Performance of a hybrid membrane bioreactor in municipal wastewater treatment

A pilot-scale hybrid membrane bioreactor (HMBR) was developed by introducing biofilm carriers into a conventional membrane bioreactor (CMBR) and operated for about one year for municipal wastewater treatment. Experiments were conducted to investigate the performances of the HMBR for organic removal, nutrients removal and membrane fouling control comparing with the CMBR. The comparative study results indicated that at a constant hydraulic retention time (HRT) of 10 h and sludge retention time (SRT) of 10 d, the HMBR apparently improved the organic removal. To be specific, the effluent COD in the CMBR averaged 44 mg/L, but it dropped to 24.5 mg/L in the HMBR. Correspondingly, the COD removal rate increased from 90.4% to 94.2%. Regarding NH4+–N, TN and TP, the HMBR improved the removal rate by 4.2%, 13.7% and 1.7%, respectively. Another eye-catching feature of the HMBR was that the increase of transmembrane pressure (TMP) was slowed down during the operation at a constant flux of 10 L/m2 h. In CMBR, the duration for TMP to reach the prescribed maximum of 20 kPa after chemical washing was 57–65 days, while in the HMBR it was prolonged to 92 days or longer. This indicated a favorable condition of membrane fouling control by HMBR operation.