William Todd French

Effect of different C/N ratios on carotenoid and lipid production by Rhodotorula glutinis.

Due to the increasing demand for sustainable biofuels, microbial oils as feedstock for the transesterification into biodiesel have gained scientific and commercial interest. Also, microbial carotenoids have a considerable market potential as natural colorants. The carbon to nitrogen (C/N) ratio of the respective cultivation media is one of the most important parameters that influence the production of microbial lipids and carotenoids. Thus, in the present experiment, the influence of different C/N ratios, initial glucose loadings, and ammonium concentrations of the cultivation medium on microbial cell growth and lipid and carotenoid production by the oleaginous red yeast Rhodotorula glutinis has been assessed. As a general trend, both lipid and carotenoid production increased at high C/N ratios. It was shown that not only the final C/N ratio but also the respectively applied initial carbon and nitrogen contents influenced the observed parameters. The lipid yield was not affected by different ammonium contents, while the carotenoid production significantly decreased both at low and high levels of ammonium supply. A glucose-based increase from C/N 70 to 120 did not lead to an increased lipid production, while carotenoid synthesis was positively affected. Generally, it can be asserted that lipid and carotenoid synthesis are stimulated at higher C/N ratios.

Lipid storage compounds in raw activated sludge microorganisms for biofuels and oleochemicals production

Activated sludge contains a microbial population responsible for the biological treatment of wastewater. This microbial population mostly consists of heterothrophic bacteria which utilize the organic content of the wastewater for growth, either as part of their cellular structures or as energy and carbon storage compounds. These compounds are mostly lipidic in nature and are or could be important raw materials for a multitude of applications in biofuel and oleochemical industries. In this study, a municipal activated sludge was analyzed for lipid storage compounds and other compound classes present in significant concentrations. Three extraction techniques, namely; Bligh & Dyer (applied on dried and partially dewatered samples) and accelerated solvent extractions, were initially investigated to identify the one resulting in the highest gravimetric and biodiesel yields. The highest yields were obtained using the Bligh & Dyer of partially dewatered sludge samples and thus, the extracts from this extraction technique were subjected to a series of analytical procedures such as precipitation, solid phase extraction, thin layer chromatography (TLC), gas chromatography with flame ionization detector (GC-FID) and gas chromatography-mass spectrometry (GC-MS) to characterize the major compound classes present. Results indicated that the major compounds in the samples were polyhydroxyalkanoates, wax esters, steryl esters, triacylglycerides, free fatty acids, free sterols and phospholipids. Hydrocarbons, diacylglycerides and monoacylglycerides were also detected. These compounds are either synthesized by microorganisms or from exogenous contributions. Regardless of the source of these compounds, their persistent presence in activated sludge offers another feedstock for a wide range of applications.

Screening of industrial wastewaters as feedstock for the microbial production of oils for biodiesel production and high-quality pigments

The production of biodiesel has notably increased over the past decade. Currently, plant oil is the main feedstock for biodiesel production, but, due to concerns related to the competition with food production, alternative oil feedstocks have to be found. Oleaginous yeasts are known to produce high amounts of lipids, but no integrated process from microbial fermentation to final biodiesel production has reached commercial realization yet due to economic constraints. Therefore, growth and lipid production of red yeast Rhodotorula glutinis was tested on low-cost substrates, namely, wastewaters from potato, fruit juice, and lettuce processing. Additionally, the production of carotenoids as high-value by-products was examined. All evaluated wastewaters met the general criteria for microbial lipid production. However, no significant increase in lipid content was observed, probably due to lack of available carbon in wastewaters from fruit juice and lettuce processing, and excess of available nitrogen in potato processing wastewater, respectively. During growth on wastewaters from fruit juice and lettuce processing the carotenoid content increased significantly in the first 48 hours. The relations between carbon content, nitrogen content, and carotenoid production need to be further assessed. For economic viability, lipid and carotenoid production needs to be increased significantly. The screening of feedstocks should be extended to other wastewaters.

Microbial cell disruption for improving lipid recovery using pressurized CO2: Role of CO2 solubility in cell suspension, sugar broth, and spent media

The study of in situ gas explosion to lyse the triglyceride‐rich cells involves the solubilization of gas (e.g., carbon dioxide, CO2) in lipid‐rich cells under pressure followed by a rapid decompression, which allows the gas inside the cell to rapidly expand and rupture the cell from inside out. The aim of this study was to perform the cell disruption using pressurized CO2 as well as to determine the solubility of CO2 in Rhodotorula glutinis cell suspension, sugar broth media, and spent media. Cell disruption of R. glutinis was performed at two pressures of 2,000 and 3,500 kPa, respectively, at 295.2 K, and it was found from both scanning electron microscopy (SEM) and plate count that a substantial amount of R. glutinis was disrupted due to the pressurized CO2. We also found a considerable portion of lipid present in the aqueous phase after the disruption at P = 3,500 kPa compared to control (no pressure) and P = 2,000 kPa, which implied that more intracellular lipid was released due to the pressurized CO2. Solubility of CO2 in R. glutinis cell suspension was found to be higher than the solubility of CO2 in both sugar broth media and spent media. Experimental solubility was correlated using the extended Henrys law, which showed a good agreement with the experimental data. Enthalpy and entropy of dissolution of CO2 were found to be −14.22 kJ mol−1 and 48.10 kJ mol−1 K−1, 9.64 kJ mol−1 and 32.52 kJ mol−1 K−1, and 7.50 kJ mol−1 and 25.22 kJ mol−1 K−1 in R. glutinis, spent media, and sugar broth media, respectively.

Economic assessment of microbial biodiesel production using heterotrophic yeasts

ABSTRACT The production of biodiesel using oleaginous microorganisms is investigated as promising alternative to produce a truly sustainable and renewable transportation fuel. While the feasibility of this approach has been shown on the laboratory scale, a commercial scale implementation is to date inhibited due to economic restraints. In order to evaluate the current cost situation and to develop suggestions to reduce production related costs, a simple cost analysis of the proposed microbial oil production process has been carried out. For closed fermentation in large-scale fermenters a break-even price of 2,350 US

Draft Genome Sequence of Enterobacter cloacae Strain JD6301

t–1 for microbial oil was calculated. In the context of a sensitivity analysis it was shown that especially alterations in capital cost can lead to overall cost reductions. Accordingly, an open pond cultivation approach was designed, cutting the cost for equipment almost in half and decreasing the break-even price to 1,723 US

Improving the lipid recovery from wet oleaginous microorganisms using different pretreatment techniques

t–1. However, these reductions are only feasible when stable biomass and lipid yields can be ensured in open-pond systems, because the sensitivity analysis identified these yield parameters as leading factors influencing the break-even price. Even under very optimistic assumptions, it was not possible to reduce the break-even price below that of conventional plant oils as competitive products. Therefore, economic feasibility of the process will probably only occur if on one hand considerable technical development and efficiency improvements of the production process are made while on the other hand plant and crude oil prices are continuously increasing.

Production of biodiesel and other valuable chemicals from wastewater treatment plant sludges

ABSTRACT Enterobacter cloacae strain JD6301 was isolated from a mixed culture with wastewater collected from a municipal treatment facility and oleaginous microorganisms. A draft genome sequence of this organism indicates that it has a genome size of 4,772,910 bp, an average G+C content of 53%, and 4,509 protein-coding genes.

Biodiesel from activated sludge through in situ transesterification.

Lipid extraction directly from the wet oleaginous microorganisms for biodiesel production is preferred as it reduces the energy input for traditional processes which require extensive drying of the biomass prior to the extraction. The high water content (≥80% on cell dry weight) in the wet biomass hinders the extraction efficiency due to the mass transfer limitation. This limitation can be overcome by pretreating wet biomass prior to the lipid extraction using pressurized gas that can be used alone or combined with other pretreatments to disrupt the cell wall. In this review, an extensive discussion on different pretreatments and the subsequent lipid extraction using these pretreatments is presented. Furthermore, a detailed account of the cell disruption using pressurized gas (e.g., CO2) treatment for microbial cell lysing is also presented. Finally, a new technique on lipid extraction directly from wet biomass using the combination of pressurized CO2 and microwave pretreatment is proposed.