Strategies of preserving lipids in microorganism after fermentation

Surfactant-assisted in situ transesterification of wet Rhodotorula glutinis biomass

In situ transesterification of oleaginous microbes with short chain alcohol has been developed as a renewable process for the production of biodiesel. Dry biomass is often a requisite for the process to avoid the adverse effect of water on the productivity. As a consequence, large amount of energy consumption is required for prior biomass drying. In this study, the wet biomass of Rhodotorula glutinis, an oleaginous yeast, was used directly in in situ transesterification without biomass drying. The reaction conditions were optimized for the production of fatty acid methyl esters (FAME) and the effects of adding different surfactants were also studied. The highest FAME yield of 110% was achieved with a methanol loading of 1:100 at 90°C for 8 h as catalyzed by 0.36 M H₂SO₄, and the FAME content was 97%, which meets the 96.5% specified in both European biodiesel standards and Taiwanese biodiesel standards. The addition of 50 mM 3-(N,N-dimethylmyristylammonio)propanesulfonate (3-DMAPS, a zwitterionic surfactant) improved the FAME yield from 69% to 83%, which was obtained with a low methanol loading of 1:10 at 90°C for 10 h. Hence, the production of FAME with wet biomass under optimized reaction conditions was as effective as that with the dry form. This clearly indicates that using wet R. glutinis as the feedstock is feasible for the production of biodiesel by in situ transesterification.

Ultra-sonication for controlling the formation of disinfection by-products in the ClO2 pre-oxidation of water containing high concentrations of algae

Eutrophication has become great concern in recent years due to the fact that rivers, lakes, and reservoirs are the main drinking water source. Studies have been performed to enhance the removal of algae with ClO₂ pre-oxidation, but there was high potential in the formation of chlorite and chlorate. In this study, ultra-sonication was employed to assist algae removal and control disinfection by-products formation in ClO₂ pre-oxidation processes. It was found that solo ultra-sonication for 10 min (algae removal 86.11 ± 2.16%) could achieve similar algae removal efficiency as that with solo ClO₂ (0.5 mg/L) pre-oxidation for 10 min (algae removal 87.10 ± 3.50%). In addition, no formations of chlorite and chlorate were detected in solo ultra-sonication process. Five-minutes ultra-sonication followed by 5-min 0.5 mg/L ClO₂ treatment (total treatment time 10 min; algae removal 93.55 ± 3.22%) provided a better performance on algae removal compared to the solo ClO₂ (0.5 mg/L) pre-oxidation for 10 min. Moreover, chlorite was undetectable. It suggests that the utilization of ultra-sonication in ClO₂ pretreatment for algae removal has highly prevented the formations of chlorite and chlorate.

Detergent assisted ultrasonication aided in situ transesterification for biodiesel production from oleaginous yeast wet biomass

In situ transesterification of oleaginous yeast wet biomass for fatty acid methyl esters (FAMEs) production using acid catalyst, methanol with or without N-Lauroyl sarcosine (N-LS) treatment was performed. The maximum FAMEs yield obtained with or without N-LS treatment in 24h reaction time was 96.1±1.9 and 71±1.4% w/w, respectively. The N-LS treatment of biomass followed by with or without ultrasonication revealed maximum FAMEs yield of 94.3±1.9% and 82.9±1.8% w/w using methanol to lipid molar ratio 360:1 and catalyst concentration 360mM (64μL H₂SO₄/g lipid) within 5 and 25min reaction time, respectively. The FAMEs composition obtained in in situ transesterification was similar to that obtained with conventional two step lipid extraction and transesterification process. Biodiesel fuel properties (density, kinematic viscosity, cetane number and total glycerol) were in accordance with international standard (ASTM D6751), which suggests the suitability of biodiesel as a fuel.

Detergent assisted lipid extraction from wet yeast biomass for biodiesel: A response surface methodology approach

The lipid extraction from the microbial biomass is a tedious and high cost dependent process. In the present study, detergent assisted lipids extraction from the culture of the yeast Yarrowia lipolytica SKY-7 was carried out. Response surface methodology (RSM) was used to investigate the effect of three principle parameters (N-LS concentration, time and temperature) on microbial lipid extraction efficiency % (w/w). The results obtained by statistical analysis showed that the quadratic model fits in all cases. Maximum lipid recovery of 95.3±0.3% w/w was obtained at the optimum level of process variables [N-LS concentration 24.42mg (equal to 48mgN-LS/g dry biomass), treatment time 8.8min and reaction temperature 30.2°C]. Whereas the conventional chloroform and methanol extraction to achieve total lipid recovery required 12h at 60°C. The study confirmed that oleaginous yeast biomass treatment with N-lauroyl sarcosine would be a promising approach for industrial scale microbial lipid recovery.