Comparison of dairy wastewater and synthetic medium for biofuels production by microalgae cultivation

This study is concerned with comparing raw dairy wastewater (DWW) with blue-green medium (BG11 medium) for biofuel production. Three microalgae strains (Chlorella sp., Scenedesmus sp., and Chlorella zofingiensis) were cultured in tubular bubble column photobioreactors with two media separately. After 8 days of cultivation, DWW was demonstrated to be more suitable medium for microalgae biomass and lipid production than BG11 medium. The biomass and lipid produced within wastewater provided suitable feedstocks for anaerobic digestion and biodiesel conversion. Nutrients in wastewater were efficiently removed (>90% total nitrogen removal, approximately 100% ammonia removal, and >85% total phosphorus removal) during this process.     

Oxidative stress-tolerant microalgae strains are highly efficient for biofuel feedstock production on wastewater

Nutrient-rich wastewater may provide a sustainable means to cultivate microalgal biomass for biofuel use, yet many microalgal strains are very sensitive to wastewater due to toxicity caused by abiotic and biotic stresses. Naturally adapted strains that can efficiently grow in wastewater effluent are therefore of interest, however, the mechanisms by which such strains tolerate wastewater conditions are unknown. This study isolated indigenous chlorophyte microalgae strains from a municipal secondary wastewater effluent tank. The strains were identified by molecular phylogenetics and characterised by their ability to utilise exogenous organic carbon sources for mixotrophic growth and on the basis of oxidative stress tolerance, in order to elucidate the mechanisms of wastewater adaptation. Two of the strains, identified as Chlorella luteoviridis and Parachlorella hussii, could grow very well in raw wastewater due to their substantial tolerance to oxidative stress, which is highly induced by the wastewater environment. These strains exhibited high ascorbate peroxidase activity allowing increased scavenging of reactive oxygen species compared to strains that are not well adapted to the wastewater conditions. Both strains displayed high biomass and lipid productivity values in wastewater effluent. The accumulated lipids were suitable for biodiesel usage with characteristics equivalent to palm oil- and sunflower oil-derived biodiesel. The strains were also efficient in nutrient remediation from the wastewater. These results demonstrate the potential of these two strains for future biofuel applications coupled to wastewater remediation and highlight the importance of oxidative stress tolerance as a key indicator of efficient wastewater growth.     

Prospects of biodiesel production from microalgae in India

Energy is essential and vital for development, and the global economy literally runs on energy. The use of fossil fuels as energy is now widely accepted as unsustainable due to depleting resources and also due to the accumulation of greenhouse gases in the environment. Renewable and carbon neutral biodiesel are necessary for environmental and economic sustainability. Biodiesel demand is constantly increasing as the reservoir of fossil fuel are depleting. Unfortunately biodiesel produced from oil crop, waste cooking oil and animal fats are not able to replace fossil fuel. The viability of the first generation biofuels production is however questionable because of the conflict with food supply. Production of biodiesel using microalgae biomass appears to be a viable alternative. The oil productivity of many microalgae exceeds the best producing oil crops. Microalgae are photosynthetic microorganisms which convert sunlight, water and CO₂ to sugars, from which macromolecules, such as lipids and triacylglycerols (TAGs) can be obtained. These TAGs are the promising and sustainable feedstock for biodiesel production. Microalgal biorefinery approach can be used to reduce the cost of making microalgal biodiesel. Microalgal-based carbon sequestration technologies cover the cost of carbon capture and sequestration. The present paper is an attempt to review the potential of microalgal biodiesel in comparison to the agricultural crops and its prospects in India.     

Cultivation of four microalgae for biomass and oil production using a two-stage culture strategy with salt stress

A two-stage culture strategy was used for maximum biomass production under nutrient-sufficient conditions, followed by cultivation under low-salt stress, to cause the accumulation of oil in the biomass. Controlled conditions of nitrate, salt concentration, and time to exposure to stress were optimized for oil production with four species of microalgae, Isochrysis galbana, Nannochloropsis oculata, Dunaliella salina, and Dunaliella tertiolecta. Using conditions with addition of nitrate to 24.0 mg/L, I. galbana and N. oculata showed higher biomass productions than D. salina and D. tertiolecta. The oil contents of the microalgae increased from 24.0% to 47.0% in I. galbana with 10 psu for 2 days, from 17.0% to 29.0% in N. oculata with 0 psu for 3 days, from 22.0% to 43.0% of D. salina with 10 psu for 1 day, and from 23.0% to 40.0% (w/w) in D. tertiolecta with 0 psu for 2 days as the second stage culture with low-salt stress. Thus, I. galbana could be a suitable candidate microalga for oil production.     

Prospects of using microalgae for biofuels production: Results of a Delphi study

Advanced biofuels, such as those obtained from microalgae, are widely accepted as better choices for achieving goals of incorporating renewables and non-food fuel sources into the transportation sector, and for overcoming land use issues due to biofuel crops. Main challenges are currently the feasibility of large-scale commercialization of microalgae biofuels, since there are still some technical problems to overcome (e.g. the high energy consumption associated with biomass processing) and the majority of economic and financial analyses are based on pilot-scale projects. Therefore, this article presents the results of a Delphi study aiming to identify the main obstacles and most critical issues affecting the potential of large-scale commercialization of microalgae biodiesel and its incorporation into the fuel market. According to the authors' knowledge, this is the first Delphi study with this objective. The respondents are worldwide market specialists in the survey themes that ranged from biofuels economics to their environmental sustainability. One of the key findings is that most of the experts believe that production of microalgae biofuels will achieve its full commercial scale until 2020, and that from 2021 till 2030 it could represent from 1% to 5% of the worldwide fuel consumption. The study results also showed that environmental issues are where expert opinion differs more.     

Application of experimental design methodology for optimization of biofuel production from microalgae

Optimization of biofuel productivity, in terms of lipid content, polysaccharide content, and calorific value, from microalgae was performed by varying four variables (temperature, light intensity, nitrogen content, and CO₂ addition) using a 2⁴ full factorial design. A statistical analysis showing the influence of each variable and their interactions was conducted. The selected variables all influence biofuel productivity, but their importance varies according to the sequence: CO₂ addition > temperature > nitrogen content > light intensity. Interactive effects of temperature with light intensity and nitrogen with CO₂ addition for lipid and polysaccharide productivities were identified, respectively. For calorific value, interactive effects of CO₂ addition with light intensity and nitrogen content were observed. The highest biofuel productivity was obtained at the following conditions: temperature (>25 °C), light intensity (>60 μmol photons m⁻² s⁻¹), nitrogen content (<50 mg L⁻¹), and CO₂ addition (>18 mL L⁻¹ d⁻¹). 10 days was found to be the most favorable cultivation time for lipid production under the investigated conditions.     

Manufacturing gaseous products by pyrolysis of microalgal biomass

Algal biomass is considered as an alternative raw material for biofuel production. The search for new types of raw materials including high-energy types of microalgae remains relevant, since the share of motor fuels in the world energy balance remains consistently high (about 35%) with the oil price characterized by high volatility. The authors have considered the advantages of microalgae as raw materials for fuel production. Biochemical and thermochemical conversion are proposed as technologies for their processing. The paper presents the results of the study on the pyrolysis of the biomass of the blue-green microalgae/cyanobacterium Arthrospira platensis rsemsu 1/02-P clonal culture from the collection of the Research Laboratory of Renewable Energy Sources of the Lomonosov Moscow State University. The experimental investigation on the pyrolysis process of microalgal biomass has been carried out with the experimental setup made at the Institute of High Temperatures RAS in pure nitrogen 6.0 to create an oxygen-free medium with a linear heating rate of 10°С/min from room temperature to 1,000°С. The entire pyrolysis process has proceeded in the endothermic region. The specific values for solid residue, pyrolysis liquid and gaseous products have been experimentally determined. The following products have been manufactured by pyrolysis of microalgal biomass weighing 15 g: 1) char with a solid residue mass of 2.68 g, or 17.7% of MAB initial mass (while 9.3% of MAB initial mass has remained in the reactor); 2) pyrolysis liquid with a mass of 3.3 g, or 21.9% of initial mass; 3) noncondensable pyrolysis gases, 1.15 L. The specific volumetric gas yield (amount of gas released from 1 kg of RM) has amounted to 0.076 nm³/kg.In the paper, the analysis of the composition and specific volumetric yield of non-condensable pyrolysis gases produced in the pyrolysis process depending on temperature has been carried out. It is shown that the proportion of high-calorific components of the gas mixture (hydrogen, methane and carbon monoxide) increases with the temperature increase. The heating value assessment for the mixture of these gases has been performed as well.     

Exploring alkaline pre-treatment of microalgal biomass for bioethanol production

We have investigated, for the first time, the alkaline pre-treatment of microalgal biomass, from the species Chlorococcum infusionum, using NaOH for bioethanol production. This pre-treatment step aims to release and breakdown entrapped polysaccharides in the microalgae cell walls into fermentable subunits. Three parameters were examined here; the concentration of NaOH, temperature and the pre-treatment time. The bioethanol concentration, glucose concentration and the cell size were studied in order to determine the effectiveness of the pre-treatment process. Microscopic analysis was performed to confirm cell rupturing, the highest glucose yield was determined to be 350 mg/g, and the maximum bioethanol yield obtained was 0.26 g ethanol/g algae using 0.75% (w/v) of NaOH and 120 °C for 30 min. Overall, the alkaline pre-treatment method proved to be promising option to pre-treat microalgal biomass for bioethanol production.     

Design of biomass processing network for biofuel production using an MILP model

This paper presents a general optimization model that enables the selection of fuel conversion technologies, capacities, biomass locations, and the logistics of transportation from the locations of forestry resources to the conversion sites and then to the final markets. A mixed integer linear programming (MILP) model has been formulated and implemented in a commercial software package (GAMS) using databases built in Excel. The MILP represents decisions regarding (1) the optimal number, locations, and sizes of various types of processing plants, (2) the amounts of biomass, intermediate products, and final products to be transported between the selected locations over a selected period, and maximizes the objective function of overall profit. The model has been tested based on an industry-representative data set that contains information on the existing wood resources, final product market locations and demands, and candidate locations and sizes for different types of processing plants, as well as the costs associated with the various processing units and transportation of materials, covering the Southeastern region of the United States. The model is applied to design both a distributed, and a more centralized, conversion system. The overall profits, values, cost, and supply network designs of both systems are analyzed using the optimization model. In particular, we investigate: 1) which parameters have major effect on the overall economics, and 2) the benefits of going to more distributed types of processing networks, in terms of the overall economics and the robustness to demand variations.     

Promises in direct conversion of cellulose and lignocellulosic biomass to chemicals and fuels: Combined solvent–nanocatalysis approach for biorefinary

This review surveys sustainable one-pot conversion methods of cellulose into two very important platform chemicals such as 5-hydroxymethylfurfural and isosorbide retaining applications in many fields. Various new techniques based on such as ionic liquids, acid functionalized mesoporous materials, organic acids, functionalized nanoparticles, and mechanocatalytic depolymerization was discussed in detail for the very important direct conversion of cellulose to 5-hydroxymethylfurfural. More emphasis is given on a comparative analysis of recently developed all successful methods for 5-hydroxymethylfurfural production from cellulose in terms of efficiency, selectivity and cost-effectiveness. The article also complements on the promising extraction methods for the 5-hydroxymethylfurfural using special solvents. The importance of another very interesting platform chemical, i.e. isosorbide is also addressed. Several factors of cellulose to isosorbide transformation including metal nanoparticle size, crystallinity order of the cellulose, and extraction medium which controls the rate of conversion and product distillation have been addressed. The article also surveys the potential discoveries in one-pot conversion of cellulose into biofuels. The strategies of cellulose and lignocellulose conversions to compounds with liquid fuel's features have been discussed focusing on the production of γ-valerolactone as important intermediates to access liquid hydrocarbons and valeric esters. Cellulose value-chain for the direct conversions to liquid fuels (e.g. cellulose to levulinic acid platform to obtain valeric biofuels) by using supported nanostructured metal catalysts are emphasized. Overall an analysis of the main prospects and constraints related to the several conversion routes are presented including the critical thinking on the technical barriers, commercial promise, and environmental issues.     

Coupling algal biomass production and anaerobic digestion: Production assessment of some native temperate and tropical microalgae

Coupling algal biomass production and anaerobic digestion is one of the most promising bioprocesses for economically viable algal production. This study assesses the production rates of some native microalgae growing in media supplemented with algal digestate, urban wastewater or digested sludge. Native microalgal populations isolated from temperate freshwaters (Scenedesmus spp.) and marine ecosystems (Nannochloris spp.) had the highest potential production rates (about 100 mg DW L⁻¹ d⁻¹) with algal digestate at about 20% loading ratio. However, no growth was measured for Nannochloris spp., when the ammonium concentration exceeded 100 mg L⁻¹ although Scenedesmus spp. appeared to be tolerant to higher NH₄⁺ concentrations. Very low production rates, or no growth, were measured when microalgae isolated from high salinity waters (Dunaliella salina, Lyngbya aestuarii) were used, suggesting that populations well adapted to extreme environmental conditions are not suitable candidates for growing on wastewater or anaerobic digestate.     

Syngas production from biomass gasification in China: A clean strategy for sustainable development

Biomass gasification, which can be categorized as a set of relatively clean processes, is a good option for hydrogen production. The main purpose of the present work was to focus on the use of natural olivine as a bed material to minimize the tar content and enhance the hydrogen yield. The catalytic gasification tests were carried out in a fluidized bed gasifier using steam as the fluidizing medium. Hydrogen yield slightly increased from 51.9 to 53.1 g/kg biomass, as biomass particle size (BP) decreased from 5.0 to 2.0 mm. The yield of tar also decreased from 0.15 to 0.07 g/Nm³ with BP decreasing from 5.0 to 2.0 mm. With an increase in the catalyst-to-biomass ratio (C/B) from 0.2 to 0.8, HY increased from 47.8 to 51.9 g/kg biomass and tar content (TC) decreased from 0.8 to 0.15 g/Nm³. Temperature and steam/biomass ratio (S/B) were also affected the syngas composition and HY, significantly.     

Mixotrophic cultivation,a preferable microalgae cultivation mode for biomass/bioenergy production,and bioremediation,advances and prospect

Microalgae have received much attention in recent years as a feedstock for producing renewable fuels. Microalgae cultivation technology is one of the main factors restricting biomass production as well as energy fuel production and bioremediation. There are four types of cultivation conditions for microalgae: photoautotrophic, heterotrophic, mixotrophic and photoheterotrophic cultivation. Though photoautotrophic and heterotrophic cultivation are two common growth modes of microalgae, some microalgae can also grow better under mixotrophic condition, which may combine the advantages of autotrophic and heterotrophic and overcome the disadvantages. This review compared these growth modes of microalgae and discussed the advantages of mixotrophic mode in bioenergy production by considering the difference in growth, photosynthesis characteristic and bioenergy production. Also, the influence factors of mixotrophic cultivation and the application of mixotrophic microalgae in bioremediation are discussed, laying theoretical foundation for large scale microalgae cultivating for biomass production, bioenergy production and environmental protection.     

Potential to retrofit existing small-scale gasifiers through steam gasification of biomass residues for hydrogen and biofuels production

This work investigates the opportunity of retrofitting existing small-scale gasifiers shifting from combined heat and power (CHP) to hydrogen and biofuels production, using steam and biomass residues (woodchips, vineyard pruning and bark). The experiments were carried out in a batch reactor at 700 °C and 800 °C and at different steam flow (SF) rates (0.04 g/min and 0.20 g/min). The composition of the producer gas is in the range of 46–70 % H₂, 9–29 % CO, 12–27 % CO₂, and 2–6 % CH₄. A producer gas specific production factor of approx. 10 NL_pg/g_char can be achieved when the lower SFs are used, which allows to provide 80 % of the hydrogen concentration required for biomethanation and MeOH synthesis. As for FT synthesis, an optimal H₂/CO ratio of approx. 2 can be achieved. The results of this work provide further evidence towards the feasibility of hydrogen and biofuels generation from residual biomass through steam gasification.     

Wood-fuel biomass from the Madeira River: A sustainable option for electricity production in the Amazon region

The universal provision of electricity remains far from achieved in the Brazilian Amazon, given the geographical obstacles, the dispersion of its inhabitants, the indistinctness of appropriate technologies, and the economic obstacles. Governmental action was taken in 2003 with the creation of the Light for All Program (PLpT), with the goal of bringing electricity to all rural consumers by 2010. In addition, the National Electric Power Agency, ANEEL (Agência Nacional de Energia Elétrica), which is responsible in Brazil for the electrical sector regulation, has issued a determination of compulsory access to electricity by 2015. This study describes research conducted on the Madeira River, in the Brazilian Amazon, where the electric needs of the communities and small towns along the river can be satisfied through the gasification system, using as a renewable feedstock the wood-fuel biomass deposited on the riverbed, derived from natural processes, which the Ministry of Transport is already legally obligated to remove in order to provide safe navigation along the river. The study concludes by comparing the competitiveness of this system to diesel thermoelectric plants, along with its advantages in reducing the emission of greenhouse gases. Our results should help future studies in others areas with similar phenomena.     

Technoeconomic analysis of a methanol plant based on gasification of biomass and electrolysis of water

Methanol production process configurations based on renewable energy sources have been designed. The processes were analyzed in the thermodynamic process simulation tool DNA. The syngas used for the catalytic methanol production was produced by gasification of biomass, electrolysis of water, CO₂ from post-combustion capture and autothermal reforming of natural gas or biogas. Underground gas storage of hydrogen and oxygen was used in connection with the electrolysis to enable the electrolyser to follow the variations in the power produced by renewables. Six plant configurations, each with a different syngas production method, were compared. The plants achieve methanol exergy efficiencies of 59–72%, the best from a configuration incorporating autothermal reforming of biogas and electrolysis of water for syngas production. The different processes in the plants are highly heat integrated, and the low-temperature waste heat is used for district heat production. This results in high total energy efficiencies (∼90%) for the plants. The specific methanol costs for the six plants are in the range 11.8–25.3 €/GJ_exergy. The lowest cost is obtained by a plant using electrolysis of water, gasification of biomass and autothermal reforming of natural gas for syngas production.     

Hydrogen economy and storage by nanoporous microalgae diatom: Special emphasis on designing photobioreactors

Storing multiple energy forms from microalgae is not only facile but also lowers the cost of culturing the microalgae. Among many microalgae, diatoms are microscopic glass menageries which are responsible for converting stored lipids and biomass into hydrogen, besides fixing 25% of global CO₂. Besides this their silica frustules are also nature's naturally available bionanomaterials which have immense applications in nanotechnology for hydrogen production and other energy storage. The diatom frustules get hybridized with various chemical and biological components to generate or store hydrogen in various fuel cells. In laboratory these live diatoms can be allowed to culture in various designed solar panel photobioreactors better known as diatom solar panels for high and low value-added products essentially biofuel and fucoxanthin. The present review thus discusses about possible scope and approaches to produce hydrogen from live diatom and as well as from its biomass in specially designed photobioreactors. This truly has economic aspects of hydrogen production from diatoms in comparison to other microalgae which needs to be explored for its wide applications due to its robustness and abundance occurrence.     

Renewable biomass production by mixotrophic algae in the presence of various carbon sources and wastewaters

This study evaluated mixotrophic growth potential of native microalgae in media supplemented with different organic carbon substrates and wastewaters. Three robust mixotrophic microalgae viz. Chlamydomonas globosa, Chlorella minutissima and Scenedesmus bijuga were isolated after long-term enrichments from industrial wastewater. The mixotrophic growth of these microalgae resulted in 3–10 times more biomass production relative to phototrophy. Glucose, sucrose and acetate supported significant mixotrophic growth. Poultry litter extract (PLE) as growth medium recorded up to 180% more biomass growth compared to standard growth medium BG11, while treated and untreated carpet industry wastewaters also supported higher biomass, compared to BG11 growth with no significant effect of additional nitrogen supplementation. Supplementing treated wastewater and PLE with glucose and nitrogen resulted in 2–7 times increase in biomass relative to the unamended wastewaters or PLE. The consortia of Chlamydomonas–Chlorella and Scenedesmus–Chlorella were the best for PLE and untreated wastewater respectively, while a combination all three strains was suitable for both PLE and wastewater. These algae can be good candidates for biofuel feedstock generation as they would not require freshwater or fertilizers. Such mixotrophic algal consortia offer great promise for production of renewable biomass for bioenergy applications using wastewaters.     

High hydrogen content syngas for biofuels production from biomass air gasification: Experimental evaluation of a char-catalyzed steam reforming unit

This work investigates the performance of a reformer reactor for the upgrading of syngas and char derived from a pilot-scale air gasifier. The proposed setup represents a circular approach for the production of hydrogen-rich syngas from air gasification. Specifically, the reforming-unit was operated under a range of temperatures (from 700 °C to 850 °C) and steam flow rates and for each the improvement in producer gas composition and reducing species yield is evaluated. The results highlight that an increase in hydrogen concentration is obtained at higher temperature, moving from 16.2% to 21.3%, without using steam, and to 45.6%, with steam injection on the char-bed, while CO concentration did not follow a monotonic behavior. Moreover, the gas quality index, defined as a ratio between reducing species and inert species, delivered the highest values at the highest temperatures and steam flow rates. These results provide a guide for future gas quality optimization studies.