Elsevier

Water Research

Volume 37, Issue 5, March 2003, Pages 1192-1197
Water Research

Technical note
Characteristics of microfiltration membranes in a membrane coupled sequencing batch reactor system

https://doi.org/10.1016/S0043-1354(02)00534-1 Get rights and content

Abstract

Factors affecting filtration performance were investigated in a sequencing batch reactor (SBR) coupled with a submerged microfiltration module. Special bioreactors for aerobic and anoxic phases were specifically designed in order to differentiate the effect of dissolved oxygen (DO) from that of mixing intensity, on membrane filterability. When the filterability of a submerged microfilter was examined at each SBR phase, DO concentration, as well as mixing intensity proved to have a major influence on the membrane performance regardless of the SBR phase. A higher DO concentration resulted in a slower rise in TMP, corresponding to less membrane fouling, which was investigated in depth through a series of analyses including resistance measurements and compressibility of the cake layer as well as particle sizes as a functions of DO for both aerobic and anoxic phases in SBR.

Introduction

Sequencing batch reactor (SBR) processes offer several advantages over other types of activated sludge reactors. In particular, the hallmark of SBR design is its inherent flexibility of cyclic phasing. The cycle format can be easily modified at any time to offset changes in process conditions, influent characteristics or effluent objectives [1], [2], [3]. However, SBR has a potential risk in that poor clarification and a turbid effluent are associated with it.

Combining a membrane process with SBR provides procedural advantages for both processes. The use of membranes can reduce the operation period since membrane separation requires no settling and clear-water can be extracted even during the mixing time. In addition, the separation of biological sludge by means of a membrane leads to complete retention of biomass resulting in a high mixed liquor suspended solids (MLSS) concentration. This allows a very high treatment capacity for a membrane-coupled sequencing batch reactor (MSBR) [4]. In a MSBR system, it would be very important, and also difficult to select the most appropriate SBR phase in which membrane filtration could be performed at its best. The reason for this is that many types of SBR systems are currently in use and include continuous influent/time based, non-continuous influent/time based, volume based, an intermittent cycle system, and various other system modifications [5], [6], [7], [8]. Although combination of membrane filtration and SBR should be reengineered to get a MSBR of good performance, the efficiency of membrane process in MSBR would certainly be dependent on the physicochemical and biological conditions of each SBR phase, as well as the type and cycle format of the SBR.

However, little information is available on comparison of membrane filtration characteristics between various SBR phases in MSBR. In this study, as an initial step to construct an efficient MSBR system, was taken and factors affecting filtration performance in MSBR were investigated in terms of dissolved oxygen (DO), soluble COD, cake properties, etc. Special bioreactors were specifically designed for aerobic and anoxic phases, in order to differentiate the effect of DO from that of mixing intensity on membrane filterability.

Section snippets

Materials and methods

The SBR system was run parallel with the MSBR. The SBR was operated at 4 h/cycle (6 cycles per day) under the following sequence: (1) filling-10 min, (2) aerobic-120 min, (3) mixed anoxic-60 min, (4) settling-40 min and (5) drawing-10 min. The exchange rate was 50% of the full reactor liquid volume. The temperature of the bioreactor was maintained at a constant temperature of 25°C using a water bath. In MSBR, a hollow fiber membrane module (Mitsubishi Rayon Co., Ltd.) was immersed in the bioreactor

Wastewater Treatment efficiency

In order to compare treatment efficiencies between SBR and MSBR, the conventional SBR system was run parallel with the MSBR. Both systems have MLSS concentrations of 5100±500 mg/L and 2 h of aerobic and 1 h of anoxic phases. The quality of the membrane permeate, in the case of the MSBR was slightly better than the SBR effluent with respect to all tested parameters. The effluent COD of the conventional SBR ranged from 9 to 15 mg/L achieving average COD removal efficiency of 96%, whereas the COD of

Conclusions

In a membrane coupled SBR (MSBR) system, membrane filtration characteristics were investigated as a function of the SBR phase and operating parameters using a specifically designed bioreactor. The following conclusions can be drawn:

  • (1)

    In MSBR, a higher DO gives rise to a better filterability because the higher DO results in lower specific resistance of cake layer which may be attributed to not only a greater particle size but also a higher porosity.

  • (2)

    A higher DO produces less amount of soluble

Acknowledgments

This work was supported by Korea Research Foundation Grant (KRF-2001-041-E00395). The authors are grateful to the Australian Research Council and the Korean Science and Engineering Foundation for support for Dr. Kyu-Jin Kim. The authors also wish to thank the Mitsubishi Rayon Co. Ltd., Japan, for providing the hollow fiber membranes.

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