I'm not studied on ...

I'm not studied on desalinization so these are reactions, but this problem seems to need a pre-treatment to avoid having pollutants get to the process, and from a focus on algae, bacteria and phytoplankton relating to wastewater purification can I suggest that by finding what species of them survives, then observing those which can digest or alter them such that they are removed or can be by another process.

Another reaction, that is if the pollution is rather constant in composition of pollutants to arrange a specific pre-process for their removal. In wastewater floccation chemicals normally are used to remove dissolved solids and perhaps some of them can be useful in saltwater for this, haven't researched that.

hth, tom