Generic Fertiliser as Inorganic NPK-TE Sources During Ethanolic Fermentation of Glucose by Saccharomyces cerevisiae

Thracesy Munah, Assan (2023) Generic Fertiliser as Inorganic NPK-TE Sources During Ethanolic Fermentation of Glucose by Saccharomyces cerevisiae. UNSPECIFIED thesis, UNSPECIFIED.

PDF Master Thesis (Thracesy Munah Anak Assan 190200225) Generic Fertiliser as Inorganic NPK-TE Sources During Ethanolic Fermentation of Glucose by Saccharomyces cerevisiae.pdf Download (3MB)

Abstract

Bioethanol is an environmentally friendly fuel that is biodegradable. It is a significantly cleaner fuel in comparison to conventional fossil based gasoline. For the production and studies related to bioethanol, Saccharomyces cerevisiae is the preferred fermenting organism. S. cerevisiae is usually cultured in liquid media that contain yeast extract and peptone. However, the use of these laboratory and scientific grade chemicals are costly, making them impractical for mass ethanol production. Therefore, in this study, fermentation by S. cerevisiae was conducted using a selected generic fertiliser formulation to provide inorganic nitrogen, phosphorus, potassium and trace elements (NPK-TE). The substrates tested were glucose and sucrose via ethanolic fermentation and sago starch using simultaneous saccharification and fermentation (SSF). Different fertiliser nitrogen equivalents (FNE) were used as fermentation media to investigate the feasibility of using generic fertiliser as the NPK-TE source for different substrates. To investigate the effect of the nutrient availability on the fermentation using S. cerevisiae, the growth and fermentation performance were compared between conventional YEP media, 0.5X, 1.0X and 2.0X FNE using different substrates including glucose, sucrose and sago starch to determine the possibility of using generic fertilisers for ethanolic fermentation of simple and complex carbohydrates at optimal concentration. Fermentations were conducted for 5 days at 150 rpm in ambient temperature. Based on the results, all YEP broth using different substrates recorded the highest cell concentration for both wet and dry cells. The cell concentration multiplied rapidly at the first 72 h of the fermentation and then decline afterwards until 120 h. For all the substrates, the YEP media contained the lowest lactic acid and acetic acid while 2.0X FNE media was the highest. For glucose, the highest was 8.08 g/l (lactic acid) and 2.67 g/l (acetic acid) while using 2.0X FNE. As for sucrose, lactic acid was 7.44 g/l and acetic acid was 2.12 g/l. The sago starch also showed the same pattern which detected the highest levels of lactic acid and acetic acid when using 2.0X FNE which was 7.26 g/l and 2.32 g/l, respectively. For an overview of the effect of nutrients of fermentation progress, the ethanol yield of each substrate was recorded until the end of fermentation. Among the different substrates, the highest ethanol productivity was observed when sucrose was used in 1.0X FNE fertiliser medium with theoretical ethanol yield (TEY) of 83.17%. On the contrary, the ability of S. cerevisiae to ferment glucose was excellent when using 0.5X FNE media with 86.18% of TEY and 2.0X FNE fertiliser medium, glucose fermentation showed the lowest ethanol yield with 51.54% TEY. When using sago starch as sole carbon source, S. cerevisiae was able to undergo fermentation in the 1.0X FNE fertiliser medium and exhibited the highest TEY compared to the other tested FNE with 69.15% TEY. The conventional YEP medium was shown to enhance ethanol production during the early stages of fermentation and it also provided optimal nutrient conditions for yeast that effect the amount of ethanol production. While among the generic fertiliser broths, results indicated that fertiliser media of 0.5X and 1.0X FNE produced almost similar ethanol yields at the end of the fermentation period. Therefore, this indicated that 0.5X and 1.0X FNE are potential fermentation media to produce high ethanol yield comparable to the use of YEP broth. The low ethanol production in all 2.0X FNE broths (compared to other fertiliser media) suggested that the higher the amounts of nitrogen, the lower the ethanol yield. Hence, it can be inferred that the 0.5X and 1.0X FNE fermentation media have the potential to be used as an alternative medium to replace the conventional YEP to produce ethanol at lower cost.

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