Biophotonics for improving algal photobioreactor performance: A review

The use of algae as a feedstock for biofuels production has drawn considerable attention due to their high biomass yield, their ability to be cultivated using degraded water on nonarable land, and their ability to recover nutrients from wastewater. Although algae have the potential to provide biomass for biofuels, some challenges remain and the limitations may be overcome by improving algal growth rates together with lipid synthesis. To achieve this, scientific researchers have focused on isolating and screening algal strains with better growth rates and lipid synthesis capabilities, bioengineering, and optimizing culture systems. The present review focuses on the biophotonic-based manipulations that can be applied to optimize solar-powered photobioreactors (PBRs). Hence, three different types of solar filters are reviewed herein, that is, the colored glass, thin-film, and thermochromic filters. This review provides evidence that bright red-colored glass filters can lower the spectral intensity of solar radiation from 1982.13 to 393.71 μmol m⁻² s⁻¹, which is preferable for improved biomass productivity. Changing filter color, once the desired biomass concentration has been amassed, to medium blue or bright pink further improves lipid yield. A 34% improvement in biomass productivity was observed for Chlorella vulgaris cultured under thin-film filters. Thin-film filters are also effective in regulating PBR temperature within the 24–31°C range, which is tolerable for most algal species. Furthermore, this study highlights that the applicability of thermochromic filters in PBR designs is still yet to be investigated. Thermochromic filters are reflective and absorptive under high and low temperatures, respectively, a technology that can be a solution to the overheating challenge of PBRs. This review recommends the coupling of these light filtration technologies to the horizontal tubular PBR for effective utilization of solar radiation in algaculture.     

Hydrogen production by Chlamydomonas reinhardtii under light-driven and sulfur-deprived conditions: Using biomass grown in outdoor photobioreactors at the Yucatan Peninsula

Photosynthesis is the ultimate natural process that supports all the biofuels generation. Photosyntetic production of hydrogen by microalgae is very attractive from the renewability point of view. Moreover, it faces several challenges: since the process itself has a low yield, a large number of considerations should be studied to optimize the hydrogen production at the lowest cost. In this work, wild-type Chlamydomonas reinhartii was grown outdoors in the Yucatán peninsula. Three different diameters of tubular photobioreactors (PBRs), two autotrophic culture media, as well as two seasons of the year were analyzed. From these variables, it was determined that the best biomass yield was during the winter season and with the Sueoka culture medium. Statistical significance differences were not found for the diameters of the PBRs. During growth, the biomass was exposed to natural light–dark cycles and at the end of the exponential phase of growth it was harvested with superabsorbent polymers. This biomass was able to produce hydrogen under anaerobic conditions in Tris-Acetate-Phosphate culture medium in indoor PBRs exposed to continuous artificial illumination. Experiments with different initial biomass concentrations in the anaerobic PBRs showed direct relationship with the hydrogen production profile.     

Prolonged hydrogen production by Nostoc in photobioreactor and multi-stage use of the biological waste for column biosorption of some dyes and metals

Hydrogen production by Nostoc linckia was studied using both free and alginate immobilized biomass of the cyanobacterium in separate lab-scale photobioreactors (PBRs). Hydrogen production rates improved significantly when immobilized cyanobacterial biomass was used in PBR and the production continued up to 25 days by maintaining required anoxic conditions and carbohydrate supplement. Average hydrogen production rate over 25 days was 132 μmolH₂/h/mg Chl a. The biological waste from the PBRs was utilized for sequestration of two toxic heavy metals (chromium and cobalt) and carcinogenic dyes (Reactive Red 198 and Crystal Violet) from aqueous solutions in packed-bed column. From the PBR containing free N. linckia cells, the spent biomass was collected after 7 d, dried and immobilized in alginate matrix, and used as a biosorbent for optimizing bed height and flow rate of the column. Breakthrough capacity of the packed-bed column was determined and breakthrough curves were analyzed using BDST model. Three PBRs containing immobilized cyanobacterial biomass were run for 5, 15 and 25 days, and the biological waste collected at the end of the operation was used for biosorption studies under optimized conditions (bed height, 25 cm; flow rate, 3 mL/min). Biosorption efficiency of the waste biomass was found to be influenced by the operation time of the hydrogen photobioreactor.     

Technical and economic analysis of biogas production in Ireland utilising three different crop rotations

The Biofuels Directive sets reference values for the quantity of biofuels and other renewable fuels to be placed on the transport market. Biogas from agricultural crops can be used to meet this directive. This paper investigates biogas production for three crop rotations: wheat, barley and sugar beet; wheat, wheat and sugar beet; wheat only. A technical and economic analysis for each crop rotation was carried out. It was found that wheat produces significantly more biogas than either barley or sugar beet, when examined on a weight basis. However sugar beet produces more biogas and subsequently more energy when examined on an area basis. When producing biofuels, land is the limiting factor to the quantity of energy that may be produced. Thus if optimising land then a crop rotation of wheat, wheat and sugar beet should be utilised, as this scenario produced the greatest quantity of energy. This scenario has a production cost of €0.90/m_N³, therefore, this scenario is competitive with petrol when the price of petrol is at least €1.09/l (VAT is charged at 21%). If optimising the production costs then a crop rotation of wheat only should be utilised when the cost of grain is less than €132/ton. This scenario has the least production cost at €0.83/m_N³, therefore, this scenario is competitive with petrol when the price of petrol is at least €1.00/l. But as this scenario produces the least quantity of biogas, it also produces the least quantity of energy. In comparing with other works by the authors it is shown that a biomethane system produces more energy from the same crops at a cheaper cost than an ethanol system.     

Future prospects for production of methanol and hydrogen from biomass

Technical and economic prospects of the future production of methanol and hydrogen from biomass have been evaluated. A technology review, including promising future components, was made, resulting in a set of promising conversion concepts. Flowsheeting models were made to analyse the technical performance. Results were used for economic evaluations. Overall energy efficiencies are around 55% HHV for methanol and around 60% for hydrogen production. Accounting for the lower energy quality of fuel compared to electricity, once-through concepts perform better than the concepts aimed for fuel only production. Hot gas cleaning can contribute to a better performance. Systems of 400 MW_th input produce biofuels at US$ 8–12/GJ, this is above the current gasoline production price of US$ 4–6/GJ. This cost price is largely dictated by the capital investments. The outcomes for the various system types are rather comparable, although concepts focussing on optimised fuel production with little or no electricity co-production perform somewhat better. Hydrogen concepts using ceramic membranes perform well due to their higher overall efficiency combined with modest investment. Long-term (2020) cost reductions reside in cheaper biomass, technological learning, and application of large scales up to 2000 MW_th. This could bring the production costs of biofuels in the US$ 5–7/GJ range. Biomass-derived methanol and hydrogen are likely to become competitive fuels tomorrow.     

Biomass production potentials in Central and Eastern Europe under different scenarios

A methodology for the assessment of biomass potentials was developed and applied to Central and Eastern European countries (CEEC). Biomass resources considered are agricultural residues, forestry residues, and wood from surplus forest and biomass from energy crops. Only land that is not needed for food and feed production is considered as available for the production of energy crops. Five scenarios were built to depict the influences of different factors on biomass potentials and costs. Scenarios, with a domination of current level of agricultural production or ecological production systems, show the smallest biomass potentials of 2–5.7 EJ for all CEEC. Highest potentials can reach up to 11.7 EJ (85% from energy crops, 12% from residues and 3% from surplus forest wood) when 44 million ha of agricultural land become available for energy crop production. This potential is, however, only realizable under high input production systems and most advanced production technology, best allocation of crop production over all CEEC and by choosing willow as energy crops. The production of lignocellulosic crops, and willow in particular, best combines high biomass production potentials and low biomass production costs. Production costs for willow biomass range from 1.6 to 8.0 €/GJ HHV in the scenario with the highest agricultural productivity and 1.0–4.5 €/GJ HHV in the scenario reflecting the current status of agricultural production. Generally the highest biomass production costs are experienced when ecological agriculture is prevailing and on land with lower quality. In most CEEC, the production potentials are larger than the current energy use in the more favourable scenarios. Bulk of the biomass potential can be produced at costs lower than 2 €/GJ. High potentials combined with the low cost levels gives CEEC major export opportunities.     

Socio-economic aspects of different biofuel development pathways

There are several policy drivers for biofuels on a larger scale in the EU transport sector, including increased security of energy supply, reduced emission of greenhouse gases (GHG), and new markets for the agricultural sector. The purpose of this socio-economic cost analysis is to provide an overview of the costs of meeting EU biofuels targets, taking into account several external costs and benefits. Biofuels are generally more expensive than traditional fossil fuels, but the expected increasing value of GHG emission reductions will over time reduce the cost gap. High crude oil prices significantly improve the economic benefit of biofuels, but increased demand for biomass for energy purposes is likely to increase the price of biofuels feedstock and biofuels costs. The key question is to what extent increasing oil prices will be passed on to biofuels costs. Socio-economic least costs for biofuels production require a market with a clear pricing of GHG emissions to ensure that this factor is included in the decision-making of actors in all links of the fuel chain.     

Estimating GHG emission mitigation supply curves of large-scale biomass use on a country level

This study evaluates the possible influences of a large-scale introduction of biomass material and energy systems and their market volumes on land, material and energy market prices and their feedback to greenhouse gas (GHG) emission mitigation costs. GHG emission mitigation supply curves for large-scale biomass use were compiled using a methodology that combines a bottom-up analysis of biomass applications, biomass cost supply curves and market prices of land, biomaterials and bioenergy carriers. These market prices depend on the scale of biomass use and the market volume of materials and energy carriers and were estimated using own-price elasticities of demand. The methodology was demonstrated for a case study of Poland in the year 2015 applying different scenarios on economic development and trade in Europe. For the key technologies considered, i.e. medium density fibreboard, poly lactic acid, electricity and methanol production, GHG emission mitigation costs increase strongly with the scale of biomass production. Large-scale introduction of biomass use decreases the GHG emission reduction potential at costs below 50 €/Mg CO_2eq with about 13–70% depending on the scenario. Biomaterial production accounts for only a small part of this GHG emission reduction potential due to relatively small material markets and the subsequent strong decrease of biomaterial market prices at large scale of production. GHG emission mitigation costs depend strongly on biomass supply curves, own-price elasticity of land and market volumes of bioenergy carriers. The analysis shows that these influences should be taken into account for developing biomass implementations strategies.     

Global land-use implications of first and second generation biofuel targets

Recently, an active debate has emerged around greenhouse gas emissions due to indirect land use change (iLUC) of expanding agricultural areas dedicated to biofuel production. In this paper we provide a detailed analysis of the iLUC effect, and further address the issues of deforestation, irrigation water use, and crop price increases due to expanding biofuel acreage. We use GLOBIOM – an economic partial equilibrium model of the global forest, agriculture, and biomass sectors with a bottom-up representation of agricultural and forestry management practices. The results indicate that second generation biofuel production fed by wood from sustainably managed existing forests would lead to a negative iLUC factor, meaning that overall emissions are 27% lower compared to the “No biofuel” scenario by 2030. The iLUC factor of first generation biofuels global expansion is generally positive, requiring some 25 years to be paid back by the GHG savings from the substitution of biofuels for conventional fuels. Second generation biofuels perform better also with respect to the other investigated criteria; on the condition that they are not sourced from dedicated plantations directly competing for agricultural land. If so, then efficient first generation systems are preferable. Since no clear technology champion for all situations exists, we would recommend targeting policy instruments directly at the positive and negative effects of biofuel production rather than at the production itself.     

The feasibility,costs, and environmental implications of large-scale biomass energy

What are the feasibility, costs, and environmental implications of large-scale bioenegry? We investigate this question by developing a detailed representation of bioenergy in a global economy-wide model. We develop a scenario with a global carbon dioxide price, applied to all anthropogenic emissions except those from land use change, that rises from $25 per metric ton in 2015 to $99 in 2050. This creates market conditions favorable to biomass energy, resulting in global non-traditional bioenergy production of ~ 150 exajoules (EJ) in 2050. By comparison, in 2010, global energy production was primarily from coal (138 EJ), oil (171 EJ), and gas (106 EJ). With this policy, 2050 emissions are 42% less in our Base Policy case than our Reference case, although extending the scope of the carbon price to include emissions from land use change would reduce 2050 emissions by 52% relative to the same baseline. Our results from various policy scenarios show that lignocellulosic (LC) ethanol may become the major form of bioenergy, if its production costs fall by amounts predicted in a recent survey and ethanol blending constraints disappear by 2030; however, if its costs remain higher than expected or the ethanol blend wall continues to bind, bioelectricity and bioheat may prevail. Higher LC ethanol costs may also result in the expanded production of first-generation biofuels (ethanol from sugarcane and corn) so that they remain in the fuel mix through 2050. Deforestation occurs if emissions from land use change are not priced, although the availability of biomass residues and improvements in crop yields and conversion efficiencies mitigate pressure on land markets. As regions are linked via international agricultural markets, irrespective of the location of bioenergy production, natural forest decreases are largest in regions with the lowest barriers to deforestation. In 2050, the combination of carbon price and bioenergy production increases food prices by 3.2%–5.2%, with bioenergy accounting for 1.3%–3.5%.     

Improved hydrogen production of the downstream bioreactor by coupling single chamber microbial fuel cells between series-connected photosynthetic biohydrogen reactors

To obtain additional hydrogen recovery from the downstream photosynthetic biohydrogen reactor (PBR), a system (PBR1–MFCs–PBR2) that combined PBRs with three single chamber microbial fuel cells (MFCs) was proposed in this study. The results revealed that the PBR2 in PBR1–MFCs–PBR2 showed a hydrogen production rate of 0.44 ± 0.22 mmol L h⁻¹, which was 15 and 4 times higher than those obtained by direct connecting the two PBRs (PBR1–PBR2) and pH regulated system (PBR1–pH regulation–PBR2), respectively. In addition, the PBR1–MFCs–PBR2 exhibited the highest glucose utilization (η_g) of 97.6 ± 2.1 %, while lower η_g values of 75.6 ± 2.2% and 70.1 ± 1.2% was obtained for PBR1–PBR2 and PBR1–pH regulation–PBR2, respectively. These improvements were due to the removal of inhibitory byproduct and H⁺ from the PBR1 effluent by the MFCs.     

Techno-economic and environmental assessment of methanol steam reforming for H2 production at various scales

According to global trend of transition to a hydrogen society, needs for alternative hydrogen (H₂) production methods have been on the rise. Among them, methanol steam reforming (MSR) in a membrane reactor (MR) has received a great attention due to its improved H₂ yield and compact design. In this study, 3 types of economic analysis – itemized cost estimation, sensitivity analysis, and uncertainty analysis – and integrative carbon footprint analysis (iCFA) were carried out to investigate economic and environmental feasibility. Unit H₂ production costs of MSR in a packed-bed reactor (PBR) and an MR for various H₂ production capacities of 30, 100, 300, and 700 m³ h⁻¹ and CO₂ emission rates for both a PBR and an MR in H₂ production capacity of 30 m³ h⁻¹ were estimated. Through itemized cost estimation, unit H₂ production costs of a PBR and an MR were obtained and scenario analysis was carried out to find a minimum H₂ production cost. Sensitivity analysis was employed to identify key economic factors. In addition, comprehensive uncertainty analysis reflecting unpredictable fluctuation of key economic factors of reactant, labor, and natural gas obtained from sensitivity analysis was also performed for a PBR and an MR by varying them both simultaneously and individually. Through iCFA, lowered CO₂ emission rates were obtained showing environmental benefit of MSR in an MR.     

Biomass for heat or as transportation fuel? A comparison between two model-based studies

In two different energy economy models of the global energy system, the cost-effective use of biomass under a stringent carbon constraint has been analyzed. Gielen et al. conclude that it is cost-effective to use biofuels for transportation, whereas Azar et al. find that it is more cost-effective to use most of the biomass to generate heat and process heat, despite the fact that assumptions about the cost of biofuels production is similar in the models. In this study, we compare the two models with the purpose of finding an explanation for these different results. It was found that both models suggest that biomass is most cost-effectively used for heat production for low carbon taxes (below 50–100 USD/tC, depending on the year in question). But for higher carbon taxes, the cost-effective choice reverses in the BEAP model, but not in the GET model. The reason for this is that GET includes hydrogen from carbon-free energy sources as a technology option, whereas that option is not allowed in the BEAP model. In all other sectors, both models include carbon-free options above biomass. Thus, with higher carbon taxes, biomass will eventually become the cost-effective choice in the transportation sector in BEAP, regardless of its technology cost parameters.     

The technical potential of first-generation biofuels obtained from energy crops in Spain

Biofuels have been recently the subject of a sustained interest due to the ambitious goals set out in developed, and some developing, countries as they transition to more sustainable and self-sufficient energy models. Thus, EU Directive 2003/30 established certain minimimun shares of biofuels in the transport sector for the member states, viz 2% by 2005 and 5.75% by 2010. More recently, the EU Directive 2009/28/EC imposes a target share of 10% renewables in the transport sector by 2020. Different roadmaps can be envisaged based on the varying contributions from first and second-generation biofuels; the controversial role of biomass imports for biofuel production adds some additional uncertainties. Against this backdrop, this work presents a comprehensive view of the technical potential for first-generation biofuels (biodiesel and bioethanol) from energy crops in Spain, and their prospects in the short and mid terms. The methodology has been implemented in a Geographical Information System. The calculated technical potentials for biodiesel range between 730 and 1830 ktoe year⁻¹ for land occupations of 10% and 25% of the arable land, respectively. The corresponding bioethanol potentials for the same levels of land occupation are 1228 and 3070 ktoe year⁻¹. The calculated potentials indicate that the Spanish agricultural system would be severely strained if the 2020 target, 4755 ktoe year⁻¹, is to be met with locally-grown biofuel crops. The study further estimates the resulting first-generation biofuel costs, and concludes that incentives are needed for the price to be competitive with that of oil-based fuels, even in a scenario of high oil prices.     

Scenarios for biofuel demands,biomass production and land use – The case of Denmark

The land potential for producing biomass for bioenergy purposes has been highly debated in recent years. The present paper analyses the possibilities and consequences for land use and agricultural production of biofuel production in Denmark based on domestic wheat and rape under specific scenario conditions for the period 2010–2030. The potential is assessed for a situation where policy targets for renewable energy carriers in the transport sector is reached using biofuels, and where second generation ethanol increasingly substitutes first generation ethanol.Three scenarios are developed and evaluated: a baseline, an alternative scenario allowing continuous growth in the now dominant livestock branch and a biofuel scenario assuming that efforts to achieve self-sufficiency in biofuel displaces part of the domestic production of fodder.Results show that the biofuel demand could be met in 2020; but only if current rape oil production is used to satisfy local bio-diesel demand. It would also imply that the Danish bio-diesel export currently supplying a minor part of the German fuel market would seize. In 2030, however, only about 60 percent of the biofuel demand would be covered by self-sufficiency. If biofuels were to displace animal production to make up for this, a reduction of the pig production between 10 and 20 percent would result. Efficiency increases across production branches would allow the animal production to continue un-affected if about half of the rape oil produced for other purposes is utilized.     

Policy plan for the use of biomass and biofuels in Greece: Part II: Logistics and economic investigation

The introduction of biomass driven energy products like bioethanol, biodiesel, Combined Heat and Power production or solid biofuels is vital for achieving the targets set from the EU for the year 2010 (20% electricity production from RES). However, in order to reach these targets, a policy plan has to be formed concerning the conversion of biomass. The aim of this paper is to examine the logistics involved in the exploitation of already available or new biomass resources and to analyse various scenarios for the economic feasibility of the use of biomass and biofuels in Greece.     

Opportunity for profitable investments in cellulosic biofuels

Research efforts to allow large-scale conversion of cellulose into biofuels are being undertaken in the US and EU. These efforts are designed to increase logistic and conversion efficiencies, enhancing the economic competitiveness of cellulosic biofuels. However, not enough attention has been paid to the future market conditions for cellulosic biofuels, which will determine whether the necessary private investment will be available to allow a cellulosic biofuels industry to emerge. We examine the future market for cellulosic biofuels, differentiating between cellulosic ethanol and ‘drop-in’ cellulosic biofuels that can be transported with petroleum fuels and have equivalent energy values. We show that emergence of a cellulosic ethanol industry is unlikely without costly government subsidies, in part because of strong competition from conventional ethanol and limits on ethanol blending. If production costs of drop-in cellulosic biofuels fall enough to become competitive, then their expansion will not necessarily cause feedstock prices to rise. As long as local supplies of feedstocks that have no or low-valued alternative uses exist, then expansion will not cause prices to rise significantly. If cellulosic feedstocks come from dedicated biomass crops, then the supply curves will have a steeper slope because of competition for land.     

Strategies for 2nd generation biofuels in EU – Co-firing to stimulate feedstock supply development and process integration to improve energy efficiency and economic competitiveness

The present biofuel policies in the European Union primarily stimulate 1st generation biofuels that are produced based on conventional food crops. They may be a distraction from lignocellulose based 2nd generation biofuels – and also from biomass use for heat and electricity – by keeping farmers' attention and significant investments focusing on first generation biofuels and the cultivation of conventional food crops as feedstocks. This article presents two strategies that can contribute to the development of 2nd generation biofuels based on lignocellulosic feedstocks. The integration of gasification-based biofuel plants in district heating systems is one option for increasing the energy efficiency and improving the economic competitiveness of such biofuels. Another option, biomass co-firing with coal, generates high-efficiency biomass electricity and reduces CO₂ emissions by replacing coal. It also offers a near-term market for lignocellulosic biomass, which can stimulate development of supply systems for biomass also suitable as feedstock for 2nd generation biofuels. Regardless of the long-term priorities of biomass use for energy, the stimulation of lignocellulosic biomass production by development of near term and cost-effective markets is judged to be a no-regrets strategy for Europe. Strategies that induce a relevant development and exploit existing energy infrastructures in order to reduce risk and reach lower costs, are proposed an attractive complement the present and prospective biofuel policies.     

Economic challenges for the future relevance of biofuels in transport in EU countries

The discussion on the promotion of biofuels is ambiguous: on the one hand benefits like reduction of greenhouse gas emissions and increase of energy supply security are expected, on the other hand low effectiveness with respect to reducing greenhouse gas emissions and high costs are being criticized. The core objective of this paper is to investigate the market prospects of biofuels for transport in the EU in a dynamic framework till 2030. The major results of this analysis are: (i) Under current policy conditions – mainly exemption of excise taxes – the economic prospects of 1st generation biofuels in Europe are rather promising; the major problems of 1st generation biofuels are lack of available land for feedstocks and the modest ecological performance; (ii) Large expectations are currently put into advanced 2nd generation biofuels production from lignocellulosic materials. With respect to the future costs development of 2nd generation biofuels, currently it can only be stated that in a favourable case by 2030 they will be close to the costs of 1st generation biofuels. However, because of the increasing prices for fossil gasoline and diesel in all international scenarios – given remaining tax exemptions – biofuels will become competitive already in the next few years.     

Bioenergy villages in Germany: Bringing a low carbon energy supply for rural areas into practice

An increasing number of rural municipalities wants to meet their entire energy demand with biomass. This article gives a system analytic view on these “bioenergy villages” by balancing pros (reduction of CO₂ emissions) and cons (increasing costs, land use) using the example of a model municipality in Germany. The results indicate that a 100% energy supply based on biomass from within the boundaries of a rural municipality is technically possible but less reasonable with respect to land use competition and costs of energy supply. Whereas heat and power demand in bioenergy villages can be covered with relatively little land use and to relatively low costs, the production of transport fuel based on energy crops (rape seed) leads to significant negative impacts. For a cost-efficient decarbonization of rural areas it can therefore be recommended to particularly expand the utilization of biomass for heat and power production and to reconsider the transport fuel production.