Abstract
Sweet sorghum seems to be one of the most promising energy crops for a wide range of ecological conditions thanks to its high yield potential and drought tolerance. A two-year field trial was conducted in a semi-arid Mediterranean environment in Turkey to evaluate the interactive effects of different nitrogen fertilizer levels (100, 150, and 200 kg ha−1) and humic substances (0, 15, 30, and 45 L ha−1) applications on the biomass and bioethanol yields of sweet sorghum, and combustion characteristics of its bagasse. Sweet sorghum showed a positive response to increased nitrogen fertilizer and humic subtances application levels in terms of biomass and bioethanol production. Lignocellulosic and total bioethanol yields significantly increased up to 2910 and 3336.6 L ha−1 as a result of the combined application of the 200 kg ha−1 N and 15 L ha−1 humic subtances (HS), respectively. However, HS application had a detrimental effect on the bagasse combustion quality, because it caused a considerable increase in the mineral and ash concentrations. Briefly, combined application of 200 kg ha−1 N and 15 L ha−1 HS may be suggested to be applied for the sustainable bioethanol production from sweet sorghum, while the application of HS likely does not provide any economic and environmental benefit if bagasse would be used as solid biofuel feedstock.
Highlights
The gradual depletion of fossil fuel reserves and raising concerns about global climate change have brought back interest in biofuels over the last few decades, which have stood out as one of the most promising and environmentally friendly renewable energy sources [1,2]
Sweet sorghum positively responded to N fertilization, achieving the significantly highest Fresh stem yield (FSY), juice yield (JY), Dry bagasse yield (DBY), lignocellulosic ethanol yield (LEY), total ethanol yield (TEY), and bagasse cellulose concentration when the crop was fertilized with N200
As we observed with N fertilization, sweet sorghum positively responded to humic subtances (HS) application with respect to FSY, JY, sugar yield (SY), juice ethanol yield (JEY), LEY, and TEY, attaining significant increases up to HS15
Summary
The gradual depletion of fossil fuel reserves and raising concerns about global climate change have brought back interest in biofuels over the last few decades, which have stood out as one of the most promising and environmentally friendly renewable energy sources [1,2]. Sweet sorghum bagasse contains considerable amounts of carbohydrate polymers (cellulose and hemicellulose), which can be hydrolyzed to fermentable sugars by various conversion technologies, and fermented to bioethanol [11]. As another option, it can be directly combusted in a bioreactor to generate heat and electricity, the energy ratio (output/input) of the bioethanol production may be increased up to 8–10, similar to the sugarcane-based bioethanol industry in Brazil [12]. The utilization of the bagasse would increase the energy efficiency of the production chain [13]
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