Incorporating Asset Management Reliability Elements in Water Resource Recovery Facility Design: A Case Study

Background and Objectives The Clark County Water Reclamation District (CCWRD) collects and reclaims water from over 240,000 business and residential accounts in Southern Nevada. CCWRD's main treatment facility, the Flamingo Water Resource Center (FWRC), has the capacity to treat 492 megaliters/day MLD (130 million gallons/day MGD) and is being expanded to 567 MLD (150 MGD) to accommodate growth. Project 19007 Secondary Treatment Aeration Basins and Secondary Clarifiers (Project) is part of this expansion. It entails the first phase of a new 190 MLD (50 MGD) secondary treatment complex, the West Secondary Treatment (WST). The first phase of the new WST facilities has a design capacity of 95 MLD (25 MGD) and includes three biological nutrient removal (BNR) trains. The design of the WST is complete, and the facilities are currently under construction. CCWRD and the WST design team developed and implemented a Reliability Centered Design (RCD) methodology for the Project with the following objectives: 1) Identify one-time opportunities to improve the design, 2) Produce a robust design that meets CCWRD's reliability requirements and risk tolerance, 3) Verify design adequacy to meet O&M needs, 4) Quantify system risk by identifying the consequences and likelihood of failure, The RCD enabled the design to be optimized and asset management reliability elements to be incorporated at early stages. It also informed stakeholders and prepared the ground for future reliability centered maintenance (RCM) activities. Methodology The RCD methodology integrated reliability with risk-based solutions from the beginning of the Project. It aligned reliability with CCWRD's risk management profile (Figure 1). CCWRD, the design team, and the Construction Manager at Risk (CMAR) contractor held several workshops to conduct the RCD process through four distinct steps: 1) Design and Operation Philosophy - The basis of design was used for the RCD process as it defined the functional requirements, operating context, and baseline design. The team reviewed design and operation philosophies to document and consolidate O&M staff input. CCWRD's risk matrix scoring was reviewed and adopted as a basis for RCD. 2) Failure Mode Effects and Criticality Analysis (FMECA) - FMECA workshops were held to review the individual systems, validate the operating requirements, provide feedback on design alternatives, discuss one-time opportunities, identify the potential failure modes, and assign consequences of failure to each system. A key goal was to identify design improvements to manage or eliminate failure modes through implementation of one-time opportunities. 3) Reliability Block Diagram (RBD) Modeling - The information gathered in steps 1 and 2 was used to create an RBD model and estimate the availability, costs, and risks. A logical representation of the different process areas was created. Failure modes and consequences of failure were entered for the various systems. Maintenance, including spares, was assigned to the failure blocks, representing failure management strategies for the different failure modes. The simulation was then developed for a 40-year life cycle. 4) Model Validation, Optimization, and Recommendations — The final RCD workshops validated the model assumptions and presented preliminary results. CCWRD provided feedback on the model results based on their experience with similar equipment and the operation of existing facilities. Model adjustments were made based on this feedback, and the RCD process was completed. Conclusion Overall, the RDC effort was successful and identified 95 one-time opportunities through the collaborative workshops and discussions with CCWRD's O&M staff, design consultant, and contractor. Many of these opportunities were included in the design and will enhance O&M conditions in future operations. The RBD model's main insights were availability, annual costs, and risk (Table 1). The model showed that availability reductions were mainly due to planned maintenance (PM) rather than random outages (Figures 2 and 3). The results indicate that the WST design will achieve full capacity almost ninety-four percent of the time. If more availability is required, an optimization of the duration or interval of the PMs can be considered. The model estimated labor, spare parts, and equipment costs over the lifetime of the assets. The estimates covered corrective, planned, and inspection activities (Figure 4). Labor costs were stable from year to year. Nevertheless, relatively high spare parts costs appeared beginning around year ten and then again approximately ten years later which were primarily due to diffuser replacements. According to the RBD model results all risk scores were under the criticality threshold, so the model showed that the WST design meets the risk criteria (Figure 5). The model indicated that highly critical systems such as the blower and electrical systems have enough redundancy and do not affect the overall risk profile. The main contributors to criticality included systems like diffusers, actuators, clarifier drives, or sludge mechanisms that do not have redundancies and impact the overall system when they fail. However, the risk profiles of these systems were low. Significance This presentation provides an RCD methodology that can be used by WRRFs to incorporate asset management reliability elements at the design stage.