Abstract

During the last decade, the application of pretreatment has been investigated to enhance methane production from lignocellulosic biomass such as wheat straw (WS). Nonetheless, most of these studies were conducted in laboratory batch tests, potentially hiding instability problems or inhibition, which may fail in truly predicting full-scale reactor performance. For this purpose, the effect of an alkaline pretreatment on process performance and methane yields from WS (0.10 g NaOH g−1 WS at 90 °C for 1 h) co-digested with fresh wastewater sludge was evaluated in a pilot-scale reactor (20 L). Results showed that alkaline pretreatment resulted in better delignification (44%) and hemicellulose solubilization (62%) compared to untreated WS. Pilot-scale study showed that the alkaline pretreatment improved the methane production (261 ± 3 Nm3 CH4 t−1 VS) compared to untreated WS (201 ± 6 Nm3 CH4 t−1 VS). Stable process without any inhibition was observed and a high alkalinity was maintained in the reactor due to the NaOH used for pretreatment. The study thus confirms that alkaline pretreatment is a promising technology for full-scale application and could improve the overall economic benefits for biogas plant at 24 EUR t−1 VS treated, improve the energy recovery per unit organic matter, reduce the digestate volume and its disposal costs.

Highlights

  • The demand for energy is continuously increasing due to worldwide population growth and rapid industrialization

  • The corresponding values for milled wheat straw (WS) were 50.3%, 31%, 7.7%, and 11.1% of initial volatile solids (VS). These results are in agreement with previous studies that demonstrated that mechanical fractionation of lignocellulosic biomass does not affect the chemical composition but affects the physical structure such as crystallinity and accessible surface area [18,19]

  • It it is important to verify whether the surplus heat obtained in Scenario 1 was sufficient for is important to verify whether the surplus heat obtained in Scenario 1 was sufficient for the heat energy required for alkaline pretreatment

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Summary

Introduction

The demand for energy is continuously increasing due to worldwide population growth and rapid industrialization. Fossil fuels are the main energy source, they are expensive and their reserves are slowly depleting, making the development of renewable energies an important step for worldwide sustainable development. For this purpose, the European Union has set the objective of achieving a 20% share of renewable energy in its overall energy consumption by 2020 (Directive 2009/28/CE, 2009). If the electricity is sold to the national public grid, the heat valorization at farm-scale is not optimal as part of the heat is lost to the ambient environment and can be used for the pretreatment step [4]

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