Preparation of Polydimethylsiloxane–Polyvinylidene Fluoride Composite Membranes for Phenol Removal in Extractive Membrane Bioreactor

Abstract

The extractive membrane bioreactor (EMBR) system combining a membrane process and a biological process has been developed to extract and biodegrade recalcitrant organic pollutants in wastewater. Removal of the organics such as phenol by EMBR requires an effective membrane to selectively extract the organic compounds while rejecting water and other harsh inorganic components. In this work, novel composite membranes consisting of a highly porous substrate, made by tiered polyvinylidene fluoride (PVDF) nanofibers with ultrafine nanofibers on top (61 ± 12 nm in diameter), and a dense polydimethylsiloxane (PDMS) selective layer have been fabricated. We have investigated (1) the effect of the pore size of PVDF nanofibrous substrates, (2) the effect of PDMS preparation method, and (3) the effect of prewetting agent on the resultant composite membranes’ morphologies, mechanical properties, and phenol removal performance. Compared with the symmetric substrate with a nanofiber diameter of 129 ± 13 nm, the tiered substrate can effectively support a uniform and defect-free PDMS coating. This is attributed to the smaller surface pore size of the tiered substrate as a result of its top ultrafine nanofibers. Besides, the use of partially precross-linked PDMS coating solution with increased viscosity and 50 wt % glycerol aqueous solution as the prewetting agent to fill the substrate pores is preferred in order to mitigate PDMS intrusion. On the basis of the resistance model, the overall membrane resistance decreases with the decrease of the PDMS intrusion level, giving rise to a higher overall mass transfer coefficient, k 0, for phenol removal. With the above-mentioned factors being taken into account, the first PDMS-coated PVDF nanofibrous composite membrane has been developed to remove phenol with a high k 0 (over 4 times higher than the existing commercial PDMS tubular membrane) for EMBR. This study provides insights and guidelines for fabricating highly efficient membranes for organic removal in the EMBR process.

Development of high-performance polydimethylsiloxane-based nanofibrous composite membranes for phenol removal from wastewater

“…The superiority of this configuration is exemplified by an EMBR where the receiving solution is biomedium [28,29,37]; (2) the capability to offer more specific and efficient point-source treatment of individual industrial effluent unlike the centralized classical techniques [37,48]; and (3) the low energy consumption due to operation at room temperature and atmospheric pressure [28,29,37,49]. In order to get a deeper understanding of the aqueous-aqueous extractive systems, a specific process, namely an EMBR process with biomedium as the receiving solution, is selected for detailed elaboration in the following section.…”

“…EMBR can be employed to treat a great number of toxic organic pollutants ranging from aromatic compounds (e.g. phenol [28,29,37], nitrobenzenes [35,51], anilines [34,48,55] and monochlorobenzene [54])…”

“…As an alternative, electrospinning is a versatile and simple technique to generate highly porous nanofibrous membranes with interconnected pore structures, controllable pore sizes, large surface area to volume ratio and excellent mechanical strengths [28,41]. These unique features, especially the high porosity,…”

“…The dope solution is stirred at elevated temperature for some time until a homogeneous mixture is formed. Subsequently, the dope solution is cooled down to room temperature and degassed overnight before use [28,[40][41][42]112]. (1) During the process of electrospinning, the dope solution is injected by a syringe pump at a certain flow rate, through a series of thin PTFE tubing into the feeding pipe and finally the nozzles;…”

“…Technologies currently available for phenol treatment include: (1) traditional methods such as distillation [14,15], extraction [16], adsorption [17], chemical oxidation [18,19], and biodegradation [20]; (2) advanced methods such as photo oxidation processes [21,22] and membrane separation technologies [23,24]; and (3) hybrid systems which combine traditional and advanced techniques, for example, reverse osmosis coupled with adsorption process [25], membrane bioreactor (MBR) [26], extractive membrane bioreactor (EMBR) [27][28][29], membrane aromatic recovery system (MARS) [30] and membrane pervaporation [31]. As presented in dealing with treatment of phenolic pollutants.…”