Real-time aeration efficiency monitoring in the activated sludge process and methods to reduce energy consumption and operating costs

Aeration is the most energy intensive unit operation in municipal wastewater treatment, and fine-pore diffusers have been widely used to minimize power consumption. Unfortunately, fine-pore diffusers suffer from fouling and scaling problems, which cause a rapid decline in aeration performance and significant increase in power consumption. Diffusers must be cleaned periodically to reduce energy costs. The cleaning frequency of diffusers is site-specific and its effectiveness can be evaluated with oxygen transfer efficiency (OTE) testing. Off-gas testing is the best technique for measuring OTE in real-time. Fine-pore diffusers have low α factors that are further reduced at high loading rate. A time-series of off-gas measurements were conducted to demonstrate the value of real-time OTE data for developing energy-conserving operating strategies. The observations confirm the inverse correlation between OTE and airflow rate as well as the economic benefits of diffuser cleaning. In addition, mathematic models were applied to simulate the transient oxygen uptake rate (OUR) and show the impact of varying load on OTE and aeration cost, especially when faced with time-of-day power rates. Regular diffuser cleaning can reduce average power costs by 18% and various equalization alternatives can reduce power costs by 6 to 16%.