Evaluation of anaerobic membrane bioreactor (AnMBR) treating confectionery wastewater at long-term operation under different organic loading rates: Performance and membrane fouling

Abstract

An anaerobic membrane bioreactor (AnMBR) system treating confectionery wastewater was operated for 247 days at various organic loading rates (OLRs) of 1.1, 2.2, 4.4, 6.6 and 7.9 kg COD m(-3) d(-1) to determine sustainable OLR. In this study, up to 99% COD removal efficiency was obtained at all OLRs, and the maximum methane production of 0.26 m(3) kg(-1) CODremoved was achieved at OLR 7.9 kg COD m(-3) d(-1). Next Generation Sequencing (NGS) analysis showed that the dominance of hydrogenotrophic methanogens shifted to acetoclastic methanogens after OLR value of 4.4 kg COD m(-3) d(-1), which caused a decrease in the biogas methane composition. The increase in OLR, negatively affected the membrane filtration performance. After OLR value of 4.4 kg COD m(-3) d(-1), TMP, filtration resistance and EPS/SMP production increased sharply. These results indicated that the AnMBR system could be efficiently operated efficiently at OLR 4.4 kg COD m(-3) d(-1). Membrane fouling mechanism was evaluated using Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX), and contact angle measurements after 247 days of operation. The results demonstrated that the membrane fouling mechanism can be attributed to cake layer formation which mainly consisted of protein and carbohydrate. In this study, the efficient treatment of confectionery wastewater showed that the AnMBR system could be applied to high-strength organic wastewater such as industries of beverage, beer, dairy, and sugar product. Filtration performance should be enhanced with further investigations.