Combining ultrafiltration and precipitation was studied to improve the productivity of xanthan separation. Changes in solution properties and the association behavior of xanthan were modified by salt (KCI) and solvent (isopropanol) addition, and were assessed using scanning electron microscopy (SEM). The concentration polarization layer produced by xanthan dissolved in buffer solution had a very high specific flux resistance that was enhanced by the addition of either KCI or isopropanol. SEM analysis revealed that the fine macromolecular structure observed with xanthan in buffer was further stabilized in the presence of KCl. Isopropanol addition induced phase separation and the formation of closely packed soft aggregate particles that significantly increased fouling layer specific resistance. The simultaneous salt and organic solvent addition resulted in surface morphologies containing aggregates that associated to create gels with varying porosities. When at least 1% (w/v) KCl and >30% (v/v) isopropyl alcohol was added to 2.5% (w/v) xanthan solution, a very porous fouling layer was created, which dramatically increased membrane flux. Membrane-assisted precipitation reduced the amount of precipitating solutes used while greatly increasing membrane flux, resulting in a large improvement in separation productivity. (C) 2007 Elsevier B.V. All rights reserved.