Woodard & Curran partnered with the City of Westfield and the Hach Company to successfully apply for a Water Innovation Grant from the Massachusetts Clean Energy Center (MassCEC). The MassCEC grant program encourages the development of innovative wastewater treatment technologies that reduce electricity consumption, cut energy costs for communities, and improve treatment process performance. The focus of this grant project was a pilot test to determine the benefits of ammonia-based aeration control (ABAC) at the Westfield Water Recovery Facility (WRF) utilizing an in-situ ammonium probe and real-time data.
The goal of the pilot test was to define benefits and impacts of using ammonia-based aeration control (ABAC), including quantify the energy savings, quantify impacts on nutrient removal, identify other process and maintenance impacts, and become a local innovation showcase from which other operators can learn. The ABAC pilot test was conducted during the summer of 2019 at the WRF, and results were positive.
About the Westfield WRF
The Westfield WRF serves approximately 50,000 people and treats wastewater from residential, commercial, industrial, and institutional sources within the city and neighboring municipality. Average daily flow is approximately 3.4 mgd (13 ML/d), and the design capacity is 6.1 mgd (23 ML/d). The Westfield WRF has 10 operations and maintenance professionals.
The WRF was designed for seasonal nitrification and phosphorus removal via chemical precipitation with sodium aluminate to achieve permit limits. The activated sludge process was subsequently modified to incorporate enhanced biological phosphorus removal, reducing the quantity of sodium aluminate that needs to be added to the system. To mitigate the alkalinity loss due to nitrification the Westfield WRF adds sodium hydroxide (NaOH) to the aeration tanks.
The activated sludge process is configured in three plug-flow aeration tanks. The first pass is anaerobic, and the second two passes are fully aerobic with air supplied via fine bubble diffusers. Prior to the pilot test, air to the activated sludge system was modulated to meet the oxygen demand using a dissolved oxygen (DO)-based aeration control system. Each train has an in-situ Hach Luminescent Dissolved Oxygen probe located at the end of the second pass that measures DO concentration, which is used to control the speed of the blowers.
ABAC Pilot Test
ABAC utilizes real-time data from an ammonia probe to optimize the quantity of air supplied to the aeration tanks. ABAC is intended to provide the system with enough dissolved oxygen for treatment without wasting energy by oversupplying air. Utilizing ABAC typically allows for lower DO concentrations to be maintained in the active sludge system. For the pilot test at the Westfield WRF, the City added a HACH ISE ammonium probe to one of the activated sludge trains and modified the aeration controls to include a control loop that adjusted the DO setpoint based on the real-time ammonia concentration measured by the ammonium probe.
The ABAC pilot test occurred between June 2019 and October 2019. Testing was divided into two phases: 1) a DO control mode to establish baseline conditions, and 2) the ABAC mode. Operational impacts of ABAC mode at the Westfield WRF were quantified, including DO concentrations, energy use, and chemical use. Additionally, overall nutrient removal performance and other operating and maintenance impacts were tracked during the pilot test.
A key to the project execution was collecting and analyzing a significant amount of data from various sources, including the laboratory results, field measurements, SCADA parameters, operational changes, and chemical usage. Woodard & Curran constructed a dashboard in Power BI that allowed the project partners to continuously monitor the impact of ABAC. The compilation and visualization of the data facilitated decisions about process changes throughout the study.
Outcomes and Benefits
The ABAC pilot project resulted in significant cost savings and reduced environmental impact. With ABAC, the WRF met the same standards of ammonia and phosphorus removal using less energy. Additionally, the WRF was able to reduce the quantity of sodium hydroxide added to the system. For the WRF, operating in ABAC mode resulted in more than $10,000 per year of savings in sodium hydroxide, which is added for pH control, and more than $6,000 annually in energy savings, which is a reduction of 15% over the baseline DO-control mode. During ABAC operation, average DO concentration was reduced from 2 mg/L to 1 mg/L.
When operating in ABAC mode, the Westfield WRF did not experience any major negative impacts on solids handling nor did the operational mode result in additional odor production. Sludge settleability also remained relatively consistent throughout the pilot test period.
ABAC was successfully implemented at the Westfield WRF. Woodard & Curran worked in partnership with the City to host outreach activities and share the successful project outcomes. The Westfield WRF plans to continue using the Hach AISE sc ISE Ammonium probe for process monitoring and ABAC.
The ABAC Pilot Test builds on a culture of innovation at the Westfield WRF. The award-winning team of operators have expertise in activated sludge systems and nutrient removal as well as a proven track record of successfully incorporating real-time data and information into their process control. Their process control approach, combined with effective asset management, have resulted in cost-effective operations and overall savings.