Abstract
The characteristics of foulant in the cake layer and bulk suspended solids of a 10 L submerged anaerobic membrane bioreactor (AnMBR) used for treatment of palm oil mill effluent (POME) were investigated in this study. Three different organic loading rates (OLRs) were applied with prolonged sludge retention time throughout a long operation time (270 days). The organic foulant was characterized by biomass concentration and concentration of extracellular polymeric substances (EPS). The thicknesses of the cake layer and foulant were analyzed by confocal laser scanning microscopy and Fourier transform infrared spectroscopy. The membrane morphology and inorganic elements were analyzed by field emission scanning electron microscope coupled with energy dispersive X-ray spectrometer. Roughness of membrane was analyzed by atomic force microscopy. The results showed that the formation and accumulation of protein EPS in the cake layer was the key contributor to most of the fouling. The transmembrane pressure evolution showed that attachment, adsorption, and entrapment of protein EPS occurred in the membrane pores. In addition, the hydrophilic charge of proteins and polysaccharides influenced the adsorption mechanism. The composition of the feed (including hydroxyl group and fatty acid compounds) and microbial metabolic products (protein) significantly affected membrane fouling in the high-rate operation.
Highlights
Alternative energy sources are widely promoted for sustainable development, including in wastewater treatment
The results showed that the formation and accumulation of protein extracellular polymeric substances (EPS) in the cake layer was the key contributor to most of the fouling
When an anaerobic membrane bioreactor (AnMBR) was operated for a long term in a low-rate condition, the EPS concentration significantly increased with the increase in organic loading rates (OLRs) [15]
Summary
Alternative energy sources are widely promoted for sustainable development, including in wastewater treatment. Reversible foulants include biomass, suspended solids, and inorganic precipitates, which form a cake layer attached at the membrane surface. A substantial amount of research has evaluated fouling behavior in AnMBR, with different operational conditions affecting cake layer formation, EPS and SMP, and inorganic precipitates [13,14,15,16,17,18]. Under medium to high OLR, EPS accumulation in the cake layer has been shown to contribute most to system fouling, as confirmed by scanning electron microscopy (SEM), EDX, Fourier transform infrared (FTIR) spectroscopy, CLSM, zeta potential, roughness, and contact angle [13]. During high-loading leachate wastewater treatment, fouling was affected by OLR > mixed liquor suspended solids (MLSS) > EPS > SMP [17]
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