Abstract
Potentially toxic concentrations of certain mineral elements may be taken up in plant biomass produced on coal fly ash (CFA) contaminated soil. This raises concerns about efficiencies of downstream processes, such as hydrolysis and fermentation involved in biomass conversions to bioethanol. A greenhouse pot experiment was conducted to assess bioethanol yield from switchgrass biomass produced on CFA-amended soil (0, 7.5 and 15 %, w/w CFA/soil). Separate aliquots of the CFA-amended soils were either inoculated with isolate of arbuscular mycorrhizal fungi (AMF), Rhizophagus clarus, or fortified with reduced glutathione (GSH). Mineral elements in the CFA-amended soils and plant tissues were determined using ICP-OES. Shoot samples of harvested biomass were subjected to microwave-assisted acid pretreatment, enzymatic hydrolysis and fermentation. The reducing sugar (glucose) and bioethanol in the biomass hydrolysate were determined by spectrophotometry. Results showed that CFA had a concentration-dependent increase on the levels of the mineral elements in soils that were amended. Subsequent uptake of the mineral elements in switchgrass tissues was modulated by CFA-soil amendment, AMF inoculation, and GSH fortification. The glucose concentrations in biomasss hyzrolysate of switchgrass grown on 7.5 and 15% CFA-amended soils were significantly higher (p < 0.05) than the unamended (control) soil without significant adverse effect on the bioethanol yield. The bioethanol concentration (µg/mg DW) in the fermented hydrolysate of switchgrass grown on 15% CFA-amended soil (26.63) was higher than the control soil (24.46). Likewise, AMF and GSH enhanced bioethanol yield from hydrolysate of switchgrass biomass grown on the CFA-amended soil. Our results indicated that coupling CFA-amended soil with either AMF or GSH can enhance bioethanol yield.
Highlights
Coal Fly ash (CFA), a byproduct of coal combustion processes consists essentially of SiO2, Al2O3, and various micro and macro mineral elements [1,2]
This study examined the effects of coal fly ash (CFA) used as soil amendment on the multitasking capability of lignocellulosic species switchgrass (Panicum virgatum)
The concentrations of P, Mg, Ca, Na, S, B, and Co increased in the CFA-soil admixtures while K, Al, Fe, and Mn decreased with increased concentrations of CFA in the admixtures compared to the control
Summary
Coal Fly ash (CFA), a byproduct of coal combustion processes consists essentially of SiO2, Al2O3, and various micro and macro mineral elements [1,2]. The concentration of these mineral elements may exceed their normal levels in agricultural. Depending on the levels of these mineral elements in soils amended or contaminated with CFA, lignocellulosic biomass and downstream bioethanol production may be affected [4,5,6]. The importance of biofuel as a sustainable approach in mitigating the increasing price and negative environmental and human impacts of fossil fuels is increasingly recognized [9,10,11]. Biofuel is a renewable energy source and more eco-friendly [12]. Despite US been the current world’s largest producer of ethanol, with an output more than double that of the next-largest producer, Brazil, there is still an increasing demand for more bioethanol [15,16]
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