Kinetic Studies on Ultra-Low DO Operations at a Full-Scale MBR Plant

Biological Nutrient Removal - Membrane Bioreactor (BNR-MBR) technology has been widely adopted in water reclamation practices; however, this technology does present considerable financial implications due to high energy and chemical input for nitrogen removal. To reduce operational costs for MBR plants, an ultra-low dissolved oxygen (DO) operation for wastewater treatment has been successfully implemented at a Wastewater Treatment Plant in California. Chemical oxygen demand (COD) and total nitrogen removal efficiencies were 97% and 98%, respectively, under ultra-low DO operation. The process blower energy consumption (kWh) for the treatment plant was reduced by approximately 12.5%. Lab-scale kinetic studies were conducted to determine half saturation coefficient for DO (KDO), which can be used for process control for the aeration system. The KDO values for ammonia oxidizing organisms (AOO) and nitrite oxidizing organisms (NOO) were 0.39 mg/L and 0.30 mg/L, respectively, before the ultra-low DO operation. Development of the aeration control strategy was based on these KDO values. After the ultra-low DO operation, increased KDO for AOO (0.56 mg/L) indicated development of novel organisms that could remove ammonia in a different pathway. Lower KDO for NOO (0.05-0.10 mg/L) suggested that nitrite oxidizing organisms with higher oxygen affinity were adopted to low DO conditions and performed well. This study provided an insight in process design and operation of MBR plants with ultra-low DO operations.