Biosolids Facility Impact Assessment


Nashville Metro Water Services makes sustainability a priority at its five facilities. Wilmot was tasked with measuring the impact of those improvements at the Central Wastewater Treatment Plant and identified $493M in community benefits.


For years, heavy truck traffic and pervasive odors from raw sewage sludge plagued the Germantown and Salemtown neighborhoods in Nashville. As part of an upgrade program at the Central Wastewater Treatment Plant, Nashville Metro Water Services invested $136M in a new Biosolids Facility. Prior to construction of the Biosolids Facility, raw, dewatered sewage sludge was hauled long distances to a landfill. At times, there was no landfill that would accept the sludge, causing backups, odors, and increased liability. There were also numerous issues community-wide with odors and truck traffic. Although the decision to build a Biosolids Facility did not offer the lowest capital cost of all options, the plant has and will continue to save millions of dollars over its lifetime by generating extremely desirable economic, social and environmental improvements. The new facility digests and dries sewage sludge and processes it into Class A biosolid pellets, used as soil amendment for agricultural, erosion control, lawns, etc.

Wilmot’s Role

To assess the impact of the investment on Nashville, Wilmot completed a triple bottom line analysis to evaluate the economic, social and environmental impacts of the new facility. Wilmot found $493M in benefits, including:

  • Avoided costs from emissions of greenhouse gases and criteria air pollutants

  • O&M savings

  • Sludge disposal savings

  • Pellet revenue

  • Savings to the agricultural industry

  • Avoided liability

  • Increased property values

  • Nitrogen runoff mitigation

  • Future benefits from biogas reuse


  • $493M triple bottom line benefits over 20 years

  • Benefit-cost ratio of 1.77


Metro Water Services

Nashville, TN


  • Municipal

  • Water/wastewater


  • Triple bottom line cost benefit analysis

  • Economic impact analysis

  • Geospatial analysis

  • Greenhouse gas inventory