Evaluating Biosolids Management Alternatives in Northeast Tennessee

Authors:

  • William Sorah - City of Bristol
  • Johann Coetzee - Town of Elizabethton
  • Lee Brown - Erwin Utilities
  • Gordon Cox - City of Johnson City
  • Niki Ensor - City of Kingsport
  • C. Michael Bullard - Hazen and Sawyer

Estimated capital and operating costs were developed for each of the alternatives. Operating costs were extended to a net present operating cost (NPOC) based on a 20-year operating horizon to develop a net present cost estimate for each of the alternatives. For each “class” of treatment options capital and operating costs tended to be grouped within a “range” for the specific treatment technology.

This technical paper and presentation will share the results of a multiple agency regional biosolids management study jointly conducted for five entities located in Northeast Tennessee. The project participants in this work include the cities of Bristol, Elizabethton, Johnson City, and Kingsport and Erwin Utilities. The scope of the study was to prepare a biosolids master plan with a focus on evaluating opportunities for a regional Class A, or other advanced treatment, residuals management option meet current and future residuals production rates for the participant agencies. The participant agencies by participating in a cooperative planning effort were able to leverage their investment in development of the masterplan such that each agencies “share” in the plan development was lower than if they had conducted independent planning efforts.

The study included site visits to each of the participant agency wastewater treatment plants and a review of plant operating data to determine current plant loading rates, current plant residuals production rates, current treatment plant solids handling infrastructure, and current residuals quality (e.g., criteria metals pollutant concentrations). Collectively the agencies currently generate approximately 4,900 dry tons per year of wastewater treatment residuals which are managed by land application and/or landfill disposal with operating costs ranging from approximately $80 to $260 per dry ton. Detailed results of the assessment of current residuals quality and quantity for each of the participant agencies and the aggregated residuals production rates will be included in this presentation.

Evaluations of selected Class A residuals treatment technologies and other advanced residuals treatment technologies were investigated and will be presented, these evaluations included:

• Aerated Static Pile Composting
• Alkaline Stabilization/Pasteurization
• Fluid Bed Thermal Oxidation
• Centralized Thermal Drying
• Decentralized Thermal Drying

Estimated capital and operating costs were developed for each of the alternatives. Operating costs were extended to a net present operating cost (NPOC) based on a 20-year operating horizon to develop a net present cost estimate for each of the alternatives. For each “class” of treatment options capital and operating costs tended to be grouped within a “range” for the specific treatment technology as shown in Table 1 (above).

Based on the estimated capital and total net present costs, it appeared that composting may offer a Class A treatment alternative which could offer a slightly reduced to equal total net present cost to the current operating practices of the participant agencies. However, several of the participant agencies had operated composting facilities in the past and reported operational challenges with materials handling and final product distribution and marketing in addition to potential for on-site odor generation. Based on the consensus of the participant agencies the Class A composting alternative was removed from further consideration following the initial screening phase.

Multiple alternatives were evaluated for alkaline stabilization (three different process approaches) and thermal drying (seven different process approaches) as part of the masterplan study. The remaining Class A treatment options (i.e., alkaline stabilization and thermal drying) each require significant initial capital investment ranging from approximately $13MM for alkaline stabilization to $25MM for thermal drying. Furthermore, total net present costs associated with these alternatives range from approximately 2X to 3X the total net present cost associated with the current participant agency management practices. Migration to any of these technologies would require participant agencies to make an initial capital investment and incur an increased annual operating cost burden. In light of these economic considerations, the participants agreed that an external stimulus would be necessary to change the current operating practice.

Fluid bed thermal oxidation (FBTO) was evaluated as a centralized residuals management option and included three different final process air pollution control trains for enhanced particulate removal (wet electrostatic precipitator) and mercury removal (activated carbon bed scrubber). Estimated capital costs for the three air pollution control trains were developed and will be presented. Operating costs for the FBTO alternative were significantly influenced by the average dewatered cake solids content from the participants which likely would be unable to burn autogenously and resultant supplemental fuel requirements resulted in higher unit processing costs than would have been expected. Based on capital investment and operating costs the FBTO was removed from further consideration as a result of the master planning effort.

In summary, this presentation will share results of a cooperative, multi-agency master plan study for a regional residuals management facility. Results from the evaluation of a full range of process technologies will be presented.

For a copy of the full presentation, please contact the author at mbullard@hazenandsawyer.com

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Horizons showcases significant water, wastewater, reuse, and stormwater projects and innovations that help our clients to achieve their goals, and can help you achieve yours. Articles are written by top engineers and process group leaders, demonstrating and explaining the beneficial application of a variety of technologies and tools.

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