Christos Nitsos

Biofuels Get in the Fast Lane: Developments in Plant Feedstock Productionand Processing

In recent years, high volatility in oil prices and global climate change led to an increased interest in biofuel production to reduce dependency on foreign fossil fuel. Domestically produced plant feedstocks are environmentally friendly renewable substitutes for fossil-derived fuel and are expected to stabilize fuel prices. Plant-derived energy can offer rural development and other environmental, social and energy security benefits for local societies. Crops, grasses, trees, forest-residues and aquatic plants, all can be used as potential biofuel feedstocks. To meet the increased global and regional demand for bioenergy, evaluation and improvement of current and emergent plant feedstocks is urgently needed to reduce the cost of the resulting biofuels.

Evaluation of Mediterranean Agricultural Residues as a Potential Feedstock for the Production of Biogas via Anaerobic Fermentation

Hydrothermal, dilute acid, and steam explosion pretreatment methods, were evaluated for their efficiency to improve the methane production yield of three Mediterranean agricultural lignocellulosic residues such as olive tree pruning, grapevine pruning, and almond shells. Hydrothermal and dilute acid pretreatments provided low to moderate increase in the digestibility of the biomass samples, whereas steam explosion enabled the highest methane yields to be achieved for almond shells at 232.2 ± 13.0 mL CH4/gVS and olive pruning at 315.4 ± 0.0 mL CH4/gVS. Introduction of an enzymatic prehydrolysis step moderately improved methane yields for hydrothermal and dilute acid pretreated samples but not for the steam exploded ones.

Investigation of different pretreatment methods of Mediterranean-type ecosystem agricultural residues: characterisation of pretreatment products, high-solids enzymatic hydrolysis and bioethanol production

ABSTRACT Agricultural and agro-industrial lignocellulosic residues represent an important renewable resource for the production of fuels and chemicals towards a bio-based economy. Olive pruning, vineyard pruning and almond shells are important residues from agricultural activities in Mediterranean-type ecosystems. In the current work, bioethanol production from the above three types of agro-residues was studied, focusing on the effect of different pretreatment methods on enzymatic saccharrification efficiency of cellulose and production of second-generation bioethanol. Dilute acid, hydrothermal and steam explosion pretreatments were compared in order to remove hemicellulose and facilitate the subsequent enzymatic hydrolysis of the hemicellulose-deficient biomass to glucose. Enzymatic hydrolysis was performed in a free-fall mixing reactor enabling high solids loading of 23% w/w. This allowed hydrolysis of up to 67% of available cellulose in almond shells and close to 50% in olive pruning samples, and facilitated high ethanol production in the subsequent fermentation step; the highest ethanol concentrations achieved were 47.8 g/L for almond shells after steam explosion and 42 g/L for hydrothermally pretreated olive pruning residue.

The Role of Catalytic Pretreatment in Biomass Valorization Toward Fuels and Chemicals

The enzymatic hydrolysis of cellulose toward fermentable glucose is of paramount importance for the production of ethanol or other high-value chemicals from lignocellulosic biomass via the biochemical route. A pretreatment step is usually required that alters the structure and composition of biomass, reduces its recalcitrance, and allows the efficient enzymatic conversion of carbohydrates into sugars. Biomass pretreatment aims mainly at the selective separation of hemicellulose and/or lignin, either as oligomers or as smaller sugar and phenolic molecules, which can be further converted enzymatically or via chemical catalysis to platform chemicals or fuel precursors. In this chapter, a review of the most widely applied pretreatment methods is presented, with the aim of elucidating the role of chemical or biochemical catalysis in this first step of biomass valorization.