Using Simulators to Innovate Operator Training: Preparing for Wet Weather and MBR Technologies in the San Mateo WWTP Expansion

Introduction
In 2014, the City of San Mateo established the Clean Water Program (CWP), a comprehensive 10-year plan to upgrade the aging wastewater collection system and wastewater treatment plant (WWTP). The San Mateo (WWTP) Nutrient Removal and Wet Weather Flow Management Upgrade and Expansion Project (Project) is the largest CWP project. The city embarked on the Project to create a state-of-the-art, reliable WWTP that will be known as the 'Gem of the Bay.' The Project is designed to address aging infrastructure, current and forthcoming discharge regulations, sanitary sewer overflows and unauthorized discharges of untreated or partially treated wastewater. The completed Project will produce high-quality effluent suitable for either potable or non-potable reuse.

Objectives
The Project will introduce a technology change from conventional secondary activated sludge to biological nutrient removal (BNR) and membrane bioreactor (MBR) treatment. In addition to the technology change, the Project will transform WWTP operation. Influent flows to the WWTP are highly variable and influenced by infiltration and inflow in the collection system, so the Project will provide several operating modes. Normal Mode utilizes the BNR and MBR to treat dry and moderate wet weather flows. Wet Weather Mode uses a high-rate biological contact process (BioActiflo™) operated in parallel to the BNR-MBR treatment during challenging peak wet weather events.

The Project will add the following new liquid stream processes: headworks, primary clarifiers, flow equalization, BioActiflo™, chemical storage and feed facilities, BNR, MBR, disinfection and Title 22 recycled water facilities. A process flow diagram of the Project facilities is shown in Figure 1.

The WWTP has an average annual design flow of 16 MGD, a maximum monthly flow of 21 MGD and a peak hourly influent of 78 MGD. The maximum design flow capacity of the MBR is 42 MGD. Peak and wet weather flows above 42 MGD will be handled by the BioActiflo™ and flow equalization.

Operators will be interactively trained on operation of the new BNR-MBR process prior to transitioning to the new system using a custom SimuWorks™ simulator. The simulator also provides a risk-free environment to design of peak flow operational strategies.

Methodology
SimuWorks™ is a simulation software specifically designed to train WWTP operators. It presents operators with an interactive representation of the WWTP with the same control points as the real system. An advanced wastewater process model then simulates plant performance using the user specified conditions.

Wet Weather Mode
During wet weather events operators can activate the following strategies:
- Flow diversion to the onsite flow equalization basins
- Flow diversion to BioActiflo™

The BioAciflo™ wet weather treatment process provides biological contact for the diluted wet weather flow. Biomass from the BNR process is sent to the BioActiflo™ process to provide biological treatment of the wet weather flow. The operator has the challenge of diverting sufficient BNR biomass while maintaining a stable MBR biomass inventory.

The custom San Mateo WWTP SimuWorks™ simulator shown in Figure 2 provides a platform for operators to evaluate potential operational strategies. After each simulation, the simulation provides operators with predictions of plant effluent quality, key process indicators (KPIs) and operating costs (aeration/pumping energy and chemical dosage) to illustrate the effect of operational changes.

Through guided training scenarios, the simulator teaches operators several operational strategies and how to troubleshoot some anticipated challenges. Included scenarios are summarized in Table 1. An interactive simulation scenario designed to educate operators on Wet Weather Mode is shown in Figure 3. The simulator dynamically simulates a storm and identifies when the MBR maximum design flow capacity is exceeded. Operators then learn how the flow control options available at the WWTP can be used to divert peak flows is consistent with the MBR maximum design flow capacity.

Status and Schedule of Ongoing Work

The end of WWTP construction and process startup is expected in Summer 2025. The configuration of the simulator is finalized and implementation as a tool for operator training will begin in early 2025.

Conclusion
Operator training is scheduled for early 2025. The operator's experiences will be presented as conclusions touching on the following topics:
- Process simulators development traditionally has focused on detailed engineering design. This adds complexity unnecessary for operational training tools, so a custom training platform was developed.
- A user interface that resembles the actual treatment process controls available during plant operation and provide dynamic response for wet weather treatment allowed operators to become familiar with the trigger points, critical controls, and fatal flaws that can occur.
- The simulator allows users to repeat rerun simulations as many times as needed to facilitate users learning at their own pace an exploring the nuances of challenging process issues
- Guided training scenarios provides training opportunities for operators to understand the critical control points
- Startup performance (including seeding) can be evaluated to prepare plant for initial startup.