Biological nutrient removal using an alternating of anoxic and anaerobic membrane bioreactor (AAAM) process

An innovative alternating of anoxic and anaerobic membrane bioreactor (AAAM) process was developed to enhance nitrogen and phosphorus removal simultaneously. The process was composed of a continuous aerated MBR and an alternating anaerobic and anoxic zone containing two separated bioreactors (reactor A and reactor B). By switching on and off the control valves, the mixed liquor in the aerobic zone was recycled to the reactor A or reactor B alternately, thus, the anoxic conditions for denitrification and anaerobic conditions for phosphorus release were implemented in two single tanks alternately. Additionally, by this operation mode, the denitrifying bacteria and phosphate-accumulating organisms (PAOs) could make full use of the organic substrate present in the wastewater alternately. A laboratory-scale experiment treating synthetic wastewater was applied to investigate the performance of the AAAM process. The results showed that COD removal efficiency was high and stable (over 93%) throughout the experiment. Nitrogen and phosphorus removal efficiency also attained high treatment levels (67.4% and 94.1% respectively). Comparing to DO and pH, oxidation–reduction potential (ORP) could provide much better information about the processes going on in reactors A and B during the 120-min cycle. Analysis of membrane fouling showed that small particles seemed to play an important role on the membrane fouling.