Improving Dewatering Performance While Reducing Polymer Consumption Using Nanobubble-Conditioned Makedown Water

Background Sludge dewatering is a critical and cost-intensive operation for municipal wastewater utilities, directly affecting biosolids handling, hauling, disposal, and overall lifecycle costs. Across a wide range of solids separation technologies including centrifuges, belt filter presses, and dissolved air flotation systems, polymer is widely used to improve floc formation, solids capture, and cake dryness. Historically, improvements in dewatering performance have been pursued through increased polymer dosing, an approach that can yield diminishing returns while escalating chemical costs, disposal costs, and operational complexity. As utilities near capacity or pursue process intensification, they increasingly operate sludge dewatering systems closer to mechanical and hydraulic limits. Field experience has shown that under these conditions, polymer solvation and activation can become a limiting factor influencing the dewatering performance of solids separation technologies. Nanobubbles, defined as ultra-fine gas bubbles less than 200 nanometers in diameter, are neutrally buoyant, highly stable, and electrochemically active. These properties enable nanobubbles to interact directly with polymer chains during solvation. Conditioning polymer makedown water with nanobubbles enhances polymer activation prior to contact with sludge, offering a mechanism to improve dewatering efficiency of solids separation technologies. Nanobubble-conditioned makedown water was first identified unexpectedly during a field trial when nanobubble-treated secondary effluent was repurposed as polymer makedown water. This observation prompted controlled studies within Moleaer's research laboratories and testing facilities, where mechanistic evaluations confirmed that nanobubbles interact with polymer chains during hydration, altering coil conformation, effective charge density, and bridging efficiency. These findings established the scientific basis for subsequent shop-scale testing and full-scale utility pilots, positioning the technology along a continuous path from research discovery to applied engineering and operational impact. This project evaluates nanobubble-conditioned makedown water as a novel and scalable approach to improving polymer efficiency, with a primary focus on full-scale centrifuge dewatering at the Rock Creek Water Resource Recovery Facility (WRRF). Supporting observations from additional municipal WRRF field studies indicate that polymer efficiency improvements have been observed across multiple dewatering technologies and sludge types. Methods Clean Water Services conducted full-scale onsite trials at the Rock Creek WRRF to evaluate polymer performance using nanobubble-conditioned makedown water for centrifuge dewatering. The pilot followed a structured multi-phase protocol that included baseline operation, functional testing, trial operation with nanobubbles, polymer dose optimization, and repeated baseline validation periods. Performance was evaluated using time-series operational data and direct comparisons of polymer dose expressed as pounds of active polymer per dry ton of feed, biosolids cake total solids, centrate clarity, makedown water quality, hydraulic throughput, and operator observations of equipment performance and process stability. These field evaluations were informed by bench-scale mechanistic testing and shop-scale engineering evaluations that established both the scientific basis and the operational feasibility of nanobubble-enhanced polymer activation. Results Full-scale centrifuge trials demonstrated that nanobubble-conditioned makedown water enabled a reduction in polymer dose while maintaining dewatering performance within mechanical limits. At Rock Creek, polymer dose was reduced from approximately 28 to 23 pounds of active polymer per dry ton of feed, representing a 17 percent reduction in polymer usage with no observed degradation in dewatering performance (Figures 1 and 2). Centrifuge cake solids were observed to plateau at approximately 23 percent total solids due to mechanical limitations of the centrifuges; therefore, performance improvements were realized primarily through reduced polymer demand rather than increased cake solids. Time-series results showed stable operation across multiple baseline and trial periods, indicating robust and repeatable performance of nanobubble-conditioned makedown water. Findings Dose-response analysis demonstrated a shift in the polymer efficiency curve when nanobubble-conditioned makedown water was applied, with comparable cake solids achieved at lower polymer doses relative to baseline operation (Figure 2). These results indicate improved polymer utilization rather than simple dose reduction. Field observations from multiple municipal wastewater treatment plants further support the transferability of the approach. Polymer reductions on the order of approximately 20 to 35 percent have been observed across different sludge types and dewatering configurations, accompanied by improvements in dewaterability, cake dryness, and filtered water quality. The consistency of these outcomes suggests that nanobubble-enhanced polymer activation represents a dewatering-technology-agnostic improvement to polymer performance. Conclusion Full-scale field data demonstrate that meaningful reductions in polymer usage can be achieved without sacrificing dewatering performance, resulting in significant potential reductions in chemical costs and biosolids hauling and disposal expenses. By targeting polymer activation upstream of the dewatering device rather than increasing polymer dose or modifying equipment, this approach offers utilities a scalable, easy-to-implement solution with broad applicability across dewatering technologies without requiring equipment modification. When considered alongside the bench-scale mechanistic findings and shop-scale validations, the results indicate a mature, transferable technology capable of delivering sustained operations and maintenance benefits across the wastewater industry.