Date of Award

8-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Engineering and Earth Sciences

Committee Member

Dr. David A. Ladner, Committee Chair

Committee Member

Dr. David L. Freedman

Committee Member

Dr. Tanju Karanfil

Abstract

Membrane fouling is a major operational issue in reverse osmosis (RO) desalination plants. In the last 25 years, over 3,000 papers were published to address this issue. Current control strategies mostly consider the use of chemicals (e.g. acids and antiscalants) in feed water, pre-treatment techniques, and clean-in-place (CIP). Due to chemical consumption, by-product formation is observed in concentrate streams, which is an environmental and human health concern. Recently, dissolved carbon dioxide has been proposed as an alternative cleaning method. Only a few studies are available on the use of CO2, but the initial results are promising. These studies have demonstrated the effective scale inhibition and reinstatement of membrane performance, which could also extend the life-cycle of RO membranes.

The primary goal of the present research was to determine the cleaning efficiency of dissolved CO2 using a carbon dioxide saturation tank to inject CO2 in water. Flux recovery was determined on different RO membranes scaled with inorganic salts, organic substances, and combined fouling.

The hypothesis of the work is that the presence of CO2 bubbles formed due to depressurization upon entrance of the membrane cell and the low pH owing to the formation of carbonic acid, help shear the foulants away. The present research showed that a 15-minutes CO2 cleaning effectively cleaned scaled membranes, with an average flux recovery of 92.5 ± 33.7% for membranes scaled with CaSO4, 95.0 ± 29.4% for CaCO3, 103.1 ± 25.6% for humic acid, 94.6 ± 24.0% for CaSiO3 and 107.9 ± 8.5% for combined fouling. Controls were performed with an acidic solution and air to isolate effects from pH and scouring present during CO2 cleaning. Furthermore, some of the experiments resulted in relatively weak foulant layers that could be removed with deionized (DI) water flushing alone.

Based on the present research, carbon dioxide has proven so far to be more eco-friendly and effective at least with some inorganic and organic scaling solutions. Furthermore, it might be even cheaper than common chemical agents.

Share

COinS