Explosive decompression pretreatment: nitrogen vs. compressed air

M. Raud*, V. Rooni and T. Kikas

Institute of Technology, Estonian University of Life Sciences, Kreutzwaldi 56
EE51014 Tartu, Estonia
*Correspondence: merlin.raud@emu.ee

Abstract:

Lignocellulosic material is the most promising feedstock for the bioethanol production however, due to complicated physico-chemical characteristics of biomasses, it is necessary to pretreat the biomass before the bioethanol production. The goal of the pretreatment is to open the biomass structure for enzymatic hydrolysis to gain higher sugar and ethanol yields in further processes. In this paper a novel explosive decompression pretreatment is studied where two gases – nitrogen and compressed air are utilized for pressure generation. For this, traditional three-step bioethanol production process was used, where explosive decompression pretreatment with N₂ gas or compressed air was applied for biomass pretreatment. Glucose and ethanol concentrations were measured during the process. Glucose and ethanol yields and process efficiencies were used to evaluate the effect of explosive decompression pretreatment and its suitability for biomass pretreatment in bioethanol production process. Results show that the highest glucose yield was gained when nitrogen gas was used, while difference in glucose yield compared to that of autohydrolysis was negligible when compressed air was applied.

Key words:

Utilization of urban waste in bioethanol production: potential and technical solutions

M. Raud¹, R. Kesperi¹, T. Oja², J. Olt¹ and T. Kikas¹,*

¹Institute of Technology, Estonian University of Life Sciences, Kreutzwaldi 56, EE51014 Tartu, Estonia; *Correspondence: timo.kikas@emu.ee 2Institute of Ecology and Earth Sciences, University of Tartu, Vanemuise 46, EE51014 Tartu, Estonia

Abstract:

In urban forestry and greening millions of tons of lignocellulosic waste is produced every year. Although lignocellulosic materials are considered one of the most promising feedstock for the bioethanol production, biomass from urban greening and forestry goes unused. Aim of this research was to investigate the potential of such waste biomass for bioethanol production. Woody and non-woody vegetation from different sources was investigated: old and fresh leaves, and mixed waste from urban greening which contained grass, twigs, and leaves. Cellulose, hemicellulose and lignin contents in the samples were determined using fibre analysis. Dilute acid was used for pre-treatment at temperature of 130°C in order to compare yields from different methods. Thermochemical pre-treatment was followed by enzymatic hydrolysis and fermentation. Produced glucose and ethanol contents were measured using electrochemical analyser. Waste from urban greening had the highest cellulose content of 22.96% and gave the best glucose and ethanol yields, 154.5 g kg-1 and 62.5 g kg-1, respectively when the sample was pre-treated with dilute H2SO4. In addition, map analysis was used to assess the area manageable by urban forestry and greening in the city of Tartu to estimate the potential of greening and forestry waste as a substrate for bioethanol production that could be used as a fuel in city’s public transportation system. In conclusion, it was shown that the waste from urban greening and forestry is a very promising raw material for biofuel production considering its localization and high cellulose content.

Key words:

bioethanol, biofuel, lignocellulose, urban green waste