Time-series image analysis for investigating SWRO fouling mechanism

Abstract

The fouling behavior of seawater reverse osmosis membranes has yet to be definitively investigated due to the complexity of seawater compositions. In this study, a time-series image analysis (TSIA) was performed to investigate the fouling mechanism using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The fouling experiments were conducted with synthetic seawater (SS) and SS mixed with humic acid substances (SHA). The effect of operational time was investigated for 2, 4, 6, 8, 12, and 20 h. According to the TSIA results, different fouling characteristics between SS and SHA experiments were observed. In the SS case, the fouling mechanism is the interaction between inorganic particles and the membrane surface as well as interaction between inorganic particles and the deposited foulants. Then, increased accumulation of deposited foulants was observed with respect to the operational time. However, in the presence of humic acid, the fouling mechanism was significantly influenced by the adsorption of humic acid onto the membrane surface at the initial stage (first 2 h). This organic layer traps inorganic particles and organic substances, and accelerates the fouling formation on the membrane surface, thereby leading to a greater flux decline compared to the SS experiment.

Keywords:

• Fouling mechanism
• Image analysis
• Membrane morphology
• Reverse osmosis
• Surface roughness

Acknowledgments

This research was supported by a grant (07seaheroB02-01) from the Plant Technology Advancement Program funded by the Ministry of Land, Transport and Maritime Affairs of the Korean government. We also thank Woongjin Chemical Co., Suwon 443-270, South Korea for supporting RO membranes.

Notes

The 4th International Desalination Workshop (IDW4), November 16–18, 2011, Jeju Island, South Korea

aConcentration based on specification sheet of sea salts.

bResults obtained by ion chromatography.

cConcentration of carbonate in feed solutions (did not analyze).

aAll experiments were carried out at an operating time of 20 h.

bEach TSFE was performed at operating times of 2, 4, 6, 8, 12, and 20 h.

cThe best image was selected as a representative of each operating time among 36 samples.