Chemical cleaning enhanced birnessite functional layer formed in gravity driven ceramic membrane for manganese-containing water purification

Excessive manganese in water proposes a challenge to potable water safety. The Gravity-Driven Ceramic Membrane (GDCM) system can achieve effectively Mn²⁺ removal, but PAC-MnOx (powdered activated carbon − manganese oxide) function layer still exhibits a “trade-off” effect because of extracellular polymeric substances (EPS) within the functional layer pores. In this study, ascorbic acid, sodium hypochlorite (NaClO) and sodium hydroxide (NaOH) were selected to clean PAC-MnOx layer to improve flux and ensure Mn²⁺ removal. The results indicate that, during a 200-day operation period, periodic chemical cleaning (2g/L NaClO + 1.5 % NaOH cleaning in 60d, 120d, 150d) enable GDCM flux to remain a desirable level. Three-dimensional fluorescence (EEM) spectroscopy and gel permeation chromatography (GPC) indicate that organic pollutants within pores and encapsulated on PAC-MnOx's surface were removed by chemical agents. Additionally, the “backwash + soak” step may alleviate dissolved bovine serum albumin (BSA) adhesion to membrane pores due to osmosis. Meanwhile, chemical actions caused extreme biological damage to the functional layer, but over time, the impact on water quality was diminishing. Raman and X-Ray Diffraction (XRD) confirm that chemical cleaning GDCM didn't hinder birnessite-type MnOx's development. X-Ray Photoelectron Spectroscopy (XPS) analysis reveals that the addition of NaClO changed the lattice structure of MnOx, enhancing its catalytic oxidation performance. Therefore, the periodic cleaning method alternating between “forward filtration” with NaClO and NaOH and “backwash + soak” is suitable for cleaning GDCM.