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Crop cultivation in greenhouses under semi-arid climatic conditions is subject to various stresses, in particular during the winter season at night, when the interior air is poorly controlled, leading to prolonged periods of low temperature. The aim is then to evaluate and control the heat exchanges of the enclosure in order to prevent low indoor air temperatures and reduce the thermal load of the greenhouse. The objectives of this study are to investigate the convective and radiative heat exchanges at the cover in order to establish new correlations for the convective heat transfer coefficients in semi arid regions. The climatic parameters were measured inside and outside a closed empty glasshouse without crop, for three different nights during the winter season in the semi-arid land of Algeria. A physical model for analysing the convective heat transfers was implemented, and new correlations were established, parameterised, calibrated and validated thoroughly. A significant difference was observed between the correlations obtained by this study and the models obtained for other greenhouse designs under different climatic conditions. Results show that the convection mode along the inside wall of the cover is free turbulent. Conversely, the convection mode along the outside greenhouse cover remains forced turbulent. A consistent performance of the correlations was observed, both in the calibration and validation stages.

Recycling of anaerobically-digested thin stillage within a corn-ethanol plant may result in the accumulation of nutrients of environmental concern in animal feed coproducts and inhibitory organic materials in the fermentation tank. Our focus is on anaerobic digestion of treated (centrifugation and lime addition) thin stillage. Suitability of digestate from anaerobic treatment for reuse as process water was also investigated. Experiments conducted at various inoculum-to-substrate ratios (ISRs) revealed that alkalinity is a critical parameter limiting digestibility of thin stillage. An ISR level of 2 appeared optimal based on high biogas production level (763 mL biogas/g volatile solids added) and organic matter removal (80.6% COD removal). The digester supernatant at this ISR level was found to contain both organic and inorganic constituents at levels that would cause no inhibition to ethanol fermentation. Anaerobic digestion of treated-thin stillage can be expected to improve the water and energy efficiencies of dry grind corn-ethanol plants.

Abstract Natural gas has been promoted as a ‘‘bridge’’ fuel toward a low-carbon future by offering near-term emissions reductions at lower cost. Existing literature is inconclusive on the short-term emissions benefits of more abundant natural gas. The long-lived nature of natural gas infrastructure also threatens to lock in emissions levels well above longer-term targets. If natural gas can offer short-to-medium term benefits, how much of a bridge should we build? Using ARTIMAS, a foresighted computable general equilibrium model of the US economy, we interact scenarios developed by the EMF-34 study group related to abundant natural gas, low-cost renewables, and a carbon tax to examine the role of natural gas in a carbon-constrained future. We find that abundant natural gas alone does not have a significant impact on CO2 emissions. We also find that, under a higher carbon tax, natural gas investment of approximately $10 billion per year declines to zero at a tax of about $40/ton and existing natural gas assets face significant risk of impairment. Last, the presence of abundant natural gas lowers the marginal welfare cost of abating small amounts of CO2 but is likely to raise the cost of abatement levels consistent with common climate objectives. The integrated welfare costs of climate policy depend on how much abatement we must undertake.

In this study, the effect of recycling the non-condensable gases (NCG) in the catalytic pyrolysis of hybrid poplar using FCC catalyst was investigated. A 50mm bench scale fluidized bed reactor at 475°C with a weight hourly space velocity (WHSV) of 2h(-1) and a gas recycling capability was used for the studies. Model fluidizing gas mixtures of CO/N(2), CO(2)/N(2), CO/CO(2)/N(2) and H(2)/N(2) were used to determine their independent effects. Recycling of the NCG in the process was found to potentially increase the liquid yield and decrease char/coke yield. The model fluidizing gases increased the liquid yield and the CO(2)/N(2) fluidizing gas had the lowest char/coke yield. The (13)C-NMR analysis showed that recycling of NCG increases the aromatic fractions and decreases the methoxy, carboxylic and sugar fractions. Recycling of NCG increased the higher heating value and the pH of the bio-oil as well as decreased the viscosity and density.

Numerous studies have examined relationships between primary production and biodiversity at higher trophic levels. However, altered production in plant communities is often tightly linked with concomitant shifts in diversity and composition, and most studies have not disentangled the direct effects of production on consumers. Furthermore, when studies do examine the effects of plant production on animals in terrestrial systems, they are primarily confined to a subset of taxonomic or functional groups instead of investigating the responses of the entire community. Using natural monocultures of the salt marsh cordgrass Spartina alterniflora, we were able to examine the impacts of increased plant production, independent of changes in plant composition and/or diversity, on the trophic structure, composition, and diversity of the entire arthropod community. If arthropod species richness increased with greater plant production, we predicted that it would be driven by: (1) an increase in the number of rare species, and/or (2) an increase in arthropod abundance. Our results largely supported our predictions: species richness of herbivores, detritivores, predators, and parasitoids increased monotonically with increasing levels of plant production, and the diversity of rare species also increased with plant production. However, rare species that accounted for this difference were predators, parasitoids, and detritivores, not herbivores. Herbivore species richness could be simply explained by the relationship between abundance and diversity. Using nonmetric multidimensional scaling (NMDS) and analysis of similarity (ANOSIM), we also found significant changes in arthropod species composition with increasing levels of production. Our findings have important implications in the intertidal salt marsh, where human activities have increased nitrogen runoff into the marsh, and demonstrate that such nitrogen inputs cascade to affect community structure, diversity, and abundance in higher trophic levels.

Anaerobic bio-digestion/energy generation complexes using animal waste raw materials represent an important component of renewable energy initiatives and policies worldwide, and are significant contributors to broaden sustainability efforts. In such projects bio-power feasibility depends heavily on generation complex access to biomass which is of costly transportation. As a result, an important component of renewable energy planning is the optimization of a logistics system to guarantee low-cost access to animal waste. This access is a function of local characteristics including number and geographic location of organic waste sources, operating and maintenance costs of the generation facility, energy prices, and marginal contribution of biomass collected and delivered to the anaerobic bio-digestion unit. Because biomass exhibits high transportation costs per unit of energy ultimately generated, and because different types of biomass have different biogas-generating properties, design of the supply logistics system can be the determinant factor towards economic viability of energy generation from an anaerobic bio-digestion plant. Indeed, to address this problem it is helpful to consider the farms, the logistics system, the anaerobic bio-digestion plant, and the generation plant as subsystems in an integrated system. Additionally, the existence of an outlet for manure may allow farmers to significantly raise boundaries of one constraint they face, namely disposing of animal waste, therefore permitting increases in farm production capacity. This paper suggests and outlines a systematic methodology to address the design of such systems.

Moss-associated N2 fixation by epiphytic microbes is a key biogeochemical process in nutrient-limited high-latitude ecosystems. Abiotic drivers, such as temperature and moisture, and the identity of host mosses are critical sources of variation in N2 fixation rates. An understanding of the potential interaction between these factors is essential for predicting N inputs as moss communities change with the climate. To further understand the drivers and results of N2 fixation rate variation, we obtained natural abundance values of C and N isotopes and an associated rate of N2 fixation with 15N2 gas incubations in 34 moss species collected in three regions across Alaska, USA. We hypothesized that δ15N values would increase toward 0‰ with higher N2 fixation to reflect the increasing contribution of fixed N2 in moss biomass. Second, we hypothesized that δ13C and N2 fixation would be positively related, as enriched δ13C signatures reflect abiotic conditions favorable to N2 fixation. We expected that the magnitude of these relationships would vary among types of host mosses, reflecting differences in anatomy and habitat. We found little support for our first hypothesis, with only a modest positive relationship between N2 fixation rates and δ15N in a structural equation model. We found a significant positive relationship between δ13C and N2 fixation only in Hypnales, where the probability of N2 fixation activity reached 95% when δ13C values exceeded - 30.4‰. We conclude that moisture and temperature interact strongly with host moss identity in determining the extent to which abiotic conditions impact associated N2 fixation rates.

In the North-Central USA, switchgrass to be used as a biomass feedstock typically will be harvested in the autumn. The accumulated area harvested over the harvest season (defined here as the harvest progression) will influence the size of the machinery fleet and seasonal labor required to complete the majority of the harvest before the first lasting snow. A harvest progression model was developed that uses drying rate, mower and baler productivity, and weather conditions as major inputs. Ten years of weather data (2005–2014) from Wisconsin, Iowa, and Nebraska (WI, IA, NE) were used. Harvest progression was modeled for four harvest systems involving conventional and intensive conditioning both swathed and tedded (CC, IC, CCT, and ICT, respectively) and two dates at which harvest began (1 September and after a killing frost). To reduce risk of exposing crop to prolonged periods of inclement weather, mowers were idled when more than 80 ha were cut but not yet baled. For all sites, the harvest start date and the mower idled constraint had greater impact on harvest progression than the type of harvest system. Harvest progression was greatest when mowing started on 1 September and continued whenever weather permitted (i.e., no mower idled constraint). Compared to the harvest system used today (CC), using the IC system resulted in more area harvested with less crop exposed to rain after cutting and considerably less area left to be baled in the spring. Starting harvest on 1 September, using intensive conditioning, and not idling the mowers might be considered the system that best balances the desire for rapid harvest progression, small equipment fleet size, low-capital expenditures, and maximum labor utilization.

Increased use of ethanol-blended gasoline (gasohol) and its potential release into the subsurface have spurred interest in studying the biodegradation of and interactions between ethanol and gasoline components such as benzene, toluene, ethylbenzene and xylene isomers (BTEX) in groundwater plumes. The preferred substrate status and the high biological oxygen demand (BOD) posed by ethanol and its biodegradation products suggests that anaerobic electron acceptors (EAs) will be required to support in situ bioremediation of BTEX. To develop a strategy for aromatic hydrocarbon bioremediation and to understand the impacts of ethanol on BTEX biodegradation under strictly anaerobic conditions, a microcosm experiment was conducted using pristine aquifer sand and groundwater obtained from Canadian Forces Base Borden, Canada. The initial electron accepter pool included nitrate, sulfate and/or ferric iron. The microcosms typically contained 400 g of sediment, 600 approximately 800 ml of groundwater, and with differing EAs added, and were run under anaerobic conditions. Ethanol was added to some at concentrations of 500 and 5000 mg/L. Trends for biodegradation of aromatic hydrocarbons for the Borden aquifer material were first developed in the absence of ethanol, The results showed that indigenous microorganisms could degrade all aromatic hydrocarbons (BTEX and trimethylbenzene isomers-TMB) under nitrate- and ferric iron-combined conditions, but not under sulfate-reducing conditions. Toluene, ethylbenzene and m/p-xylene were biodegraded under denitrifying conditions. However, the persistence of benzene indicated that enhancing denitrification alone was insufficient. Both benzene and o-xylene biodegraded significantly under iron-reducing conditions, but only after denitrification had removed other aromatics. For the trimethylbenzene isomers, 1,3,5-TMB biodegradation was found under denitrifying and then iron-reducing conditions. Biodegradation of 1,2,3-TMB or 1,2,4-TMB was slower under iron-reducing conditions. This study suggests that addition of excess ferric iron combined with limited nitrate has promise for in situ bioremediation of BTEX and TMB in the Borden aquifer and possibly for other sites contaminated by hydrocarbons. This study is the first to report 1,2,3-TMB biodegradation under strictly anaerobic condition. With the addition of 500 mg/L ethanol but without EA addition, ethanol and its main intermediate, acetate, were quickly biodegraded within 41 d with methane as a major product. Ethanol initially present at 5000 mg/L without EA addition declined slowly with the persistence of unidentified volatile fatty acids, likely propionate and butyrate, but less methane. In contrast, all ethanol disappeared with repeated additions of either nitrate or ferric iron, but acetate and unidentified intermediates persisted under iron-enhanced conditions. With the addition of 500 mg/L ethanol and nitrate, only minor toluene biodegradation was observed under denitrifying conditions and only after ethanol and acetate were utilized. The higher ethanol concentration (5000 mg/L) essentially shut down BTEX biodegradation likely due to high EA demand provided by ethanol and its intermediates. The negative findings for anaerobic BTEX biodegradation in the presence of ethanol and/or its biodegradation products are in contrast to recent research reported by Da Silva et al. [Da Silva, M.L.B., Ruiz-Aguilar, G.M.L., Alvarez, P.J.J., 2005. Enhanced anaerobic biodegradation of BTEX-ethanol mixtures in aquifer columns amended with sulfate, chelated ferric iron or nitrate. Biodegradation. 16, 105-114]. Our results suggest that the apparent conservation of high residual labile carbon as biodegradation products such as acetate makes natural attenuation of aromatics less effective, and makes subsequent addition of EAs to promote in situ BTEX biodegradation problematic.