Abstract
Gravity-Driven Ceramic Membrane (GDCM) technology has gained popularity and recognition in water purification on account of its low energy consumption and convenient operation. This study aimed to comprehensively assess the effects of different disinfectants, including hydrogen peroxide (H2O2) and sodium hypochlorite (NaClO), on GDCM performance. It focused on the change in manganese removal and structure of the powdered activated carbon (PAC) - manganese oxides (MnOx) pre-deposited at the membrane interface and as well membrane fouling mitigation. The results showed that after the first two disinfection cycles, the flux recovery was 15 LMH for H2O2, while using NaClO only achieved an average recovery of 2 LMH and increased the effluent manganese, exceeding 0.1 mg/L within a short period of time. During the disinfection process, H2O2 exhibited better performance in mitigating membrane fouling compared to NaClO in the GDCM system. Additionally, by observing the recovery time of Mn2+ after disinfection, it can be deduced that the initial manganese removal mainly resulted from biological action of manganese-oxidizing bacteria (MnOB), while the later stage relied primarily on the catalytic oxidation action of birnessite. Fluorescence excitation–emission matrix analysis (EEM) indicated that most organic compounds dissolved in the disinfectant solution after disinfection, with some permeating through the membrane, while the remaining portion continued to accumulate in the filter cake layer. This accumulation was further confirmed by the enhanced absorbance peaks of functional groups (–NH and –OH) in the Fourier-transform infrared spectroscopy (FTIR). Scanning electron microscope - energy dispersive x-ray spectroscopy (SEM-EDS) mapping analysis revealed that MnOx formed more lamellar structures between nano-flower balls after disinfection. This increased the number of active sites and opened up water flow channels, contributing to improved flux. X-ray photoelectron spectroscopy (XPS) analysis demonstrated that Mn3+ as the dominant valence in MnOx exhibited excellent catalytic oxidation ability. Raman analysis and X-ray diffraction (XRD) indicated that MnOx showed consistent Raman spectra with birnessite before and after disinfection, and the oxidative effect of disinfection did not alter the crystal structure of MnOx. This result demonstrates the importance of applying effective disinfection in the GDCMs.
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