Nitrification kinetics and microbial communities of activated sludge as a full-scale membrane bioreactor plant transitioned to low dissolved oxygen operation

With population growth, water scarcity, and strict regulations, there is an increasing need for the water industry to search for advanced treatment technologies to reuse effluent from wastewater treatment plants. To accomplish an energy efficient and environment friendly facility for producing reclaimed water, a Water Recycling Plant successfully transitioned its aeration tank dissolved oxygen from moderate (0.8 mg/L) to low (<0.5 mg/L) level. Compared with the moderate dissolved oxygen operation, the low oxygen operation decreased aeration energy consumption by 11.2% while treatment performance was improved. Microbial response to dissolved oxygen change in activated sludge for simultaneous nitrification and denitrification has been studied by operating bench-scale bioreactors in parallel rather than at a full-scale treatment plant with a gradual change of dissolved oxygen set point over time. This study tracked nitrification kinetics and microbial community evolution at this Plant for understanding the low dissolved oxygen activated sludge process. Oxygen half saturation coefficient decreased from 0.23 to 0.19 mg/L for ammonia-oxidizing organisms and 0.19 to 0.08 mg/L for nitrite-oxidizing organisms, indicating a shift to nitrifiers with a high oxygen affinity. In the low dissolved oxygen operation, all the aerobic, anoxic and membrane tanks had similar microbial communities for simultaneous nitrification and denitrification. Nitrospira that has a high oxygen affinity was the only known genus of autotrophic nitrifiers, having a relative abundance of 0.6-1.7%. Denitrifying bacteria were detected in 15 genera at a total relative abundance of 0.8-1.2% in individual tanks. The kinetic results are key to aeration control and process optimization. This study also provides insights into design and operation of wastewater treatment plants to produce reclaimed water in an energy efficient and environment friendly manner. (C) 2019 Elsevier Ltd. All rights reserved.