Reducing Energy Footprint of a Waste Water Treatment Plant by Increasing Harvesting Efficiency of Solids during Primary Clarification

This paper 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 substantial amounts of those organic solids, which are nearly neutrally buoyant and do not sediment out, before they enter the secondary treatment step. Most WWTPs include a primary treatment consisting of clarifiers to remove settleable solids before biological treatment. This process is sometimes enhanced by chemical precipitation to remove a greater portion of the suspended solids. 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. In this paper we introduce the basic physical concept behind HDS and discuss the impacts of geometry and channel design on harvesting efficiencies. We then present separation results on primary effluent samples from different locations in the San Francisco Bay Area using single channels in the laboratory. A brief description of a pilot system that is scheduled to be moved to a local (Silicon Valley, California) WWTP in fall of 2013 for tests in a real environment will be discussed last. Construction of this trailer-mountable pilot system 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 is underway. This California State Energy Commission-sponsored pilot study will be furnished with thirdparty 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.