Abstract
Conversion of lignocellulosic biomass into bioethanol is essential to reduce dependency on fossil fuels. After the grass pea and wild oat straws were characterized, they were hydrolyzed by live fungi (in situ), crude fungal enzymes, and chemical methods (sodium hydroxide and sulphuric acids at 0.5, 1, 2, and 3%). The fungi used for in situ degradation and crude lignocellulosic enzymes were Aspergillus niger JMC22344, Trichoderma reesei JMC22, Pleurotus ostreatus M2191, and Pleurotus sajor-caju M2145. Furfural content of hydrolysates was analyzed by GC–MS. The potential of activated charcoal, overliming, and sequential activated charcoal-overliming potential to reduce furfural in the acid hydrolysates were evaluated. The hydrolysates were fermented by S. cerevisiae ETP53, K. marxianus ETP87, and P. fermentans ETP22. Sulphuric acid hydrolyzed common wild oat (8.91 g/L) yielded higher sugars than NaOH (3.88 g/L) and NaOH treated wild oat (8.14 g/L) was superior in terms of sugars released than grass pea (4.21 g/L). P. ostreatus M2191 liberated the highest sugar (18.63 g/L) extracts than T. reesei JMC22676, A. niger ETP22344 and P. sajor-caju M2145. The 23–77% of the furfural in acid hydrolysates was reduced by overliming, activated charcoal, and the sequential activated charcoal-overliming. Yeasts produced optimal ethanol from straws hydrolyzed by crude enzymes from A. niger JMC22344. Generally, the ethanol titer was directly proportional to the amount of sugars released.
Highlights
The ever-increasing demand for energy and the problem of environmental pollution necessitate the search for renewable energy from various alternatives [1]
Pleurotus ostreatus M2191 and Pleurotus sajor-caju M2345 were obtained from MYCELIA, Belgium whereas Aspergillus niger JCM22344 and Trichoderma reesei JCM22676 were obtained from Japan Collection of Microorganisms, Japan were used as source for cellulase enzyme
The sugar yield of acid treated was between 5.3–8.9 g/L and 7.3–13.9 g/L from wild oat and grass pea, respectively compared with 3.4–4.2 g/L and 6.5–8 g/L obtained from the alkali treated wild oat and grass pea respectively, indicating that the sugar released from acid hydrolysis was 1.5 times higher than alkali hydrolysis
Summary
The ever-increasing demand for energy and the problem of environmental pollution necessitate the search for renewable energy from various alternatives [1]. The biofuels obtained from agricultural residues, industrial wastes, and other lignocellulose sources are alternative cheap and sustainable sources of energy supply. Agricultural residues are important sources of biomass for ethanol production in Africa and the estimated total ethanol from agricultural residues and municipal solid waste (excluding paper) is 20.2 and 1.8 Billion liters per year respectively [3]. The highest available biomass was estimated to be 136 million tons per year in Western. Africa followed by 123 million tons per year in Eastern Africa [3]. According to a World Bank report in 2012, Ethiopia has the potential to generate up to 14 million litter of ethanol that can be produced from its lignocellulosic agricultural and municipal residues
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