Harnessing the Residual Nutrients in Anaerobic Digestate for Ethanol Fermentation and Digestate Remediation Using <i>Saccharomyces cerevisiae</i>

• Main Authors: Victor Chinomso Ujor, Christopher Chukwudi Okonkwo, Brennen Bradley Rush, Grace Ellen McCrea, Thaddeus Chukwuemeka Ezeji
• Format: Article
• Language: English
• Published: MDPI AG 2020-05-01
• Series: Fermentation
• Subjects: ethanol fermentation; anaerobic digestate; <i>Saccharomyces cerevisiae</i>; ammonia; phosphorus; heavy metals
• Online Access: https://www.mdpi.com/2311-5637/6/2/52

This study evaluated the feasibility of concomitant nutrient removal, cleaner water recovery, and improved ethanol production via glucose fermentation in the liquid fraction of anaerobic digestate (ADE) by <i>Saccharomyces cerevisiae</i>. The 25%, 50%, and 100% (v/v) ADE supported the growth of <i>S. cerevisiae</i>, glucose utilization (~100 g/L) and ethanol production (up to 50.4 ± 6.4 g/L). After a 144 h fermentation in the 50% ADE, the concentrations of ammonia, total nitrogen, phosphate, and total phosphorus decreased 1000-, 104.43-, 1.94-, and 2.20-fold, respectively. Notably, only 0.40 ± 0.61 mg/L ammonia was detected in the 50% ADE post-fermentation. Similarly, the concentrations of aluminum, copper, magnesium, manganese, molybdenum, potassium, sodium, iron, sulfur, zinc, chloride, and sulfate decreased significantly in the ADE. Further analysis suggests that the nitrogen (ammonia and protein), phosphate, and the metal contents of the digestate work in tandem to promote growth and ethanol production. Among these, ammonia and protein appear to exert considerable effects on <i>S. cerevisiae</i>. These results represent a significant first step towards repurposing ADE as a resource in bio-production of fuels and chemicals, whilst generating effluent that is economically treatable by conventional wastewater treatment technologies.