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Reducing Energy Footprint of a Waste Water Treatment Plant by Increasing Harvesting Efficiency of Solids following Primary Clarification
Conferences & Talks


15 June 2013



This presentation describes a novel hydrodynamic separation (HDS) technology that has the potential to dramatically reduce the energy footprint of a wastewater treatment plant (WWTP) by reducing the energy required for aeration and by increasing biogas production to offset plant energy demand. These goals are achieved because of the ability of HDS to effectively harvest from primary effluent those organic solids, which are nearly neutrally buoyant and do not sediment in the primary clarifier before they enter the secondary treatment step. Biodegradable solids not removed in primary treatment translate into greater oxygen demand in the downstream biological processes. In addition, organic solids harvested in primary treatment have higher energy content than the biomass in the waste activated sludge, both of which are often anaerobically digested to produce biogas for energy. Therefore, improved primary treatment performance can yield energy benefits not only from the increased mass of organic solids for biogas production but also from reduced oxygen demand (aeration) in secondary treatment. Hydrodynamic Separation (HDS) is a purely fluidic approach to concentrate suspended solids in a liquid. By carefully controlling the geometry and the flow through a curved channel the resulting hydrodynamic forces will cause particles beyond a certain cut-off size to focus near one side wall, independent of their density (Fig. 1). By splitting the flow at the channel exit two separate streams with high and low particle concentrations are produced. Further concentration can be achieved by cascading several HDS stages and using the concentrate stream of one stage as the input for the next stage (Fig. 2). Using laboratory HDS prototypes, we have demonstrated successful separation of 50-70 % of the suspended solids in primary effluent samples from different WWTPs. In this paper we present separation results on primary effluent samples from different locations in the San Francisco Bay Area using single HDS channels in the laboratory. These results will be compared to tests from a 4-stage, 30 liter per minute pilot system that is located at a local (Sunnyvale, Silicon Valley, California) WWTP for operation in a real environment (Fig. 3). This trailer-mountable pilot system is capable of unattended operation at a flow rate upward of 10,000 gallons per day with complete fluidic actuation, sensing, pumping, controls and data recording. This California State Energy Commission-sponsored pilot study will be furnished with third–party engineering Measurements and Verification that include HDS energy consumption and calculations for biogas production, installed cost, payback time, and economic impacts when and if HDS-based water treatment systems are widely deployed in wastewater treatment plants for primary solids harvesting in the State of California and beyond.