Characteristics of an A2O–MBR system for reclaimed water production under constant flux at low TMP

A full scale anaerobic–anoxic–oxic (A2O) biological unit followed by a submerged MBR was applied for domestic wastewater treatment and reclaimed water production. Under a constant flux of 16 L/m2h, TMP varied narrowly between 12 and 22 KPa over the duration of 9 months with only enhanced flux maintenance (EFM) for restoring membrane permeability. By analyzing the particle size distribution (PSD) and extracellular substances (EPS) in the mixed liquor at different steps, it was found that fine particles, proteins and polysaccharides, as potential foulants, decreased along the A2O–MBR array. Fluorescent excitation–emission matrix (3DEEM) analysis further revealed the characteristics of dissolved organic substances throughout the treatment process. Nevertheless, the deposition of organic foulants was identified in the cake layer on the membrane surface by scanning electron microscopy and Fourier transform infrared spectroscopy. The advantage of the A2O–MBR system over the conventional MBR was not only in the effectiveness for high quality reclaimed water production, but also in the reduction of potential foulants through the A2O biological process prior to entering the MBR unit.

► A full scale A–A–O–MBR system was operated in a 9-month cycle without CIP.
► High quality reclaimed water was produced under constant flux and at low TMP.
► EPS concentration was found to decrease along the A–A–O–MBR array.
► EPS did not accumulate in the MBR unit as time elapsed.
► The low TMP was attributed to foulants reduction by the A–A–O prior to the MBR.