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.

3.3.2. Particle size distribution (PSD) Foulant sizes may strongly affect fouling mechanisms in membrane filtration systems [15]. To evaluate the causes of membrane fouling in the AAAM process, particle size distributions (PSD), including activated sludge suspension in aerobic zone, exterior cake layer and interior cake layer, were analyzed in the range of 0.1–560 μm at the day of 42. As shown in Fig. 6, the PSDs of the different fractions were quite different. The Fig. 6. Particle size distributions (PSD) related to membrane fouling An innovative alternating of anoxic and anaerobic membrane bioreactor (AAAM) process was developed to enhance nitrogen and phosphorus removal simultaneously and its performance was investigated on a laboratory-scale system. Major findings from this study are summarized as follows: (1) The AAAM process exhibited high performance in removing carbon, nitrogen and phosphorus simultaneously. Under the operational conditions imposed, the removal efficiencies of COD, total nitrogen and total phosphorus were achieved at 93%, 67.4% and 94.1%, respectively. (2) The AAAM system could be improved by adjusting the duration of the recycling cycle and the recycling rate according to the influent quality to meet the different requirement of nitrogen or phosphorus removal. ORP could be used as an effective parameter to determine the optimum operation mode for the best removal efficiency of both nitrogen and phosphorus. (3) The operation mode of AMMM system might reduce the accumulation of EPS in membrane zone, and thus alleviate membrane fouling.