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Energies, Volume 7, Issue 7 (July 2014), Pages 4054-4726

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Open AccessArticle Research on Cellular Instabilities of Lean Premixed Syngas Flames under Various Hydrogen Fractions Using a Constant Volume Vessel
Energies 2014, 7(7), 4710-4726; https://doi.org/10.3390/en7074710
Received: 2 April 2014 / Revised: 10 July 2014 / Accepted: 15 July 2014 / Published: 22 July 2014
Cited by 4 | PDF Full-text (1346 KB) | HTML Full-text | XML Full-text
Abstract
An experimental study of the intrinsic instabilities of H2/CO lean (φ = 0.4 to φ = 1.0) premixed flames at different hydrogen fractions ranging from 0% to 100% at elevated pressure and room temperature was performed in a constant volume vessel
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An experimental study of the intrinsic instabilities of H2/CO lean (φ = 0.4 to φ = 1.0) premixed flames at different hydrogen fractions ranging from 0% to 100% at elevated pressure and room temperature was performed in a constant volume vessel using a Schlieren system. The unstretched laminar burning velocities were compared with data from the previous literature and simulated results. The results indicate that excellent agreements are obtained. The cellular instabilities of syngas-air flames were discussed and critical flame radii were measured. When hydrogen fractions are above 50%, the flame tends to be more stable as the equivalence ratio increases; however, the instability increases for flames of lower hydrogen fractions. For the premixed syngas flame with hydrogen fractions greater than 50%, the decline in cellular instabilities induced by the increase in equivalence ratio can be attributed to a reduction of diffusive-thermal instabilities rather than increased hydrodynamic instabilities. For premixed syngas flames with hydrogen fractions lower than 50%, as the equivalence ratio increases, the cellular instabilities become more evident because the enhanced hydrodynamic instabilities become the dominant effect. For premixed syngas flames, the enhancement of cellular instabilities induced by the increase in hydrogen fraction is the result of both increasing diffusive-thermal and hydrodynamic instabilities. Full article
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Open AccessArticle Modeling and Simulation of Enzymatic Biofuel Cells with Three-Dimensional Microelectrodes
Energies 2014, 7(7), 4694-4709; https://doi.org/10.3390/en7074694
Received: 19 March 2014 / Revised: 2 July 2014 / Accepted: 4 July 2014 / Published: 22 July 2014
Cited by 12 | PDF Full-text (3279 KB) | HTML Full-text | XML Full-text
Abstract
The enzymatic biofuel cells (EBFCs) are considered as an attractive candidate for powering future implantable medical devices. In this study, a computational model of EBFCs based on three-dimensional (3-D) interdigitated microelectrode arrays was conducted. The main focus of this research is to investigate
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The enzymatic biofuel cells (EBFCs) are considered as an attractive candidate for powering future implantable medical devices. In this study, a computational model of EBFCs based on three-dimensional (3-D) interdigitated microelectrode arrays was conducted. The main focus of this research is to investigate the effect of different designs and spatial distributions of the microelectrode arrays on mass transport of fuels, enzymatic reaction rate, open circuit output potential and current density. To optimize the performance of the EBFCs, numerical simulations have been performed for cylindrical electrodes with various electrode heights and well widths. Optimized cell performance was obtained when the well width is half of the height of the 3-D electrode. In addition, semi-elliptical shaped electrode is preferred based on the results from current density and resistive heating simulation. Full article
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Open AccessArticle Current State of Technology of Fuel Cell Power Systems for Autonomous Underwater Vehicles
Energies 2014, 7(7), 4676-4693; https://doi.org/10.3390/en7074676
Received: 3 June 2014 / Revised: 8 July 2014 / Accepted: 16 July 2014 / Published: 22 July 2014
Cited by 23 | PDF Full-text (210 KB) | HTML Full-text | XML Full-text
Abstract
Autonomous Underwater Vehicles (AUVs) are vehicles that are primarily used to accomplish oceanographic research data collection and auxiliary offshore tasks. At the present time, they are usually powered by lithium-ion secondary batteries, which have insufficient specific energies. In order for this technology to
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Autonomous Underwater Vehicles (AUVs) are vehicles that are primarily used to accomplish oceanographic research data collection and auxiliary offshore tasks. At the present time, they are usually powered by lithium-ion secondary batteries, which have insufficient specific energies. In order for this technology to achieve a mature state, increased endurance is required. Fuel cell power systems have been identified as an effective means to achieve this endurance but no implementation in a commercial device has yet been realized. This paper summarizes the current state of development of the technology in this field of research. First, the most adequate type of fuel cell for this application is discussed. The prototypes and design concepts of AUVs powered by fuel cells which have been developed in the last few years are described. Possible commercial and experimental fuel cell stack options are analyzed, examining solutions adopted in the analogous aerial vehicle applications, as well as the underwater ones, to see if integration in an AUV is feasible. Current solutions in oxygen and hydrogen storage systems are overviewed and energy density is objectively compared between battery power systems and fuel cell power systems for AUVs. A couple of system configuration solutions are described including the necessary lithium-ion battery hybrid system. Finally, some closing remarks on the future of this technology are given. Full article
Open AccessArticle SDP Policy Iteration-Based Energy Management Strategy Using Traffic Information for Commuter Hybrid Electric Vehicles
Energies 2014, 7(7), 4648-4675; https://doi.org/10.3390/en7074648
Received: 17 April 2014 / Revised: 26 May 2014 / Accepted: 18 June 2014 / Published: 22 July 2014
Cited by 10 | PDF Full-text (2387 KB) | HTML Full-text | XML Full-text
Abstract
This paper demonstrates an energy management method using traffic information for commuter hybrid electric vehicles. A control strategy based on stochastic dynamic programming (SDP) is developed, which minimizes on average the equivalent fuel consumption, while satisfying the battery charge-sustaining constraints and the overall
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This paper demonstrates an energy management method using traffic information for commuter hybrid electric vehicles. A control strategy based on stochastic dynamic programming (SDP) is developed, which minimizes on average the equivalent fuel consumption, while satisfying the battery charge-sustaining constraints and the overall vehicle power demand for drivability. First, according to the sample information of the traffic speed profiles, the regular route is divided into several segments and the statistic characteristics in the different segments are constructed from gathered data on the averaged vehicle speeds. And then, the energy management problem is formulated as a stochastic nonlinear and constrained optimal control problem and a modified policy iteration algorithm is utilized to generate a time-invariant state-dependent power split strategy. Finally, simulation results over some driving cycles are presented to demonstrate the effectiveness of the proposed energy management strategy. Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)
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Open AccessArticle Finite Action-Set Learning Automata for Economic Dispatch Considering Electric Vehicles and Renewable Energy Sources
Energies 2014, 7(7), 4629-4647; https://doi.org/10.3390/en7074629
Received: 19 May 2014 / Revised: 10 July 2014 / Accepted: 11 July 2014 / Published: 22 July 2014
Cited by 2 | PDF Full-text (466 KB) | HTML Full-text | XML Full-text
Abstract
The coming interaction between a growing electrified vehicle fleet and the desired growth in renewable energy provides new insights into the economic dispatch (ED) problem. This paper presents an economic dispatch model that considers electric vehicle charging, battery exchange stations, and wind farms.
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The coming interaction between a growing electrified vehicle fleet and the desired growth in renewable energy provides new insights into the economic dispatch (ED) problem. This paper presents an economic dispatch model that considers electric vehicle charging, battery exchange stations, and wind farms. This ED model is a high-dimensional, non-linear, and stochastic problem and its solution requires powerful methods. A new finite action-set learning automata (FALA)-based approach that has the ability to adapt to a stochastic environment is proposed. The feasibility of the proposed approach is demonstrated in a modified IEEE 30 bus system. It is compared with continuous action-set learning automata and particle swarm optimization-based approaches in terms of convergence characteristics, computational efficiency, and solution quality. Simulation results show that the proposed FALA-based approach was indeed capable of more efficiently obtaining the approximately optimal solution. In addition, by using an optimal dispatch schedule for the interaction between electric vehicle stations and power systems, it is possible to reduce the gap between demand and power generation at different times of the day. Full article
(This article belongs to the Special Issue Energy Transitions and Economic Change)
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Open AccessArticle A Neural Network Combined Inverse Controller for a Two-Rear-Wheel Independently Driven Electric Vehicle
Energies 2014, 7(7), 4614-4628; https://doi.org/10.3390/en7074614
Received: 14 April 2014 / Revised: 12 June 2014 / Accepted: 8 July 2014 / Published: 22 July 2014
Cited by 6 | PDF Full-text (705 KB) | HTML Full-text | XML Full-text
Abstract
Vehicle active safety control is attracting ever increasing attention in the attempt to improve the stability and the maneuverability of electric vehicles. In this paper, a neural network combined inverse (NNCI) controller is proposed, incorporating the merits of left-inversion and right-inversion. As the
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Vehicle active safety control is attracting ever increasing attention in the attempt to improve the stability and the maneuverability of electric vehicles. In this paper, a neural network combined inverse (NNCI) controller is proposed, incorporating the merits of left-inversion and right-inversion. As the left-inversion soft-sensor can estimate the sideslip angle, while the right-inversion is utilized to decouple control. Then, the proposed NNCI controller not only linearizes and decouples the original nonlinear system, but also directly obtains immeasurable state feedback in constructing the right-inversion. Hence, the proposed controller is very practical in engineering applications. The proposed system is co-simulated based on the vehicle simulation package CarSim in connection with Matlab/Simulink. The results verify the effectiveness of the proposed control strategy. Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)
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Open AccessArticle Electrical Performance and Carbon Deposition Differences between the Bi-Layer Interconnector and Conventional Straight Interconnector Solid Oxide Fuel Cell
Energies 2014, 7(7), 4601-4613; https://doi.org/10.3390/en7074601
Received: 20 May 2014 / Revised: 7 July 2014 / Accepted: 16 July 2014 / Published: 22 July 2014
Cited by 4 | PDF Full-text (1020 KB) | HTML Full-text | XML Full-text
Abstract
Carbon deposition considered in a solid oxide fuel cell (SOFC) model may be influenced by the operating voltage, inlet water/methane ratio, working temperature and pressure, inlet molar fraction of fuel and so on. The effects of these parameters in a planar SOFC implementing
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Carbon deposition considered in a solid oxide fuel cell (SOFC) model may be influenced by the operating voltage, inlet water/methane ratio, working temperature and pressure, inlet molar fraction of fuel and so on. The effects of these parameters in a planar SOFC implementing a novel bi-layer interconnector are not well understood. This paper is focused on the numerical study of carbon deposition and electrical performance of a bi-layer interconnector planar SOFC. The results illustrate that the electrical performance of the bi-layer interconnector SOFC is 11% higher than that of the conventional straight interconnector SOFC with initial state. After 120 days of operation, the electrical performance of the bi-layer interconnector SOFC has a slight decrease and more carbon deposit because of the increased electrochemical reaction rate. However, these differences minimize if higher operating voltages are involved. Full article
(This article belongs to the Special Issue Reacting Transport Phenomena in Solid Oxide Fuel Cells)
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Open AccessDiscussion Understanding of Sulfurized Polyacrylonitrile for Superior Performance Lithium/Sulfur Battery
Energies 2014, 7(7), 4588-4600; https://doi.org/10.3390/en7074588
Received: 20 May 2014 / Revised: 17 June 2014 / Accepted: 10 July 2014 / Published: 18 July 2014
Cited by 47 | PDF Full-text (998 KB) | HTML Full-text | XML Full-text
Abstract
Sulfurized polyacrylonitrile (SPAN) is one of the most important sulfurized carbon materials that can potentially be coupled with the carbonaceous anode to fabricate a safe and low cost “all carbon” lithium-ion battery. However, its chemical structure and electrochemical properties have been poorly understood.
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Sulfurized polyacrylonitrile (SPAN) is one of the most important sulfurized carbon materials that can potentially be coupled with the carbonaceous anode to fabricate a safe and low cost “all carbon” lithium-ion battery. However, its chemical structure and electrochemical properties have been poorly understood. In this discussion, we analyze the previously published data in combination with our own results to propose a more reasonable chemical structure that consists of short –Sx– chains covalently bonded onto cyclized, partially dehydrogenated, and ribbon-like polyacrylonitrile backbones. The proposed structure fits all previous structural characterizations and explains many unique electrochemical phenomena that were observed from the Li/SPAN cells but have not been understood clearly. Full article
(This article belongs to the Special Issue Electrochemical Energy Storage—Battery and Capacitor)
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Open AccessArticle Saturation Detection-Based Blocking Scheme for Transformer Differential Protection
Energies 2014, 7(7), 4571-4587; https://doi.org/10.3390/en7074571
Received: 26 February 2014 / Revised: 27 June 2014 / Accepted: 10 July 2014 / Published: 18 July 2014
Cited by 1 | PDF Full-text (794 KB) | HTML Full-text | XML Full-text
Abstract
This paper describes a current differential relay for transformer protection that operates in conjunction with a core saturation detection-based blocking algorithm. The differential current for the magnetic inrush or over-excitation has a point of inflection at the start and end of each saturation
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This paper describes a current differential relay for transformer protection that operates in conjunction with a core saturation detection-based blocking algorithm. The differential current for the magnetic inrush or over-excitation has a point of inflection at the start and end of each saturation period of the transformer core. At these instants, discontinuities arise in the first-difference function of the differential current. The second- and third-difference functions convert the points of inflection into pulses, the magnitudes of which are large enough to detect core saturation. The blocking signal is activated if the third-difference of the differential current is larger than the threshold and is maintained for one cycle. In addition, a method to discriminate between transformer saturation and current transformer (CT) saturation is included. The performance of the proposed blocking scheme was compared with that of a conventional harmonic blocking method. The test results indicate that the proposed scheme successfully discriminates internal faults even with CT saturation from the magnetic inrush, over-excitation, and external faults with CT saturation, and can significantly reduce the operating time delay of the relay. Full article
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Open AccessArticle Real World Operation of a Complex Plug-in Hybrid Electric Vehicle: Analysis of Its CO2 Emissions and Operating Costs
Energies 2014, 7(7), 4554-4570; https://doi.org/10.3390/en7074554
Received: 16 April 2014 / Revised: 7 July 2014 / Accepted: 7 July 2014 / Published: 16 July 2014
Cited by 3 | PDF Full-text (1888 KB) | HTML Full-text | XML Full-text
Abstract
Plug-in hybrid electric vehicles (pHEVs) could represent the stepping stone to move towards a more sustainable mobility and combine the benefits of electric powertrains with the high range capability of conventional vehicles. Nevertheless, despite the huge potential in terms of CO2 emissions
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Plug-in hybrid electric vehicles (pHEVs) could represent the stepping stone to move towards a more sustainable mobility and combine the benefits of electric powertrains with the high range capability of conventional vehicles. Nevertheless, despite the huge potential in terms of CO2 emissions reduction, the performance of such vehicles has to be deeply investigated in real world driving conditions considering also the CO2 production related to battery recharge which, on the contrary, is currently only partially considered by the European regulation to foster the diffusion of pHEVs. Therefore, this paper aims to assess, through numerical simulation, the real performance of a test case pHEV, the energy management system (EMS) of which is targeted to the minimization of its overall CO2 emissions. The paper highlights, at the same time, the relevance of the CO2 production related to the battery recharge from the power grid. Different technologies mixes used to produce the electricity required for the battery recharge are also taken into account in order to assess the influence of this parameter on the vehicle CO2 emissions. Finally, since the operating cost still represents the main driver in orienting the customer’s choice, an alternative approach for the EMS, targeted to the minimization of this variable, is also analyzed. Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)
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Open AccessArticle On the Design and Response of Domestic Ground-Source Heat Pumps in the UK
Energies 2014, 7(7), 4532-4553; https://doi.org/10.3390/en7074532
Received: 30 April 2014 / Revised: 7 July 2014 / Accepted: 9 July 2014 / Published: 15 July 2014
Cited by 6 | PDF Full-text (1013 KB) | HTML Full-text | XML Full-text
Abstract
The design and response of ground source heat pumps coupled to vertical closed loop arrays in UK domestic applications are investigated in this article. Two typical UK house types are selected as the vehicle for the study and a detailed dynamic thermal modelling
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The design and response of ground source heat pumps coupled to vertical closed loop arrays in UK domestic applications are investigated in this article. Two typical UK house types are selected as the vehicle for the study and a detailed dynamic thermal modelling method is used to arrive at time-series heating demands for the two houses. A new empirical heat pump model is derived using experimental data taking into account the deteriorating performance of the heat pump during periods of light load. The heat pump model is incorporated into an existing numerical ground model and completed with a classical effectiveness type heat exchange model of the closed loop array. The model is used to analyse array sizing and performance over an extended time period, as well as sensitivity of the design to soil conductivity and borehole heat exchanger resistance and sensitivity to over-sizing and part-load behavior of the heat pump. Results show that the UK’s standard for ground source design (the Microgeneration Certification Scheme) may lead to under-estimated array sizes and that heating system over-sizing and deleterious part-load heat pump performance can add up to 20% to the electrical consumption of these systems. Full article
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Open AccessArticle Experimental and Numerical Study of Jet Controlled Compression Ignition on Combustion Phasing Control in Diesel Premixed Compression Ignition Systems
Energies 2014, 7(7), 4519-4531; https://doi.org/10.3390/en7074519
Received: 8 April 2014 / Revised: 27 May 2014 / Accepted: 8 July 2014 / Published: 15 July 2014
Cited by 3 | PDF Full-text (583 KB) | HTML Full-text | XML Full-text
Abstract
In order to directly control the premixed combustion phasing, a Jet Controlled Compression Ignition (JCCI) for diesel premixed compression ignition systems is investigated. Experiments were conducted on a single cylinder natural aspirated diesel engine without EGR at 3000 rpm. Numerical models were validated
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In order to directly control the premixed combustion phasing, a Jet Controlled Compression Ignition (JCCI) for diesel premixed compression ignition systems is investigated. Experiments were conducted on a single cylinder natural aspirated diesel engine without EGR at 3000 rpm. Numerical models were validated by load sweep experiments at fixed spark timing. Detailed combustion characteristics were analyzed based on the BMEP of 2.18 bar. The simulation results showed that the high temperature jets of reacting active radical species issued from the ignition chamber played an important role on the onset of combustion in the JCCI system. The combustion of diesel pre-mixtures was initiated rapidly by the combustion products issued from the ignition chamber. Moreover, the flame propagation was not obvious, similar to that in Pre-mixed Charge Compression Ignition (PCCI). Consequently, spark timing sweep experiments were conducted. The results showed a good linear relationship between spark timing in the ignition chamber and CA10 and CA50, which indicated the ability for direct combustion phasing control in diesel PCCI. The NOx and soot emissions gradually changed with the decrease of spark advance angle. The maximum reduction of NOx and soot were both over 90%, and HC and CO emissions were increased. Full article
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Open AccessArticle Gain Scheduling Control of an Islanded Microgrid Voltage
Energies 2014, 7(7), 4498-4518; https://doi.org/10.3390/en7074498
Received: 19 May 2014 / Revised: 20 June 2014 / Accepted: 4 July 2014 / Published: 14 July 2014
Cited by 6 | PDF Full-text (925 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this research study has been to design a gain scheduling (GS) digital controller in order to control the voltage of an islanded microgrid in the presence of fast varying loads (FVLs), and to compare it to a robust controller. The
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The aim of this research study has been to design a gain scheduling (GS) digital controller in order to control the voltage of an islanded microgrid in the presence of fast varying loads (FVLs), and to compare it to a robust controller. The inverter which feeds the microgrid is connected to it through an inductance-capacitor-inductance (LCL) filter. The oscillatory and nonlinear behaviour of the plant is analyzed in the whole operating zone. Afterwards, the design of the controllers which contain two loops in cascade are described. The first loop concerns the current control, while the second is linked to the voltage regulation. Two controllers, one defined as Robust and another one as GS controller, are designed for the two loops, emphasizing in their robustness and their ability to damp the oscillatory plant behaviour. To finish, some simulations are carried out to study and compare the two kinds of controllers in different operating points. The results show that both controllers damp the oscillatory behaviour of the plant in closed loop (CL), and that the GS controller ensures a better rejection of current disturbances from FVLs. Full article
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Open AccessArticle Thermoeconomic Analysis of Hybrid Power Plant Concepts for Geothermal Combined Heat and Power Generation
Energies 2014, 7(7), 4482-4497; https://doi.org/10.3390/en7074482
Received: 11 April 2014 / Revised: 20 May 2014 / Accepted: 1 July 2014 / Published: 14 July 2014
Cited by 12 | PDF Full-text (317 KB) | HTML Full-text | XML Full-text
Abstract
We present a thermo-economic analysis for a low-temperature Organic Rankine Cycle (ORC) in a combined heat and power generation (CHP) case. For the hybrid power plant, thermal energy input is provided by a geothermal resource coupled with the exhaust gases of a biogas
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We present a thermo-economic analysis for a low-temperature Organic Rankine Cycle (ORC) in a combined heat and power generation (CHP) case. For the hybrid power plant, thermal energy input is provided by a geothermal resource coupled with the exhaust gases of a biogas engine. A comparison to alternative geothermal CHP concepts is performed by considering variable parameters like ORC working fluid, supply temperature of the heating network or geothermal water temperature. Second law efficiency as well as economic parameters show that hybrid power plants are more efficient compared to conventional CHP concepts or separate use of the energy sources. Full article
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Open AccessReview Effect of Lignocellulose Related Compounds on Microalgae Growth and Product Biosynthesis: A Review
Energies 2014, 7(7), 4446-4481; https://doi.org/10.3390/en7074446
Received: 4 May 2014 / Revised: 30 June 2014 / Accepted: 1 July 2014 / Published: 11 July 2014
Cited by 13 | PDF Full-text (936 KB) | HTML Full-text | XML Full-text
Abstract
Microalgae contain valuable compounds that can be harnessed for industrial applications. Lignocellulose biomass is a plant material containing in abundance organic substances such as carbohydrates, phenolics, organic acids and other secondary compounds. As growth of microalgae on organic substances was confirmed during heterotrophic
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Microalgae contain valuable compounds that can be harnessed for industrial applications. Lignocellulose biomass is a plant material containing in abundance organic substances such as carbohydrates, phenolics, organic acids and other secondary compounds. As growth of microalgae on organic substances was confirmed during heterotrophic and mixotrophic cultivation, lignocellulose derived compounds can become a feedstock to cultivate microalgae and produce target compounds. In this review, different treatment methods to hydrolyse lignocellulose into organic substrates are presented first. Secondly, the effect of lignocellulosic hydrolysates, organic substances typically present in lignocellulosic hydrolysates, as well as minor co-products, on growth and accumulation of target compounds in microalgae cultures is described. Finally, the possibilities of using lignocellulose hydrolysates as a common feedstock for microalgae cultures are evaluated. Full article
(This article belongs to the Special Issue Algae Based Technologies)
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