Application of Bacterial Quorum Quenching in a MBR with a Multi-Layer Hollow Fiber Module for Wastewater Treatment

Abstract

Membrane fouling is one of the major problems which not only reduce membrane permeability but also increase energy cost in operation of a membrane bioreactor (MBR) for wastewater treatment. Among many approaches for alleviating membrane fouling, the quorum quenching (QQ) has been introduced as simple and promising biological approach

QQ is the process of disrupting cell-to-cell communication of microorganisms, as known as quorum sensing (QS). Previous studies have revealed that bacterial QQ with lactonase producing bacteria, Rhodococcus sp. BH4, mitigates the biofouling in MBR. The mitigation of biofouling was described by delay in trans-membrane pressure (TMP) rise-up. Also, QQ effect was verified in pilot-scale flat sheet MBR fed with a real wastewater. In this study, we focused on the potential application of bacterial QQ to a hollow fiber MBR because approximately 80% of MBR plants in operation worldwide are equipped with a hollow fiber (HF) module instead of a flat sheet module. While narrower spacing of fibers are unavoidable in a in a multi-layer HF module, foulants are more likely to deposit in a multi-layer HF module than a flat sheet module. To manipulate such a problem, a lab-scale multi-layer HF module was fabricated with similar spacing of fibers to a commercial one and then QQ-bead entrapping Rhodococcus sp. BH4 was applied. However, QQ effect was not observed in a multi-layer HF module unlike in a mono-layer HF module. Two new approaches were carried out to improve the QQ efficiency in a multi-layer HF module. Firstly, QQ bacteria (BH4) without any type of entrapment was directly inserted into the MBR, so that QQ bacteria can freely move to decompose signal molecules inside the multi-layer HF module. However, BH4 without entrapment did not show QQ activity. It is speculated that QQ activity of BH4 is suppressed by other microorganisms which are more competitive to survive in MBR The second approach was to entrap BH4 to protect them against other microorganisms as well as to apply backwashing process to make BH4 contact easier signal molecules inside of the multi-layer hollow fiber module. As entrapped BH4 was introduced to the backwashing system, BH4 could delay TMP rise-up by 1 fold compare to the MBR operated with backwashing but without entrapped BH4. But the QQ effect disappeared when backwashing stopped. It seems like physically removing foulants from inside of multi-layer module could help BH4 to contact signal molecules easier and thus to mitigate biofilm formation on the surface of membrane.