Tuesday, September 10, 2024
3:15 PM - 3:45 PM
Elements of a Successful Fast-Tracked Filter Rehabilitation
Drinking Water Quality

Nashville Metro Water Services (MWS) operates the K.R. Harrington Water Treatment Plant (KRH) to supply drinking water to the city of Nashville. KRH is a conventional water treatment plant with 18 granular media filters and a capacity of 90 mgd. While the existing KRH filters consistently produce low effluent turbidities, MWS has experienced increasing challenges including short filter run times and frequent backwashes. With a near-term need to address these challenges and a larger project to replace the filters underway, MWS was faced with the decision of what to do with the existing filters to address these urgent challenges until the new filters could be brought online. Meeting two needs with one approach, MWS decided to rehabilitate and modernize the existing filters, with the goal of achieving longer filter runs and less operation and maintenance attention in the near term, while planning for conversion of these existing filters to post-filter GAC contactors after the new filters are commissioned. As the first step in the design, MWS and Carollo developed a rehabilitation plan based on a suite of diagnostic tests including filter operational data and backwash analyses, lower gullet inspection, gravel profile evaluation, media sieve analysis, and a structural assessment. Knowing that the filters were already strapped by short run times, one of the key design and construction challenges was maintaining operations through other filters to minimize impacts to the plant. MWS, Carollo, and Sundt, the Construction Manager at Risk (CMAR) responsible for constructing the improvements, worked together to implement a construction sequence before the first filter was taken offline. This sequence was then reviewed and modified regularly throughout construction to meet plant needs and keep water flowing. Beyond the sequencing challenges, the project also had to contend with anthracite supply chain issues, air intrusion into the filters during backwashing, backwash flow distribution, and several unanticipated conditions in the existing filters. MWS and the design and construction teams persevered through these challenges and learned several key lessons: 1. Creating a construction sequence with plant staff, the engineer, and the contractor, and reviewing the construction sequence weekly are critical to keeping the project on schedule and the existing plant functional. 2. Supply chain issues are best handled with persistent planning and communication between all parties. 3. Regularly collecting and analyzing filter operational data identified startup issues early and allowed timely resolution. This presentation will explore lessons learned and present the successful outcome of this challenging project, demonstrated by a comparison of operational performance between old and rehabilitated filters.