Process Intensification Using MBR and S2EBPR Technologies

Background
Fulton County embarked on its largest capital project in history, a $350 million initiative to upgrade its Big Creek WRF. Originally permitted for 24 MGD with an average daily flow of 20 MGD, the County aimed to modernize its treatment facility by constructing a greenfield BNR and MBR facility. This upgrade not only increased the plant's capacity to 32 MGD, with potential expansion to 38 MGD, but also addressed critical issues such as odor control, noise, and lighting that affect the surrounding neighborhood.

As Fulton County's first Progressive Design Build project, this endeavor emphasized a collaborative approach with constant owner involvement, building on the County's experience with Construction Manager at Risk (CMAR) and Fixed Price Design Build methods. The project also focused on minimizing life cycle operating costs, improving sludge handling and disposal processes, and meeting both existing and future waste load allocations for nitrogen and phosphorus.

Material and Methods
The existing Big Creek WRF was replaced and expanded to a 32 MGD greenfield BNR and MBR facility that was commissioned in 2024. As shown in Figure 1, the new facility consists of a headworks with coarse screens and vortex grit removal followed by primary clarifiers, fine screens, BNR trains, membrane tanks, UV disinfection, and post aeration. As shown in Figure 2, the BNR system utilizes the MLE process and anaerobic sidestream reactors (S2EBPR) to achieve biological N and P removal. The aerobic zones of the BNR trains were design to operate using convention DO control (i.e., DO setpoint) or ammonia-based aeration control (ABAC) utilizing an ammonia setpoint. By using ABAC, the system was designed to achieve simultaneous nitrification and denitrification (SND). The MBR system consists of 10 tanks each with 38 Kubota flat sheet membrane modules. Detailed design parameters for the MBR system for both 32 and 38 MGD flow conditions are provided in Table 1.

Results and Discussion
The liquid treatment portion of the new facility was started up at the end of July 2024 after transferring mixed liquor from the old plant to seed the new plant. The old plant only consisted of aeration tanks and ferric chloride addition for phosphorus removal. The new facility is currently operated with 4 out of 5 BNR trains and operating at a MLSS of 8-9 g/L. Although the facility currently does not have permit limits for total nitrogen (only ammonia), the facility was designed to meet 8 mg/L TN while utilizing ABAC to achieve SND. However, to date the effluent TN has averaged 4-6 mg/L using conventional DO control. The ABAC system will be commissioned and performance tested early in 2025 to optimize both biological N and P removal.

Effluent TP performance is provided in Figure 3. Although the facility is currently permitted for 0.75 mg/L TP, plant staff have been operating well below that to ensure that the future limit of 0.3 mg/L TP can be maintained. The facility utilizes PHOS-SORB (proprietary alum/caustic product) for effluent TP polishing. The facility currently utilized approximately 1.7 lb-Al/lb-P removed, which is about half of the recommended dose based on chemical P removal only. This indicates that biological P removal is contributing to a significant portion of the P removal activity and the PHOS-SORB is only used to remove residual P and achieve such low concentrations. Biological P removal attributed to the sidestream anaerobic reactors is also supported by P release in these tanks with PO4-P concentrations ranging from 30-50 mg-P/L as shown in Figure 4.

The presentation will cover the design, construction, and commissioning of the WRF while focusing on the BNR, S2EBPR, and MBR processes. The facility is currently still in a construction and commissioning phase with anticipated completion in the Spring of 2025. Additional testing to assess S2EBPR performance and optimize treatment with the ultimate goal of eliminating PHOS-SORB addition will be included in the final paper and presentation.