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Abstract Predicting the distribution and resource of gas hydrates and understanding gas hydrate forming mechanisms are critical for assessing natural gas hydrate exploration potential, as well as exploiting hydrates. This study aims to provide a portable solution for evaluating resource of natural gas hydrate and quantifying contribution of methane sources via numerical simulations constrained by site-specific data. To numerically describe the complex process of biogenic methane production, an integrated simulation package, TOUGH + Hydrate + React (TOUGH + HR), was developed by coupling reactive transport, biodegradation and deposition of organic matter with behavior of hydrate-bearing system. Based on observed data from site SH2 in the South China Sea, a growing one-dimensional column model was constructed, and simulated via the developed TOUGH + HR tool. The results showed that when considering biogenic methane was the only source for hydrate, simulated maximum saturation of hydrate reached ~ 0.19, which is much lower than the observed value (~0.46), suggesting that the in-situ biogenic methane is not enough to form the high-saturation hydrate. When the upward flux of methane (considered as thermogenic methane) increased to 1.00 × 10−11 k g · m - 2 · s - 1 , both simulated saturation and distribution of hydrates matched the observed data well, including the profile of remained total organic carbon (TOC), the location of interface between dissolved methane and sulfate (SMI), and the derived chlorinity. Simulation results suggest that the ratio of biogenic methane to thermogenic methane forming hydrates was about 1:3. Predicted amount of methane hydrate using the column model was 3258.33 kg, very close to the estimated based on field observation (3112.82 kg).

The photosynthetic capacity of algae as a primary producer in nature and the relative ease of its cultivation on a large scale make it attractive to explore opportunities and develop algal technology for simultaneous sequestration of industrial and atmospheric CO2 (to mitigate climate change), whilst developing sustainable processes for manufacturing renewable fuels alongside biochemicals of value. The development of strategies that maximise algal product yield while optimising the CO2 gas supply is needed for the appropriate scale-up of algal technology. One of the main targets of this technology is the potential exploitation of flue gases, an inexpensive and carbon-rich source. So far, the growth of microalgae has predominantly been investigated using relatively low CO2 concentrations that are far from the levels offered by flue gas (6–25%), which are more useful for energy generation with concomitant development of carbon neutral processes. Here, we tested a series of gas supply strategies to investigate microalgal growth at high CO2 levels with the aim to improve algal CO2 fixation and lipid accumulation. Optimal growth of Nannochloropsis salina (a marine algae) occurred at 6% CO2, whilst few cells grew under 20% CO2. Excess CO2 resulted in medium acidification, pigment reduction, and growth inhibition. However, the fixation capacity of CO2 and the production of specific lipids were improved by O2 removal from the inlet gas by up to 4.8-fold and 4.4-fold, respectively. These parameters were further improved by 72% and 25%, respectively, via a gradual increase in CO2 concentration. Extremely high CO2 levels (100%) completely inhibited cell growth, but this effect was reversed when air containing atmospheric CO2 levels was introduced in place of 100% CO2. These findings will allow for the future development of more effective strategies using algal biotechnology for producing biofuel while mitigating carbon emissions.

Abstract The effect of different structural designs on the performance of electrical double layer capacitors (EDLCs) has been studied through a mathematical model that considers the mass transfer and conservation of charge equations. The structural design parameters considered in this study are the electrode thickness, electrode porosity, and initial electrolyte concentration. The performance parameters studied are the cell capacitance, specific energy, specific power, and electrolyte concentration for a range of discharge rates. The results of this study can be used to optimize EDLCs at various operating conditions.

Abstract The oil industry faces economic and environmental challenges due to its energy- and water-intensive processes. Surplus residual feedstocks and the water produced via heavy oil upgrading and processing are among the most challenging problems in the oil industry. Utilization these waste materials and a lack of efficient technologies to treat them are the main challenges causing the industry to consider them as waste materials. Existing technologies only add a small value, require high capital investment, and generate high greenhouse gas emissions. Therefore, in this study, we review and highlight the major findings regarding the oxy-cracking process, which is introduced as an alternative beyond combustion, as an environmentally friendly technique for converting these feedstocks into value-added products and also enhances the recyclability of wastewater. Through these residual feedstocks are partially oxidized in basic aqueous media at mild operational temperatures (150–230 °C) and pressures (3.4–5.2 MPa). Several operating conditions have been reported to optimize the conversion and selectivity of the products, and the results showed that the temperature and residence time have significant impacts on the yield and environmental impact. The experimental findings were validated with theoretical calculations, which provided insights on understanding the kinetic behavior based on the radical mechanism. The characterization findings revealed that the oxy-cracking could be a platform for a wide range of products such as humic acids, clean fuel, and carbon nanomaterials, and to recover valuable metals. Moreover, this process could be implemented for treatment of oil sand processes affected water and for decomposing emerging pharmaceuticals.

Abstract An approach to developing a wood pellet supply chain (SC) which selects among several sources of biomass feedstock is proposed. The approach is based on a downstream to upstream analysis of the SC and includes five phases: (1) Identifying potential markets and projected demands. (2) Determining feedstock types, locations, and available quantities. (3) Evaluation of raw material and final product transportation options, potential plant location, and logistics components that can be integrated with existing forest products SCs. (4) Cost estimation of raw material supply, production, and final product delivery. (5) Utilizing a spatially explicit optimization and generic model to determine the optimal operational conditions under which the wood pellet SC is profitable while taking into account economies of scale. The model selects the best feedstock locations and determines the optimal quantities to supply as well as the optimal production capacity. The associated ROI is calculated to assess economic feasibility. To show the value of the approach, we applied it to a real case study proposed by a regional development agency interested in developing the wood pellet sector in Eastern Canada. The results show that implementing a 100,000-tonne plant using biomass harvested in the forest as the sole feedstock is profitable. However, harvesting costs must be shared among the pellet mill and other forest companies and the government must provide financial support. The use of sawmill residues in the mix of feedstock allows implementing a highly profitable 50,000-tonne plant without any government support or harvesting cost sharing mechanism. Under a high wood pellet selling price, harvesting cost sharing and government support, the production capacity can reach 150,000 tonnes/year. An important finding is that government support is not necessary for ensuring profitability in all cases. Government support has a significant impact on profitability in the case where sawmill residues are not available as a feedstock for manufacturing pellets or the selling price is high enough to allow operating a profitable plant of large size.

Abstract Significant reduction of CO 2 emissions on a global scale may be achieved by reduction of energy intensity, by reduction of carbon intensity or by capture and storage of CO 2 . A portfolio of these methods is required to achieve the large reductions required; of which utilization of carbon sinks (i.e. material, geosphere and biosphere) will be an important player. Material sinks will probably only play a minor role as compared to biosphere and geosphere sinks in storage of CO 2 . Biosphere sinks are attractive because they can sequester CO 2 from a diffuse source whereas geosphere sinks require a pure waste stream of CO 2 (obtained by using expensive separation methods). On the other hand, environmental factors and storage time favor geosphere sinks. It is expected that a combination of the two will be used in order to meet emission reduction targets over the next 100 yr. A critical look is taken at capacities, retention/residence times, rates of uptake and relative cost of utilization of biosphere and geosphere sinks at three scales – global, national (Canada) and provincial (Alberta). Biosphere sinks considered are oceans, forests and soils. Geosphere sinks considered are enhanced oil recovery, coal beds, depleted oil and gas reservoirs and deep aquifers. The largest sinks are oceans and deep aquifers. The other biosphere and geosphere sinks have total capacities approximately of an order of lower magnitude. The sinks that will probably be used first are those that are economically viable such as enhanced oil-recovery, agriculture, forestry and possibly enhanced coalbed methane-recovery. The other sinks will be used when these options have been exhausted or are not available or a penalty (e.g. carbon tax) exists. Although the data tabulated for these sinks is only regarded as preliminary, it provides a starting point for assessment of the role of large sinks in meeting greenhouse gas emission reduction targets.

Abstract Captured biogas produced within wastewater treatment facilities can be the remedy to offset its increasing energy requirements. Furthermore, the conversion of methane to methanol is quite attractive as it is more transportable and has higher energy yield. Methane can be utilized by methanotrophs in which methanol is produced as a metabolic intermediate. Compared to type II, type I methanotrophs are more advantageous due to its higher growth yields and energy efficiency. This work objective is to optimize methanol bio-production using type I methanotrophs enriched from activated sludge process. This study demonstrates methanol production using mixed culture from wastewater sludge. Optimization of methanol dehydrogenase inhibitors, sodium formate, and copper concentrations, as well as, the gaseous headspace composition and biomass density resulted in a significant enhancement in methanol production. The maximum methanol concentration achieved in this study was 485 ± 21 mg/L. Whereas, the highest methanol productivity obtained was equal to 2115 ± 81 mg/L/day. Those findings show the high potential of producing methanol using mixed culture enriched from activated sludge process.

Abstract The gasification of cellulose was examined from 350 to 650°C in helium and helium/water vapour mixtures up to total pressures of 2500 kPa. Particular attention was paid to the effects on the [ (CO 2 + H 2 ) CO ] molar ratio in the product gases of the selected additives—iron(III)oxide, zinc(II)chromite and potassium carbonate. The results are interpreted in terms of catalytic influences on key steps in the reaction sequence. Thus, the most effective additive in realising the highest gaseous fuel potential was potassium carbonate which may act as a catalyst for the carbon/steam reaction. Although the calorific value of the gases produced was not altered much by pressure, it did slightly affect the distribution of the product gases, probably by influencing the secondary reactions of tars. Scanning electron micrographs of the various solid samples are presented.

Abstract Microalgae are renewable and promising feedstock rich in biochemicals for biofuel and bioenergy production. The viability of this technology relies on the energy- and cost-efficient cultivation (culture medium used) and harvesting (coagulant applied) processes. The natural coagulant of crystalline nanocellulose modified with 1-(3-aminopropyl) imidazole (CNC-APIm) was demonstrated as a green and recyclable coagulant for microalgal harvesting. However, optimisation is still needed to ensure its applicability to microalgae cultivated on wastewaters, no effect on biomass composition, as well as cost-effective harvesting. In this study, microalgal growth and nutrient removal capacity of Chlorella vulgaris (C. vulgaris) were first investigated on two types of municipal wastewaters. C. vulgaris grew well on both primary and 30% (v/v) diluted centrate wastewaters with biomass productivities of 0.071 ± 0.005 and 0.062 ± 0.006 g/(L·d), respectively. High nitrogen and phosphorus removal efficiencies (91.1–100%) were obtained. Subsequently, the wastewater-cultivated C. vulgaris was harvested using a novel natural coagulant of crystalline nanocellulose modified with 1-(3-aminopropyl) imidazole (CNC-APIm). Based on the optimization results of the Design of Experiments driven response surface methodology approach, the optimal conditions for maximum HEs (86.5%) and RCs (38.5 g-algae/g-CNC) responses were determined for C. vulgaris under the following conditions: 0.02 g-CNC-APIm/g-algae of mass ratio, 5 s of CO2 sparging time, 8 min of air sparging time, and 50 ml/min of air flow rate. Moreover, no statistically significant differences were observed in the contents of carbohydrate, protein, lipid and fatty acids in the biomass harvested by centrifugation and CNC-APIm, respectively, suggesting that CNC-APIm would not impact the downstream microalgal application. According to the rough technical and economical estimation, CNC-APIm will be an alternative to conventional coagulants for commercial microalgal harvesting application.