Anaerobic digested sludge: a new supplementary nutrient source for ethanol production

Effluent sludge from an anaerobic digester was used as a source of nitrogen, phosphate, sulfur, and other nutrients in the culture medium of ethanol production by the yeast Saccharomyces cerevisiae. Several pretreatments (mechanical, chemical, thermal, and thermo-chemical) were performed on the anaerobic digested sludge (ADS) to make the nutrients accessible to the yeast cells. Preliminary experiments revealed that S. cerevisiae is not able to assimilate the carbon content of the ADS. However, when glucose was added to the medium, ethanol production was observed. The yield of ethanol using untreated ADS was only 10 % of the theoretical yield, but alkaline pretreatment improved it up to 43 %. By separating the hydrolysate of alkaline-treated ADS from the suspended solids, the ethanol yield from the supernatant was further improved up to 65 % of theoretical yield. Alkaline-treated ADS exhibited competitive performance with the mixture of yeast extract and mineral salts in ethanol fermentation.