Biosolids Master Planning in Tulsa, Oklahoma to Develop a Sustainable Biosolids Management Program

Biosolids Master Planning in Tulsa, Oklahoma to Develop a Sustainable Biosolids Management Program The Regional Metropolitan Utility Authority (RMUA) is responsible for the plant infrastructure as well as the operation and maintenance of the 16 million gallon per day (MGD) capacity Haikey Creek Wastewater Treatment Plant (HCWWTP) in Tulsa, Oklahoma. To evaluate the future needs for treating and handling biosolids generated at the HCWWTP, the RMUA authorized engineering development of a biosolids improvements facility plan and concept level design of needed facility upgrades. For the past 19 years, unstabilized biological sludge from the aeration process has been thickened and then hauled to the Tulsa Southside WWTP for treatment via anaerobic digestion and land application. However, this practice requires hauling of 9-10 tanker trucks a day to the City of Tulsa's Southside WWTP and requires significant coordination between the two plants. The goals of this study were to identify existing conditions, estimate future loadings (up to 24 MGD) , and evaluate cost-effective alternatives to upgrade the HCWWTP to a stand-alone facility, produce biosolids product that could be beneficially used, and define a solution that is not only within the RMUA budget constraints, but defensible (with no regrets) to RMUA and its two partner agencies, the Tulsa Municipal Utility Authority (TMUA) and Broken Arrow Municipal Authority (BAMA). The study provided an opportunity to not only investigate technologies for producing Class B or Class A biosolids for beneficial use, but also to consider adaptability to changing regulations and potential energy savings and reductions in carbon emissions. The following outlines the steps which were used to develop an updated solids management plan and concept level design for RMUA. 1.Existing and Future Conditions - This task included an evaluation of existing solids handling processes at the HCWWTP and the ability of the existing facilities to meet future projected loadings. Estimates of future quantities of solids production were made to determine appropriate sizing of solids management equipment in the near term (next 5 years) and into the future (20 years). This analysis was used to develop appropriate sizing criteria for all solids handling system components such that any deficits in capacity needs and the timing of equipment upgrades to eliminate those deficits were identified for future planning tasks. 2.Evaluation Criteria Development and Identification of Appropriate Technology Solutions -Through a workshop discussion with RMUA staff, the universe of technology alternatives was discussed with the goal of identifying potential biosolids management solutions and appropriate evaluation criteria consistent with RMUA goals and objectives were established. These criteria and potential technology options were defined in a workshop with RMUA stakeholders as well as engineering subject matter experts and the relative importance of these criteria determined. Fifteen biosolids management options as compared to the status quo were then identified in a collaborative process for consideration by the stakeholder team. The evaluation criteria previously developed was then applied against the potential technology solutions aimed at meeting RMUA goals. Figure 1 shows the result of the weighted scoring of these alternatives. At the conclusion of this criteria development and technology options identification, six potentially viable alternatives were selected by RMUA for further evaluation compared to status quo including: - Chemical-Thermal Hydrolysis - Mesophilic Anaerobic Digestion - Composting - Thermal Drying - Mesophilic Anaerobic Digestion plus Thermal Drying - Mesophilic Anaerobic Digestion, Thermal Drying plus Pyrolysis 3.Plant Simulation Evaluations - Existing whole plant simulation models for the HCWWTP were modified to analyze and evaluate the 7 alternatives identified to determine overall impacts on process performance, energy recovery and use of existing assets (tankages and equipment). Outputs of the simulations included overall energy balances, green-house gas emissions, and process performance compared to status quo. The outputs of this modeling exercise were then presented in a workshop with RMUA staff and used to further define the short-listed alternatives for further investigation and refinement. 4.Cost Evaluations - The simulation models formed the basis for conducting capital, O&M and life-cycle cost analysis of the 8 short-listed alternatives identified. Comparative cost evaluations were developed including vendor quotes for large equipment and cost estimating data from previous engineering project experience. Cost estimating tools were then used to compare capital, O&M and life-cycle costs for each alternative. These costs were then considered alongside the non-monetary evaluation criteria identified to develop a cost-benefit analysis. Figures 2&3 show the results of these cost and cost-benefit analyses. An interactive workshop was then held with RMUA stakeholders to fully vet the alternatives and determine three potential technology options for implementation. 5.Site Visits - The RMUA stakeholders then toured three representative technologies in Oklahoma including anaerobic digestion, thermal drying and composting. At the conclusion of the site visits, RMUA stakeholders agreed that while all three technologies could work for them, composting was the best choice due to simplicity of the process and production of a marketable product. 6.Implementation Planning - Implementation of the composting alternative was defined in terms of phasing, scheduling and budget planning to ensure the design and building of composting dewatering and composting facilities with the right capacity will be developed at the right time to meet the City's near-term and long-term needs. Through their engineering partner, City of Tulsa was able to apply for and secure grant funding from the USDA for 20 percent or$ 9.8 million of the total project cost (estimated at $48 million). Project Status One of the most interesting aspects of the project was that based on the previous biosolids management study done in 2014, preconceived solutions of anaerobic digestion and improved dewatering to then land apply biosolids cake was thought to be the solution that would be recommended. However, by revisiting potential solution options and redefining what criteria were most important, several different solutions were reconsidered. Ultimately, site visits conducted by RMUA Staff proved to be extremely helpful in the selection of the composting process that is proven, simple to operate and produces a biosolids product with multiple uses. This selection really paid off when grant funding became available that the compost production process proved to be qualified for, saving the RMUA nearly $10M in costs. This part of the story will be detailed in the paper and presentation. The Haikey Creek Wastewater Treatment Plant Biosolids Improvements Project has been approved and is in the design phase of a 10.2 dry ton per day capacity aerated static pile composting facility expandable to 15.3 dry tons per day in 2060. Major facility components include gravity thickener improvements, sludge storage, new centrifuge dewatering as well as a new covered aerated static pile facility. This case study will present details and results of the entire planning process which will provide planners, engineers, administrators, and owners with insight into the planning process used to select the right solution using specific owner driven criteria as well as costs to choose the right solution for their biosolids management needs.