Ohanusi, Irene N.2025-06-242025-06-242024-02Ohanusi, I. N. (2024). Optimization of bioethanol production from selected agricultural wastes (Unpublished Doctoral Thesis). Federal University of Technology, Owerri, Nigeriahttps://repository.futo.edu.ng/handle/20.500.14562/2048This thesis is for the award of Doctor of Philosophy (PhD) in Industrial MicrobiologyThis study investigated the production of bioethanol from agricultural wastes: tigernut (Cyperus esculentus) waste, beans (Phaseolus vulgaris) husk, and groundnut (Arachis hypogea) shell. The use of agricultural wastes in bioethanol production helps in decreasing the reliance on conventional food crops such as corn, sugarcane, cassava etc. Saccharomyces cerevisiae and a new strain of mold, Aspergillus niger isolate HEFAPhR, were used to ferment tigernut waste, beans husk, groundnut shell to produce bioethanol. The proximate and amino acid analysis of these substrates was carried out to determine the moisture, fat, protein, ash and carbohydrate content of each of the wastes. Effects of substrate weight, inoculum size, pH, fermentation time and temperature were studied; Response surface methodology of Box-Behnken design of five factors at three levels was adopted to determine optimal conditions for improved bioethanol yield. This design gave a total of 46 experimental runs per substrate evaluated. The substrates were independently subjected to physical and biological pretreatments using Cellulase enzyme to hydrolyze the lignocellulose to fermentable sugars. The isolate from food samples and brewers yeast were identified and molecularly characterized. Aspergillus niger isolate HEFAPhR and Saccharomyces cerevisiae respectively and were able to withstand stress and tolerated exposure to ethanol of different concentration up to 94%. Optimum conditions for brix production were determined and were used to obtain maximum yield of ethanol. A comparative study of bioethanol production between Saccharomyces cerevisiae and Aspergillus niger isolate HEFAPhR was ascertained. The results showed that the fermentation of tigernut waste with Saccharomyces cerevisiae maximum brix of 2.28oBx and 1.6g/l ethanol was observed at optimum conditions of pH 6.8, temperature 25oC, fermentation time 93h, inoculum size 5 and substrate weight of 11g, brix value of 0.53oBx and ethanol content of 1.64g/l with actualized volume of 0.2479(ml) were obtained. Fermentation of tigernut waste with Aspergillus niger isolate HEFAPhR of observed brix of 8.0oBx and 4.8g/l ethanol. At optimum conditions of pH 6, temperature of 34oC, time 96h, inoculum size 5 and substrate weight of 11g/l, maximum value of brix of 6.7oBx and ethanol yield of 5.1g/l with actualized volume of 0.772(ml). Fermentation of beans husk with Saccharomyces cerevisiae maximum brix was observed to be 6.7oBx and 3.0g/l ethanol, at optimum conditions of pH 6, temperature 30oC, fermentation time of 48h, inoculum size of 5.4 and substrate weight of 12g, a maximum brix of 2.8oBx and 5.47g/l ethanol was obtained with a final volume of 0.829(ml). Fermentation of beans husk with Aspergillus niger isolate HEFAPhR resulted in a maximum brix of 3.8oBx and 2.20g/l ethanol at optimal condition of pH 6, temperature 35oC, time 96h, inoculum size 5, substrate weight of 10g, maximum brix of 2.09oBx and 2.48g/l ethanol with actualized volume of 0.373(ml). In the fermentation of groundnut shell with Saccharomyces cerevisiae, a maximum brix of 4.6oBx and 2.6g/l ethanol was observed at optimum conditions of pH 6, temperature 35oC, substrate weight of 12g, time 72h, a maximum brix 2.84oBx and 3.47g/l ethanol with an actualized volume of 0.524(ml) were obtained, while groundnut shell with Aspergillus niger isolate HEFAPhR gave a maximum brix of 9.9oBx and 5.20g/l ethanol at optimum conditions of temperature 35oC, time 96h, substrate weight 15g, pH 6, inoculum, a maximum brix of 10.0oBx and 23.43g/l with actualized volume of 3.634(ml) indicating that groundnut shell with Aspergillus niger isolate HEFAPhR gave the highest production of bioethanol, followed by beans husk with Saccharomyces cerevisiae, demostrating that at optimal conditions these agro wastes are best alternative substrates for maximum yield of bioethanol.enAttribution-NonCommercial-ShareAlike 4.0 InternationalAgricultural wastesbioethanolbrixoptimizationresponse surface methodologyDepartment of MicrobiologyDoctoral Thesis