769 research outputs found

    Keck Deep Fields. I. Observations, Reductions, and the Selection of Faint Star-Forming Galaxies at Redshifts z~4, 3, and 2

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    We introduce a very deep, R_lim~27, multicolor imaging survey of very faint star-forming galaxies at z~4, z~3, z~2.2, and z~1.7. This survey, carried out on the Keck I telescope, uses the very same UGRI filter system that is employed by the Steidel team to select galaxies at these redshifts, and thus allows us to construct identically-selected, but much fainter, samples. However, our survey reaches ~1.5 mag deeper than the work of Steidel and his group, letting us probe substantially below the characteristic luminosity L* and thus study the properties and redshift evolution of the faint component of the high-z galaxy population. The survey covers 169 square arcminutes in three spatially independent patches on the sky and -- to R<~27 -- contains 427 GRI-selected z~4 LBGs, 1481 UGR-selected z~3 LBGs, 2417 UGR-selected z~2.2 star-forming galaxies, and 2043 UGR-selected z~1.7 star-forming galaxies. In this paper, the first in a series, we introduce the survey, describe our observing and data reduction strategies, and outline the selection of our z~4, z~3, z~2.2, and z~1.7 samples.Comment: To appear in Ap

    Aperçu de la méthanisation agricole en Italie

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    La mise en place et le dĂ©veloppement de la mĂ©thanisation sont intrinsĂšquement liĂ©s Ă  des questions gĂ©ographiques et aux prises de position des institutions. Il est intĂ©ressant d’observer comment cela s’opĂšre en Italie, de voir oĂč les prioritĂ©s sont placĂ©es et quels choix sont fait, notamment ici dans la rĂ©gion de VĂ©nĂ©tie

    Bio-hythane production from food waste by dark fermentation coupled with anaerobic digestion process: A long-term pilot scale experience

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    In this paper are presented the results of the investigation on optimal process operational conditions of thermophilic dark fermentation and anaerobic digestion of food waste, testing a long term run, applying an organic loading rate of 16.3 kgTVS/m3d in the first phase and 4.8 kgTVS/m3d in the second phase. The hydraulic retention times were maintained at 3.3 days and 12.6 days, respectively, for the first and second phase. Recirculation of anaerobic digested sludge, after a mild solid separation, was applied to the dark fermentation reactor in order to control the pH in the optimal hydrogen production range of 5-6. It was confirmed the possibility to obtain a stable hydrogen production, without using external chemicals for pH control, in a long term test, with a specific hydrogen production of 66.7 l per kg of total volatile solid (TVS) fed and a specific biogas production in the second phase of 0.72 m3 per kgTVS fed; the produced biogas presented a typical composition with a stable presence of hydrogen and methane in the biogas mixture around 6 and 58%, respectively, carbon dioxide being the rest

    Exploitation of Solar Energy for Ammonium Sulfate Recovery from Anaerobic Digestate of Different Origin

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    Digestate represents the semi-liquid byproduct of the anaerobic digestion process. It was estimated that 56 Mtonnes of digestate are annually produced only in Europe. Digestate composition depends on the initial total solids (TS) mixture fed to the digester and by its origin (manure, food wastes, agricultural residues, wastewater sludge). Typical values for the different components include a stabilized organic matter content between 20 and 50 g/L, a good content of nitrogen compounds (2–8 g/kg) and of phosphorous compounds (up to 3 g/kg). In particular, ammonia presence in digestate is interesting for ammonium sulfate production, a fertilizer which favors plants' growth. Traditional ammonium sulfate synthesis is conducted by stripping followed by sulfuric acid absorption, a process which requires high energy and chemicals consumptions. This work investigates the exploitation of solar energy to evaporate the liquid phase of digestate in a lab-scale greenhouse. Digestate vapors, rich in ammonia, are sent in a Drechsler trap, filled with 38% w/w sulfuric acid solution, through three solar air fans. The process has been tested on digestates differing for TS content and origin. It emerged that the process is favored by digestates with high ammonia content, as those originated from manure, and a TS content of about 10% w/w, which allowed to obtain an ammonium sulfate concentration of about 2 M in the final solution

    Optimization of Volatile Fatty Acids Production for Phas Synthesis from Food Wastes

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    Food wastage is an ethical and environmental wrong practice. Considering a circular economy optic, food waste is a carbon rich substrate, suited for anaerobic fermentation to produce not only biogas, but also highvalue chemical compounds, such as Volatile Fatty Acids (VFAs), that can be recovered in order to synthetize polyhydroxyalkanoates (PHAs). This work represented a step in a larger biorefinery process for food waste treatment, having the aim to explore the production and the profile of VFAs from of three different food waste substrates: Stillage, Condensate and Spent Coffee Ground. The substrates were considered at three different pH conditions (uncontrolled, 7, 12), anaerobically digested in batch reactors for VFAs accumulation. The best VFAs yields belonged to pH 7 tests for all the substrates. The best one on terms of VFAs productivity was Food Stillage with 36.17 gCOD/L of VFAs concentration, corresponding to a VFAs yield of 49.48 % w/w

    Production, purification and recovery of caproic acid, Volatile fatty acids and methane from Opuntia ficus indica

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    Opuntia ficus-indica can grow in arid and semi-arid environments characterized by low water and nutrients availability. These features make it a more sustainable alternative to the common energy crops for biorefinery purposes. This work focused on the potential benefits of anaerobic processes applied to this plant. Specifically, it considered i) the substrate preparation, demonstrating the effect of the apparent viscosity on the process; ii) the evaluation of biomethane, Volatile Fatty Acids (VFAs), and caproic acid production in semi-continuous mode at different hydraulic retention times; iii) the purification of the Fatty Acids-rich output through pressure-driven membrane filtration. The rheology analysis found that a 5 %w/w water dilution of the substrate is needed to lower the apparent viscosity to 173 cP, which is below the acceptable apparent viscosity level of 200 cP for a good bioreactor mixing. Keeping this condition, the semi-continuous trials with the best biomethane performance was at HRT of 20 days, with 210 mLCH4/gVS and 232 mLCH4/gCODin of production and specific yield, respectively. The VFAs and caproic acid production reached their best at Hydraulic Retention Time 5, with 26 and 7.9 gCOD/L of VFAs and caproic acid, corresponding to specific yields of 79 and 30 % respectively. Pressuredriven filtration at 330 kDa allowed to obtain a permeate with a VFAs and caproic acid content of 96.72%w/w. Finally, the adsorption and desorption tests allowed to separate caproic acid from the permeate and to concentrate it from about 7.5 gCOD/L to about 26 gCOD/L

    Anaerobic co-digestion effluent as substrate for chlorella vulgaris and scenedesmus obliquus cultivation

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    Anaerobic digestate supernatant can be used as a nutrient source for microalgae cultivation, thus integrating phytoremediation processes with high value products storage in microalgae biomass. Microalgae are able to use nitrogen and phosphorous from digestate, but high nutrient concentration can cause growth inhibition. In this study, two microalgae strains (C. vulgaris and S. obliquus) were cultivated on the anaerobic co-digestion supernatant (obtained from the organic fraction of municipal solid waste (OFMSW) and waste activated sludge (WAS)) in a preliminary Petri plate screening at different dilutions (1:10 and 1:5) using a synthetic medium (ISO) and tap water (TW). Direct Nile red screening was applied on colonies to preliminarily identify hydrophobic compound storage and then a batch test was performed (without air insufflation). Results show that C. vulgaris was able to grow on digestate supernatant 1:5 diluted, while Nile red screening allowed the preliminary detection of hydrophobic compound storage in colonies. The analysis carried out at the end of the test on ammonia, phosphate, nitrate and sulphate showed a removal percentage of 47.5 ± 0.8%, 65.0 ± 6.0%, 95.0 ± 3.0% and 99.5 ± 0.1%, respectively

    Old and Young X-ray Point Source Populations in Nearby Galaxies

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    We analyzed 1441 Chandra X-ray point sources in 32 nearby galaxies. The total point-source X-ray luminosity L_XP is well correlated with B, K, and FIR+UV luminosities of spiral host galaxies, and with the B and K luminosities for ellipticals. This suggests an intimate connection between L_XP and both the old and young stellar populations, for which K and FIR+UV luminosities are proxies for the galaxy mass M and star-formation rate SFR. We derive proportionality constants 1.3E29 erg/s/Msol and 0.7E39 erg/s/(Msol/yr), which can be used to estimate the old and young components from M and SFR, respectively. The cumulative X-ray luminosity functions for the point sources have quite different slopes for the spirals (gamma ~= 0.5-0.8) and ellipticals (gamma ~= 1.4), implying *the most luminous point sources dominate L_XP* for the spirals. Most of the point sources have X-ray colors that are consistent with either LMXBs or Ultraluminous X-ray sources (ULXs a.k.a. IXOs) and we rule out classical HMXBs (e.g. neutron-star X-ray pulsars) as contributing much to L_XP. Thus, for spirals, the ULXs dominate L_XP. We estimate that >~20% of all ULXs found in spirals originate from the older (pop II) stellar populations, indicating that many of the ULXs that have been found in spiral galaxies are in fact pop II ULXs, like those in elliptical galaxies. The linear dependence of L_XP on the SFR argues for either a steepening in the X-ray luminosity function of the young (pop I) X-ray source population at L_X >~10^(38.5-39) erg/s, or a decreasing efficiency for producing all types of young X-ray point sources as the galaxy SFR increases.Comment: 33 pages AASTEX, ApJ accepted. Please download full version with figures from http://www.pha.jhu.edu/~colbert/chps_accepted.p

    Microalgae Cultivation on Anaerobic Digestate of Municipal Wastewater, Sewage Sludge and Agro-Waste

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    Microalgae are fast-growing photosynthetic organisms which have the potential to be exploited as an alternative source of liquid fuels to meet growing global energy demand. The cultivation of microalgae, however, still needs to be improved in order to reduce the cost of the biomass produced. Among the major costs encountered for algal cultivation are the costs for nutrients such as CO2, nitrogen and phosphorous. In this work, therefore, different microalgal strains were cultivated using as nutrient sources three different anaerobic digestates deriving from municipal wastewater, sewage sludge or agro-waste treatment plants. In particular, anaerobic digestates deriving from agro-waste or sewage sludge treatment induced a more than 300% increase in lipid production per volume in Chlorella vulgaris cultures grown in a closed photobioreactor, and a strong increase in carotenoid accumulation in different microalgae species. Conversely, a digestate originating from a pilot scale anaerobic upflow sludge blanket (UASB) was used to increase biomass production when added to an artificial nutrient-supplemented medium. The results herein demonstrate the possibility of improving biomass accumulation or lipid production using different anaerobic digestates. \ua9 2016 by the authors; licensee MDPI, Basel, Switzerland
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