Study On Membrane Fouling Characteristics Of Novel Rotating Membrane Bioreactors

Membrane bioreactor (MBR) is an efficient technology using membrane filtration for wastewater treatment; however, the membrane fouling is the main bottleneck in the market popularization and application of MBR. The previous study has proved that increasing the shear rate on membrane surface is one of the most effective ways to mitigate fouling. And dynamic shear-enhanced filtration utilizing moving membrane modules to obtain high shear rate is a hot spot of research. But the fouling characteristics of dynamic shear-enhanced filtration MBR, as well as the change in hydrodynamic conditions induced by the movement of membrane module is still needed to be investigated.Employing two novel dynamic shear-enhanced filtration MBRs, i.e. rotating tubular MBR (RTMBR) and rotating flat-sheet MBR (RFMBR), this study analyzed the basic capability of RTMBR such as oxygen transfer, developed membrane fouling models using partial least squares (PLS), and investigated the effect of hydrodynamic conditions changed by mechanical forces on membrane fouling using particle image velocimetry (PIV) in RFMBR, providing the theoretical guidance and reference for design and application of dynamic shear-enhanced filtration MBR.The main research conclusions are summarized as following:(1) As the rotary speed of RTMBR rose, both oxygen transfer coefficient and oxygen transfer efficiency exponentially increased, and the fine bubble aerator was superior in oxygen transfer than coarse bubble aeration device. The PIV images and Reynolds number in the bioreactor illustrated that as the rotary speed of membrane module increased, the turbulence of the fluid was intensified.(2) It is feasible to employ PLS to predict membrane fouling rate (MFR) in RTMBR using rotary speed (RS), aeration rate (AR), suspended solids (SS), extracellular polymeric substances (EPS) and mean particle size (MPS) as predictor variables. The PLS models owned good goodness-of-fit, robustness and predictive power. Model results suggested that membrane fouling rate decreased as RS increased, and the impact of RS on MFR was relatively significance, indicating shear-enhanced membrane filtration in our MBR system was effective. Furthermore, the factors in order of decreasing influences on membrane fouling rate were MLSS, EPS, RS, MPS and AR.(3) The fluid velocity had a very slight impact on membrane fouling in RFMBR. With the increase in fluid velocity, the fouling did not necessarily mitigate. Membrane fouling was strongly affected by turbulence intensity. In detail, the variations in turbulence intensity had a great negative correlation with the changes in fouling rate, i.e., the turbulence induced by fluctuating velocities was helpful for alleviating fouling. When comparing the membrane fouling between RFMBR and a common MBR (CMBR), it can be concluded that the fouling rate for RFMBR was much slower than that for CMBR when consuming the same energy, indicating a more outstanding filtration performance of RFMBR.