JEA Monterey Wastewater Treatment Facility: Sequencing Success Through Simplified Controls

Alexander Gex

The Monterey Wastewater Treatment Facility (WWTF) was recognized in 2022 by the Florida Water Environment

Federation (FWEA) as the Earle B. Phelps Award winner in the secondary treatment category. This award is presented annually to wastewater treatment facilities that demonstrate excellent secondary treatment throughout the year and maintain the highest removal of major pollutioncausing constituents.

Facility Overview

The WWTF is a 3.6-million-gallon-perday (mgd) average annual daily flow (AADF) sequencing batch reactor (SBR) domestic wastewater treatment facility consisting of three SBRs in parallel with sequencing feed. There is a fourth SBR basin that currently operates as an aerobic digester for waste activated sludge (WAS) from the other basins.

Raw wastewater enters an influent channel where an automatic bar screen removes debris prior to pumping at the master influent pump station. Influent is pumped to three parallel SBRs that operate in a sequence. While one basin is accepting influent flow, another basin is treating influent, settling solids, and discharging treated influent. The timing of each step in an SBR’s cycle depends on the type of treatment that is desired.

After decanting a previous batch of treated influent, the liquid level and retained biomass in one of the SBRs is near the bottom level. As influent flow is redirected to fill this basin, no aeration is provided. This fill step mimics an anoxic selector, promoting the proliferation of floc-forming bacteria during anoxic conditions, while the concentration of readily biodegradable substrate is highest. By not running blowers to provide supplemental oxygen during this step, when the biological oxygen demand (BOD) is high, significant energy and cost savings result.

During the react phase, aeration and mixing are provided to create aerobic conditions, facilitating nitrification and allowing BOD to be rapidly consumed. During this phase, aeration can be cycled off to leave nitrate as the terminal electron acceptor, facilitating denitrification. Once sufficient biomass has accumulated in the form of activated sludge, aeration and mixing are both turned off to form quiescent conditions, allowing mixed liquor suspended solids to settle and clear supernatant to remain at the top. The supernatant will then discharge as effluent from the basin through the decant valve to the disinfection process.

At this point in the process, the SBR acts as a secondary clarifier with two protocols for settled sludge:

S The settled sludge can be retained in the basin for the next cycle, simulating return activated sludge (RAS).

S Excess settled sludge can be wasted for further solids handling in an idle cycle. This is typically performed at lower flow periods during the day.

Once the effluent has been discharged and the basin has emptied, influent flow will be diverted to fill the basin, starting the cycle again. Sludge wasted during an idle cycle from the SBRs goes to the aerobic digester (SBR #4) where solids are treated to meet Class B pathogen standards. Supernatant from the digester is discharged through the decant valve to the plant drain system and digested sludge is discharged to a sludge storage tank via sludge transfer pumps. Sludge is dewatered via polymer and centrifuge to approximately 15 percent solids prior to loading into trucks below the centrifuge canopy. Effluent from the SBRs goes through two parallel concrete ultraviolet (UV) disinfection channels, each containing five, 40-lamp modules in series.

During the time of the award, the UV system was undergoing upgrades while operating the old equipment during construction. Today, the new UV disinfection channels have six, 10-lamp modules with three modules per channel (two duty/one standby). This upgrade eliminated the need for a chemical cleaning system in favor of a wiper and gel cleaning system, and included a hydraulic lift system, which removed the need for a jib crane to lift the equipment out of the channels. Disinfected effluent flows into the effluent pump station where it’s discharged to the St. Johns River.

Table 1 summarizes the typical plant loadings and effluent quality from January to December 2021.

Sequencing Batch Reactors: A Complex Operational Challenge

Sequencing batch reactors are the most flexible biological treatment system currently available for wastewater treatment, capable of changing their sequence, timing, and duration of cycle steps, and type of treatment, to achieve the desired pollutant removal. An SBR can achieve aerobic, anoxic, and even anaerobic conditions for BOD and biological nutrient removal (BNR), while still acting as a secondary clarifier for solids removal; however, an intimate knowledge of cycle operation is needed to alter treatment in order to meet permit requirements. As noted in their application, the Monterey operations team described the original, complicated SBR process control system as follows:

“The original control scheme was set up using run timers and multipliers based off of percentages of calculated tank capacities. This system was so specialized and complex you almost needed an engineering degree to understand the controls.”

In 2019, WWTF operators designed a simplified program to control the SBR treatment process for BNR. This involved developing a written process protocol utilizing the SBR instrumentation and backup timers as a fail-safe if a given process set point was not reached in a given cycle time for optimal treatment. This protocol significantly reduced the learning curve needed to operate the SBRs at peak performance, resulting in the best overall performance in the plant’s history in 2020 after it was developed.

Two Class A operators and one Class B operator are responsible for the treatment facility and its success. The operations team consists of Josh Williams, Robert Graves, and Jackson Robertson. If there was ever a treatment facility award attributed to the excellent operational skills of its staff, JEA’s Monterey WWTF would be it.

Congratulations to the Monterey operations team for winning the 2022 Earle B. Phelps Award!

Alexander Gex is an engineering associate with Ardurra in Jacksonville. He is secretary of the FWEA Wastewater Process Committee and webmaster for FWEA’s First Coast Chapter. S