Abstract
The reverse osmosis membrane (RO) is a popular instrument for desalinating seawater and quality control of RO is an essential part of the desalination industry. The critical factor for the control of RO is fouling caused by the turbidity of seawater, such as by suspended solids, soluble salts, or biological growth. To reduce turbidity, seawater is first treated with sand, film, or other substances, resulting in so-called “pretreated seawater”. The fouling potential of this pretreated seawater should be assessed quickly and accurately.
The silt density index (SDI) and the modified fouling index (MFI) are predominantly used fouling indices, however, they do not always correctly represent the fouling potential. Thus, we sampled seawater under various environmental conditions and conducted a controlled experiment. Statistically analyzing the data, we developed a new fouling index, termed “permeation index β “ which was verified to be superior to SDI. Additionally, we found that the MFI depends upon the difference in filter holders, but not SDI and β.
Customarily, SDI is measured several times a day, although environmental conditions and characteristics of pre-treated seawater are continuously measured. Thus, regression analysis was conducted with β and those measurements, which resulted in a continuous monitoring system of the fouling potential that will tell us the fouling status of RO immediately when accidental changes in seawater or environmental conditions occur.
