Catalytic Ozonation and Membrane Contactors—A Review Concerning Fouling Occurrence and Pollutant Removal

Abstract

Membrane filtration has been widely used in water and wastewater treatment. However, this process is not very effective for the removal of refractory organic compounds (e.g., of pharmaceutical origin). Coupling membrane filtration with ozonation (or other Advanced Oxidation Methods) can enhance the degradation of these compounds and, subsequently, the incidence of membrane fouling (i.e., the major problem of membrane uses) would be also limited. Ozonation is an efficient oxidative process, although ozone is considered to be a rather selective oxidant agent and sometimes it presents quite low mineralization rates. An improvement of this advanced oxidation process is catalytic ozonation, which can decrease the by-product formation via the acceleration of hydroxyl radicals production. The hydroxyl radicals are unselective oxidative species, presenting high reaction constants with organic compounds. An efficient way to couple membrane filtration with catalytic ozonation is the deposition of an appropriate solid catalyst onto the membrane surface. However, it must be noted that only metal oxides have been used as catalysts in this process, while the membrane material can be of either polymeric or ceramic origin. The relevant studies regarding the application of polymeric membranes are rather scarce, because only a few polymeric materials can be ozone-resistant and the deposition of metal oxides on their surface presents several difficulties (e.g., affinity etc.). The respective literature about catalytic membrane ozonation is quite limited; however, some studies have been performed concerning membrane fouling and the degradation of micropollutants, which will be presented in this review. From the relevant results it seems that this hybrid process can be an efficient technology both for the reduction of fouling occurrence as well as of enhancement of micropollutant removal, when compared to the application of single filtration or ozonation.

Catalytic Membrane Ozonation

“…When a solid material is used as catalyst, catalytic ozonation can be also divided in two sub-categories. Whether the catalyst is a solid material, suspended in the aqueous phase (usually in powdered form), the process is termed as "single heterogeneous catalytic ozonation"; whereas the process is commonly referred as "membrane catalytic ozonation", whether the solid material is appropriately immobilized onto the surface of membrane [4]. In this hybrid ozonation process the membrane can act simultaneously as catalyst for the acceleration of the hydroxyl radicals' production, as well as a membrane contactor for the improvement of transfer and diffusion of ozone gas to the aqueous phase during treatment [9].…”

“…As a consequence the use of common polymeric membrane contactors are quite limited [12]. It seems that only polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and polydimethylsiloxane (PDMS) polymeric membranes are presenting sufficient resistance, when contacting with ozone [4,14]. Alternatively, ceramic membranes can be often selected [12].…”

“…There are five main factors that influence the catalytic performance of a membrane: (1) surface charge; (2) coating times; (3) pore size; (4) preparation method regarding the metal oxide deposition; and (5) adsorption capacity [15,18,27]. More specific information about how these factors are influencing the catalytic membrane ozonation can be found in the respective reference of Psaltou and Zouboulis [4].…”

“…The decontamination technologies generally have to be effective, cheap and ecofriendly in order to be widely applicable [1]. The Advanced Oxidation Processes (AOPs) present relevant advantages; among them belongs the membrane catalytic ozonation, a hybrid technique that can combine the processes of catalytic ozonation and of membrane filtration [4].…”

“…In membrane ozonation there is a strong linear relationship between the BrO 3 − concentration in the permeate and the dissolved ozone concentration [36]. 4.…”