Aligning Asset Management and Process Strategies at Wastewater Treatment Plants

Last Modified: Sep 08, 2016


  • Eric Antmann EI, George A. Brown PE, Janeen Wietgrefe PE - Hazen and Sawyer
  • Vincent Morello PE - Broward County Water and Wastewater Services

The Broward County North Regional Wastewater Treatment Plant (NRWWTP) is a 95 mgd plant that has been operating since 1975. In 2014 the NRWWTP embarked on a major Facility Improvements Project. This project addresses both long term process strategies and renewal and rehabilitation needs, on a 20 year planning horizon. As a component of the Facility Improvements Project, a asset management plan for equipment renewal and replacement was developed. The asset management plan was charged with coordinating and scheduling asset replacement needs identified by three studies: a security assessment, a condition assessment, and the long term process strategy. The security assessment identified building and process-level needs, from a threat assessment and vulnerability perspective. The condition assessment identified equipment renewal and replacement needs, based on the remaining useful life of selected plant assets. The long term process strategies focused on regulatory drivers and other plant-level needs.

Coordinating the results of these three studies into a single, unified asset management plan presented several challenges. Decisions on if, when, and how to replace or rehabilitate plant assets had to consider the age and condition, consequences of failure, and role in long term process strategies of each asset. As an example, replacing obsolete equipment may not be worthwhile at facilities soon to be retired due to new or modified processes. However, particular assets at these facilities which carry high consequences of failure, are in poor condition, or have a security risk may still pose a risk to utilities. A risk scoring framework was developed to identify such assets. There were also logistical challenges in managing the large volume of data and risk computations, as approximately 1,200 plant assets were included in the asset management plan. To address these challenges, a novel Asset Management and Decision Support (AMDS) software tool was developed and implemented. This tool utilized a network connected database to automate data storage and analysis tasks. The AMDS Tool also supported field inspections using network-connected tables, resulting in better organization and time savings.

This paper describes the robust risk scoring framework applied to each asset and AMDS software tool. The results of the study, and how they were coordinated ongoing plant projects, will also be discussed. Results of this paper provided an efficient condition assessment process and strategic equipment R/R program.

Status of the Investigation:
The Facility Improvements Project at the NRWWTP began in 2014, and construction will be completed around 2020. The security, condition assessment, and long term process strategy development began in 2014 and was completed in 2015. The small number of high risk assets identified in the asset management plan were addressed in, or added to, the construction portion of the Facility Improvements Project. Others were added to the scope of future projects developed as part of the long term process strategy. Needs identified by the asset management plan that did not fit into existing projects were added to special equipment renewal and replacement projects. These projects were scheduled into the NRWWTP future plans.

Means and Methods:
Asset renewal and replacement needs were identified and prioritized using two metrics: probability of failure (PoF) and consequence of failure (CoF). PoF was determined from the condition assessment. Assets were selected for condition assessment based on their relative significance to overall operations. Each selected asset was visually inspected in the field and assigned a condition score. The database component of the AMDS software tool stored the results of each inspection and photographs. Inspectors entered scores directly into network connected tablets, and uploaded photographs form the device cameras. This improved the efficiency of field efforts and reduced opportunities for errors to occur.

CoF were scored for each asset using a multiparameter risk analysis matrix. Criteria in the risk analysis matrix included Health and Safety, Reliability, Regulatory Compliance, and Redundancy. Results of the security assessment were utilized as one of the bases to score assets in these criteria.

Both PoF and CoF were scored on a scale of 1 through 5. After scores were determined, they were multiplied to compute a Risk Score, which ranged from 1 to 25. Assets with higher risk scores were prioritized in the preliminary list of asset renewal and replacement needs. In addition, the age of each asset was collected from plant records. Those assets with low risk scores were scheduled for renewal or replacement when they reach the end of their useful life. The small number of high risk assets were scheduled for renewal or replacement in the immediate term. Results of this analysis are presented in Table 1, which shows that the bulk of assets had low PoF and CoF scores.

This preliminary asset renewal and replacement schedule was then compared to the long term process strategies. Assets with high risk scores were addressed in the scope of these facility projects. An example of this was the addition of digester piping to mitigate a potential single point of failure in the biosolids treatment process that was found during the condition assessment. Assets which will be replaced by long term facility projects before or the end of their useful life were removed from the asset management plan. Assets which will reach the end of their useful life shortly before they are replaced by long term facility projects were considered for limited overhaul needs via a risk based decision. As an example, variable speed drives at an effluent pump station posed a modest risk because of their age and consequence of failure. The pump station was scheduled to be replaced in the intermediate term. As a result, these drives were scheduled for rebuilds, instead of replacement, to conserve funds but provide the required pumping capacity.

This paper presents an example of an organized approach to asset management which considers long term process strategies, security needs, and asset condition. The asset management plan developed mitigated risks arising from security concerns as well as asset age and condition, while achieving synergies with the ongoing Facility Improvements project and long term facilities plan. The paper will discuss the implementation of this project, recommendations for future asset management plans, and the benefits of a unified asset management plan at treatment facilities.

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