Photocatalytic membrane filtration and its advantages over conventional approaches in the treatment of oily wastewater: A review

Abstract

Clean water supply has become one of the biggest challenges of the 21st century; therefore, water source protection is of increasing importance. Beyond environmental protection reasons, economic concerns-derived from increasing costs of processing water and wastewater discharge-also prompt industries to use advanced wastewater treatment methods, which ensure higher purification efficiency or even the recycling of water. Therefore, highly effective treatment of oily wastewaters has become an urgent necessity because they are produced in high quantities and have harmful effects on both the environment and human population. However, high purification efficiency can be difficult to achieve, because some compounds are hard to eliminate. Conventional methods are effective for the removal of floating and dispersed oil, but for finely dispersed, emulsified and dissolved oil advanced methods must be used, such as membrane filtration which exhibits several advantages. The application of this technology is restricted by fouling-the major limiting factor-which jeopardizes the membrane performance. In order to reduce fouling, in-depth research is being conducted to make the treatment of oilcontaminated water technically and economically feasible. The present work aims to review the conventional oil separation methods with their limitations and to focus on membrane filtration, which ensures significantly higher purification efficiencies, including the main problem: the flux reduction caused by fouling. This paper also discusses promising solutions, such as membrane modification methods, mostly with hydrophilic and/or photocatalytic nanoparticles and nanocomposites, overviewing the efforts that are being made to develop feasible technologies to treat oil-contaminated waters.

Investigation of the applicability of TiO2, BiVO4, and WO3 nanomaterials for advanced photocatalytic membranes used for oil‐in‐water emulsion separation

“…The presented (i) high flux (464 L m −2 h −1 ) which exceeded all the mentioned results, (ii) the estimated low FDR (FDR = 45%) and (iii) the high FRR (FRR = 66%) in the case of pure BiVO 4 (BV‐I) coating, and finally, (iv) the effective solar photocatalytic recovery—especially in the case of the TiO 2 (80%)/BiVO 4 (20%) composite—indicate that BiVO 4 photocatalysts and their composites deserve attention in the research area of nanocomposite‐based photocatalytic membranes and that they are worth applying for oil‐in‐water emulsion separation. Investigation of other immobilization methods—like blending or chemical immobilization—is also highly recommended as during long‐term application, these methods are more beneficial to preparing composite membranes 44 . Although WO 3 did not live up to our expectations in the present study, the investigation of three‐component composites is recommended as they are promising in achieving low band gap and suppressed recombination ratio at the same time.…”

“…Therefore, photocatalytic membrane reactors (PMRs)—equipped with photocatalyst‐modified membrane surfaces—are able to eliminate organic fouling contaminants and to recover the flux via an efficient and chemical‐free way that is based on the photocatalytically generated oxidative species 40,41,43,44 . Immobilization of photocatalytic nanoparticles can be carried out by physical deposition, 37,45,46 cross‐linking, 47 in situ precipitation, 33 dip coating, 48 grafting, 35 blending, 34,39,43,49 and so forth.…”

The Potential Role of Membrane Technology in the Removal of Microplastics from Wastewater

“…Ultrafiltration membrane is presently receiving attention in photocatalysis with treatment in wastewater. Such photocatalytic ultrafiltration membranes are produced with the incorporation of inorganics [76].…”

Statistical Analysis of Synthesis Parameters to Fabricate PVDF/PVP/TiO2 Membranes via Phase-Inversion with Enhanced Filtration Performance and Photocatalytic Properties

“…[ 12 ]. Additives can be included in the membrane matrix via different methods, such as: (i) coating and grafting, in which the membrane is modified after its fabrication; and (ii) blending, which includes the addition of the given material in the matrix during the fabrication process [ 6 , 13 , 14 ]. The functionalization of membranes can enhance the immobilization of additives, thereby enhancing their stability and properties [ 15 , 16 , 17 , 18 ].…”

“…The addition of materials can increase the permeability, selectivity, flux, and anti-fouling properties of PVDF membranes [ 6 , 19 , 20 , 21 ]. Hydrophilic polymers such as polyvinylpyrrolidone (PVP) [ 10 , 14 , 15 ] and polyethylene glycol (PEG) [ 22 , 23 ] are widely used for the enhancement of the membrane, as well as hydrophilic nanoparticles, for instance, such as silicon dioxide (SiO 2 ) [ 24 ], zinc oxide (ZnO) [ 19 ], and titanium dioxide (TiO 2 ) [ 21 , 25 ]. Using nanoparticles with photocatalytic properties can also result in self-cleaning membranes when activated by light [ 14 , 26 ].…”