Kaiming Peng

Culture strategies for lipid production using acetic acid as sole carbon source by Rhodosporidium toruloides

Rhodosporidium toruloides AS 2.1389 was tested using different concentrations of acetic acid as a low-cost carbon source for the production of microbial lipids, which are good raw materials for biodiesel production. It grew and had higher lipid contents in media containing 4-20 g/L acetic acid as the sole carbon source, compared with that in glucose-containing media under the same culture conditions. At acetic acid concentrations as high as 20 g/L and the optimal carbon-to-nitrogen ratio (C/N) of 200 in a batch culture, the highest biomass production was 4.35 g/L, with a lipid content of 48.2%. At acetic acid concentrations as low as 4 g/L, a sequencing batch culture (SBC) with a C/N of 100 increased biomass production to 4.21 g/L, with a lipid content of 38.6%. These results provide usable culture strategies for lipid production by R. toruloides AS 2.1389 when using diverse waste-derived volatile fatty acids.

Separation and characterization of effective demulsifying substances from surface of Alcaligenes sp. S-XJ-1 and its application in water-in-kerosene emulsion.

The main goal of this work was to analyze the effect of surface substances on demulsifying capability of the demulsifying strain Alcaligenes sp. S-XJ-1. The demulsifying substances were successfully separated from the cell surface with dichloromethane-alkali treatment, and exhibited 67.5% of the demulsification ratio for water-in-kerosene emulsions at a dosage of 356mg/L. FT-IR, TLC and ESI-MS analysis confirmed the presence of a carbohydrate-protein-lipid complex in the demulsifying substances with the major molecular ions from mass-to-charge ratio (m/z) 165 to 814. After the substances separated, the cell morphology changed from aggregated to dispersed, and the concentration of cell surface functional groups decreased. Cell surface hydrophobicity and the ability of cell adhesion to hydrophobic surface of the treated cells was also reduced compared with original cell. It was proved that the demulsifying substances had a significant effect on cell surface properties and accordingly with demulsifying capability of Alcaligenes sp. S-XJ-1.

Application of waste frying oils in the biosynthesis of biodemulsifier by a demulsifying strain Alcaligenes sp. S-XJ-1.

Exploration of biodemulsifiers has become a new research aspect. Using waste frying oils (WFOs) as carbon source to synthesize biodemulsifiers has a potential prospect to decrease production cost and to improve the application of biodemulsifiers in the oilfield. In this study, a demulsifying strain, Alcaligenes sp. S-XJ-1, was investigated to synthesize a biodemulsifier using waste frying oils as carbon source. It was found that the increase of initial pH of culture medium could increase the biodemulsifier yield but decrease the demulsification ratio compared to that using paraffin as carbon source. In addition, a biodemulsifier produced by waste frying oils and paraffin as mixed carbon source had a lower demulsification capability compared with that produced by paraffin or waste frying oil as sole carbon source. Fed-batch fermentation of biodemulsifier using waste frying oils as supplementary carbon source was found to be a suitable method. Mechanism of waste frying oils utilization was studied by using tripalmitin, olein and tristearin as sole carbon sources to synthesize biodemulsifier. The results showed saturated long-chain fatty acid was difficult for S-XJ-1 to utilize but could effectively enhance the demulsification ability of the produced biodemulsifier. Moreover, FT-IR result showed that the demulsification capability of biodemulsifiers was associated with the content of C=O group and nitrogen element.

Carbon source dependence of cell surface composition and demulsifying capability of Alcaligenes sp. S-XJ-1.

Biodemulsifiers are environmentally friendly agents used in recycling oil or purifying water from emulsion, yet the demulsifying feature of cell-surface composition remains unclear. In this study, potentiometric titration, attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry were combined to characterize cell-surface chemical composition of demulsifying strain Alcaligenes sp. S-XJ-1 cultivated with different carbon sources. Cells cultivated with alkane contained abundant elemental nitrogen and basic functional groups, indicating that their surface was rich in proteins or peptides, which contributed to their highest demulsifying efficiency. For cells cultivated with fatty acid ester, the relatively abundant surface lipid contributed to a 50% demulsification ratio owing to the presence of more acidic functional group. The cells cultivated with glucose exhibited a high oxygen concentration (O/C ∼0.28), which indicated the presence of more polysaccharides on the cell surface. This induced the lowest demulsification ratio of 30%. It can be concluded that cell surface-associated proteins or lipids other than the polysaccharide of the demulsifying strain played a positive role in the demulsification activity. In addition, the cell-surface oligoglutamate compounds identified in situ were crucial to the demulsifying capability.

Bioconversion of volatile fatty acids derived from waste activated sludge into lipids by Cryptococcus curvatus.

Pure volatile fatty acid (VFA) solution derived from waste activated sludge (WAS) was used to produce microbial lipids as culture medium in this study, which aimed to realize the resource recovery of WAS and provide low-cost feedstock for biodiesel production simultaneously. Cryptococcus curvatus was selected among three oleaginous yeast to produce lipids with VFAs derived from WAS. In batch cultivation, lipid contents increased from 10.2% to 16.8% when carbon to nitrogen ratio increased from about 3.5 to 165 after removal of ammonia nitrogen by struvite precipitation. The lipid content further increased to 39.6% and the biomass increased from 1.56g/L to 4.53g/L after cultivation for five cycles using sequencing batch culture (SBC) strategy. The lipids produced from WAS-derived VFA solution contained nearly 50% of monounsaturated fatty acids, including palmitic acid, heptadecanoic acid, ginkgolic acid, stearic acid, oleic acid, and linoleic acid, which showed the adequacy of biodiesel production.

Cell surface properties of the demulsifying strain Alcaligenes sp. S-XJ-1 governing its behavior in oil–water biphasic systems

Abstract Bacterial behavior in oil–water biphasic systems plays an essential role in hydrophobic contaminant degradation, oil recovery, and emulsion breaking. Less is known about the cell surface properties that govern their behaviors in oil–water biphasic systems. In this study, biphasic partitioning and aggregation of a demulsifying strain of Alcaligenes sp. S-XJ-1 were experimentally measured and evaluated based on the cell surface properties of surface charge, surface free energy, and cell surface hydrophobicity (CSH). The S-XJ-1 was cultivated with five different carbon sources, and the results showed a highly varied partitioning, aggregation behavior, and cell surface properties. The calculated interaction energies, based on the cell surface properties, were consistent with the results of their behavior. Among the cell surface properties, the electron-donor character (γ−, range 8.8–57.0 mJ/m2), which correlated well with CSH (ΔGbwb), was an essential indicator of cell behavior. A low γ− value enhanced the cell–interface and cell–cell interaction energies, which promoted cell partitioning and aggregation eventually leading to demulsification. The results and analysis provide important information for researchers concerned with cell–cell and cell–interface interactions.

Microbial conversion of mixed volatile fatty acids into microbial lipids by sequencing batch culture strategy

Four mixed volatile fatty acids (VFAs) were used as sole carbon source to culture oleaginous yeast Cryptococcus curvatus by sequencing batch culture strategy. The highest lipid content (42.7%) and concentration (1.77g/L) were achieved when the ratio of VFAs (acetic, propionic, and butyric acids) was 6:3:1. The oleaginous yeast favored to use VFAs for lipid biosynthesis rather than cell proliferation. With regard to the utilization ratio of VFAs, acetic acid reached over 99%, whereas propionic acid was barely 35%. The produced lipids contained nearly 45% of monounsaturated fatty acids, which can be the ideal raw materials for biodiesel production. Additionally, the produced odd-numbered fatty acid content reached 23.6% when the propionate acid content of VFAs was 50%. Further analysis showed that increasing the ratio of acetic acid was most beneficial to cell mass and lipid production, whereas propionic acid and butyric acid were more conducive to lipid and cell mass synthesis, respectively.

Saponin-enhanced biomass accumulation and demulsification capability of the demulsifying bacteria Alcaligenes sp. S-XJ-1

Surfactants have been widely applied to the bioremediation of hydrophobic organic compound (HOC) contamination. In this study, the biosurfactant saponin was used for improving rape oil utilization to increase the biomass and demulsification capability of the demulsifying bacterial strain Alcaligenes sp. S-XJ-1. A saponin concentration of 0.05%, near its critical micelle concentration, was optimal to enhance biodemulsifier synthesis; the biomass and demulsification ratio increased by 2.4-fold and 18%, respectively. Biomass promotion was revealed to be attributed to the saponin-enhanced utilization of rape oil resulting from improved oil solubilization, cell membrane permeability, and cell activity. The demulsification boost was found to correlate to saponin-strengthened hydrophobicity via an increased protein content and decreased polysaccharide content of the cell-surface. This study advances our understanding of surfactant-enhanced biodemulsifier synthesis with respect to HOC utilization and cell-surface composition responses.

Enhanced biodiesel production from glucose-fed activated sludge microbial cultures by addition of nZVI and FeCl3

The effect of different iron additives on biodiesel production from activated sludge was investigated under an optimal lipid accumulation condition (pH = 4 & C/N = 100). Iron addition, ranging from 0.1 to 2.5 mmol L−1, had a positive effect on biodiesel production. Among separate iron tests, 0.25 mmol L−1 nZVI and 2.5 mmol L−1 FeCl3 performed the best. The gravimetric fatty acid methyl ester yields of the two treatments reached 215.3 (0.25 mmol L−1 nZVI) and 274.9 mg g−1 dry sludge (2.5 mmol L−1 FeCl3) and increased by 36.1% and 74.0% compared with control run (131.0 mg g−1 dry sludge), respectively. At the end of the culture period, the genus Gluconacetobacter (56.4%) was enriched in the sludge under the 2.5 mmol L−1 FeCl3 treatment while the other treatments were only dominated by Gluconobacter (∼80%). The accumulated lipids mainly contained around 60% of monounsaturated fatty acids, indicating the suitability for biodiesel production. Furthermore, indicators related to production costs showed iron addition could notably improve the biotechnical feasibility.