Achieving a high‐density oleaginous yeast culture: Comparison of four processing strategies using <i>Metschnikowia pulcherrima</i>

Microbial lipids have the potential to displace terrestrial oils for fuel, value chemical, and food production, curbing the growth in tropical oil plantations and helping to reduce deforestation. However, commercialization remains elusive partly due to the lack of suitably robust organisms and their low lipid productivity. Extremely high cell densities in oleaginous cultures are needed to increase reaction rates, reduce reactor volume, and facilitate downstream processing. In this investigation, the oleaginous yeast Metschnikowia pulcherrima, a known antimicrobial producer, was cultured using four different processing strategies to achieve high cell densities and gain suitable lipid productivity. In batch mode, the yeast demonstrated lipid contents more than 40% (w/w) under high osmotic pressure. In fed‐batch mode, however, high‐lipid titers were prevented through inhibition above 70.0 g L−1 yeast biomass. Highly promising were a semi‐continuous and continuous mode with cell recycle where cell densities of up to 122.6 g L−1 and maximum lipid production rates of 0.37 g L−1 h−1 (daily average), a nearly two‐fold increase from the batch, were achieved. The findings demonstrate the importance of considering multiple fermentation modes to achieve high‐density oleaginous yeast cultures generally and indicate the limitations of processing these organisms under the extreme conditions necessary for economic lipid production.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 665992

Multifunctional Role of Magnetic Nanoparticles in Efficient Microalgae Separation and Catalytic Hydrothermal Liquefaction

In this work, the efficiency of extracting algae from culture medium using magnetic nanoparticles (MNPs), converting the algal/particle slurry to biocrude using hydrothermal liquefaction (HTL), and successfully recycling the MNPs from the char phase was fully demonstrated for the first time. MNPs were synthesized by coprecipitation and used to extract algae from aqueous phase at a separation efficiency (SE) of 99%. The SE was optimized at pH 4. Liquefaction of algal/MNPs slurry gave a biocrude yield of 37.1% while algae only yielded 23.2%. The percentage areas in the GC-MS chromatogram corresponding to hydrocarbons (HCs) in Zn-ferrite catalyzed and uncatalyzed biocrude were 46.5% and 19.9%, respectively, while the percentage areas of heptadecane from Zn-ferrite catalyzed and uncatalyzed biocrude were 37.8% and 10%, respectively. Furthermore, the percentage area of heteroatom compounds in biocrude reduced substantially when liquefaction was done in the presence of Zn/Mg ferrites. The nanoparticles were recovered from biochar by sonication and recycled at a SE of 96.1%. Recycling of MNPs for magnetic separation of algae and catalytic HTL could lower the cost of microalgae harvesting and improve the yield and quality of biocrude. This could potentially reduce the cost of advanced biofuel processing from microalgae, making them more affordable in comparison to petroleum-derived fuels.</p

The microalgae biorefinery:A perspective on the current status and future opportunities using genetic modification

There is clear scientific evidence that emissions of greenhouse gases (GHG), arising from fossil fuel combustion and land-use change as a result of human activities, are perturbing the Earth's climate. Microalgae-derived biofuels have been chased since the 1980swithout success but, lately, a new biorefinery concept is receiving increasing attention. Here, we discuss the possible solutions to the many problems that make this process unrealised to date, considering also the possibility of including genetically modified (GM) organisms to improve the productivity and process economics. Currently, unless coupled to a service or higher value product production, biofuels derived from microalgae fail to achieve economic reality. However, provided sufficient development of new technologies, potentially including new or improved organisms to lower both production and processing costs, as well as looking at the utility of distributed versus centralised production models, algae biofuels could achieve an impact, off-setting our heavy reliance on petroleum-based liquid fuels.</p

Production of fermentable species by microwave-assisted hydrothermal treatment of biomass carbohydrates:Reactivity and fermentability assessments

This work addresses and compares the production of fermentable species by microwave-assisted hydrothermal treatment of cellulose and hemicellulose (from lignocellulose) and alginic acid (from macroalgae). A reliable reactivity comparison was established at different temperatures (160-210 °C), reaction times (0 and 5 min) and solid/water mass ratios (1/20 and 1/10 g/g). The nature of the carbohydrates and the hydrothermal conditions had a significant influence on the reactivity, which increased as follows: cellulose &lt; hemicellulose &lt; alginic acid. The operating conditions did not influence the global conversion obtained during hydrothermal treatment of cellulose. Conversely, the temperature and reaction time played an important role when processing hemicellulose or alginic acid. In these two cases, increasing the temperature and/or reaction time increased the overall conversion and liquid and gas yields. The liquid hydrolysates were made up of a mixture of oligo-(DP 3-6 and DP &gt; 6) and mono-/di-saccharides, carboxylic acids, ketones and furans. While the chemical composition of the hydrolysates produced from hemicellulose was not affected by the microwave operating conditions, the liquids having a high concentration of DP &gt; 6 oligosaccharides in all cases, the microwave conditions substantially influenced the composition of the liquids produced from cellulose and alginic acid. The former contained high proportions of oligosacharides and saccharides and the latter comprised water soluble DP &gt; 6 oligomers/oligosaccharides, saccharides, carboxylic acids and furans. The yeast Metschnikowia pulcherrima, previously demonstrated to be inhibitor tolerant and to metabolise a range of oligosacchaides, was used to assess the fermentability of the liquid fraction. All the hydrolysates produced were fermentable; their efficiency (standarised yeast biomass growth) decreasing as follows: cellulose (high/low saccharides/inhibitors proportion) &gt; hemicellulose (high/low oligosaccharides/inhibitors proportion) &gt; alginic acid (low/high saccharides/inhibitors proportion). Therefore, the promising results obtained in this work and the intrinsic green nature of the process make this method a very promising route for biomass valorisation, which can help to enable the development of new thermochemical and biological linked routes.</p

Multifunctional Role of Magnetic Nanoparticles in Efficient Microalgae Separation and Catalytic Hydrothermal Liquefaction

In this work, the efficiency of extracting algae from culture medium using magnetic nanoparticles (MNPs), converting the algal/particle slurry to biocrude using hydrothermal liquefaction (HTL), and successfully recycling the MNPs from the char phase was fully demonstrated for the first time. MNPs were synthesized by coprecipitation and used to extract algae from aqueous phase at a separation efficiency (SE) of 99%. The SE was optimized at pH 4. Liquefaction of algal/MNPs slurry gave a biocrude yield of 37.1% while algae only yielded 23.2%. The percentage areas in the GC-MS chromatogram corresponding to hydrocarbons (HCs) in Zn-ferrite catalyzed and uncatalyzed biocrude were 46.5% and 19.9%, respectively, while the percentage areas of heptadecane from Zn-ferrite catalyzed and uncatalyzed biocrude were 37.8% and 10%, respectively. Furthermore, the percentage area of heteroatom compounds in biocrude reduced substantially when liquefaction was done in the presence of Zn/Mg ferrites. The nanoparticles were recovered from biochar by sonication and recycled at a SE of 96.1%. Recycling of MNPs for magnetic separation of algae and catalytic HTL could lower the cost of microalgae harvesting and improve the yield and quality of biocrude. This could potentially reduce the cost of advanced biofuel processing from microalgae, making them more affordable in comparison to petroleum-derived fuels

Production of Biodiesel from Vietnamese Waste Coffee Beans: Biofuel Yield, Saturation and Stability are All Elevated Compared with Conventional Coffee Biodiesel

The suitability of biodiesel produced from spent Vietnamese coffee was examined. Previous work shows that the geographical origin of coffee beans has little effect on the composition and physical properties of the biodiesel produced Jenkins et al. [1]. Vietnamese coffee, however, is roasted in a range of fats and oils for flavour enhancement and therefore has a unique fatty acid profile. The oil yield and biodiesel properties of three Vietnamese coffees were assessed and compared to a coffee of more typical composition—Colombian—and traditional biodiesel feedstocks (rapeseed, sunflower and palm). The oil yield from fresh Vietnamese coffee was higher (12.0–14.0 %) than Colombian coffee (9.3 %), while the oil yield from spent Vietnamese coffee (9.3–10.4 %) was comparable to the Colombian coffee (9.5 %). The unsaponifiable matter was only present in low levels in the Vietnamese coffee (1.9–4.9 %) compared to Colombian coffee (30.4 % fresh, 21.4 % spent). Vietnamese coffee biodiesel was more saturated than Columbian coffee biodiesel. It was therefore more viscous and had a higher pour point than the Colombian coffee, and possessed properties more akin to palm biodiesel. Vietnamese coffee biodiesel would therefore be a suitable feedstock for use locally due to the more suitable climate and compatibility with the palm feedstock that is currently used