Rapid analysis of polyhydroxyalkanoate contents and its monomer compositions by pyrolysis-gas chromatography combined with mass spectrometry (Py-GC/MS).

Here, we report an analysis method for determining PHA (polyhydroxyalkanoates) contents and their monomer composition in microbial cells based on pyrolysis gas chromatography combined with mass spectrometry (Py-GC/MS). Various kinds of microbial cells accumulating different PHA contents and monomer compositions were prepared through the cultivation of Ralstonia eutropha and recombinant Escherichia coli. Py-GC/MS could analyse these samples in a short time without complicated pretreatment steps. Characteristic peaks such as 2-butenoic acid, 2-pentenoic acid, and hexadecanoic acid regarding PHA compositions and cell components were identified. Considering constituents of cells and ratios of peak areas of dehydrated monomers to hexadecanoic acid, a simple equation for estimation of PHA contents in microbial cells was derived. Also, monomer compositions of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) in R. eutropha could be successfully determined based on peak area of 2-butenoic acid and 2-pentenoic acid of Py-GC/MS, which are the corresponding species of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) in PHBV. Correlation of results between GC-FID and Py-GC/MS could be fitted very well. This method shows similar results for the samples obtained from same experimental conditions, allowing rapid and reliable analysis. Py-GC/MS can be a promising tool to rapidly screen PHA-positive strains based on polymer contents along with monomer compositions.

Mild pressure induces rapid accumulation of neutral lipid (triacylglycerol) in Chlorella spp.

Effective enhancement of neutral lipid (especially triacylglycerol, TAG) content in microalgae is an important issue for commercialization of microalgal biorefineries. Pressure is a key physical factor affecting the morphological, physiological, and biochemical behaviors of organisms. In this paper, we report a new stress-based method for induction of TAG accumulation in microalgae (specifically, Chlorella sp. KR-1 and Ch. sp. AG20150) by very-short-duration application of mild pressure. Pressure treatments of 10-15bar for 2h resulted in a considerable, ∼55% improvement of the 10-100g/Lcells' TAG contents compared with the untreated control. The post-pressure-treatment increase of cytoplasmic TAG granules was further confirmed by transmission electron microscopy (TEM). Notwithstanding the increased TAG content, the total lipid content was not changed by pressurization, implying that pressure stress possibly induces rapid remodeling/transformation of algal lipids rather than de novo biosynthesis of TAG.

High-Temperature CO2 Sorption on Hydrotalcite Having a High Mg/Al Molar Ratio.

Hydrotalcites having a Mg/Al molar ratio between 3 and 30 have been synthesized as promising high-temperature CO2 sorbents. The existence of NaNO3 in the hydrotalcite structure, which originates from excess magnesium nitrate in the precursor, markedly increases CO2 sorption uptake by hydrotalcite up to the record high value of 9.27 mol kg(-1) at 240 °C and 1 atm CO2.

Magnetic-Nanoflocculant-Assisted Water-Nonpolar Solvent Interface Sieve for Microalgae Harvesting.

Exploitation of magnetic flocculants is regarded as a very promising energy-saving approach to microalgae harvesting. However, its practical applicability remains limited, mainly because of the problem of the postharvest separation of magnetic flocculants from microalgal flocs, which is crucial both for magnetic-flocculant recycling and high-purity microalgal biomasses, but which is also a very challenging and energy-consuming step. In the present study, we designed magnetic nanoflocculants dually functionalizable by two different organosilane compounds, (3-aminopropyl)triethoxysilane (APTES) and octyltriethoxysilane (OTES), which flocculate negatively charged microalgae and are readily detachable at the water-nonpolar organic solvent (NOS) interface only by application of an external magnetic field. APTES functionalization imparts a positive zeta potential charge (29.6 mV) to magnetic nanoflocculants, thereby enabling microalgae flocculation with 98.5% harvesting efficiency (with a dosage of 1.6 g of dMNF/g of cells). OTES functionalization imparts lipophilicity to magnetic nanoflocculants to make them compatible with NOS, thus effecting efficient separation of magnetic flocculants passing through the water-NOS interface sieve from hydrophilic microalgae. Our new energy-saving approach to microalgae harvesting concentrates microalgal cultures (∼1.5 g/L) up to 60 g/L, which can be directly connected to the following process of NOS-assisted wet lipid extraction or biodiesel production, and therefore provides, by simplifying multiple downstream processes, a great potential cost reduction in microalgae-based biorefinement.

Repeated use of stable magnetic flocculant for efficient harvest of oleaginous Chlorella sp.

In the present study, a simple magnetic-particle recycling strategy was developed for harvest of the oleaginous microalga Chlorella sp. KR-1. The method entails the flocculation of microalgal cells and bare-Fe3O4 magnetic particles (bMP) by electrostatic attraction and the subsequent recovery of the bMP from the harvested flocs by electrostatic repulsion below and above the isoelectric points (IEP), respectively. For 10 recycles, the bMP showed 94-99% and 90-97% harvest and recovery efficiencies, respectively. Furthermore, neither the use of bMP nor pH adjustment showed any adverse effect on the microalgal cell growth or the co-existing bacterial species, as confirmed from the subsequent medium-recycling test and denaturing gradient gel electrophoresis (DGGE) analysis.

Effect of barium ferrite particle size on detachment efficiency in magnetophoretic harvesting of oleaginous Chlorella sp.

Microalgal biofuel is garnering many positive and promising reviews as a fuel for the next generation while research effort continues to improve the efficiency of its harvesting for commercial success. In this report, magnetophoretic harvesting of microalgae is conducted through a three-step process, which includes functionalization of magnetic particles by (3-aminopropyl)triethoxysilane (APTES), magnetic separation, and detachment of magnetic particles by increasing pH to higher than the isoelectric point. Detachment process is specifically focused and found that the use of larger magnetic particles is more efficient for detachment of magnetic particles from algae-particle conglomerates. The detaching efficiency improves from 12.5% to 85% when the particle size is increased from 108 nm to 1.17 µm. Smaller magnetic particles provide larger contact area to microalgae and form strong electrostatic binding to negatively-charged microalgae when pH is lower than the isoelectric point.

Magnetophoretic harvesting of oleaginous Chlorella sp. by using biocompatible chitosan/magnetic nanoparticle composites.

The consumption of energy and resources such as water in the cultivation and harvesting steps should be minimized to reduce the overall cost of biodiesel production from microalgae. Here we present a biocompatible and rapid magnetophoretic harvesting process of oleaginous microalgae by using chitosan-Fe3O4 nanoparticle composites. Over 99% of microalgae was harvested by using the composites and the external magnetic field without changing the pH of culture medium so that it may be reused for microalgal culture without adverse effect on the cell growth. Depending on the working volume (20-500 mL) and the strength of surface magnetic-field (3400-9200 G), the process of harvesting microalgae took only 2-5 min. The method presented here not only utilizes permanent magnets without additional energy for fast harvesting but also recycles the medium effectively for further cultivation of microalgae, looking ahead to a large scale economic microalgae-based biorefinement.

Rapid estimation of triacylglycerol content of Chlorella sp. by thermogravimetric analysis.

A simple and reliable method based on thermogravimetric analysis has been developed for determining triacylglycerol content in Chlorella sp. KR-1. There are two decomposing steps during pyrolysis of the microalgal cells and the second step of weight loss may be attributed to degradation and volatilization of triacylglycerols. The second peak height in the temperature derivatives of weight loss increased with the triacylglycerol content of the microalgal cells and the peak was around 390 °C regardless of the triacylglycerol contents. Based on these findings, a linear equation for determining triacylglycerol content was derived. The proposed method gives satisfactory results, showing small variance and a good interpolation capability.

Enhancement of CO2 sorption uptake on hydrotalcite by impregnation with K2CO3.

The awareness of symptoms of global warming and its seriousness urges the development of technologies to reduce greenhouse gas emissions. Carbon dioxide (CO(2)) is a representative greenhouse gas, and numerous methods to capture and storage CO(2) have been considered. Recently, the technology to remove high-temperature CO(2) by sorption has received lots of attention. In this study, hydrotalcite, which has been known to have CO(2) sorption capability at high temperature, was impregnated with K(2)CO(3) to enhance CO(2) sorption uptake, and the mechanism of CO(2) sorption enhancement on K(2)CO(3)-promoted hydrotalcite was investigated. Thermogravimetric analysis was used to measure equilibrium CO(2) sorption uptake and to estimate CO(2) sorption kinetics. The analyses based on N(2) gas physisorption, X-ray diffractometry, Fourier transform infrared spectrometry, Raman spectrometry, transmission electron microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy were carried out to elucidate the characteristics of sorbents and the mechanism of enhanced CO(2) sorption. The equilibrium CO(2) sorption uptake on hydrotalcite could be increased up to 10 times by impregnation with K(2)CO(3), and there was an optimal amount of K(2)CO(3) for a maximum equilibrium CO(2) sorption uptake. In the K(2)CO(3)-promoted hydrotalcite, K(2)CO(3) was incorporated without changing the structure of hydrotalcite and it was thermally stabilized, resulting in the enhanced equilibrium CO(2) sorption uptake and fast CO(2) sorption kinetics.