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Abstract Microorganisms used in syngas fermentation require nutrients to grow and convert syngas (CO, H2 and CO2) into various products. Many of the essential nutrients can be provided by biochar. Poultry litter biochar (PLBC) contains minerals and trace metals and has a high pH buffering capacity, making it suitable as a nutrient supplement. The effects of PLBC loadings from 1 to 20 g L−1 on syngas fermentation were determined in 250 ml bottle assays. Results showed that 10 and 20 g L−1 PLBC significantly increased ethanol production compared to standard yeast extract (YE) medium. Fermentations in a 3L continuous stirred tank reactor (CSTR) with 10 g L−1 PLBC with and without 4-morpholineethanesulfonic acid (MES) showed 64% and 36% more ethanol production, respectively, than standard medium. The acetic acid accumulated at the beginning of fermentation was completely converted to ethanol in all media tested in the CSTR. These results demonstrate the feasibility of using PLBC medium without costly MES in the CSTR to enhance ethanol production from syngas for potential use at commercial scale.

This paper investigates thermal mixing caused by the inflow from one or two round, horizontal, buoyant jets in a water storage tank, which is part of a thermal solar installation. A set of experiments was carried out in a rectangular tank with a capacity of 0.3 m3, with one or two constant temperature inflows. As a result, two correlations based on temperature measurements have been developed. One of the correlations predicts the size of a zone of homogenous temperature, referred to herein as the mixing zone, which develops when a single hot inflow impinges on the opposite wall of the tank. The other identifies the degree of mixing resulting from the interaction between a hot inflow and a cold inflow located below the hot one. The correlations are combined with energy balances to predict the amount of hot water available in a tank with open side inlets and the corresponding temperatures of the outflows. Outdoor measurements were also performed in a solar installation, in which a commercial water storage tank with a 1.5 m3 capacity, heated by a solar collector array with a useful surface area of 42.2 m2, drives a LiBr–H2O absorption chiller. Comparison of the predicted and measured outflow temperatures under a variety of weather conditions shows a maximum difference of 3 °C.

Abstract Uninterrupted energy harvest is critical for self-sustained wastewater monitoring in order to achieve efficient and resilient operation of decentralized onsite wastewater treatment facilities. To address this long-standing challenge, an integrated power entity consisting of a miniature microbial fuel cell (volume: 1.5 mL) and a triggered power management system was developed in this study to power the potentiometric millimeter-sized solid-state water sensors for real-time in situ monitoring and uninterrupted transmission of sensor readings (indicating ammonium concentration) under both ammonium shock and toxic shock in wastewater. Specifically, a data trigger including two capacitors, an operation amplifier and a low-power comparator is equipped in the power management system as a switch for turning on power discharge for data transmission once the ammonium shock is captured by the potentiometric sensors, enabling a sufficient recharge duration to store the power needed for high frequency data transmission (16.23 times/min) required under shocks. Furthermore, this power-sensor entity possesses a unique dual-screening capability of capturing the ammonium and toxic shocks, providing an early warning for swift decision making, reducing ~17% of ammonium discharge and saving ~42% of energy consumption in decentralized onsite wastewater treatment facilities.

Abstract This paper examines the dynamic cell performance of a kW-grade proton exchange membrane fuel cell stack with anode dead-ended mode fuel supply. A self-made kW-grade 40 cells stack with reaction area of 112.85 cm 2 has been used in the experiment. A single-chip (DSPIC30F4011) is utilized for establishing a control circuit to monitor the voltage and current with constant-current loading. The stack temperature is controlled at a low-level temperature rise. To enhance the hydrogen utilization and reduce the water flooding in the fuel cell stack, the dead-ended anode operation is accomplished by controlling the open or close of the anode outlet solenoid valve. As the loading is heavy, the anode outlet solenoid valve is purged frequently to force the water to flow out. While a light load, the anode outlet solenoid valve is shut down for a period time for hydrogen saving. The solenoid valve is controlled to be opened, referred as purge interval, reaching the discharge amount for 1000 C, 1500 C, and 2000 C as parameter, respectively. The open period of solenoid valve, referred as purge duration, is set as 1 s, 3 s, and 5 s for this study. Experimental results indicate an optimal purge interval and duration for water management and cell performance of the fuel cell stack.

Abstract Sustainable design methods focus on reducing or minimizing the demand for ecosystem goods and services, quantified as natural resources and pollutant mitigation. However, the capacity of ecosystems to supply these demands is routinely ignored, leading to decisions that overburden ecological processes and cause environmental damage. This work develops a techno-ecological synergy (TES) design methodology that balances the ecosystem services that can be provided by nature with the ecosystem service demands created by human activities. The methodology includes the design of technological processes that require ecosystem services as well as the ecological processes that supply those services. The TES Design methodology is demonstrated by application to a renewable energy production system that includes both land use activities, such as agriculture and wind turbines, and biomass conversion activities such as corn ethanol and soybean biodiesel. Under TES Design, the system is optimized to balance the demand and supply of ecosystem services, within constraints imposed on energy production and system economics. The system is also optimized under a more conventional approach that reduces ecosystem service demand while neglecting ecosystem service supply and the relevant ecological processes. Results show that only the TES methodology produces system designs in which ecosystem service supply meets or exceeds the demand. TES system designs produce the same amount of energy as conventional designs, have similar system economics, and use land both for energy production and for ecosystem service supply. The additional supply enables the use of intensive agricultural practices with higher ecosystem service demands and higher biomass yields. These results encourage further efforts toward TES Design with additional ecosystem services.

Abstract With impending climate change and ever decreasing supplies of easily extractable fossil fuel, means to produce renewable and sustainable replacement fuels are being sought. Plants or algae appear ideal since they can use sunlight to fix CO2 into usable fuel or fuel feedstocks. However, as the world population approaches the 1010 (10 billion) mark, the use of agricultural land to produce fuel instead of food cannot be justified. Microalgal biofuel production is under intense investigation due to its promise as a sustainable, renewable biofuel that can be produced using non-arable land and brackish or non-potable water. Some species accumulate high levels of TAGs (triacylglycerols) that can be converted to fatty acid esters suitable as replacement diesel fuels. However, there are many technical barriers to the practical application of microalgae for biofuel production and thus a number of significant challenges need to be met before microalgal biodiesel production becomes a practical reality. These include developing cost-effective cultivation strategies, low energy requiring harvesting technologies, and energy efficient and sustainable lipid conversion technologies. The large culture volumes that will be necessary dictate that the necessary nutrients come from wastewaters, such as the effluents from secondary treatment of sewage. Economical and energy sparing harvesting will require the development of novel flocculation or floatation strategies and new methods of oil extraction/catalysis that avoid the extensive use of solvents. Recent advances in these critical areas are reviewed and some of the possible strategies for moving forward are outlined.

Abstract Sustainable mass production of algal biofuels requires a reduction in nutrient demand and efficient conversion into fuels of all biomass including lipid-extracted algal residues (LEA). This study evaluated methane production, nutrient recovery and recycling from untreated and enzymatically pretreated Nannochloropsis LEA using semi-continuous anaerobic digestion (AD). Additionally, this process was compared to methane generation from whole Nannochloropsis alga (WA) and thermally pretreated WA. The methane production from untreated LEA and WA reached up to 0.22 L and 0.24 L per gram of biomass volatile solids (VS), respectively, corresponding to only 36–38% of the theoretical potential. Additionally, observed VS reduction was only 40–50% confirming biomass recalcitrance to biodegradation. While enzymatic treatment hydrolyzed up to 65% of the LEA polysaccharides, the methane production increased by only 15%. Alternatively, WA thermal pretreatment at 150–170 °C enhanced methane production up to 40%. Overall, an integrated process of lipid conversion into biodiesel coupled with LEA conversion into methane generates nearly 40% more energy compared to methane production from WA, and about 100% more energy than from biodiesel alone. Additionally, the AD effluent contained up to 60–70% of the LEA phosphorus content, 30–50% of the nitrogen, sulfur, calcium and boron, 20% of the iron and cobalt, and 10% of manganese, zinc and copper, which can partially replace chemical fertilizers during algal cultivation. Consequently, supplementation of Nannochloropsis cultures with 5% AD effluent was optimal for a high algal growth rate. Therefore, coupling biodiesel and methane production provides significant energy advantages along with sustainability and economic benefits from nutrient recycling.

Abstract The world has huge reserves of gas hydrates which are considered to be a potential energy resource. Therefore, developing methods for commercial gas production from hydrate reservoirs are attracting extensive attention. In order to mimic the geological condition of the practical oceanic hydrate reservoir, water-saturated hydrate sample with low gas saturation (8.27%) was obtained by the formation process of multi-step water injection. The huff and puff (H&P) method (above or below the equilibrium pressure for hydrate dissociation) was applied for hydrate dissociation. Results show that the system pressure rises with the increase of the H&P cycle for the H&P method above the equilibrium pressure. Furthermore, the dissociated hydrate in the injection period can be reformed in the soaking and production periods, and hydrate saturation increases mildly after each cycle of H&P. Hence, the H&P method above the equilibrium pressure is unpractical for hydrate dissociation with low gas saturation. However, the hydrate in the reservoir can be completely dissociated by the H&P method below the equilibrium pressure. Therefore, in the water-saturated hydrate reservoir, the regular H&P method is not suitable. The regular H&P should combine with depressurization method for gas recovery from the water-saturated hydrate reservoir.

Different from conventional compressed air energy storage (CAES) systems, the advanced adiabatic compressed air energy storage (AA-CAES) system can store the compression heat which can be used to reheat air during the electricity generation stage. Thus, AA-CAES system can achieve a higher energy storage efficiency. Similar to the AA-CAES system, a compressed air energy storage in aquifers (CAESA) system, which is integrated with an aquifer thermal energy storage (ATES) could possibly achieve the same objective. In order to investigate the impact of ATES on the performance of CAESA, different injection air temperature schemes are designed and analyzed by using numerical simulations. Key parameters relative to energy recovery efficiencies of the different injection schemes, such as pressure distribution and temperature variation within the aquifers as well as energy flow rate in the injection well, are also investigated in this study. The simulations show that, although different injection schemes have a similar overall energy recovery efficiency (~97%) as well as a thermal energy recovery efficiency (~ 79.2%), the higher injection air temperature has a higher energy storage capability. Our results show the total energy storage for the injection air temperature at 80 ̊C is about 10% greater than the base model scheme at 40 °C. Sensitivity analysis reveal that permeability of the reservoir boundary could have significant impact on the system performance. However, other hydrodynamic and thermodynamic properties, such as the storage reservoir permeability, thermal conductivity, rock grain specific heat and rock grain density, have little impact on storage capability and the energy flow rate. Overall, our study suggests that the combination of ATES and CAESA can help keep the high efficiency of energy storage so as to make CAESA system more efficiency.