IMPLEMENTATION AND EVALUATION OF ENERGY SAVINGS FOCUSED AERATION DESIGN AND CONTROL OF SEQUENCING BATCH REACTORS IN WASHINGTON

The design and operation of activated sludge process aeration systems has become a major focal point of study in regards to improving plant robustness, treatment capacity, and energy efficiency. This paper demonstrates the importance of selecting proper blower technology, size, and control ideology to best optimize operational returns on Cap-Ex, especially when given funding opportunities where specific energy savings milestones must be achieved.

This case study of the Quincy, Washington WWTP involves replacing (1) defunct 447 kW (600 HP) multi-stage blower with two smaller 242 kW (325 HP) screw type positive displacement blowers equipped with VFDs, and implementing a bioprocess aeration control system focused on maintaining plant defined DO setpoints in two separate lagoon style sequencing batch reactors. By designing the system to provide the appropriate amount of blower turndown to match typical loading conditions and implementing proper controls techniques which minimize over aeration, the facility has demonstrated 57% aeration energy savings compared to the 2013 baseline, despite unusually high loading conditions during the monitoring and verification period. The upgrade, designed to qualify the facility for an energy savings rebate, exceeded performance expectations by approximately 330,000 kWh during the four month monitoring and verification period (62% greater than the original estimate) and qualified the facility for the maximum rebate value amounting to approximately 40% of the total cost of the project.

Despite the North-West’s characteristically low energy rates, the remaining 60% capital cost of the project has a projected payback period of 3 years 8 Months assuming 2,344,000 kWh/year savings at $0.0413 per kW, a rate 58% of the national average.