Gravity driven membrane resilience to seasonal Mn shocks in reservoir water enhanced by abiotic-biotic cyclic synergy.

Membrane technology is widely utilized in reservoir treatment due to its reliable performance in ensuring drinking-water quality. However, seasonal Mn shocks pose a challenge to the stable operation. Herein, we proposed membrane modification strategies for gravity driven membrane (GDM) systems, incorporating Fe/Mn oxides (FeMnOx), Fe/Mn-oxidizing bacteria (FeMnOB), and their coupled system to enhance resistance against Mn shocks. The FeMnOx-FeMnOB group exhibited excellent manganese adsorption-retention and oxidative removal performance. This system reduced initiation time by over 11 days under Mn shocks of 0.5-2.3 mg/L, significantly improving the responsiveness and adaptability to sudden Mn contamination. Based on existing evidence, FeMnOx and FeMnOB may form an efficient synergistic cycle. Specifically, FeMnOx-mediated oxidation triggered microbial extracellular polymeric substances (EPS) secretion via interfacial electron transfer. The resultant EPS, in turn, promoted FeMnOB colonization and concurrently supplied FeMnOx with a stable microenvironment and substrates. Moreover, FeMnOB metabolically oxidized and solubilized manganese to regenerate the active sites of FeMnOx in situ. This cycle was further reinforced by abiotic Fe(II)/Fe(III) and Mn(II)/Mn(IV) redox couples, which mitigated dissolved-oxygen competition under high manganese stress and ensured favorable conditions for FeMnOB. Therefore, this study unravels the abiotic-biotic synergy in Mn removal, informing green membrane strategies for emergency treatment of sudden reservoir contamination.