Graduation Year

2021

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Mauricio E. Arias, Ph.D.

Co-Major Professor

Qiong Zhang, Ph.D.

Committee Member

Nancy Diaz-Elsayed, Ph.D.

Committee Member

Andres Tejada-Martinez, Ph.D.

Committee Member

Heather Rothrock, Ph.D.

Keywords

Computational Fluid Dynamics, Optimization, Process Model, Membrane fouling, Water reuse

Abstract

Currently, a significant challenge with reverse osmosis-based desalination is reducing the energy consumption and environmental impacts of the process. This project analyzed the viability of using pressure-retarded osmosis (PRO) for energy recovery in seawater desalination facilities using brine concentrate (the draw solution) and other water sources (the feed solution) such as wastewater effluent. The primary goal of this project is to decrease the cost and overall energy consumption of seawater desalination through PRO-based energy recovery. Process modeling, statistical and sensitivity analysis, energy and cost analysis, geospatial and GIS analysis, laboratory-scale testing, water quality analysis, SEM-EDS microscopy, computational fluid dynamics (CFD), and optimization were used to create design schemes that help reduce the environmental impact and energy consumption of seawater desalination.

The first task involved creating a steady-state process model to inform the selection of draw/feed (high salinity/low salinity) solutions and membrane materials for a lab-scale reactor based on their potential for energy recovery and the results from a preliminary economic evaluation. It was found that using reverse osmosis concentrate and high-quality reclaimed wastewater can be economically viable as long as the plants are co-located. The second task involved using the process model to select potential sites in the United States where PRO would have the highest chance of succeeding. It was found that PRO could succeed in Santa Barbara California, where a desalination plant is located across the street from a wastewater plant, and on St. Thomas in the Virgin Islands, which has some of the highest electricity prices in the nation. The third task involved using a bench-scale PRO system to validate a developed CFD model that could investigate the effect that membrane spacer configuration has on the internal hydraulics of a PRO membrane system. It was found that there is a tradeoff between decreased pressure buildup in the feed side of the membrane versus increased transport across the membrane, and that spacer manufacturers should place emphasis on keeping spacer strands more linear and decreasing the length of the sloped section of the thin cross-strand in a spacer to increase system performance. The fourth task focused on determining the impacts that spacer geometry and pretreatment have on membrane fouling and short-term performance. It was found that using a medium-sized diamond-oriented spacer combined with UV pretreatment was the most effective treatment protocol for minimizing the effects of membrane fouling.

Overall, the results from this study suggest that there is potential for PRO to be an economically viable form of energy recovery and brine management for seawater desalination. To maximize performance, PRO should be implemented using a pressure and foulant resistant integrated membrane/spacer combination, combined with source streams that require minimal pretreatment in areas where seawater desalination plants are co-located with wastewater plants and/or have high energy prices. It is recommended that future work focus on conducting additional physical experiments with different water quality and pressure levels, integrating fouling processes and additional water quality variables into the predictive models, and conducting more in-depth comparative analyses against alternative brine management and energy recovery technologies. These three tasks are recommended to be completed before a larger-scale system is constructed to investigate how the system would perform over an extended period. This study primarily used Tampa Bay (Florida) as a case study, although the information and models from this study can be used for other coastal water systems that seek to use seawater desalination that is augmented using PRO-based energy recovery and brine management technology.

Download

Share

COinS