A novel wastewater treatment and biomass cultivation system combining photosynthetic bacteria and membrane bioreactor technology

• A novel PSB-MBR system is constructed for pollutants removal and biomass recovery.
• This system was very effective in pollutants reduction, COD was removed by 99.3%.
• MBR solved the problem of PSB collection, and 99.5% of biomass was collected.
• PSB produced low EPS, which reduced membrane fouling.
• The backwash cycle lasted 48 h, which prolonged the service life of membrane.

A new system combining photosynthetic bacteria (PSB) treatment with membrane bioreactor (MBR) separation, PSB-MBR, was constructed in this work to treat wastewater and cultivate biomass. PSB were used to remove pollutants and membrane was used to separate biomass from the effluent. The optimal light and oxygen condition for PSB treatment section was natural light–micro aerobic, and the optimal ratio of food to microbe (F/M) was 2.0. The optimal membrane operation pressure and flow rate for membrane separation was 0.1/0.2 MPa and 27.5 L/h, respectively. Under the optimal conditions, COD removal reached 99.3% and the biomass recovery efficiency was 99.5%. The backwash cycle of PSB-MBR system lasted for 48 h, while the backwash cycle for conventional MBR systems is usually 0.5–3.0 h. The prolonged backwash interval means simple operation, little backwash water consumption, and long service life of membrane. That could be caused by the low extracellular polymeric substance contain of PSB (9–11 mg/g-VSS).