Orpanic fouling of seawater Reverse Osmosis (RC) membranes is a uhenomenon not well understood; it can result in a loss of membrane productivity and salt rejection properties.
Two seawater RO plants using DuPont B-10 hollow fiber rrermeators had experienced organic fouling and were studied.
The two plants used different sources of feedwater; one RO plant at Culebra, Puerto Rico, used open seawater; while the other RO slant at Grand Cavman Island, British West Indies, used a sea well.
Both feed water sources possessed high concentrations of soluble orpanics (40-80mgll) which WOT~ mainly humic acids.
In an attempt to remove these owanics with in-line cationic polyelectrolyte coagulation, the nlants experienwd orpanic fouling which caused excessive loss of productivity and salt rejection; both plants initially failed their acceptance tests.
It was discovered that the fouiing was actually caused by interactions between the humic acids and in-line cationic nolyelcctrolvte coqwlants which were not removed by in-depth and cartridge filtrstiop.
Rather than remove the humic acid material, acid addition was initiatedsand in-line caticnic coaeulants use discontinued to keep the humic acids soluble.
It shoul,! be not-d that with the open seawater intake ferrous sulfate was still used to r?mcwe colloidal material and reduce the SDI.
Both slants subseouently have uassed their 7'20-hour acceptance test.
Culebra and Grand Cayman plants have now exceeded design snecification for both productivity and salt rejection.
The aramid hollow fibrr nermeators on acidified feed have shown 100% rejection o f these orpanics at both 25% and 50% conversion and organic fouling has not been evident.