A pilot-scale modified submerged membrane bioreactor (SMBR) with the capacity of 18.1 m3d−1 was developed on the basis of the principle of air-lift internal-loop reactor. Economical aeration intensity of the SMBR was determined as 96 m3m−2h−1 according to hydrodynamic investigation. Corresponding economical air-flow rate was selected as the working air-flow rate in the long-term run. Under economical aeration intensity, the critical flux zone of the modified SMBR was as high as 30–35 Lm−2h−1 when MLSS was less than 13 gL−1. Therefore, a sub-critical flux of 30 Lm−2h−1 was selected as the working membrane flux in the long-term run. Membrane fouling was effectively controlled by sub-critical flux operation and periodic on-line chemical cleaning in the long-term run. When the average influent CODCr, NH3-N and turbidity were 310 and 44.3 mgL−1 and 161 NTU, respectively, the average permeate were 38.5 and 19.5 mgL−1 and 0.96 NTU under hydraulic retention time (HRT) was only 2.8 h. Corresponding removal was 86, 58.2 and 99.4%. DO deficiency caused by high MLSS was demonstrated as the main reason for low NH3-N removal.

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