A tube-in-tube membrane microreactor for tertiary treatment of urban wastewaters by photo-Fenton at neutral pH: A proof of concept

This work presents a disruptive approach to promote highly-efficient photo-Fenton process at neutral pH under continuous mode operation. The system consists of a tube-in-tube membrane reactor designed for continuous-flow titration of low iron doses to the annular reaction zone (ARZ). A concentrated acidic ferrous ion (Fe2+) solution is fed by the lumen-side of the membrane, permeating through the membrane pores (inside-out mode), being dosed and uniformly delivered to the membrane shell-side. Polluted water, containing amoxicillin (AMX) and oxidant (H2O2), flows continuously in the reactor annulus (space between the membrane shell-side and an outer quartz tube). The catalyst radial dispersion is enhanced by the helicoidal movement of water around the membrane shell-side, efficiently promoting its contact with H2O2 and UV light. The efficiency of photochemical and photocatalytic oxidation was evaluated as a function of catalyst dose, catalyst injection mode (radial permeation vs injection upstream from the reactor inlet), light source (UVA vs UVC) and aqueous solution matrix (synthetic vs real wastewater). At steady-state, photo-Fenton reaction with Fe2+ radial addition, driven by UVC light, showed the highest AMX removal for synthetic (∼65%, removal rate of 44 μMAMX/min, using [Fe2+]ARZ = 2 mg/L and [H2O2]inlet = 10 mg/L) and real municipal wastewaters (∼45%, removal rate of 31 μMAMX/min, with [Fe2+]ARZ = 5 mg/L and [H2O2]inlet = 40 mg/L), with a residence time of only 4.6 s. [Display omitted] •Tube-in-tube membrane reactor for photo-Fenton at neutral pH in continuous mode.•Virtually unlimited number of Fe2+ dosing points across the membrane length.•Smart-dosing and homogeneous supply of the catalyst in the annular reaction zone.•AMX removal ∼65% with radial “titration” of 2 mg Fe2+/L, at pH ∼6.5, UVC-10 mg H2O2/L.•Acidic pH values in local points of the membrane shell-side enhances.•OH production.