Dave Stropky, Paul Nowak, Suqin Dong Process Simulations Ltd. Konstantin Pougatch, Martha Salcudean University of British Columbia P.S. Pagoria, W.A. Barkley, C.W. Bryant Weyerhaeuser Paper Company CFD Predictions in Large Mechanically Aerated Lagoons

Contents  Introduction  Aerated Lagoon CFD Model  Lagoon Hydraulics  RTD Predictions  Biological Model  Application  Weyerhaeuser Grande Prairie Industrial Application  Conclusions

Introduction

Introduction Motivation: Improvement of lagoon performance through a deeper understanding of the hydraulics. Development of Residence Time Distribution (RTD) curves without dye studies. Goal: Develop a 3-D Computational Fluid Dynamics (CFD) hydraulic model of a large aerated industrial lagoon.

Introduction Performance Factors Incorporated in Model  Basin shape  Inflow rate and position  Aerators: Number, position, HP  Baffles/Curtains  Sludge accumulation profile  Biology

Aerated Lagoon CFD Model

Aerated Lagoon Geometry Aerators Inlets Baffles Outlet CFD Grid

Bottom Sludge Profiles Measurement Data Surface Generation Algorithm

RTD Prediction Methods Particle vs. Dye Mean Age

Aeration Biological Model

Rate Equations Throttled by DO (both) and PO4 (growth)

Applications

Weyerhaeuser Grande Prairie Grande Prairie is a >850,000 m 3, two cell lagoon 5.29m deep (18ft) with an operating water depth of 4.57m (15ft) when clean. Cell 1 is 326m x 323m, and cell 2 is 326m x 312m. Cell 2 has two flow baffles. The 1997 volume flow rate is 622 l/s from the south inlet, and the 2005 flow is 632 l/s from the north inlet. Each floating aerator is 75HP and circulates 1286 l/s of liquid. The 1997 configuration has 25 aerators (18 in cell1 and 7 in cell2). The 2005 configuration has 27 aerators (19 in cell 1 and 8 in cell 2).

2005 Hydraulic Flowfield Vertical magnification x10

1997 Grande Prairie Field Study Comparison Model sludge profile estimated. Unknown at time of dye study.

Grande Prairie Aerator Optimization Initial Optimized

Biological Model

 A three dimensional CFD model has been developed for predicting detailed hydraulic performance (including RTD curve prediction) in large mechanically aerated lagoons.  Using this model, wastewater engineers can combine their existing knowledge and expertise with the established power of CFD. The operation of an existing aerated lagoon can be fully analyzed over a range of operational parameters (aerator numbers, positions, and capacities; baffle installation; influent flowrate and location; bottom sludge profile, etc.) without running field dye studies. The method constitutes an efficient and powerful tool for improving lagoon performance and optimizing lagoon Conclusions

 A simplified aerobic biological model has been developed and coupled into the hydraulic CFD model. Through this coupling, three dimensional variation and evolution of the biological processes can be predicted within the lagoon. Prediction of BOD removal is a natural consequence of the three dimensional interplay (including deposition and feedback) between bacteria solids, BOD, and nutrients, and also of the dissolved oxygen supplied through individual aerators. Initial results show promise and provide a pathway towards a deeper understanding of the wastewater treatment in these lagoons. Conclusions