Life cycle assessment of dewatering routes for algae derived biodiesel processes

Biodiesel derived from algae is considered as a sustainable fuel, but proper downstream processing is necessary to minimize the environmental footprint of this process. Algae is grown in dilute liquid cultures, and achieving the low water contents required for extraction represents one of the greatest challenges for the production of algae derived biodiesel. An analysis of the life cycle emissions associated with harvesting, dewatering, extraction, reaction, and product purification stages for algae biodiesel were performed. This “base case” found 10,500 kg of total emissions per t of biodiesel with 96 % of those attributed to the spray dryer used for dewatering. Alternative cases were evaluated for various sequences of mechanical and thermal dewatering techniques. The best case, consisted of a disk-stack centrifuge, followed by the chamber filter press, and a heat integrated dryer. This resulted in 875 kg emissions/t of biodiesel, a 91 % reduction from the base case. Significant reductions in life cycle emissions were achieved for all mechanical dewatering alternatives compared to the base case, but further improvements using these existing technologies were limited. Additional improvements will require the development of new techniques for water removal or wet extractions.     

Spectral induced polarization signatures of hydroxide adsorption and mineral precipitation in porous media

The spectral induced polarization (SIP) technique is a promising approach for delineating subsurface physical and chemical property changes in a minimally invasive manner. To facilitate the understanding of position and chemical properties of reaction fronts that involve mineral precipitation in porous media, we investigated spatiotemporal variations in complex conductivity during evolution of urea hydrolysis and calcite precipitation reaction fronts within a silica gel column. The real and imaginary parts of complex conductivity were shown to be sensitive to changes in both solution chemistry and calcium carbonate precipitation. Distinct changes in imaginary conductivity coincided with increased hydroxide ion concentration during urea hydrolysis. In a separate experiment focused on the effect of hydroxide concentration on interfacial polarization of silica gel and well-sorted sand, we found a significant dependence of the polarization response on pH changes of the solution. We propose a conceptual model describing hydroxide ion adsorption behavior in silica gel and its control on interfacial polarizability. Our results demonstrate the utility of SIP for noninvasive monitoring of reaction fronts, and indicate its potential for quantifying geochemical processes that control the polarization responses of porous media at larger spatial scales in the natural environment.     

Variability in carbon isotopic fractionation during biodegradation of chlorinated ethenes: implications for field applications

Stable carbon isotopic analysis has the potential to assess biodegradation of chlorinated ethenes. Significant isotopic shifts, which can be described by Rayleigh enrichment factors, have been observed for the biodegradation of trichloroethlyene (TCE), cis-dichloroethylene (cDCE), and vinyl chloride (VC). However, until this time, no systematic investigation of isotopic fractionation during perchloroethylene (PCE) degradation has been undertaken. In addition, there has been no comparison of isotopic fractionation by different microbial consortia, nor has there been a comparison of isotopic fractionation by consortia generated from the same source, but growing under different conditions. This study characterized carbon isotopic fractionation during reductive dechlorination of the chlorinated ethenes, PCE in particular, for microbial consortia from two different sources growing under different environmental conditions in order to assess the extent to which different microbial consortia result in different fractionation factors. Rayleigh enrichment factors of -13.8@1000, -20.4@1000, and -22.4@1000 were observed for TCE, cDCE, and VC, respectively, for dechlorination by the KB-1 consortium. In contrast, isotopic fractionation during reductive dechlorination of perchloroethylene (PCE) could not always be approximated by a Rayleigh model. Dechlorination by one consortium followed Rayleigh behavior (epsilon = -5.2), while a systematic change in the enrichment factor was observed over the course of PCE degradation by two other consortia. Comparison of all reported enrichment factors for reductive dechlorination of the chlorinated ethenes shows significant variation between experiments. Despite this variability, these results demonstrate that carbon isotopic analysis can provide qualitative evidence of the occurrence and relative extent of microbial reductive dechlorination of the chlorinated ethenes.     

A Comparison Between a Semi-Continuous Analyzer and Filter-Based Method for Measuring Anion and Cation Concentrations in PM10 at an Urban Background Site in London

A comparison between the filter-based, laboratory ion chromatography technique and a semi-continuous analyzer (URG 9000B Ambient Ion Monitor [AIM]) was conducted to evaluate the performance of the AIM in measuring the concentrations of the main airborne ionic species in PM₁₀. The study was carried out in an urban background area of London (UK) in 2013. The two methods showed an overall good correlation (R² > 0.83) for nitrate, sulfate, chloride, ammonium, and magnesium and poor correlation was found for sodium, potassium, and calcium (R² < 0.50). The AIM gave consistently higher concentrations for sodium and potassium, possibly due to a positive bias within the sampling unit. During high concentration episodes, both the efficiency of the particle extraction and removal of gases by the denuder may be reduced. A HEPA filter test demonstrated that the denuder was removing gaseous components effectively but that there was some potential for contamination. Overall, the AIM was found to be a good instrument for measuring hourly anion and cation concentrations in PM₁₀ in urban sites.

Copyright 2015 American Association for Aerosol Research     

Ambi-site substitution of Mn in lanthanum germanate apatites

A neutron diffraction study at 4 K of the Mn doped lanthanum germanate apatite-type oxide ion conductor of nominal starting composition “La_9.5Mn_0.5(GeO₄)₆O_2.75” is reported. The structure was refined in space group P6₃/m, although high thermal displacement parameters were observed for the oxide ion sites (particularly O3, and O4). Reduced thermal displacement parameters were obtained by splitting the O3 site, and allowing the O4 oxygen to move off site, which may indicate local regions of lower symmetry within the structure. In addition, the data suggested ambi-site substitution of Mn, with it being present on both the Ge site and the La site. Assuming no change in La:Mn:Ge ratio, a composition of La_9.18Mn_0.28(GeO₄)_5.8(MnO₄)_0.2O₂ was determined. As such there are nominally no interstitial oxide ions, but rather cation vacancies on the La site. Therefore, the high conductivity for this sample is most likely related to the introduction of Frenkel-type defects at higher temperature, as previously proposed for other apatite-type systems containing vacancies on the La site.     

Mental rotation of representations of two-dimensional and three-dimensional objects.

Empirical and theoretical considerations suggest that representations of three-dimensional objects should be more difficult to rotate mentally than representations of two-dimensional objects. In this study, subjects were asked to make mirror-normal decisions with stimuli that differed in perceived dimensionality and in angle of rotation in the image plane. In a series of four experiments, the time to make mirror-normal decisions increased with increased orientation discrepancy between the stimuli, as found previously in the literature. In every experiment, however, response times were smaller for representations of two-dimensional shapes than for representations of three-dimensional shapes when the stimuli being compared were presented with a large angular discrepancy. Whereas response times increased linearly with orientation when representations of three-dimensional shapes were rotated, the increase in response time for representations of two-dimensional shapes was generally nonlinear. Overall, the evidence suggests that representations of three-dimensional shapes are mentally rotated at the same rate as representations of two-dimensional shapes for angles of rotation between 0° and 60°. For larger angles of rotation, however, the rate of mental rotation is greater for representations of two-dimensional shapes than for representations of three-dimensional shapes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

分子育种提高甜菜抗病性(续完)

通过国内外在分子育种水平上对甜菜多种病害抗病性研究的分析和总结，综述了国内外分子育种方面提高甜菜抗病性的研究进展。     

Nested PCR assay for detection of granulocytic ehrlichiae

A sensitive and specific nested PCR assay was developed for the detection of granulocytic ehrlichiae. The assay amplifies the 16S rRNA gene and was used to examine acute-phase EDTA-blood and serum samples obtained from seven humans with clinical presentations compatible with human granulocytic ehrlichiosis. Five of the seven suspected cases were positive by the PCR assay using DNA extracted from whole blood as the template, compared with a serologic assay that identified only one positive sample. The PCR assay using DNA extracted from the corresponding serum samples as the template identified three positive samples. The sensitivity of the assay on human samples was examined, and the limit of detection was shown to be fewer than 2 copies of the 16S rRNA gene. The application of the assay to nonhuman samples demonstrated products amplified from template DNA extracted from Ixodes scapularis ticks collected in Rhode Island and from EDTA-blood specimens obtained from white-tailed deer in Maryland. All PCR products were sequenced and identified as specific to granulocytic ehrlichiae. A putative variant granulocytic ehrlichia 16S rRNA gene sequence was detected among products amplified from both the ticks and the deer blood specimens.