Which Configuration of Photocatalytic Membrane Reactors Has a Major Potential to Be Used at an Industrial Level in Tertiary Sewage Wastewater Treatment?

Abstract

Photocatalytic membrane reactors (PMRs) have been found to be very effective in the removal of organic pollutants (particularly recalcitrant compounds) from wastewater because they allow for the mineralization of organic pollutants to innocuous by-products, thus achieving high-quality treated water. Owing to the very high volumes of water involved, treated sewage wastewater could be reused if a very efficient tertiary stage, like a PMR, can be foreseen. In this review, the two main PMR configurations (photocatalytic membranes and slurry PMRs) were analyzed as requirements of a tertiary treatment of sewage wastewater considering six design and operational parameters of such plants: (i) continuous wastewater flow rate from the secondary stage; (ii) the self-control of the photodegradation rate related to wastewater chemical–physical parameters; (iii) ability to handle variations of wastewater concentration and flow rate; (iv) the control of the quality of treated wastewater; (v) low plant footprint; and (vi) easy maintenance. In this analysis, some characteristics of photocatalysis (which involves three phases: solid (the photocatalyst), liquid (the wastewater), and gas (oxygen or air)) and those of membranes (they can be produced using different materials and configurations, different processes (pressure-driven or not pressure-driven), etc.) were considered. The obtained results show that slurry PMRs seem more suitable than photocatalytic membranes for such applications. We believe this review can trigger a shift in research from the laboratory to industry in using photocatalytic membrane reactors.

Performance of a Solar-Driven Photocatalytic Membrane Reactor for Municipal Wastewater Treatment

“…It should be stressed that the overall COD removal efficiency is comparable to similar results obtained for solar-driven advanced oxidation, membrane-based, or hybrid processes that can be found in the literature [3,4,[31][32][33][34] (see Table 7).…”

“…On the other hand, all the separation flows were determined to be between 120 L/m 2 h (with a total difference less than 25%; average value: 101.89 L/m 2 h), p that the photocatalytic step prolongs the membrane lifetime and avoids the issues to membrane fouling. It should be stressed that the overall COD removal efficiency is comparable to results obtained for solar-driven advanced oxidation, membrane-based, or hybr cesses that can be found in the literature [3,4,[31][32][33][34] (see Table 7). L/m h. On the other hand, all the separation flows were determined to be between 120 L/m 2 h (with a total difference less than 25%; average value: 101.89 L/m 2 h), that the photocatalytic step prolongs the membrane lifetime and avoids the issues to membrane fouling.…”

“…A custom-made installation was operated for the photocatalytic degradation tests. A CPC (component parabolic collector) reactor configuration was chosen due to its advantages in terms of good degradation efficiencies and lower energy losses [3,4,10]. The installation (presented in Figure 1) consists of the following main elements:…”

“…The coupling of membrane-based processes with heterogeneous photocatalysis (photocatalytic membrane reactors-PMRs) has proven to be an efficient and effective alternative for municipal wastewater treatment. Among the two mains PMR configurations, the slurry PMR system showed promising results compared with both the PMR design with an immobilized catalyst and other tertiary treatment processes such as chlorination, constructed wetlands, microalga cultivation, ozonation, and photo-Fenton methods [4].…”

“…The use of solar-light-driven PMRs for the advanced removal of organic loadings may offer the advantages of using visible light as a renewable irradiation source and having an increased lifetime for the polymeric membrane, but there are relatively few studies using real wastewater, the vast majority focused on the degradation of emerging organic pollutants from synthetic solutions [3,4].…”