No abstract

Biodiesel, the fatty acid methyl ester (FAME) of vegetable and animal oil, is now used extensively worldwide, with blends of up to 7% common. The blending level is still somewhat limited due to a perceived susceptibility of these fuels to oxidation. Oxidation follows a number of pathways, with the primary mechanism being auto-oxidation, a radical process that results in the production of a range of oxygenated components. These eventually increase the viscosity of the fuel and form deposits detrimental to operation. Further fuel properties are also heavily reliant on the level of oxidation. As such, one of the main challenges in the use of biodiesel is its long-term instability when stored. Typically synthetic antioxidants have been used to address this issue; however, these systems can also add to the formation of deposits, as well as hazardous emissions, on combustion. Recently, research has focused on novel antioxidant development mainly from plant extracts, although there are a number of other routes for improved performance, including the commercialization of hydrogenated vegetable oil (HVO), a prominent alternative to FAME-based biodiesel due to its higher stability, straight chain paraffin composition, and better cold flow properties. In this review, the factors that promote this oxidation are presented, including molecular composition, metal contamination, temperature and light exposure, as well as the latest findings on the inclusion of HVO, the current state-of-the-art analytical techniques employed, and the impact of higher pressure injection systems on vehicles that demonstrate deposit formation is not solely due to the unsaturated biodiesel components.

BACKGROUND: Succinic acid (SA) biotechnological production represents a promising alternative to the fossil-fuel based chemical production route. The goal of this study was to develop a SA production process conducted with biofilms of Actinobacillus succinogenes and fed with cheese whey, a lactose-rich by-product of the cheese-making processes.

Background: Heterotrophic microbial oils are potentially a more sustainable alternative to vegetable or fossil oils for food and fuel applications. However, as almost all work in the area is conducted on the laboratory scale, such studies carry limited industrial relevance and do not give a clear indication of what is required to produce an actual industrial process. Metschnikowia pulcherrima is a non-pathogenic industrially promising oleaginous yeast which exhibits numerous advantages for cost-effective lipid production, including a wide substrate uptake, antimicrobial activity and fermentation inhibitor tolerance. In this study, M. pulcherrima was fermented in stirred tank reactors of up to 350 L with 250-L working volume in both batch and semi-continuous operation to highlight the potential industrial relevance. Due to being food-grade, suitable for handling at scale and to demonstrate the oligosaccharide uptake capacity of M. pulcherrima, enzyme-hydrolysed starch in the form of glucose syrup was selected as fermentation feedstock. Results: In batch fermentations on the 2-L scale, a lipid concentration of 14.6 g L −1 and productivity of 0.11 g L −1 h −1 were achieved, which was confirmed at 50 L (15.8 g L −1 ; 0.10 g L −1 h −1). The maximum lipid production rate was 0.33 g L −1 h −1 (daily average), but the substrate uptake rate decreased with oligosaccharide chain length. To produce 1 kg of dry yeast biomass containing up to 43% (w/w) lipids, 5.2 kg of the glucose syrup was required, with a lipid yield of up to 0.21 g g −1 consumed saccharides. In semi-continuous operation, for the first time, an oleaginous yeast was cultured for over 2 months with a relatively stable lipid production rate (around 0.08 g L −1 h −1) and fatty acid profile (degree of fatty acid saturation around 27.6% w/w), and without contamination. On the 250-L scale, comparable results were observed, culminating in the generation of nearly 10 kg lipids with a lipid productivity of 0.10 g L −1 h −1. Conclusions: The results establish the importance of M. pulcherrima for industrial biotechnology and its suitability to commercially produce a food-grade oil. Further improvements in the productivity are required to make M. pulcherrima lipid production industrial reality, particularly when longer-chain saccharides are involved.

This is a repository copy of Valorisation of sawdust through the combined microwaveassisted hydrothermal pre-treatment and fermentation using an oleaginous yeast.