification effect was achieved and this provided theoretical reference for production practice to a certain degree.The segmented MBBR flooded municipal wastewater from the bottom and the third reaction zone(two-point flooding)for the experiment under these conditions that the DO concentration was about of 5.3 mg/L and pH value was about of 6.5.The two-point flooding could take use of carbon source reasonably and the results showed that two-point flooding was helpful for the growth and reproduction of autotrophic bacteria,and the removal efficiency of the system was improved to a certain level.With the DO concentration,abou 5.3 mg/L and pH value,about of 6.5,the experiment was carried out in the segmented MBBR when the raw water was flooded to the bottom and the carbon source was added to the third reaction zone.Glucose,starch and sodium acetate was used as the carbon source,respectively.Experiments indicated that the system had the worst nitrogen removal ability when the starch was added.While,the removal ability with the glucose as addtional carbon source was almostly as the same as that with the sodium acetate.Using which one of the three additional carbon source,the cost of drugs and the reaction time should be considered.