APPLICATION AND OPTIMIZATION OF MEMBRANE PROCESSES TREATING BRACKISH AND SURFICIAL GROUNDWATER FOR POTABLE WATER PRODUCTION by JAYAPREGASHAM THARAMAPALAN B.Eng (Civil & Structural), Nanyang Technological University, Singapore, 1994 MSc (Environmental), Nanyang Technological University, Singapore, 2003 A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Civil, Environmental, and Construction Engineering in the College of Engineering and Computer Science at the University of Central Florida Orlando, Florida Fall Term 2012 Major Professor: Steven J. Duranceau © 2012 Jayapregasham Tharamapalan ii ABSTRACT The research presented in this dissertation provides the results of a comprehensive assessment of the water treatment requirements for the City of Sarasota. The City’s drinking water supply originates from two sources: (1) brackish groundwater from the Downtown well field, and (2) Floridan surficial groundwater from the City’s Verna well field. At the time the study was initiated, the City treated the brackish water supply using a reverse osmosis process that relied on sulfuric acid for pH adjustment as a pretreatment method. The Verna supply was aerated at the well field before transfer to the City’s water treatment facility, either for softening using an ion exchange process, or for final blending before supply. For the first phase of the study to evaluate whether the City can operate its brackish groundwater RO process without acid pretreatment, a three-step approach was undertaken that involved: (1) pilot testing the plan to reduce the dependence on acid, (2) implementing the plan on the full- scale system with conservative pH increments, and (3) continuous screening for scale formation potential by means of a “canary” monitoring device. Implementation of the study was successful and the annual savings in operating expenditure to the City is projected to be about $120,000. From the acid elimination study, using the relationship between electrical conductivity in water and total dissolved solids in water samples tested, a dynamic approach to evaluate the performance of the reverse osmosis plant was developed. This trending approach uses the mass transfer coefficient principles of the Homogeneous Solution Diffusion Model. Empirical models iii were also developed to predict mass transfer coefficients for solutes in terms of total dissolved solids and sodium. In the second phase of the study, the use of nanofiltration technology to treat aerated Verna well field water was investigated. The goal was to replace the City’s existing ion exchange process for the removal of hardness and total dissolved solids. Different pretreatment options were evaluated for the nanofiltration pilot to remove colloidal sulfur formed during pre-aeration of the groundwater. Sandfilters and ultrafiltration technology were evaluated as pretreatment. The sandfilter was inadequate as a pre-screen to the nanofiltration pilot. The ultrafiltration pilot (with and without a sandfilter as a pre-screen) proved to be an adequate pretreatment to remove particulates and colloids, especially the sulfur colloids in the surficial groundwater source. The nanofiltration pilot, was shown to be an efficient softening process for the Verna well field water, but it was impacted by biofoulants like algae. The algae growth was downstream of the ultrafiltration process, and so chlorination was used in the feed stream of the ultrafiltration process with dechlorination in the nanofiltration feed stream using excess bisulfite to achieve stable operations. Non-phosphonate based scale inhibitors were also used to reduce the availability of nutrients for biofilm growth on the nanofiltration membranes. The combined ultrafiltration-nanofiltration option for treatment of the highly fouling Verna water samples is feasible with chlorination (to control biofouling) and subsequent dechlorination. Alternatively, the study has shown that the City can also more economically and more reliably use ultrafiltration technology to filter all water from its Verna well field and use its current ion exchange process for removal of excess hardness in the water that it supplies. iv Dedicated to my wife Seetha, who has been my inspiration and support and to my boys Sambath and Seshan for making this a fun and enjoyable journey. v ACKNOWLEDGMENTS This document is the culmination of work that could not have been completed without the support provided by the many individuals involved in this study. Special thanks are given to Dr. Steven J. Duranceau for providing me with the opportunity to be a graduate student, grooming me towards doing research and then serving as my advisor for this dissertation project. His feedback and guidance have been immense and were greatly appreciated during the course of this study. Special thanks are also due to Christopher Boyd for his youthful energy, enthusiasm and research ideas, as we made long trips every week to the field to do our research work. Research work with Christopher Boyd has been one of the main highlights of the work leading to my dissertation. I would like to thank Dr. C. David Cooper, Dr Andrew A. Randall and Dr Christian A. Clausen for their service as committee members and for offering their time and effort in reviewing this research document. I am also grateful for the time and effort that Laboratory Coordinator Maria Pia Real-Robert has spent towards training and checking to ensure that the quality of laboratory work conducted and reported in this dissertation are of the highest standard. Additional thanks are offered to UCF research students Vito Trupiano, Andrea Cumming, Jennifer Roque, David Yonge, Juan Rueda, Nick Webber, Nancy Holt, Genesis Rios, Yuming Fang, Alyssa Filippi, Paul Biscardi and Marzieh Gasemi who dedicated their efforts to assist with laboratory and field tasks. vi I would also like to thank the municipality, companies and individuals who were involved in assisting the UCF research team in this effort. This work would not have been feasible without the City of Sarasota Public Works and Utilities Division (1750-12th Street, Sarasota, FL 34236), particularly Pedro Perez, Katherine Gusie, Javier Vargas, Gerald Boyce and the City’s water treatment plant operators. The support offered by Harn R/O Systems, Inc. (310 Center Court, Venice, FL 34285) is also greatly appreciated, notably Julie Nemeth-Harn, Jimmy Harn, Jonathan Harn and Bill Youels. vii TABLE OF CONTENTS LIST OF FIGURES........................................................................................................................ xi LIST OF TABLES ....................................................................................................................... xiv LIST OF EQUATIONS ............................................................................................................. xviii LIST OF ABBREVIATIONS ...................................................................................................... xxi 1. INTRODUCTION .................................................................................................................... 1 Project Description ................................................................................................................... 3 Objectives ................................................................................................................................. 5 2. REVIEW OF PROJECT SITE.................................................................................................. 7 Water Treatment Facility Description ...................................................................................... 7 Ion Exchange Process ......................................................................................................... 9 Reverse Osmosis Process .................................................................................................. 10 Post-Treatment Processes ................................................................................................. 11 Discharge Permits ............................................................................................................. 11 3. LITERATURE REVIEW ....................................................................................................... 12 Overview ................................................................................................................................. 12 Typical Reverse Osmosis Treatment Processes ...................................................................... 12 Membrane Scaling and Control .............................................................................................. 15 City of Cape Coral’s North Reverse Osmosis Water Treatment Plant ............................. 17 City of Boca Raton’s Glade Road Water Treatment Plant ............................................... 18 Pilot Testing for United Water Florida’s Floridan Aquifer Supply .................................. 18 North Lee County RO Water Treatment Plant ................................................................. 19 Existing Pretreatment to Surficial Groundwater from Verna Well field ................................ 20 Biological Sulfur Cycle..................................................................................................... 20 Sulfur Oxidation ........................................................................................................... 22 Sulfate and Sulfur Reduction ......................................................................................