| At present,with people’s increasing concern about environmental protection and water shortage,the control of sewage treatment plants in various countries is becoming more and more strict.Therefore,sewage biological treatment technology is widely used in various types of sewage treatment scenes to meet increasingly stringent sewage discharge standards.In MBBR system,microorganisms are used as the key to remove nutrients such as carbon,nitrogen,and phosphorus.Studying the biofilm attachment on non-living surfaces and the dynamic changes of active biomass during the whole process of biofilm formation,the responses law of active biomass in MBBR system under different operating conditions,and the succession law of microbial community structure play extremely important roles for the understanding the biochemical reaction kinetics of microbial communities and optimizing MBBR system.Therefore,a laboratory-scale MBBR system and a more complex pilot-scale MBBR system were constructed to carry out the studies.The dynamic changes of active autotrophic and heterotrophic biomass during the whole process of biofilm growth and under different working conditions were studied by combining the respiration rate method with actived sludge models.The apparent morphological and structural characteristics of biofilms and the succession rule of microbial community structure are in-depth analyzed by scanning electron microscopy and high-throughput sequencing.In addition,this study analyzed the correlation between microbial community composition and kinetic parameters,the correlation between microbial morphology and active biomass,in order to simplify the kinetic parameter correction method of the biochemical reaction kinetic model of sewage treatment,develop the online monitoring method of active biomass,and promoted the digital transformation of the water industry.The main results are as follows:(1)Research on the dynamic changes of active autotrophic and heterotrophic biomass during the whole process of biofilm growth shows that,during the adaptation period of biofilm growth,only a small amount of active biomass is attached;After entering the rapid growth period,for every 1 mg·L-1 of SCOD removed from reactors A1 and A2,0.16 mg COD·L-1·m-2 of active heterotrophic biomass can be increased on each filler.In the aerobic reactor O3 and O4,for every 1 mg·L-1 of NH4+-N removed,the active autotrophic biomass of 0.11 mg COD·L-1·m-2 and 0.27 mg COD·L-1·m-2 can be added to each filler,respectively;During the slow growth period,the growth rate of the active biomass in each reactor decreases to varying degrees;After the biofilm grows and matures,the microorganisms in each reactor are mainly active heterotrophic microorganisms,the heterotrophic biomass in reactors A1 and A2 were 133.28 mg COD·L-1·m-2 and 111.52 mg COD·L-1·m-2,respectively,and the active autotrophic biomass in reactors O3 and O4 were 46.24 mg COD·L-1 and 54.40 mg COD·L-1·m-2,respectively.(2)Through scanning electroscope observations at different locations of the filler,it is shown that during the growth adaptation period of the film,the cells are densely distributed,mainly cocci and bacilli.And the outermost layer of the filler surface needs to be magnified more than 10000 times to observe whether there are microorganisms attached to the filler surface.A magnification of 20000 times and above is required to obtain a clear microbial cell morphology and structure;During the growth period,the biofilm formed a mushroom-like microbial community,with a large number of bacilli,cocci and filamentous bacteria symbiosis,during this period or during the growth and adaptation period of the film on the inner layer where microorganisms are easier to adhere to,the magnification of 1000 times can be used to observe whether there are microorganisms attached,and the magnification of 10000 and above can be used to obtain a clear microbial cell morphology and structure.(3)Study on the succession law of microbial community in the whole process of biofilm growth.In reactors of A1 and A2,Proteobacteria,Bacteroidota,Chloroflexi,Firmicutes are the main components of the microorganisms in the biofilm of each sample,accounts for more than 77%of the total microbial content.The microorganisms in reactors O3 and O4 are mainly composed of Proteobacteria,Chloroflexi,Bacteroidota,Actinobacteriota,Acidobacteriota,Firmicutes,Patescibacteria,and Nitrospirota.Nitrosomonas was detected as a typical ammonia nitrogen oxidizing bacteria,and Nitrospira was detected as a typical nitrite oxidizing bacteria.(4)According to the dynamic changes of the active autotrophic and heterotrophic biomass of the pilot-scale MBBR system under different working conditions,the study shows that when the SCOD load is in the range of 8.53 g SCOD·m-2·d-1～14.60 g SCOD·m-2·d-1 in reactor A1,the active heterotrophic biomass on each filler can reach 223.04±0.08 mg COD·L-1·m-2,for Reactor A2,when the SCOD load range of 8.05 g SCOD·m2·d-1～14.07 g SCOD·m-2·d-1,the active autotrophic biomass on each filler can only to 168.64±0.06 mg COD·L-1·m-2.When the SCOD load in reactor A6 is 9.63±0.22 g SCOD·m2·d-1,the active heterotrophic biomass on each filler is 250.24±0.03 mg COD·L-1·m-2.In the reactor O3,when the ammonia nitrogen load is less than 1.02 g NH4+-N·m-2·d-1,the active autotrophic biomass on each filler is 10.88±0.02 mg COD·L-1·m-2,after that,with the increase of ammonia nitrogen load,the active autotrophic biomass no longer increased.In the reactor O4 and O5,the ammonia nitrogen load is less than 1.31 g NH4+-N·m-2·d-1,1.31 g NH4+-N·m2·d-1～3.49 g NH4+-N·m-2·d-1 and greater than 3.72 g NH4+-N·m-2·d-1,the active autotrophic biomass on each filler is 19.04±0.01 mg COD·L-1·m-2,27.20±0.01 mg COD·L-1·m-2,38.08±0.01 mg COD·L-1·m-2,respectively.(5)Research on the simplified correction method for the kinetic parameters of the kinetic model of sewage treatment biochemical reaction shows that,under working condition I,the correlation between the corrected oxygen consumption rate OURA of active autotrophic organisms and the oxygen consumption rate OURH of active heterotrophic organisms is as follows:In the aerobic reactor O3,μH,Max=4.70·μA,Max;In the aerobic reactor O4,μH,Max=5.43·μA,Max;In the aerobic reactor O5,μH,Max=3.46·μA,Max;In the aerobic reactor O8,μH,Max=6.86·μA,Max,the correlation coefficients are all lower than the default coefficient of 7.50 in the ASM1 model.(6)The results of the study on the active biomass monitoring model are as follows.The active biomass monitoring model and the fit model of the number of days of continuous culture of biofilms were constructed from the parameter data of microbial morphological characteristics of SEM images.The model fitting results show that the adjusted R2 is 0.8947,0.6815,0.7997 and 0.737,0.7485,0.9023,respectively.The P-value of each model is less than 0.05,and the P-value of each variable is less than 0.05,which indicates that it is feasible to develop the online monitoring model by this method.This helps solve the problem that key microbial indicators cannot be incorporated into the water Internet of Things as control variables. |
PDF Full Text Request