• Energy Research
• Closed Access close
• Restricted close
• IN close
• RU close
• VBN close

The oleaginous alga Chlorella protothecoides accumulates lipid in its biomass when grown in nitrogen-restricted conditions. To assess the relationship between nitrogen provision and lipid accumulation and to determine the contribution of photosynthesis in mixotrophic growth, C. protothecoides was grown in mixo- and heterotrophic nitrogen-limited continuous flow cultures. Lipid content increased with decreasing C/N, while biomass yield on glucose was not affected. Continuous production of high lipid levels (57% of biomass) was possible at high C/N (87-94). However, the lipid production rate (2.48 g L(-1) d(-1)) was higher at D=0.84 d(-1) with C/N 37 than at D=0.44 d(-1) and C/N 87 even though the lipid content of the biomass was lower (38%). Photosynthesis contributed to biomass and lipid production in mixotrophic conditions, resulting in 13-38% reduction in CO2 production compared with heterotrophic cultures, demonstrating that photo- and heterotrophic growth occurred simultaneously in the same population.

Abstract There are technical problems related to storage and transport of biogas gas that should be addressed before practical injection of these fuels into the existing natural gas networks. In addition, their different final applications resulting in the presence of various components and in various concentrations make the problem harder. Therefore, it is indispensable for designers of the pipeline network to know exactly what the thermodynamic properties of a gas mixture are, especially its density, which would vary a lot. In this work, a MLP (Multi-layer Perceptron) neural network is used for the development of the desired biogas properties predictor model. In order to train the network, the biogas thermodynamic properties created using ISO 20765-2 (2015) (where applicable) and experimental values are employed. Results are compared with the values estimated from the GERG2008 equations of state, which are the reference equations for natural gases and experimental values. The results indicate that the developed MLP model presents a high accuracy in the calculations over a wide range of biogas mixtures and input properties ranges for all the output properties including density, compressibility factor, isochoric heat capacity, isobaric heat capacity, isentropic exponent, internal energy, enthalpy, entropy, Joule-Thomson coefficient, and speed of sound. The Root Mean Square Error (RMSE) of the mentioned properties of test data are 0.00012536, 0.00016593, 0.0025213, 0.0016208, 0.00337, 0.0096329, 0.0099837, 0.0035625, 0.01055, and 0.00039428 respectively.

Abstract The aim of the present study was to assess the influence of substrate concentration on the fermentative hydrogen production from sweet sorghum extract, in a continuous stirred tank bioreactor. The reactor was operated at a Hydraulic Retention Time (HRT) of 12 h and carbohydrate concentrations ranging from 9.89 to 20.99 g/L, in glucose equivalents. The maximum hydrogen production rate and yield were obtained at the concentration of 17.50 g carbohydrates/L and were 2.93 ± 0.09 L H 2 /L reactor/d and 0.74 ± 0.02 mol H 2 /mol glucose consumed, corresponding to 8.81 ± 0.02 L H 2 /kg sweet sorghum, respectively. The main metabolic product at all steady states was butyric acid, while ethanol production was high at high substrate concentrations. The experiments showed that hydrogen productivity depends significantly on the initial carbohydrate concentration, which also influences the distribution of the metabolic products.

The electricity demand is increasing day by day. On the other side, fossil fuels are depleting at a higher rate. The abundantly available renewable energy sources like solar, wind, and fuel cells a...

Nepal is heavily dependent on the traditional energy sources and imported fossil fuel, which has an adverse impact on the environment and economy. Renewable energy technologies promoted in the country are regarded as a means of satisfying rural energy needs of the country for operating different rural end-uses. In this context, this article is prepared to investigate energy alternatives to pump drinking water in one of the remote rural village of Nepal, which has no means of running water source. Analyses in this article are based on the formulation of three technical scenarios of water pumping using petro-diesel, jatropha-based biodiesel and solar photovoltaic pumps. The technical system design consists of system sizing of prime mover (engine, solar panel and pumps) and estimation of reservoir capacity, which are based on the annual aggregate water demand modelling. With these investigations, detailed financial modelling is carried out in a spreadsheet to compare the alternatives on the basis of the econ...

Improper management of pig manure has resulted in environmental problems such as surface water eutrophication, ground water pollution, and greenhouse gas emissions. This study develops and compares 14 alternative manure management scenarios aiming at energy and nutrient extraction. The scenarios based on combinations of thermal pretreatment, anaerobic digestion, anaerobic co-digestion, liquid/solid separation, drying, incineration, and thermal gasification were compared with respect to their energy, nutrient and greenhouse gas balances. Both sole pig manure and pig manure mixed with other types of waste materials were considered. Data for the analyses were obtained from existing waste treatment facilities, experimental plants, laboratory measurements and literature. The assessment reveals that incineration combined with liquid/solid separation and drying of the solids is a promising management option yielding a high potential energy utilization rate and greenhouse gas savings. If maximum electricity production is desired, anaerobic digestion is advantageous as the biogas can be converted to electricity at high efficiency in a gas engine while allowing production of heat for operation of the digestion process. In conclusion, this study shows that the choice of technology has a strong influence on energy, nutrient and greenhouse gas balances. Thus, to get the most reliable results, it is important to consider the most representative (and up-to-date) technology combined with data representing the area or region in question.

Six hydrothermal liquefaction experiments on Nannochloropsis salina and Spirulina platensis at subcritical and supercritical water conditions (220–375 °C, 20–255 bar) were carried out to explore the feasibility of extracting lipids from wet algae, preserving nutrients in lipid-extracted algae solid residue, and recycling process water for algae cultivation. GC–MS, elemental analyzer, FT-IR, calorimeter and nutrient analysis were used to analyze bio-crude, lipid-extracted algae and water samples produced in the hydrothermal liquefaction process. The highest bio-crude yield of 46% was obtained on N. salina at 350 °C and 175 bar. For S. platensis algae sample, the optimal hydrothermal liquefaction condition appears to be at 310 °C and 115 bar, while the optimal condition for N. salina is at 350 °C and 175 bar. Preliminary data also indicate that a lipid-extracted algae solid residue sample obtained in the hydrothermal liquefaction process contains a high level of proteins.

Traditional fire stoves are characterized by low efficiency. In this experimental study, the combustion chamber of the stove is augmented by two devices. An electric fan can increase the air-to-fuel ratio in order to increase the system’s efficiency and decrease air pollution by providing complete combustion of wood. In addition, thermoelectric generators (TEGs) produce power that can be used to satisfy all basic needs. In this study, a water-based cooling system is designed to increase the efficiency of the TEGs and also produce hot water for residential use. Through a range of tests, an average of 7.9 W was achieved by a commercial TEG with substrate area of 56 mm × 56 mm, which can produce 14.7 W output power at the maximum matched load. The total power generated by the stove is 166 W. Also, in this study a reasonable ratio of fuel to time is described for residential use. The presented prototype is designed to fulfill the basic needs of domestic electricity, hot water, and essential heat for warming the room and cooking.