Application of activated sludge as a complementary in bioethanol production

Excess activated sludge contains large amounts of components such as phosphorus, nitrogen, and sulfur which can theoretically be used as a nutrient source in fermentation processes to produce value added materials. In the present study, the possibility to grow Saccharomyces cerevisiae and produce ethanol on pretreated and untreated activated sludge as a nutrient source was investigated. In this article, Saccharomyces cerevisiae, CEN.PK 113-7D, was used as an ethanol producer microorganism. In order to release the organic matter of the sludge and increase the efficiency of ethanol production, four pretreatments, i.e. acidic, alkaline, thermal and ultrasonic were performed on the sludge. The effectiveness of each pretreatment on biomass growth at aerobic conditions was measured by CFU method. Moreover, the yield of ethanol at anaerobic conditions was measured using gas-chromatography. The highest biomass yield of yeast on the wet sludge at aerobic conditions was obtained after alkaline pretreatment, in which the biomass concentration increased from 1.2 105 (CFU/ml) to 1.5 106 (cell/ml) after 36 hour of cultivation. At anaerobic conditions, the yield of ethanol on alkaline pretreated sludge was 0.11 g ethanol/g initial glucose. Additionally, by drying the sludge and performing the alkaline pretreatment, the ethanol production was increased up to 0.41 g ethanol/g initial glucose. Discussion and The results showed that the excess activated sludge from wastewater treatment plants can be used as nutrient source for ethanol production. However, it needs to be treated and alkaline pretreatment of dried sludge is suggested to produce a high yield of ethanol.