A Study On The Hybrid Submerged Membrane Bioreactor Process For Municipal Wastewater Treatment

A hybrid submerged membrane bioreactor (HSMBR) was devised for a pilot study in Beishiqiao Wastewater Purification Center for municipal wastewater treatment and reuse. The HSMBR combines both suspended growth-activated sludge and attached growth-biofilm in one bioreactor by adding suspended carriers into the mixed suspension. A submerged MF membrane module (PVDF hollow fiber with pore size as 0.2μm) was equipped in the bioreactor for solid/liquid separation.The results show that, the filtrate turbidity was always lower than 1 NTU (average turbidity as 0.59 NTU), showing a remarkable SS removal by the HSMBR to meet the requirement for any reuse purpose. Regarding color, which is an important parameter related to water reuse, it ranged from 9 to 39 c.u. (average color as 30 c.u.) in the filtrate, marginally meeting the requirement for domestic reuse (Chinese standard as 30 c.u.). The average COD removal by the HSMBR was as high as 95.5%, resulting in a residual COD in the filtrate from 6.0 to 22.8 mg/L (average as 14.5 mg/L). This meets the requirement for any reuse purpose.In addition, the HSMBR performed nitrogen and phosphorus removal well. It can be seen, as raw water NH3-N concentration fluctuated from 10.7 to 57.5 mg/L (average as 35.6 mg/L), that of the filtrate was between 0.1 and 1.6 mg/L (average as 0.77 mg/L). The average NH3-N removal was as high as 97.8%. Regarding total nitrogen, the average removal was 71.7% and the TN of the filtrate was between 8.2 and 20.0 mg/L (average as 13.6 mg/L). The average TP removal was 72.5%, almost identical to TN removal and the TP of the filtrate was between 0.33 and 2.7 mg/L (average as 1.22 mg/L). Comparing with a conventional activated sludge process or MBR based on it, the TN and TP removals obtained by HSMBR in this study are considered to be good.The HSMBR system was operated intermittently with the suction pump working but without backwashing. In the initial period for about 50 days, the TMP increased linearly from about 2 KPa to 18 KPa. This is considered to be a typical process of cake formation. Afterwards, the TMP almost kept unchanged, indicating a dynamic equilibrium condition. Further increase of the cake layer waseffectively prevented by mechanical vibration of the hollow fiber membrane immersed in the suspension and the hydraulic shearing of the turbulent flow in the aeration tank.It can be concluded from this study that (1) the HSMBR system with a combination of the suspended growth biomass and attached growth biomass can achieve an efficient removal of SS, COD and color to meet the quality requirement for water reuse; (2) the HSMBR has also the advantage over conventional MBR for its ability of effective nitrification/denitrification and phosphorus removal; (3) the HSMBR system is free from back washing and chemical cleaning due to an effective control of membrane fouling by mechanical vibration and hydraulic shearing provided in the aeration tank.