Investigation Of The Membrane Foulingbehavior Of EPS In Membrane Bioreactor Coupled With Worm Reactor

A membrane bioreactor coupled with a Worm Reactor was proposed for simultaneous wastewater treatment and sludge reduction, and the combined system indicated excellent sludge reduction efficiency and wastewater treatment performance. It was noted that worm predation could cause the changes in EPS characteristics. EPS was identified as the key membrane foulants. The predated sludge recycle containing changed EPS may induce the variation of membrane fouling.This research focused on investigation the membrane fouling behavior of EPS in MBR coupled with worm reactor. We used the FTIR and EEM to analyze the composition and content of EPS in hybrid MBR. We utilized the batch filtration experiments, CLSM and AFM to investigate the fouling potential of EPS in hybrid MBR. We used the XDLVO theory to research the relationship between EPS and sluge aggregation in hybrid MBR. We utilized the PCR-DGGE and16sRNA to study the rule of development of microbial community in hybrid MBR. The mechanism of membrane fouling mitigation in hybrid MBR was thoroughly researched.The membrane fouling and EPS characteristics of the control and hybrid MBRs were studied. It was revealed that the recycling of predated sludge from the worm reactor to the MBR could reduce the rate of membrane fouling, change the characteristics of soluble EPS, and decrease the content of protein and carbohydrate. The concentration of bound EPS was reduced11.6mg/g MLSS. The fluorescence intensity of tryptophan protein-like substances in the bound EPS of the S-MBR was41%lower than that of the C-MBR. Meanwhile, it was seen that the Peak locations of tryptophan protein-like substances demonstrated a blue-shifted toward shorter wavelength along the emission axis.The filtration characteristics of bound EPS in the hybrid MBR and in the control MBR were studied. The results indicated that the predated sludge recycle decreased adsorption efficiency for protein in the bound EPS in the hybrid MBR. This reduced the bio-volume of protein on the membrane fouled by the bound EPS in the hybrid MBR, and the bio-cake in the filtration of bound EPS in the hybrid MBR showed a larger porosity than that in the filtration of bound EPS in the control MBR. The interaction energies between the bound EPS constituents and the membrane surface were decreased. Therefore, the flux decline of the bound EPS in control MBR decreased to76%, whereas the bound EPS in the hybrid MBR resulted in only67%of flux decrement.The fouling potentials of soluble EPS in the control MBR and the hybrid MBR were evaluated. The result showed predated sludge recycle significantly decreased the proportion of aromatic protein-like substance in soluble EPS, resulting in the soluble EPS tend to be less hydrophobic. Apparently, the predated sludge recycle decreased the interaction energy between soluble EPS and membrane (Adhesion) and between soluble EPS themselves (Cohesion). The fouling layer formed by soluble EPS in the hybrid MBR showed a higher porosity than fouling layer formed by the soluble EPS in the control MBR. Meanwhile, lower biovolume and thinner average thickness of fouling layer formed by the soluble EPS in the hybrid MBR compared to fouling layer formed by the soluble EPS in the control MBR were found. Accordingly, the soluble EPS in the hybrid MBR resulted in only74.0%of flux decrement, which was19.2%lower than that of soluble EPS in the control MBR (c.a.93.2%decrement).The sludge aggregation and microbial community structure of the control and hybrid MBRs were studied. It was shown that the decreased secondary energy minimums and increased energy barriers in the interaction energy profiles of slime, LB-EPS and TB-EPS due to predated sludge recycle were found. It might be one reason for the reduction of sludge aggregation in the hybrid MBR. Further identification of the bacterial populations suggested that predated sludge recycle decreased the content of Betaproteobacteria and Gammaproteobacteria and change in Alphaproteobacteria. Therefore, the microbial community structure were changed due to the predated sludge recycle.Based on above analysis, it could be concluded that the decreased content of bound EPS, the changed composition of soluble and bound EPS, the reduced fouling potential of soluble and bound EPS, the decreased sludge aggregation and changed microbial community structure due to the predated sludge recyce were important responsible for the improved membrane permeability in the hybrid MBR.