Surface Mixers for Destratification and Management of Anabaena Circinalis -Dàta"
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I Surface Mixers for Destratification and Management of Anøbøenü circinølis IDy David Milton Lewis l|l4arch-2004 A Thesis Submitted for the Degree of Doctor of Philosophy School of Civil and Environmental Engineering The University of Adelaide Australia "Philosophy is written in this grand book the universe, which stands continually open to our gaze, but the book cannot be understood unless one first learns to comprehend the language of mathematics, and its chøracters ore triangles, circles, and other geometricfigures, without which it is humanly impossible to understand a single word of it; without these, one wanders about in a dark labYrinth. " Galilei, Galileo (161 8) Abstract ABSTRACT for In 199g, the South Australian water utility SAWater and the Cooperative Centre for Water euality and Treatment commenced project 2.5.1, entitled Destratification control of Phytoplankton, for which this research forms apart. The major objective of the project was to assess a novel method for destratification and control of the cyanobacteria, in particular Anabaena circinalis Rabenh. ex Born' et Flah, with referred to use of raft-mounted mechanical surface mixers with draft-tubes, hereafter as surface mixers. prevent the The primary aims of destratification are to maintain aerobic conditions to release of iron, manganese and nutrient from the sediment, and to control excessive growth of nuisance phytoplankton, in particular cyanobacteria. The overall objectives for this research were to: l. Ascertain if the surface mixers could be used as an effective management tool to improve water quality in lakes and reservoirs' mixers. 2. Quantify the hydrodynamic behaviour of the surface 3. Use numerical modelling techniques to extend the assessment of the surface mixers beyond the analysis of field data. This thesis describes the investigation undertaken used to quantify the impact of the surface mixers upon the thermal structure and phytoplankton assembly' The surface mixers are essentially large impellers with a diameter of 4.9 m, which are suspended below the surface water at a depth of 1.8 m that pump water from the surface down through a 13 m draft-tube (suspended below the impeller). A critical factor to assess the surface mixers was to understand the hydrodynamics imparted by the large diameter, high Reynolds number impeller-induced swirling jet upon the water column. Historically, analysis of jets generated by impellers has been either restricted to laboratory scale experiments or based upon limited f,reld observation. The investigation of the impeller-induced swirling jet at this scale was unique and provided the opportunity to determine if the published literature on impeller-induced Abstract swirling jets were relevant to large-scale impellers. The surface mixers generate a very large swirling jet that can change from being purely momentum driven to buoyancy driven over relatively short time periods (hours to days) depending on the meteorological conditions. The surface mixers were installed, and subsequent field investigations were carried out in Myponga Reservoir, South Australia. The monitoring of the meteorological conditions and thermal structure of the water column was achieved with two meteorological monitoring stations. The phytoplankton assemblage was also monitored with integrated phytoplankton samples from 0 to 5 m below water surface collected regularly (daily, weekly or monthly, depending on the season) for identification and enumeration. This had inherent limitations, which restricted the ability to recommend the use of surface mixers in other water bodies. Consequently, the use of numerical modelling was employed so that the surface mixers could be assessed under different operating conditions. Surface mixers of this scale and configuration had not been modelled before, so the development of an appropriate surface mixer algorithm was undertaken, and validated against field data. The primary contributions from this research have been to provide insight into the capabilities of surface mixers, quantiff the characteristics of large impeller-swirling jets, determine the effects of their impact upon cyanobacteria growth and destratif,rcation capabilities, and has enhanced the role of numerical modelling for reservoir management. It was concluded that the surface mixers are able to remove buoyant cyanobacteria from the surface water and transport them to below the draft-tube depth, and limit the severity of stratification. The penetration of the surface mixer jet was found to be a function of the surface water temperature and the ambient water temperature at the exit point of the draft-tube. Consequently, during periods of excessive solar insolation, the jet issuing from the draft-tube becomes buoyant and is not able to reach the sediment surface, thus limiting the destratif,rcation capabilities and reducing the time that entrained cyanobacteria remain below the surface. ll Abstract The characterisation of the surface mixer flow showed that the large diameter' high Reynolds number impeller-induced swirling jet fully develops at shorter distances than jets reported in the literature, during both stratified and isothermal conditions. The radial spread for the surface mixer flow under isothermal conditions is jet approximately three times that of a non-swirling jet. The entrainment into the has been analysed and can be predicted under isothermal and stratifîed conditions. This enabled the development of the surface mixer algorithm that describes the diffusion of the efflux, which allows the surface mixers to be assessed in any water body under varying meteorological conditions and enables informed decisions to be made. 111 Acknowledgements ACKNOWLEDGMENTS Throughout the entire project I have received continuous guidance and support from my supervisors, Dr Martin Lambert (School of Civil and Environmental Engineering, University of Adelaide) and Dr Justin Brookes (Cooperative Research Centre for Water Quality and Control, CRCV/QT). I am honoured to work with these two outstanding academics and thank them for their input, encouragement and assisting with my professional development. Also, I would like to acknowledge the Cooperative Research Centre for Water Quality and Treatment for funding project 2.5.1, for which this thesis forms apart, and in particular I would like to thank Dr Dennis Steffensen and Mr Michael Burch for their support and giving me the opportunity to be part of the project team. I have also had the privilege to collaborate with several world-class researchers during the course of the project that gave invaluable suggestions and provided opportunities for exploration of new ideas. I would like to express my gratitude to Associate professor George Ganf from the School of Earth and Environmental Sciences, University of Adelaide; Professor Colin Reynolds, Dr Alex Elliott and Dr Tony Irish from the Centre for Ecology and Hydrology, UK; and Dr Jason Antenucci from the Centre for Water Research, University of Western Australia. I would like to thank the many people who assisted with the extensive fieldwork carried out at Myponga Reservoir. Firstly, my fellow PhD student Rudi Regel, for his insight into freshwater ecology; Leon Linden and Dr John Vítkovsk¡f for their assistance with all the measurements; Dr Bradford Sherman for advising me to read the manual; Dr Jason Cassells for surveying Myponga River and the catchment; Mr Allan Broyn, Mr Rod Boothey and Mr Vivien Pigeon who manage the reservoir operations, and Mr Gregory Atkins, Mr Jeffrey Hiorns and Mr Steven Huskinson for laboratory support. Finally, I would like to thank my wife Joanne and my parents for their patience and encouragement throughout my PhD studies. List of Publications LIST OF PUBLICATIONS The publications produced during this research are listed below. These represented the developmental nature of the research. JounN¡.r, PAPERS Lewis, D.M., Elliott J.4., Brookes, J.D., Lambert, M.F., Irish, 4.E., and c.s. Reynolds, (2003). The effects of artificial mixing and copper sulphate dosing on phytoplankton in a simulated Australian reservoir. Lakes and Reserttoirs: Research and Management. S, 31 - 40. Linden, L., Lewis, D.M., Burch, M.D. and J.D. Brookes, (2003) Nutrient load is determined by high flow episodes in the Mediterranean Myponga Reservoir. Marine and Freshwater Research (In Review). Antenucci, J., Brookes, J.D. and D.M. Lewis, (2003). The use of mechanical destratification for the management of water quality in reservoirs. Water, (In Review)' Lewis D.M., Elliott J.4., Lambert M.F., and C.S. Reynolds (2002) The simulation of an Australian reservoir using a phytoplankton community model (PROTECH)' Ecological Modelling.150(1-2), 107 - 116 Brookes, J.D., Lewis, D.M., Linden, L., and M.D. Burch, (2002) On-line monitoring of reservoirs for risk management: linking reservoir data and treatment for improved management. Water,29(5),20 - 27. Lewis, D.M., Antenucci, J.P., Brookes, J.D., and M.F. Lambert, (2002) Surface mixing for destratification: simulating the impact. Water,29(5),27 - 29. VI List of Publications CoNrnnnNcE PAPERS Lewis, D.M., Brookes, J.D. and M.F. Lambert, (2003). Numerical models for cyanobacteria management. Fifth Asia-Pacffic Conference on Algal Biotechnology. Focus: Algaefor Human and Environment. P.R. China. October 2003. Brookes, J.D., Lewis, D.M. and L.G. Linden, (2002). Predicting, detecting and managing cyanobacteria in source water. American Water and Wastewater Association. Water Technology Congress, Seattle. November