Deciphering advanced coagulation strategies for AGMBR membrane fouling control: Comparative analysis of five inorganic/modified microbial flocculant systems
Aerobic granular sludge membrane bioreactor (AGMBR) is highly efficient in treating urban sewage but is susceptible to membrane fouling caused by extracellular polymeric substances. In this study, we have developed five novel coagulation systems by combining commercially available inorganic coagulants with a self-made modified microbial flocculant (MMF), focusing on evaluating the effects of these systems on normalized fluxes, fouling resistances, wastewater quality characteristics, and membrane surface morphology. The results indicated that the compound coagulation systems had a dual impact on controlling membrane fouling in AGMBRs. Specifically, ferric chloride, polyaluminum chloride, and polyaluminum ferric chloride combined with MMF exacerbated membrane fouling by forming dense cake layers. On the other hand, the composite systems of aluminum sulfate (AS) and MMF, as well as polyferric sulfate and MMF, positively influenced membrane fouling control. Among them, AS neutralized the negative charges of colloidal particles via the positive charges of aluminum ions, thereby destabilizing and aggregating the particles. Meanwhile, the long carbon chains and numerous functional groups in MMF endow it with excellent adsorption bridging capabilities. AS/MMF was found to be the most effective in reducing both reversible and irreversible resistances through electrostatic neutralization and adsorption bridging. The superior performance of the AS/MMF system, characterized by membrane fouling mechanism as standard blocking and an increase in membrane flux associated with reduced turbidity and elevated zeta potential, was further confirmed through extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory analysis. The findings validate the efficacy of AS/MMF composite coagulation pretreatment in mitigating AGMBR membrane fouling, offering a novel solution for sustainable wastewater management.
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