Pressurized membrane photoreactors

MoUnari R, Caruso A, Argurio P and Poerio T (2008), Degradation of the drugs Gemfibrozil and Tamoxifen in pressurized and de-pressurized membrane photoreactors using suspended polycrystalline TiOj as catalyst , / Membr Sci, 319, 54-63. 

Closed and continuous procedures were used to investigate the behavior of pressurized membrane photoreactors. The obtained data of the closed membrane system showed a complete photodegradation of GEM and TAM, with an abatement of 99% after 20 min and a mineralization higher than 90% after approximately 120 min. 

Membrane distillation - photocatalysis To solve the problem of membrane fouling observed in the pressure-driven membrane photoreactor, Mozia et al. [90] studied a new type of PMR in which photocatalysis was combined with a direct contact membrane distillation (DCMD). MD can be used for the preparation of ultrapure water or for the separation and concentration of organic matter, acids and salt solutions. In the M D the feed volatile components are separated by means of a porous hydrophobic membrane thanks to a vapor-pressure difference that acts as driving force and then they are condensed in cold distillate (distilled water), whereas the nonvolatile compounds were retained on the feed side. 

Chin S S, Lim T M, Chiang K and Fane A G (2007a), Hybrid low-pressure submerged membrane photoreactor for the removal of bisphenol A , Desalination, 202,253-261. 

However, the submerged membrane photoreactor offered more advantages in terms of permeate flux than those obtained operating with pressurized module. 

FIGURE 3.9 Circulating water photoreactor system for determination of photomicro-biocidal activity under water flow conditions, a, reinforced membrane used in the study b, water jacket, continuous flow, infrared filter c, light source d, air pump e, bacterial air filter f, 3-way tap/pressure release g, 2-way taps h, frit for aeration J, peristaltic pump k, reservoir 1, ground glass Joints for ease of cleaning and sterilization (Bonnett et ai, 2006). 

The obtained results have shown that the configuration where the recirculation tank was irradiated and the catalyst was used in suspension appeared to be the most interesting for industrial applications [73]. Moreover, it was observed that the degradation rate was higher when an immersed lamp was used compared to a system with an external lamp [81]. Therefore, actually the studies in progress are realized in the system described elsewhere [39] consisting of a Pyrex annular photoreactor with a 125-W medium-pressure Hg lamp axially positioned inside the reactor. The separation module containing the flat-sheet membrane was connected to the photoreactor in a recirculation loop. 

Selection of a membrane the membrane should have both the capability to retain the catalyst and to partially reject organic species, enabling control of the residence time in the reaction environment. In order to select a suitable membrane, rejection should be determined during operation of the photoreactor. Parameters such as transmembrane pressure, solution pH, molecular size of the pollutants and products/by-products of their degradation should be especially considered. In the case of NF an improvement of permeate quality could be obtained by taking advantage of the Donnan exclusion effect, provided that the membrane is selected properly. 

The experimental plant consisted of an annular photoreactor with an immersed UV lamp connected with the permeation cell in which a pressurized flat sheet membrane or a submerged membrane module was located. 

The catalyst deposition on the membrane surface and fouling caused flux decUne during the photocatalytic process. To overcome these problems the depressurized (submerged) membrane system, in which the membrane module was located separately from the photoreactor, was studied. The achieved results showed pharmaceuticals abatement of 100% after ca. 20 min and mineralization of 44.5% after ca. 150 min in the retentate. The UF membrane used in the submerged system did not allow the rejection of GEM and of its oxidation products compared to the NF membranes of the pressurized system. 

Picture and scheme of the photoreacting batch systems (i) and of the photoreacting continuous system (ii) (a) switch valve (b) thermocouple (c) non-reacting tank (d) pump (e) regulation valve (f) manometer (g) membrane vessel (h) line under pressure (i) rotameter (I) feed tank. PFP, plug flow photoreactor (adapted from Augugliaro et al., 2005). 

Similarly, as in case of the MCs described above, the mass transfer in the presented PMR was achieved without any transmembrane pressure. This allowed avoidance of membrane fouling, even in the case of highly turbid water. Moreover, due to keeping the bentonite away from the photoreactor, it was possible to avoid the loss of radiation due to screening by bentonite particles. 

Figure 20 J SchematizatioD of the experimental setup of the integrated photocatalysis-MD process. (1) Magnetic stirrer, (2) feed (artificial turhid water) tank, (3) and (4) circulation pumps, (5) hoUow-liher module or flat-sheet membrane, (6) thermostated photoreactor, (7) pressure regulation valve, and (8) oxygen cylinder.

---