Sludge Pump Sizing for the Pine Creek WWTP using Non-Newtonian Hydraulic Modelling

Abstract

In response to significant growth, the City of Calgary is currently building a third wastewater treatment facility, the Pine Creek Wastewater Treatment Plant (WWTP), to accommodate Calgary's immediate and long-term wastewater treatment needs. The first stage of this project will include a state-of-the-art 100 ML/day biological nutrient removal (BNR) wastewater treatment plant with tertiary filtration.Water is a "Newtonian" fluid, in which the pressure drop is proportional to the velocity and viscosity. However, most wastewater sludges exhibit non-Newtonian characteristics that are best modeled as Bingham plastics. The approach to modeling sludge flows described in this poster accounts for the much larger values of yield stress at low flow velocities.A Bingham plastic exhibits an initial resistance to flow, followed by a straight-line relationship between shear stress and flow. As the velocity approaches the transition to turbulent flow, it begins to show characteristics similar to Newtonian fluids. Each type of sludge resists movement with different intensity. Below the material's Yield Stress (Y s ), the Bingham plastic retains a solid-like matrix and no movement is observed. Above the Y s , the material will induce friction losses at a rate proportional to the shear stress as flow increases. In clean water, shear in proportion to shear stress is identified as the viscosity. For a Bingham plastic, the Coefficient of Rigidity (R c ) identifies this relationship.With municipal sludges, several factors affect the response of the sludge to shear stress. Solids content of the sludge is critical and is commonly used as a guide to selection of appropriate values for the yield stress and the coefficient of rigidity. The source of the sludge has also been demonstrated to have an impact on the selection of the rheological factors. Thickened waste activated sludge tends to have a higher yield stress and coefficient of rigidity than a thickened primary sludge of equivalent solids content.To gain a better understanding of the flow properties of the sludge at the Bonnybrook WWTP, the City of Calgary undertook sludge rheology testing to more accurately estimate pressure drop. Viscometer tests were performed to determine the viscosity of various sludge streams, at varying flow rates, to simulate both start-up and steady state conditions respectively.Because the Buckingham equation describes laminar flow, limits are placed on its use. A transition zone is defined by the upper critical velocity and lower critical velocity. The 3000 WEFTEC®.07