Dynamic membranes with sparse nanofibers as the skeletons yield better and more stable effluent quality without sacrificing the flux in bioreactors

Abstract

Previous studies found that the inhabitation of filamentous bacteria on the support materials with large apertures in dynamic membrane bioreactor (DMBR) could stabilize the DM structure and resulted in stable effluent quality. However, it is hard to cultivate the filamentous bacteria on support materials in DMBR intentionally. In present study, a polyvinyl alcohol (PVA) nanofiber layer was coated on 180-μm nylon mesh to simulate the inhabitation of filamentous bacteria. The nanofiber coated mesh with 1 h spinning time (referred as PVA-1h) had a similar porosity (14.9%) to that of 25-μm nylon mesh and dominant pore size of 1.0–2.5 μm. Short-term test indicated that the PVA-1h had a low initial effluent turbidity of 5.3 NTU and could form DM within 5 min. Long-term test in DMBR demonstrated that better and more stable effluent quality (0.71 ± 0.31 NTU) was achieved by PVA-1h compared to typical used support materials of 25-μm mesh (1.04 ± 0.60 NTU). However, the PVA-1h had an operation flux of 30–50 L/(m2·h) with a water head loss ≤2 cm, which was comparable with the 25-μm mesh but much greater than that of 2.6-μm mesh (<5 L/(m2·h)). In addition, the filtration resistance change between the PVA-1h and 25-μm mesh were very similar. Therefore, this study demonstrated that with proper density of nanofiber as the skeletons, DMs would be formed more quickly and stably, resulting in better and more stable effluent quality in DMBR without sacrificing operation flux.