Investigations into Problem Ethanol Fermentations

Problems were experienced at Triangle's fuel ethanol plant with extended and incomplete fermentations. Direct lactic acid residual sugars and heavy metal analyses were done on plant samples to isolate the cause of the sub-optimal fermentations. Laboratory fermentation experiments were done using Triangle yeast and nutrients. Tests were done at various pHs and temperatures to ascertain levels of stress on the yeast. Copper was found in toxic levels in the proble~ fermentations, and the most probable source was the fertilizer-grade diammonium phosphate used as nutrient. Laboratory tests incorporating copper at varying conc~ntrations were done to investigate the effect on yeast population levels and on the fermentative capability of the yeast. Laboratory tests showed an effect on yeast populations at 16 ppm copper, and the level affecting ethanol fermentations was between 20 and 40 ppm. Laboratory tests confirmed that the problem of extended fermentations and incomplete sugar utilization was due to copper toxicity.