Changes in biofilm architecture with addition of membrane fouling reducer in a membrane bioreactor
Introduction
Membrane bioreactor (MBR) processes have been widely applied to wastewater treatment in the past decades due to their exceptional separation capabilities. Thousands of MBR plants are currently in operation over the world. However, biofouling, a significant problem in MBR, remains to be solved because frequent membrane cleaning and replacement are required, thereby increasing in operation and maintenance costs. Therefore, many studies have been focused on the alleviation of membrane fouling, for example, by backwashing [1], aeration [2], intermittent suction [3], module modification [4], [5], and addition of an inorganic coagulant [6] in attempts to control membrane fouling in MBR.
A membrane fouling reducer (MFR), a type of cationic polymer, was recently developed to control membrane fouling in MBR [7]. However, the details of how MFR reduces membrane fouling have not been fully clarified yet. To thoroughly elucidate the mechanism of how MFR alleviates membrane biofouling, an analysis of biofilm architecture is needed because the biofilm, which is formed on the membrane surfaces is mainly responsible for the loss of membrane filterability in MBR. However, very few studies have been reported, in which biofilm architecture has been examined [8], [9], [10].
The purpose of this study was to elucidate how MFR mitigates membrane fouling, with a particular focus on changes that occur in biofilm architecture. The spatial distributions of porosities and biovolumes along the length of membrane fibers were analyzed by confocal laser scanning microscopy (CLSM) and image analysis techniques.
Section snippets
MBR systems
Two MBRs, a control MBR (conventional type of MBR) and membrane fouling reducer-added MBR were operated over 2 months prior to membrane filtration. Fig. 1 shows a schematic diagram of the experimental setup used to evaluate the two MBRs. Compressed air (air flow rate = 2 L/min) was supplied through a bubble stone on the bottom of each reactor to provide dissolved oxygen and turbulence. Both MBRs were run in parallel under the same experimental conditions (Table 1), except that MFR was added only
Effect of MFR addition on membrane permeability
Fig. 3 shows TMP increase as a function of time for the control and MFR reactor. The TMP reached 30 kPa in 5.2 days in the MFR reactor, while only 0.7 days was required in the control reactor, indicating that the membrane filterability of the MFR reactor was 7.4 times higher than that of the control reactor. This improvement in membrane permeability with MFR has been previously reported [7].
To further study the effect of MFR on the membrane filterability, different doses of MFR were applied in
Conclusions
In this study, the mechanism of how MFR addition to an MBR reduced membrane fouling was investigated. The following conclusions were reached:
- (1)
Adding MFR to a conventional MBR gave rise to the flocculation of activated sludge, creating a larger floc size and lower attached biomass on membrane surface and, as a result, membrane filterability was substantially enhanced.
- (2)
Soluble foulants in the bulk phase of MBR, such as soluble COD and soluble EPS were entrapped in the microbial flocs during the
Acknowledgements
The authors wish to thank the Korean Ministry of Science & Technology for their financial support under Grant M6-0403-00-0098. The authors also thank the National Instrumentation Center for Environment Management (NICEM) for the use of the confocal laser scanning microscope system, and Nalco company for supporting MPE.
References (21)
- et al.
Application of air backflushing technique in membrane bioreactor
Water Sci Technol
(1997) - et al.
Effects of aeration on suction pressure in an submerged membrane bioreactor
Water Res
(1997) - et al.
Membrane filtration characteristics in membrane coupled activated sludge system—the effect of physiological states of activated sludge on membrane fouling
Desalination
(1998) - et al.
Optimization model of submerged hollow fiber membrane modules
J Membr Sci
(2004) - et al.
Potentials and limitation of alum or zeolite addition to improve the performance of submerged membrane bioreactor
Water Sci Technol
(2002) - et al.
Three-dimensional biofilm structure quantification
J Microbiol Methods
(2004) - et al.
Removal of soluble COD by a biofilm formed on a membrane in a jet loop type membrane bioreactor
Water Res
(2005) - et al.
Characterization of biofilm structure and its effect on membrane permeability in MBR for dye wastewater treatment
Water Res
(2006) - et al.
Effect of DO concentration on biofilm structure and membrane filterability in submerged membrane bioreactor
Water Res
(2006) - et al.
Correlation between dissolved oxygen concentration, microbial community and membrane permeability in a membrane bioreactor
Process Biochem
(2006)
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