Integration of a 3D-printed electrochemical reactor with a tubular membrane photoreactor to promote sulfate-based advanced oxidation processes

This study investigates the integration of an in-house 3D printed electrochemical cell - SERPIC-UCLM® cell - for the in situ generation of peroxymonosulfuric acid (PMSA) with a lab-scale tubular membrane photoreactor (TMPr) to evaluate the effectiveness of sulfate-radical advanced oxidation processes (SR-AOPs) in eliminating contaminants of emerging concern (CECs) from reverse osmosis and nanofiltration concentrates (ROC and NFC, respectively). First, the SERPIC-UCLM® cell was evaluated in terms of mass transport features employing the limiting current technique, demonstrating favorable volumetric mass transport rates (kmA ∼ 10-3 s-1) and Sherwood values (Sh > 300) under the laminar flow regime (110 < Reynolds (Re) < 790). Afterward, the effect of the electrolyte (sulfuric acid, H2SO4) initial pH in the electrochemical generation of PMSA was studied, with an initial pH of 1 selected as optimal. PMSA is a highly reactive peroxyacid that undergoes self-decomposition at neutral pH media (e.g., ROC and NFC with a pH of 7.6 and 7.9, respectively), primarily existing in the form of peroxomonosulfate (PMS). Additionally, the phototreatment of the ROC and NFC was assessed using the electrogenerated PMS and commercial peroxydisulfate (PDS) under the same conditions. The results indicated comparable degradation patterns for CECs in both ROC and NFC. Furthermore, the application of 2.4 mM PMS resulted in removals higher than 60 % for 7 of the 11 CECs identified in the NFC, and ensured compliance with wastewater discharge regulations for pH, chemical oxygen demand (COD), and total suspended solids (TSS) levels. These findings emphasize the importance of this technology, showing its advantages in terms of versatility and logistics.