DAFT Optimization - Success and Struggles of Operating DAFTs without Polymer

Introduction South Platte Renew (SPR) is the third largest Water Resource Recovery Facility (WRRF) in Colorado, utilizing advanced treatment processes, including Dissolved Air Flotation Tanks (DAFTs). The ongoing DAFT Optimization Study aims to evaluate the feasibility of eliminating polymer dosing to the DAFTs, potentially leading to significant cost savings. Expected to conclude in December 2024, this study could save SPR up to $85,000 annually in chemical expenses. The research is being conducted by SPR staff using internal resources. Main Objectives 1.Evaluate the modifications implemented in DAFT Operations to achieve the elimination of polymer usage. 2.Provide a framework for other WRRFs to use insights from this study, facilitating the operation of DAFTS without the need for polymer. DAFT Background DAFTs are a technology that are used in a WRRF to thicken solids, effectively reducing the volume of water sent to digesters and, subsequently, to centrifuges. By minimizing the water content in the solids before they reach the dewatering stage, DAFTs create a more energy efficient process for dewatering, ultimately producing drier solids that are suitable for agricultural applications. DAFTs operate through a process called dissolved air floatation: air is dissolved in water under high pressure and then released at atmospheric pressure, forming tiny bubbles. These bubbles attach to particles, causing them to rise and form a sludge layer, known as the float blanket, which is skimmed off and sent to the digesters. Remaining solids sink to the bottom and are either recycled back into the DAFTs for additional floatation attempts or send back to the plant headworks. Study Timeline Project Kickoff: September 1, 2024 Phase 1: October 2 -- November 6, 2024 Phase 2: November 6 -- December 4, 2024 Phase 3: Dependent on outcome of Phase 2 Methodology SPR has three DAFTs on the facility, but typically, only one DAFT is in operation at a time. In Phase 1 of the Study, an additional DAFT was brought online to facilitate a comparative analysis. DAFT 4, the control, continues to operate with polymer dosing, while DAFT 3 operates without polymer. This approach limits the impact of operational changes by confining them to only half of the flow, reducing risks to downstream processes. The initial design criteria is shown in Table 1. While the design criteria served as the initial baseline, parameters were adjusted throughout the study to optimize the performance of DAFT 3 without polymer. Phase 1 is currently showing promising results, so the project team has decided to move forward with Phase 2 of the study. In Phase 2, both DAFTs will continue to operate, but neither will receive polymer. This phase will continue to explore the ideal configurations for both DAFTs as they operate without polymer. This phase will also explore the ideal configuration for wasting and recirculating the bottom blanket. Depending on Phase 2 results, Phase 3 may be pursued. This final phase would involve running a single DAFT (as SPR typically operates) without polymer to test the operational limits of the DAFTs. For all three phases of the study, a mass balance will be conducted to track solids flow, as well as an energy balance to assess any changes in energy consumption. Results Throughout Phase 1, the project team has been closely monitoring subnatant total suspended solids (TSS) and float blanket total solids (TS) to assess the effectiveness of the Study. Table 2 provides the TSS and TS values for DAFTs 3 and 4 throughout the duration of Phase 1. The data shows a decreasing trend in subnantant TSS as the Study progresses, indicating that the solids concentration in the subnantant is reducing -- a positive outcome for the Study. This decrease in TSS is attributed to operational changes that have optimized the process. Details of these changes and their direct impacts will be described in detail during the presentation. DAFT 4 demonstrates typical DAFT performance at SPR, while DAFT 3 is showing slightly lower efficiency compared to operations that use polymer. For Float TS, the ideal operation is around 6%, with DAFT 3 averaging about 5.2%, which, while slightly lower than ideal, remains within the acceptable range of 5-6%. Further operational adjustments are planned to bring DAFT 3 performance closer to that of DAFT 4/ normal operation performance. A full analysis of the data and lessons learned from all the phases of the study will be shared during the presentation, offering valuable insight into optimizing DAFT operations without polymer. These findings have the potential to reduce chemical and energy costs and provide a model for other WRRFs to adopt similar practices.