Correlation Of Structural Extracellular Polymeric Substances In The Biofilms Formed On Support Layer With Biofilm Structure And Hydraulic Resistance In DMBR

Structural extracellular polymeric substance（structural EPS）refers to a high molecular polymer secreted by microorganisms to the outside of cells,which can form stable hydrogels.Different from other extracellular polymers（EPS）,structural extracellular polymeric substance plays a key role in the structure and adhesion of bioaggregates such as granular sludge and biofilms.As the decisive factor affecting the filtration performance of dynamic membrane bioreactor（DMBR）,the structure and hydraulic resistance of biofilm formed on DMBR support layer are inseparable from its structural EPS.In this study,how the structural EPS represented by alginate-like extracellular polysaccharide（ALE）and amyloid-like protein（AP）correlated to biofilm structure and hydraulic resistance was elucidated by analyzing the filtration performance,morphological structure and structural EPS composition of the biofilm formed on DMBR support layer.The research is divided into three stages.The first stage is a pre-experiment.The cell lysis and extraction yield of different EPS extraction methods are compared to screen out optimal EPS extraction method and a structural EPS analysis method for biofilm formed on DMBR support layer is established;Then in the second stage of the formal experiment,the simulated domestic sewage was used as the influent to make research on the relationship between the structural EPS,the support layer biofilm structure and hydraulic resistance under different SRT conditions;Finally,in the third stage of the formal experiment,using real domestic sewage as the influent to make research on the relationship between the structural EPS and the biofilm structure of the support layer and the hydraulic resistance under different process conditions.The main findings are as follows:（1）A structural EPS analysis method for DMBR support layer biofilm was established.For activated sludge in DMBR,by comparing the degree of cell lysis and extraction yield of different methods,it was found that the heating-Na₂CO₃ method has the two advantages of higher EPS extraction yield and lower degree of cell lysis,which was used as the basic method for total EPS extraction in this study.The identification test demonstrated the reliability of the alginate-like extracellular polymer extraction method,indicating that ALE exists in the DMBR support layer biofilm.（2）Using simulated domestic sewage as the influent,and running DMBR under long and short SRT,the hydraulic resistance of the support layer biofilm was positively correlated to the proportion of amyloid-like proteins and negatively correlated to the content of alginate-like extracellular polysaccharides.This suggests that amyloid-like proteins play a more important role in forming dense,hydrophobic support biofilms than alginate-like extracellular polysaccharides.（3）Using real domestic sewage as the influent,running DMBR in split MBBR+DMBR,combined MBBR+DMBR and pure DMBR process,it was also found that the hydraulic resistance of the support layer biofilm was positively correlated to the proportion of amyloid-like protein and negatively correlated to the content of alginate-like extracellular polysaccharides.It was further shown that amyloid-like protein played a more important role in forming a dense,hydrophobic support layer biofilm than alginate-like extracellular polysaccharides.（4）Three DMBR reactors with different processes can achieve excellent removal of organic pollutants,which reflects the excellent wastewater filtration performance of dynamic membrane bioreactors.Among them,the combined MBBR+DMBR process has lower average effluent turbidity and stable water quality than the other two.（5）The addition of MBBR fillers is beneficial to reduce the hydraulic resistance of the biofilm formed on the support layer and the frequency of membrane biofouling.Whether the reactor is run with the split MBBR+DMBR or combined MBBR+DMBR process,the biofilm grown on the MBBR packing can adhere to the DMBR support layer after shedding and reduce the organic load in the reactor,which promoted the ability of DMBR.A loose,porous biofilm is formed,which effectively alleviates membrane fouling.（6）The type and content of structural extracellular polymers are the key factors affecting the biofilm structure and hydraulic resistance of the support layer of the dynamic membrane bioreactor.The research on the adjustment measures of the structural EPS yield of the DMBR support layer biofilm and the control scheme of the membrane fouling caused by the structural EPS will provide a broad application prospect for the resource utilization of wastewater.