Dissolved Carbon Dioxide for Scale Removal in Reverse Osmosis

Author

Erin Partlan, Clemson UniversityFollow

Date of Award

12-2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Environmental Engineering and Science

Committee Chair/Advisor

Ladner, David A

Committee Member

Karanfil , Tanju

Committee Member

Freedman , David L

Abstract

Membrane fouling is a major operational issue in reverse osmosis (RO) desalination plants. In particular, plants treating brackish groundwater can encounter troublesome inorganic scales, including carbonates, sulfates, and silicates. A novel cleaning method is proposed to remove inorganic scales from fouled RO membranes usinag dissolved CO ₂ . As CO₂ molecules encounter membrane foulants, the surfaces serve as nucleation sites for small bubbles to form and shear off foulants. Dissolved CO₂ solutions were prepared by bubbling CO₂ gas into water held in a pressure vessel. Gas dissolution was confirmed by enhanced exit velocities for water containing CO₂ , due to the increase in volume from exsolution, when compared to water containing less soluble N₂ . A dissolved CO₂ solution was effective in removing scale from RO membranes through bubble nucleation. Membranes scaled with CaCO₃ were cleaned for 10 minutes with a once-through dissolved CO₂ solution of approximately pH 4.5, achieving an average 80% flux recovery. Controls were performed with other cleaning regimes to isolate effects from pH and air scouring present in CO₂ cleaning. An HCl solution at pH 3 provided an average flux recovery of 79% after circulating through the system for 30 minutes, while an HCl solution at pH 4 only gave an average 20% flux recovery. Trials using N₂ gas in place of CO₂ only produced a 6% flux recovery on average. Lowering the pH of the N₂ solution to pH 4 with HCl boosted cleaning slightly to an average 8% flux recovery. Thus, the low pH of the CO₂ solution at pH 4.5 and bulk phase air scouring are minor mechanisms in scale removal. In addition, membranes scaled with calcium silicates were not cleaned using dissolved CO₂ - only NaOH at pH 12 plus sodium dodecyl sulfate provided significant cleaning. Future work should be done with additional scale types to narrow in on the mechanism for cleaning by dissolved CO₂ .

Recommended Citation

Partlan, Erin, "Dissolved Carbon Dioxide for Scale Removal in Reverse Osmosis" (2013). All Theses. 1788.
https://open.clemson.edu/all_theses/1788