Abstract
The membrane bioreactor (MBR), as one of the promising technologies, has been widely applied for treatments of wastewater. However, serious membrane fouling and low microbial activity have been reported as major problems hindering the development of the MBR. To overcome these drawbacks, we intend to improve the MBR process in the view of membrane surface modification and efficient granular bacteria cultivation. In the present study, immobilized photosynthetic bacteria integration with graphene oxide (GO)/polysulfone (PSF) composite membrane separation (IPMBR) was first applied for textile wastewater treatment. Due to the high activity of immobilized cells, the IPMBR system exhibited higher efficiency on the removal of color, ammonia–nitrogen, and chemical oxygen demand than the conventional MBR system. In comparison with a pure PSF membrane, GO/PSF composite membrane presented the higher hydrophilicity (water contact angles of 62.9°) and more attractive permeability (178.5 L/m2h) by reducing the adhesion of hydrophobic foulants. During the whole operation, the immobilized photobioreactor exhibited approximately seven times higher membrane permeability that that of the conventional MBR. Meanwhile, the effect of the structure and character of immobilized photosynthetic bacteria on the membrane fouling reduction was investigated in detail. The change of extracellular polymeric substance concentration, settleability and particle size of flocs was very beneficial to alleviate membrane fouling. As a result, this research will open a new avenue for developing efficient and anti-fouling MBR technology in the future.
Highlights
The surface structure of the prepared graphene oxide (GO)/PSF composite membranes was characterized by surface morphology for cell-encapsulated parelectron microscopy (SEM) images and is shown in Figure 2a and b
As apparent from the figure, it was found that the modified GO/PSF membrane presented the rough surface owing to the exposure of blended GO nanosheets
The cross-sectional image displays that the prepared ultrafiltration membranes present a typical construction with an asymmetric finger-like porous sub-layer and a dense skin layer
Summary
Treatment of dye wastewater is a very difficult task, since it still has properties of high color, heavy poisonousness and is non-biodegradable even in a very low concentration [3,4]. Graphene oxide (GO) nanosheets, as a new type of two-dimensional structural material, gained more attentions in membrane modification due to their high surface area, strong hydrophilicity of oxygen-contained groups, and good compatible and mechanical properties [31]. Based on the previous observations and our research, we intend to develop a novel immobilized PSB integrated with GO/polysulfone (PSF) composite membrane for methylene blue wastewater treatment, in which gathering of highly active PSB on chemical oxygen demand (COD) and NH3 -N removal can be performed on a large scale and membrane biofouling can be effectively mitigated by the incorporation of GO nanosheets and granular bacteria. The variations on the properties and microscopic structure of flocs in two MBRs, such as settleability, particle size and extracellular polymeric substance concentration (EPS) were analyzed for a better understanding of the anti-fouling behavior
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