A study on the high-flux MBR system using PTFE flat sheet membranes with chemical backwashing

Currently, polyvinylidene fluoride (PVDF) membranes are widely used because of their chlorine resistance and durability. However, membrane bioreactor (MBR) processes still have obstacles to overcome to be cost effective for wastewater treatment. To overcome these obstacles, stable, long-term operations of MBRs with high permeate flux and low membrane fouling are strongly desired. In this study, both a lab and a pilot scale membrane system with new polytetrafluoroethylene (PTFE)-based flat sheet membrane modules were operated to monitor the effectiveness of chemical backwashing for membrane fouling control. There were two operation modes in the lab experiment. One (MBR2) was applied by chemical backwashing once a day and the other (MBR1) was operated without chemical backwashing. The transmembrane pressure (TMP) remained stable in MBR2 after 25 days, while the TMP increased continuously and eventually reached the upper limit in MBR1. The Rt (total resistance), Rc (cake resistance) and Rf (fouling resistance) of both MBR1 and MBR2 were 8.88 × 1011 m− 1, 3.52 × 1011 m− 1, 4.07 × 1011 m− 1 and 5.34 × 1011 m− 1, 2.10 × 1011 m− 1, 1.91 × 1011 m− 1, respectively, after 30 days of operation. In the pilot scale test, chemical backwashing had similar effects on Rf, but minimal influence on the control of Rc. Chemical backwashing was effective for controlling Rf, but there were differences in Rc reduction by aeration according to membrane position. High quality effluent from filtration indicated that the activity of the microorganisms had not been harmed by chemical backwashing. Through lab and pilot scale experiments, it was confirmed that using a PTFE flat sheet membrane with chemical backwashing in an MBR system could provide high flux, twice as much as that from a conventional system. In conclusion, PTFE membranes have significant potential as next generation membrane materials replacing the currently used PVDF membranes, and chemical backwashing will compensate for the weaknesses associated with the use of flat sheet membranes in field applications.

► PTFE membranes were used to monitor the effectiveness of chemical backwashing.
► Using a PTFE flat sheet membrane with chemical backwashing could provide high flux.
► Fouling in PTFE flat sheet membranes could be controlled by chemical backwashing.
► PTFE membranes have potential to replace the currently used PVDF membranes.