Among 2402 strains of yeast isolated from various sources in Thailand, a strain No. SF9-246 identified as Issatchenkia orientalis, showed the highest potential for use in decolorization of molasses wastewater. In a malt extract-glucose-peptone broth (MYGP) culture containing melanoidin pigment (NIP) at 30 degrees C a 60.2% decolorization was obtained within 7 days. The strain appeared to enhance both MP-degradation and MP-adsorption. The strain showed MP, chemical oxygen demand (COD) and biological oxygen demand (130135) removal efficiencies of 91.2%, 80.0% and 77.4%, respectively from anaerobic-treated molasses wastewater solution (T-MWW), collected from an anaerobic pond. The wastewater contained 2.5% glucose, 0.1% NH4Cl, and 0.1% KH2PO4. The pH was adjusted to 5.0 at 30 degrees C for 7 days batch type culture system. The strain showed almost constant decolorization yield of 75-80% over 7 days in a periodical feeding system of 10%, fresh T-MWW with the culture system. The strain provided a constant decolorization yield about 70% during 3 replacement cycles. Gel filtration chromatography showed that larger molecular weight fraction of NIP solution was rapidly removed, while the smaller molecular weight fraction remained in the effluent. (C) 2007 Elsevier Ltd. All rights reserved.