LaRocque, Bryan Gayoso, Alonso Griborio, Paul Pitt, and Eric Stanley

FWRJ Brevard County South Central Regional Wastewater Treatment Facility Expansion With Integrated Fixed Film Activated Sludge

Kevin Lee, Pia Prohaska, and Larry Li

Figure 1. Clarifiers With Perimeter Walkways and Launder Covers (photo: Lucas Lustik, Sure Thing Photography)

Figure 2. Integrated Fixed Film Activated Sludge System Layout Kevin Lee, P.E., is project manager with Mead & Hunt Inc. in Port Orange. Pia Prohaska is process engineer and Larry Li is product manager with Kruger in Cary, N.C.

The Brevard County Utilities South Central Wastewater Treatment Facility (WWTF) serves the growing area of Viera. The WWTF had a rated capacity of 6 mil gal per day (mgd) and needed additional capacity to serve further development in the area. Brevard County (county) issued a request for qualifications to select a design engineer for a 3-mgd expansion. Due to the high rate of development and population growth projections in the service area, a 6-mgd expansion was recommended. Ultimately, the WWTF was expanded from a rated capacity of 6 to 12 mgd.

Project Components

The overall project consisted of the following: S A new 12-mgd pretreatment structure. S Rehabilitation of the existing 6-mgd biological process mixing equipment. S Installation of a new 6-mgd biological process train. S Clarifiers, cloth media filters, chlorine contact, aerated sludge holding, and sludge dewatering expansion. S 1-mil gal (MG) reuse storage tank. S High-service pumping reuse. S Remodel of the existing operations building and laboratory. S Construction of a new maintenance building for the service area’s maintenance staff.

The conceptual design was started in 2015 and construction was completed in 2019. The design was funded by the utilities’ capital budget and the construction was funded by the Florida Department of Environmental Protection (FDEP) State Revolving Fund (SRF) program.

Figure 3. Mixed Liquor Flowing From the Preanoxic Basin to the Integrated Fixed Film Activated Sludge Zone Covers (photo: Lucas Lustik, Sure Thing Photography) Figure 4. Stainless Steel Retention Screens in Integrated Fixed Film Activated Sludge Zone

The existing 6-mgd biological nutrient removal (BNR) train uses a five-stage oxidation ditch process. The initial design concept was to mirror the existing process for the capacity expansion; however, the site did not have enough available area to install a mirror of the existing process train. The limited site area led to a treatment process evaluation to select the best option for the WWTF expansion.

Treatment Plant Expansion Details

The owner and engineer decided to use an integrated fixed film activated sludge (IFAS) process for the expansion. The IFAS process provides high-efficiency wastewater treatment and allows for smaller basins than conventional activated sludge processes. The process provides efficient wastewater treatment meeting advanced wastewater treatment (AWT) standards with smaller basins and less energy.

The 6-mgd expansion was installed in 50 percent less area and has 33 percent less installed horsepower (HP) than the existing 6-mgd wastewater process.

The WWTF design included a focus on low-maintenance processes for ease of operation and maintenance for the lifespan of the facility. The pretreatment structure provides 3-millimeter (mm) screens, grit removal, and 1-mm fine screens. The wastewater is “cleaned” by the pretreatment structure, which reduces the county’s maintenance by reducing rags and the wear on downstream equipment. This clean wastewater also makes it possible to add IFAS media in the BNR to improve nutrient removal.

Conventional clarifiers with launder covers require no maintenance of weirs and launders. Low-speed conical mixers are used in the anaerobic and anoxic basins. These mixers are very high efficiency and virtually rag-free, which

Figure 5. Effluent Produced by the Integrated Fixed Film Activated Sludge Process

also reduces maintenance. Figure 1 shows the capacity without increasing the solids loading clarifiers with perimeter walkways and launder rate to the clarifiers, and the second one being covers, and the elevated walkways that connect an aerated polishing reactor without any media. the process basins, another feature for easy The first aerobic reactor operates at a operation and maintenance. dynamic residual dissolved oxygen (DO) A conceptual schematic of IFAS basins is concentration within the range of 2 to 4 mg/L. shown in Figure 2.The IFAS process constructed The second aerobic reactor operates at a constant at this WWTF is a five-stage BNR process that residual DO concentration of 0.5 to 1 mg/L to includes one anaerobic zone for biological minimize DO carryover in the mixed liquor phosphorus (P) removal, followed by a pre- recycle to the pre-anoxic zone. The DO control in anoxic zone for denitrification. The aeration the IFAS zone is based on a patented ammoniumvolume consist of two reactors, with the first based aeration control (ABAC) algorithm where one having plastic media at a fill fraction of 42 the DO setpoint is dynamically controlled by percent (IFAS zone) to increase nitrification Continued on page 26 Florida Water Resources Journal • January 2021 25

Figure 6. Three 200-Horsepower Turbo Blowers (photo: Lucas Lustik, Sure Thing Photography) Figure 7. Aerial View of 6-mgd Integrated Fixed Film Activated Sludge Process Train (photo: Lucas Lustik, Sure Thing Photography)

Continued from page 25 the in situ online measurements of ammonium concentrations in the polishing reactor. The ABAC algorithm ensures that the IFAS system operates at the appropriate DO concentration, depending on the incoming total Kjeldahl nitrogen (TKN) load to the plant at any given time, contributing to a substantial reduction in energy use, as well as a more stable effluent ammonium and total nitrogen (TN). The overall control and operation of the five-stage IFAS BNR system at the WWTF is similar to conventional activated sludge processes with no media. Figure 3 shows the mixed liquor flowing over a weir from the preanoxic basin into the IFAS zone

Effluent from the aerobic zones flows to the postanoxic zone for further polishing of the nitrates to meet the effluent TN limit. Prior to the postanoxic zone, a portion of the polishing zone effluent is diverted and recycled back to the pre-anoxic zone to enhance denitrification. Following the postanoxic zone is a re-aeration zone for burning off any excess carbon. Effluent from the re-aeration zone is clarified and filtered prior to disinfection and discharge from the facility.

The IFAS system combines suspended growth and fixed film within the same bioreactor, which increase the overall biomass of bacteria that can be maintained, and thus reduces the required activated sludge volume. In this process, plastic media is added to the aeration basin and maintained in suspension. Stainless steel retention screens, shown in Figure 4, are used to retain the media within the IFAS basins, thereby increasing the overall solids inventory by up to 100 percent without increasing the solids loading to the final clarifiers.

The large protected surface area on the IFAS plastic media allows for biofilm growth. As an added bonus, the biomass growth on the media will also act as a constant source of nitrifiers, as the biofilm in the protected area will constantly slough off and seed the aerobic reactors with nitrifying bacteria. This will result in mixed liquor suspended solids (MLSS) having an increased potential for nitrification compared to traditional nitrifying activated sludge systems with no media.

The five-stage BNR system was designed with a total suspended growth of seven days, including the nonaerated zones. Experience shows that denitrification is more efficient at lower solids retention times (SRT). In the overall design, the SRT of the system at the WWTF is lower than a nitrifying activated sludge system and the mixed liquor has a larger population of denitrifiers, enhancing the overall denitrification removal rate.

The BNR process was placed into service at the end of February 2019. The new IFAS process train was started at about 60 percent of the total plant influent flow at an average daily flow of

about 2.5 mgd. The new process acclimated presence of additional nitrifiers provides much S 50 percent smaller footprint quickly and was producing AWT-quality more stable and efficient ammonia removal S 33 percent less installed HP effluent within 60 days. After initial start-up throughout the year within a smaller footprint and process optimization, the existing process than is otherwise needed in conventional For these reasons, the IFAS process should be train was taken out of service in June 2019 for processes. evaluated if a facility needs to improve treatment equipment replacement. This time the actual These advantages resulted in a 6-mgd IFAS level, expand capacity, or has limited site area. S load of biochemical oxygen demand (BOD) and process train (Figures 7 and 8) that has the total suspended solids (TSS), as well as the TKN following features, compared to the adjacent in the influent, was close to the design capacity, 6-mgd activated sludge process at this site: with an AADF of 4.62 mgd and slightly higher influent concentration of BOD and TSS. Figure 5 shows effluent TN and TP concentrations from July 2017 to June 2018 compared to July 2019 to June 2020. These data illustrate the improved nitrogen removal capabilities of the IFAS process train. Figure 5 also shows that the IFAS process produces effluent, which meets AWT standards without any addition of external carbon. The process air is provided by three turbo blowers: two duty and one standby. Figure 6 shows the turbo blowers within a building lined with sound-attenuating wall coverings. The blowers provide 750 standard cu ft per minute TREATING YOU RIGHT (SCFM) of process air each and have 200-HP motors. The power requirement from aeration is the majority of connected HP for the BNR process. The total connected HP for the 6-mgd IFAS process train is 33 percent less than the adjacent five-stage oxidation ditch process.

Based on the experience of designing and operating the IFAS system at the WWTF, the main advantages of this process are: S Plastic media is a host site for nitrifying bacteria. S Constant seeding of nitrifiers to the MLSS for high ammonium potential. S Aerated volume and footprint is smaller than conventional BNR. S Can handle varying seasonal loads throughout the year. S Operates similar to conventional BNR processes. S Stainless steel medium-bubble diffused aeration with no need for maintenance or replacement. S Both media and media retention screen are maintenance-free. Mead & Hunt has been treating Conclusion the Florida water/wastewater

The five-stage biological IFAS process industry since 1968. We know provides several enhancements to conventional what it takes to get the job done BNR processes. The performance data have shown that this facility consistently meets the right. From treatment to distribution, AWT effluent standards, while operating near we are here to serve you.capacity without any external carbon addition.

The media within the IFAS zone allows nitrifying bacteria to attach themselves and reside in the aerated basin with sufficient DO, lowering the suspended aerobic SRT significantly. The EXPERIENCE EXCEPTIONAL meadhunt.com

Test Yourself What Do You Know About Water Quality Credit Trading?

Donna Kaluzniak

1. Florida Administrative Code (FAC) 62-306,

Water Quality Credit Trading, establishes requirements for water quality credit trading between pollutant sources to reduce or eliminate what type of pollutants?

a. Disinfection byproducts b. Heavy metals c. Nutrients d. Suspended solids

2. Per FAC 62-306, the intent of trading of water quality credits is to provide flexibility among pollutant sources to meet the requirements of a reasonable assurance plan (RAP) or a(n)

a. administrative order (AO). b. basin management action plan (BMAP). c. consent order (CO). d. total maximum daily load (TMDL).

3. Per FAC 62-306, the annual pollutant load from a pollutant source after performing all required pollution control activities, below which water quality credits may be generated, is the

a. baseline. b. credit allowance. c. pollutant limit. d. water quality allowance.

4. Per FAC 62-306, a credit is the amount of an entity’s pollutant load reduction below the baseline that will be available for trading.

Credits shall be in

a. average parts per million per month. b. maximum parts per million per day. c. pounds or kilograms per month. d. pounds or kilograms per year. 5. Per FAC 62-306, which of the following activities is eligible to generate credits?

a. Implementing best management practices (BMPs) as required under a permit. b. Changing a process to reduce the quantity of water discharged through reuse. c. Reducing a pollutant loading as required under a BMAP. d. Reducing a pollutant loading as required under a RAP.

6. Per FAC 62-306, a credit buyer must submit information on the term of the trade, the number of credits traded, documentation to calculate the credits generated, the date when the credits will be generated, the time frame the credits will be applied under the trade, the unit price for each purchased credit, and the amount of any state funding used to generate the credits traded to the Florida Department of

Environmental Protection (FDEP). How must this information be submitted to FDEP?

a. Complete a water quality credit trading web form on FDEP’s water quality credit trading website. b. Submit an engineering analysis report on water quality credits to FDEP. c. Submit a water quality credit trading affidavit form to FDEP. d. Submit a water quality credit trading request letter to FDEP.

7. Per FAC 62-306, for trades where the seller and buyer discharge to different water body identification units (WBIDs), the amount of credits proposed to be traded shall be adjusted by what means?

a. Cost agreement between buyer and seller to ensure equitable costs for the buyer and income for the seller. b. Consent order through FDEP to provide assurance that the seller will adjust modifications commensurate with differences in WBIDs. c. Location factors (LFs) to provide reasonable assurance that the proposed trade does not result in localized adverse impacts to the waterbody or water segment. d. A WBID adjustment control document to automatically adjust credits month by month. 8. Per FAC 62-306, an uncertainty factor (UF) reflects the uncertainty associated with estimated credits. For proposed trades involving estimated credits, FDEP uses what default UF ratios for urban stormwater?

a. 1:2 c. 2:1 b. 1:3 d. 3:1

9. Per FAC 62-306, how are water quality credit trades monitored and reviewed?

a. Credits are tracked by each of the water management districts, and credits in each district are posted on the district website. b. Credit buyers and sellers discharging to each WBID track the credits and record them on an FDEP website. c. The FDEP tracks all credit generation preapprovals and all credits traded, and posts the information on its website. d. The managers for each BMAP or RAP track all credits traded and post them on the individual BMAP or RAP website.

10. Per FAC 62-306, who is responsible for achieving the load reductions on which the credits are based and complying with the terms of the permit, or the BMAP or RAP, and any trading agreements entered?

a. The buyer of credits. b. The seller of credits. c. Both the buyer and seller of credits, equally. d. Both the buyer and seller of credits, as detailed in the agreement between the parties.

Answers on page 54

References used for this quiz: • Florida Administrative Code 62-306, Water

Quality Credit Trading • FDEP Florida Water Quality Trading Registry

Website: https://floridadep.gov/dear/waterquality-restoration/content/florida-water-qualitycredit-trading-registry

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