Photocatalytic space-time yield, a new benchmark for photoreactors

Different designs for photocatalytic wastewater treatment were compared with a new benchmark measure, photocatalytic space-time yield (PSTY).[1] This benchmark is the ratio of the reactor space-time yield to the standardized lamp power, defined as the volume of water treated for each kW lamp power per volume of reactor per unit of time. This benchmark gives a clearer view of the reactor performance than the current benchmarks such as pseudo first order rate constant or photonic efficiency. Using the benchmark, 14 reactors with 12 different designs were compared. The reactors compared had wastewater throughputs varying between mL.min-1 to m3.min-1 order of magnitude. [2,3] Comparison shows that the new benchmark assesses reactor performances normalizing very different designs. The highest scoring reactors are the pilot-scale slurry reactors. This is no surprise since they are also applied designs. The benchmark also shows that high area-to-volume geometries such as the microreactor technology is the most effective approach to introduce immobilized catalyst reactors to wastewater treatment processes. PSTY shows the weak points in a reactor concept as well. It is clear that the microreactor concept does not have a throughput problem but an illumination scale-up limitation although LED technology can help address this issue. Provided effective scale up, the benchmark also shows that the microreactor concept can perform significantly better than the slurry reactor. In this context, we also conclude that new concepts in immobilized catalyst reactors such as foam, fiber and capillary array reactors should be integrated in microreactor concepts to become competitive technologies to slurry type reactors for wastewater treatment. The new benchmark has potential to be used in photochemical organic synthesis processes as well. [1] M.E. Leblebici, G.D. Stefanidis, T. Van Gerven, Comparison of photocatalytic space-time yields of 12 reactor designs for wastewater treatment, Chem. Eng. Process. Process Intensif. 97 (2015) 106–111. [2] A. Visan, D. Rafieian, W. Ogieglo, R.G.H. Lammertink, Modeling intrinsic kinetics in immobilized photocatalytic microreactors, Appl. Catal. B Environ. 150-151 (2014) 93–100. [3] M.J. Benotti, B.D. Stanford, E.C. Wert, S. a. Snyder, Evaluation of a photocatalytic reactor membrane pilot system for the removal of pharmaceuticals and endocrine disrupting compounds from water, Water Res. 43 (2009) 1513–1522.status: publishe