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 fullscale 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 iv 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

A modified two-element membrane pressure vessel assembly has been used to monitor process operational changes in a full-scale reverse osmosis (RO) water treatment plant (WTP). This study evaluated the effectiveness of the assembly as an on-line monitoring device intended to detect scale formation conditions when connected to an operating RO process train. This study was implemented to support the requirements of a larger University of Central Florida (UCF) research project ongoing at the city of Sarasota’s Public Works and Utilities (City) water treatment facilities located in Sarasota, Florida. During the time-frame of this study, the City was in the process of eliminating their sulfuric acid feed from the pretreatment system of their existing 4.5 million gallon per day (MGD) RO membrane process. The City was motivated to eliminate its dependence on sulfuric acid to reduce operating costs as well as reduce operation health and safety risks associated with the use of the acid as a pretreatment chemical. Because the City was concerned with secondary process impacts associated with acid elimination, additional measures were desired in order to protect the full-scale process. This thesis reports on the design, fabrication and installation of a third-stage two membrane element pressure vessel “canary” sentinel monitoring device (Canary), its effectiveness as an online scaling monitor during full-scale acid elimination, and presents the results of the study. The Canary sentinel device was controlled using the normalized specific flux of the two membrane elements fed by a portion of the second stage concentrate of one of the City’s full-scale RO process skids. Although the Canary demonstrated the ability to detect changes in an RO process operation, scaling did not occur under the conditions evaluated in this study. An autopsy of one iv of the Canary elements revealed that no scaling had occurred during the acid elimination process. Therefore, the Canary was found to be useful in its function as a sentinel, even though no scaling was detected by the device after acid elimination at the City’s full-scale plant had been accomplished.