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Abstract It has been recognized that oils derived from microorganism and wastewater sludge are comparable replacements of traditional biodiesel production feedstock, which is energy intensive and costly. Energy balance and greenhouse gas (GHG) emissions are essential factors to assess the feasibility of the production. This study evaluated the energy balance and GHG emissions of biodiesel production from microbial and wastewater sludge oil. The results show that energy balance and GHG emissions of biodiesel produced from microbial oil are significantly impacted by the cultivation methods and carbon source. For phototrophic microorganism (microalgae), open pond system gives 3.6 GJ higher energy gain than photo bioreactor system in per tonne biodiesel produced. For heterotrophic microorganisms, the energy balance depends on the type of carbon source. Three carbon sources including starch, cellulose, and starch industry wastewater (SIW) used in this study showed that utilization of SIW as carbon source provided the most favorable energy balance. When oil extracted from municipal sludge is used for biodiesel production, the energy gain is up to 29.7 GJ per tonne biodiesel produced, which is higher than the energy gain per tonne of biodiesel produced from SIW cultivated microbes. GHG emissions study shows that biodiesel production from microbes or sludge oil is a net carbon dioxide capture process except when starch is used as raw material for microbial oil production, and the highest capture is around 40 tonnes carbon dioxide per tonne of biodiesel produced.

Hot water heat stores with stratification are a common technology used in solar energy systems and reuse of waste heat. Adding a PCM module at the top of the water tank would give the system higher storage density, and compensate heat loss in the top layer. The work presented here includes experimental results and numerical simulation of the system using an explicit finite-difference method. Experiments and simulations were carried out using different cylindrical PCM modules. With only 1/16 of the volume of the store being PCM, 3/16 of water at the top of the store was held warm for 50% to 200% longer and the average energy density was increased by 20% to 45%. Furthermore, these 3/16 of water were reheated by the heat from the module after being cooled down in only 20 min.

Abstract Water management is a critical issue for proton exchange membrane (PEM) fuel cells, and the use of a microporous layer (MPL) substantially improves the PEM fuel cell performance, reliability and durability through improved water management. In this study, graphene, technically a yet-to-be-developed category of material, is investigated as a potential MPL material, due to its high electrical and thermal conductivity. MPLs made of graphene (G-MPL) have been fabricated and assessed through morphological, microstructural, physical, and electrochemical characterizations and performance testing in a single scaled-up cell. Comparison is also made with MPLs made of a conventional material, Vulcan (V-MPL). The results show that the G-MPL has a unique morphology composed of horizontally packaged graphene flakes that improves water management, in-plane electrical conductivity (up to 2 times), catalyst activity, and platinum (Pt) utilization (up to 10%). The cell with the G-MPL has a better performance than the cell with the V-MPL under both fully (100% RH) and partially (40% RH) humidified conditions, with the peak power densities of 0.98 W cm−2 and 0.60 W cm−2, respectively – these peak power densities are about 7% and 43% higher than those obtained for the cell with the V-MPL at 100% and 40% RH, respectively.

Abstract Synthetic oleochemical esters of polyols and fatty acids are biodegradable and possess desirable technical and ecological properties. Trimethylolpropane (TMP) triester has been widely applied as a hydraulic fluid. TMP triester was effectively synthesized by lipase-catalyzed esterification from TMP and high oleic fatty acid from palm oil using an immobilized lipase. The immobilized lipase was prepared with liquid Lipozyme TL 100 L from Thermomyces lanuginosus with Duolite A568 as a carrier. The effects of temperature, enzyme loading, vacuum level, and water activity of the enzyme on the synthesis of TMP triester were investigated. The optimum temperature, enzyme loading, and vacuum level were 60 °C, 15% (based on total substrate), and 6.7 kPa, respectively. The optimum water activity range of the enzyme was 0.5–0.9. Under the optimum conditions, the maximum conversion reached up to 95% after 9 h. No significant differences in physical properties were observed between TMP triester from this study and a commercial TMP triester prepared by chemical catalyst.

Abstract Xylose is a by-product of lignocellulosic biomass processing for production of second-generation biofuels and could be suitable for bioproduct manufacturing. This paper describes an innovative approach that enables the system to achieve high yielding for hydrogen production. The study compared 4 physicochemical pre-treatments performed in an anaerobic mixed culture (acidic, thermal, acidic-thermal and thermal acidic) to achieve an inoculum with a high-efficiency xylose to hydrogen conversion under mesophilic conditions (30 °C). The acidic pre-treatment was the most efficient to select microorganisms able to produce hydrogen and volatile acid from xylose. Kinetics has shown that acidic pre-treatment had a hydrogen/xylose molar yielding factor of 1.57 (molar base) and a hydrogen maximum production rate of 253 mL H2 h−1. Mass balance considered all possible metabolic pathways using xylose as a substrate. Anaerobic degradation of ethanol was the most active pathway for hydrogen production in all experiments, except for the control. Each pre-treatment performed for the original inoculum resulted in different microbiological profiles, but the genus Clostridium was the most abundant in all assays. Acidic pre-treatment stimulated the growth of organisms from the genera Peptostreptococcaceae, Truepera and Kurthia, which could be related to the better results in hydrogen production found in this condition.

Efficient solar thermal collectors incorporate thermosiphon effect to rid the costs associated with force flow systems, yet they lack the functions of solar photocatalytic collectors for water cleaning. The combination of hot and clean water from one collector is demonstrated in the present study by utilizing two chambers under Mirotherm® solar selective absorber. Top glazing has a transmittance of 71%. One chamber was closed and transports captured heat to the mixture chamber, which is open to a cold reservoir in a loop method. MB dye in water and AEROXIDE TiO2 P90 were utilized as the reagents. It has been observed that 1.2 ppm of MB dye can be cleaned using 127.4 mg*L-1 suspended UV-activated AEROXIDE TiO2 P90 that exhibits no sedimentation in the collector with thermosiphon flow. Thermal analysis was performed using ten thermocouples within the collector and non-contact temperature sensors above. The analysis of water heating thermal collector was studied for two modes; one with a controlled cold inlet and other with rising temperature inlet. We recommend that a controlled inlet temperature of 21.5 °C be utilized to acquire 40.1 °C increase in temperature, at which point the thermal efficiency of the collector is 67%.

Abstract Aquatic biomass is promising due to its high productivity in less nutrient environment. Gasification is one of the frontier technologies to convert biomass into energy, mainly to produce electricity. Recent development in electrochemical technologies allows the utilization of electricity to upgrade waste CO2 into chemical products. In the present study, the performance of integrated gasification and electrolyzer is evaluated. The gasification converts biomass into syngas and electricity, while the electrolyzer convert CO2 from the gasification residue into chemicals such as CO and methanol by utilizing the electric power from the gasification. The variation of the gasifying agent flow rate (O2 equivalence ratio between 0.36 and 1.00) provides the variation of syngas composition (H2: 28–65%; CO: 25–43%) and heating value (12–30 MJ/kg). The production of CO or methanol is significantly influenced by O2 equivalence ratio and fraction of syngas into power generator. The highest exergy loss is found to be in the cooling system. The net CO2 emission of the proposed configuration is negative (−0.09 to −0.17 kg CO2/GJ at O2 equivalence ratio of 0.36) by considering the CO2 consumption of the biomass feed. Therefore, this system is promising for further investigation as the future renewable technology for energy conversion.

Abstract The current study presents the experimental results investigating combustion characteristics of sewage sludge fuels (SS) reference to coal and wood pellet as the two typical base fuels. Two types of SS were produced by drying and hydrothermal carbonization technology. The composition analysis and the thermogravimetric analysis (TGA) showed that SS were highly volatile with low ignition temperature than coal and wood pellet. In the lab-scale bubbling fluidized bed experiments, the combustion gas composition and bed temperature were measured for the cases of single fuel and blended fuel. The morphology and the composition of fly ash collected at the cyclone were analyzed using particle size analyzer, ICP-OES, and SEM-EDS. In the single fuel cases, NOx and SO2 emission of SS were several times higher than the base fuels, but those could be reduced in the blend fuel cases while maintaining overall thermal input and bed temperature. The different size distribution and overall composition of fly ash for the single fuel cases became similar in the blend fuel cases. The change in the characteristics of fly ash was considered to be related to the distribution of mineral matters, such as Ca, K, and P in particular.

Abstract Excessive growth of macroalgae like sea lettuce causes problems in the aquatic environment by creating an anoxic event. Algae have been gaining attention in production of biofuel and other chemical products through biochemical process, which requires drying. In this research, hydrothermal carbonization process is used for studying the potential utilization of sea lettuce to produce products for application in fuel and agriculture. The reaction was carried out at four temperatures of 150 °C, 180 °C, 200 °C, 220 °C for the residence time of 0.5,1 and 2 h. Hydrochar obtained had heating value in the range of 13.4–20.2 MJ kg−1 and higher carbon content as compared to raw sea lettuce. The analysis of the process water showed recovery of nutrients. The co-digestion of process water with food waste at 37 °C increased the production of gas till 10 days. The research showed that sea lettuce is a promising feedstock for hydrothermal carbonization to produce value-added products.