Effects of operational parameters on aeration on/off time in an intermittent aeration membrane bioreactor

This study was performed to evaluate the operational parameters on aeration on/off time in an intermittent aeration membrane bioreactor for wastewater treatment. The membrane bioreactor has 5.5 L of effective working volume including a microfiber membrane. The influent wastewater contained 133 mg/L of BOD, 195 mg/L COD, 98 mg/L SS, 30 mg/L total nitrogen, and 3.8 mg/L total phosphorous. Operational conditions related to aeration on/off time were 8.8 h HRT, 10 LMH flux, 10 L/min air flow, and 6300 mg/L MLSS. For 2 h/cycle, aeration on/off time was operated for 12 cycles in three variations: 60/60 min, 50/70 min (I), and 40/80 min. Suction on/off time was 10/2 min, 8/2 min, and 8/2 min, respectively, but also 50/70 min (II) when aeration on/off time was operated at 8300 mg/L MLSS. The BOD removal efficiency rate of this process was higher than 97% regardless of the aeration on/off time distribution. To get higher than 82% total nitrogen removal efficiency rate, aeration off time in the reactor needs to be more than 70 min. The specific denitrification rate was 2.68 mgNO3-N/gMv/h at 40/80 min on/off aeration times, which was 2.6 times more than at 60/60 min, and 1.4 times more than at 50/70 min (I) for 6300 mg/L MLSS. The specific nitrification rate was 1.96 mgNH4-N/gMv/h at on/off aeration times of 50/70 min, 1.4 times less than at 40/80 min, but was ineffective for nitrification. Microbial activity was affected only a little by variation in aeration on/off time, though oxygen demand was reduced by aeration off time and allowed microbial concentration to increased. EPS (extracellular polymeric substance) per unit of microorganisms increased with aeration off time.

This study was performed to evaluate parameters such as removal efficiency rate of organics and nitrogen, EPS content, and TMP by aeration on/off time in an intermittent aeration membrane bioreactor for wastewater treatment. The BOD removal efficiency rate of this process was higher than 97% regardless of the aeration on/ off time distribution and reached a maximum of 99% at 40/80 min aeration on/off time. Nitrification of more than 99% was attained without relation to the aeration on/off time distribution. To get a rate of total nitrogen removal higher than 82%, aeration off time in the reactor needs to be more than 70 min. The specific denitrification rate at 40/80 min aeration on/off time was 2.68 mgNO3-N/gMv/h, which was 2.6 times more than at 60/60 min, and 1.4 times more than at 50/70 min (I) for 6300 mg/L MLSS. The specific nitrification rate at 50/70 min aeration on/off time was 1.96 mgNH4-N/gMv/h and 1.4 times less than at 40/80 min, but was no effective for nitrification. Microbial activity was a little more effective according to the aeration on/off time. During aeration off times, oxygen demand was reduced and microbial concentration increased. EPS per unit of microorganisms increased as the aeration off time got longer. The content at 50/70 min and 40/80 min aeration on/off time increased 1.6 times and 2.7 times respectively, compared with 60/60 min.