Decolorization of molasses wastewater by yeast strain, Issatchenkia orientalis No. SF9-246

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 (MP) at 30 °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 (BOD5) 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 °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 MP solution was rapidly removed, while the smaller molecular weight fraction remained in the effluent.