Improvement of hydrogen production with expression of lba gene in chloroplast of Chlamydomonas reinhardtii

An ORF cDNA fragment of one of leghemoglobin genes, lba was cloned from Glycine max and transferred into chloroplasts of Chlamydomonas reinhardtii. More rapidly O₂ consumption, lower O₂ content and higher H₂ output were monitored in the transgenic algal cultures than those in WT cultures either in S-free or S-containing medium. Maximum expression of lba in the transgenic algae consisted with the time when minimal O₂ contents and maximal H₂ evolution occurred. The highest H₂ production achieved in sulfur-free medium for both algal cultures. When restoring sulfate in the medium, H₂ production in the transgenic algal cultures kept steadily around 130–145 μl per bottle while that in WT cultures decreased gradually from 98 μl per bottle at 12.5 μM sulfate to 40 μl per bottle at 100 μM sulfate. The results indicated that heteroexpression of lehemoglaobin genes in chloroplasts of green algae improved H₂ yield by decreasing O₂ content in the medium. This protein had potential to be used in improvement of H₂ production in green algae.     

GIS based multi-criteria decision making for solar hydrogen production sites selection in Algeria

Hydrogen production from renewable energy sources appears to be an interesting solution for reducing greenhouse gas emissions and ensuring the energy security supply. This paper develops an integrated framework to evaluate land suitability for hydrogen production from solar energy site selection that combines multi-criteria decision making (MCDM) with geographical information systems (GIS); an application of the proposed framework for Algerian country. In GIS two types of criteria will be taken: constraints and weighting criteria. Constraints criteria will make it possible to reduce the area of study by discarding those areas that prevent the implementation of installing solar hydrogen production systems. These criteria will be obtained from the legislation (land use, water bodies, waterways, roads, railways, power lines, and also their buffer around them). Weighting criteria will be chosen according to the objective to be reached, in this case they will be the hydrogen demand, potential solar hydrogen production, digital elevation models (DEMs), slope, proximity to roads, railways, and power lines. Through the use of MCDM the criteria mentioned will be weighted in order to evaluate potential sites to locate a solar hydrogen production installation system. Analysis and calculation of the weights of these criteria will be conducted using Analytic Hierarchy Process (AHP). As a result, the final index model was grouped into four categories as “very low suitability”, “low suitability”, “moderate suitability” and “high suitability” with a manual interval classification method. The results indicate that 10.34% (246,272.02 km²), of the study area has very low suitability, 60.75% (1,446,907.65 km²) has low suitability, 6.68% (159,100.3 km²) has moderate suitability and 0.49% (11,669.21 km²) has high suitability for a solar-powered hydrogen production installation system. The other 21.74% (517,790.5 km²) of the study area is not suitable for such projects. The sensitivity analysis highlights that the suitable sites for solar hydrogen production installation system are dependent on the weights of the criteria that influence the decision. The MCDM methodology integrated with GIS is a powerful tool for effective evaluation of the solar-powered hydrogen production sites selection.     

Comparative study of bio-ethanol production from mahula (Madhuca latifolia L.) flowers by Saccharomyces cerevisiae cells immobilized in agar agar and Ca-alginate matrices

Batch fermentation of mahula (Madhuca latifolia L., a tree commonly found in tropical rain forest) flowers was carried out using immobilized cells (in agar agar and calcium alginate) and free cells of Saccharomyces cerevisiae. The ethanol yields were 151.2, 154.5 and 149.1 g kg⁻¹ flowers using immobilized (in agar agar and calcium alginate) and free cells, respectively. Cell entrapment in calcium alginate was found to be marginally superior to those in agar agar (2.2% more) as well as over free cell (3.5% more) as regard to ethanol yield from mahula flowers is concerned. Further, the immobilized cells were physiologically active at least for three cycles [150.6, 148.5 and 146.5 g kg⁻¹ (agar agar) and 152.8, 151.5 and 149.5 g kg⁻¹ flowers (calcium alginate) for first, second and third cycle, respectively] of ethanol fermentation without apparently lowering the productivity. Mahula flowers, a renewable, non-food-grade cheap carbohydrate substrate from non-agricultural environment such as forest can serve as an alternative to food grade sugar/starchy crops such as maize, sugarcane for bio-ethanol production.     

Fed-batch operation for bio-H2 production by Rhodopseudomonas palustris (strain 42OL)

Interest in renewable and clean energies such as hydrogen has increased because of the high level of polluting emissions, increasing costs associated with petroleum and the escalating problems of global climate change. In the presence of a light source, a microbial photosynthetic process provides a system for the conversion of some organic compounds into biomass and hydrogen. Using Rhodopseudomonas palustris as a cell-factory, hydrogen photo-evolution was investigated in a photobioreactor (PBR) irradiated either from one or two opposite sides. Irradiating the photobioreactor from only one side, in the presence of malic acid, a reactor hydrogen production of 2.786 l(H₂) PBR⁻¹ was achieved. When the PBR was irradiated from two opposite sides, hydrogen photo-evolution increased to 3.162 l(H₂) PBR⁻¹. Experiments were carried out using inoculum from either the retardation or the exponential growth phases. Using the latter, the highest hydrogen photo-evolution rate based on the bacteriochlorophyll (Bchl) concentration was achieved (3295 μl(H₂) mg (Bchl⁻¹ h⁻¹). The hydrogen to biomass ratio (r_g) was 1.91 l g⁻¹ in the medium containing malic acid and 1.07 l g⁻¹ in that containing acetic acid. It was found that the hydrogen production rate was higher with malic than with acetic acid. Although photobiological hydrogen production cannot furnish alone the greater and greater world requirements of clean renewable energy, it is desirable that photobiological hydrogen technology will grow, in the near future, because photobioreactors for bio-hydrogen production can be positioned in fringe areas without competition with agricultural lands.     

Efficient hydrogen gas production from cassava and food waste by a two-step process of dark fermentation and photo-fermentation

A two-step process of sequential anaerobic (dark) and photo-heterotrophic fermentation was employed to produce hydrogen from cassava and food waste. In dark fermentation, the average yield of hydrogen was approximately 199 ml H₂ g⁻¹ cassava and 220 ml H₂ g⁻¹ food waste. In subsequent photo-fermentation, the average yield of hydrogen from the effluent of dark fermentation was approximately 611 ml H₂ g⁻¹ cassava and 451 ml H₂ g⁻¹ food waste. The total hydrogen yield in the two-step process was estimated as 810 ml H₂ g⁻¹ cassava and 671 ml H₂ g⁻¹ food waste. Meanwhile, the COD decreased greatly with a removal efficiency of 84.3% in cassava batch and 80.2% in food waste batch. These results demonstrate that cassava and food waste could be ideal substrates for bio-hydrogen production. And a two-step process combining dark fermentation and photo-fermentation was highly improving both bio-hydrogen production and removal of substrates and fatty acids.     

Water use impact of ethanol at a gasoline substitution ratio of 5% from cassava in Nigeria

The process of fuel ethanol production from cassava root is connected to a chain of impacts on the water resource of the country where the cassava plant is grown and the root processed into fuel ethanol. The paper assesses the impact of the domestic production of 5 per cent ethanol (E5) needed under the Nigerian biofuel programme from cassava root on the water resource of Nigeria. Using the 2007 Premium Motor Spirit (PMS) consumption as the baseline, Nigeria will require about 0.49 hm³ of ethanol to blend 9.32 hm³ of PMS to arrive at the 2007 consumption estimates. The impact of the domestic production of this ethanol requirement translates to about 6.0 km³ of water; out of which about 48 per cent is green and about 52 per cent is blue. Addressing future impact typical of a developing economy like Nigeria, a three-scenario analysis was adopted to examine the impact of future growth in cassava-fuel ethanol requirement on the water resource of Nigeria, and also, the impact of improved water use on the future water footprint of E5. The projected water impact of cassava-ethanol production into the future ranges from 6.02 to 7.28 km³, while improved water use could lower these values by about 0.04–2.35 km³ for the same period, 2010 to 2020, under the projection assumptions made.     

Long-term biomass production and nutrient uptake of birch, alder and willow plantations on cut-away peatland

The leafless above-ground biomass production of planted silver birch (Betula pendula), downy birch (Betula pubescens), grey alder (Alnus incana), indigenous willows (Salix triandra and Salix phylicifolia) and an alder-willow mixture growing on a cut-away peatland area in Central Finland was investigated during a period of 18 (willows) or 19 (birches and alders) years. Biannual fertilization of the birches (0, NPK) and alders (0, PK) and annual fertilization of the willows (NPK1, NPK2) were continued for 10 years. S. phylicifolia had the highest yield (123 t ha⁻¹). The yield of the fertilized downy and silver birch was 112 t ha⁻¹ and 108 t ha⁻¹ respectively, and that of fertilized grey alder 85 t ha⁻¹, and alder S. triandra mixture 93 t ha⁻¹. The mean annual increment of willow was highest at the age of 10 years (S. phylicifolia 7.9 t ha⁻¹ a⁻¹; S. triandra 5.6 t ha⁻¹ a⁻¹). NPK-fertilization increased the 19-year biomass production of downy and silver birch by 14 and 29 t ha⁻¹ respectively and PK fertilization that of alders by 25 t ha⁻¹. The alder plantations bound more N, P, K, Ca and Mg per unit leafless biomass produced after 10–11 growing seasons than the silver birch and downy birch plantations. The silver birch used more N, K and Ca, but similar amounts of P and Mg per unit leafless biomass produced than the downy birch. S. triandra used more N, P, K and Mg per unit biomass produced than S. phylicifolia and both birch species.     

Modeling the land requirements and potential productivity of sugarcane and jatropha in Brazil and India using the LPJmL dynamic global vegetation model

The governments of Brazil and India are planning a large expansion of bioethanol and biodiesel production in the next decade. Considering that limitation of suitable land and/or competition with other land uses might occur in both countries, assessments of potential crop productivity can contribute to an improved planning of land requirements for biofuels under high productivity or marginal conditions. In this paper we model the potential productivity of sugarcane and jatropha in both countries. Land requirements for such expansions are calculated according to policy scenarios based on government targets for biofuel production in 2015. Spatial variations in the potential productivity lead to rather different land requirements, depending on where plantations are located. If jatropha is not irrigated, land requirements to fulfill the Indian government plans in 2015 would be of 410 000 to 95 000 km² if grown in low or high productivity areas respectively (mean of 212 000 km²). In Brazil land requirements, are of 18 000–89 000 km² (mean of 29 000 km²), suggesting a promising substitute to soybean biodiesel. Although future demand for sugarcane ethanol in Brazil is approximately ten times larger than in India, land requirements are comparable in both countries due to large differences in ethanol production systems. In Brazil this requirement ranges from 25 000 to 211 000 km² (mean of 33 000 km²) and in India from 7000 to 161 000 km² (mean 17 000 km²). Irrigation could reduce the land requirements by 63% and 41% (24% and 15%) in India (Brazil) for jatropha and sugarcane respectively.     

Electrical power generation from ocean currents in the Straits of Florida: Some environmental considerations

Ocean currents contain a remarkable amount of kinetic energy and have potential worldwide capability. Initial tests to harness current power focus on the Straits of Florida where the Florida Current has a total flow capacity of about 30 × 10⁶ m³ s⁻¹. Generation of clean electricity from ocean currents off southeast Florida is based on a power extractor comprising open-center turbine technology. This innovative turbine provides safe passage for fish and other aquatic species. The water-column array of energy production units (EPUs) will have a 350 km² footprint, based on a 600 m (10 rotor diameters) downstream separation distance between EPUs with a lateral separation of 400 m. Water depths for the EPU field are in the range of 100–500 m. With such a large area of water column and benthic habitat utilized, environmental concerns must be overcome, including routing of transmission lines to shore. Risks and vulnerabilities of the proposed ocean current generated electricity include failure of individual EPUs and damage to sensitive coastal marine environments during installation.     

An analysis of the feasibility for increasing woody biomass production from pine plantations in the southern United States

In the near future, wood from the 130 000 km² of pine plantations in the southern United States could provide much of the feedstock for emerging bioenergy industries. Research and operational experience show that total plantation biomass productivity exceeding 22.4 Mg ha^?1 y^?1 green weight basis with rotations less than 25 years are biologically possible, financially attractive, and environmentally sustainable. These gains become possible when intensively managed forest plantations are treated as agro-ecosystems where both the crop trees and the soil are managed to optimize productivity and value. Intensive management of southern US pine plantations could significantly increase the amount of biomass available to supply bioenergy firms. Results from growth and yield simulations using models and a financial analysis suggest that if the 130 000 km² of cutover pine plantations and an additional 20 000 km² of planted idle farmland are intensively managed in the most profitable regimes, up to 77.5 Tg green weight basis of woody biomass could be produced annually. However, questions exist about the extent to which intensive management for biomass production can improve financial returns to owners and whether they would adopt these systems. The financial analysis suggests providing biomass for energy from pine plantations on cutover sites is most profitable when intensive management is used to produce a mixture of traditional forest products and biomass for energy. Returns from dedicated biomass plantations on cutover sites and idle farmland will be lower than integrated product plantations unless prices for biomass increase or subsidies are available.     

Fermentative hydrogen production by two novel strains of Enterobacter aerogenes HGN-2 and HT 34 isolated from sea buried crude oil pipelines

Present study investigated fermentative hydrogen production of two novel isolates of Enterobacter aerogenes HGN-2 and HT 34 isolated from oil water mixtures. The two isolates were identified as novel strains of E. aerogenes based on 16S rRNA gene. The batch fermentations of two strains from glucose and xylose were carried out using economical culture medium under various conditions such as temperature, initial pH, NaCl, Ni⁺/Fe⁺⁺, substrate concentrations for enhanced fermentation process. Both the strains favoured wide range of pH (6.5–8.0) at 37 °C for optimum production (2.20–2.23 mol H₂/mol-glucose), which occurred through acetate/butyrate pathway. At 55 °C, both strains favoured 6.0–6.5 and acetate type fermentation was predominant in HT 34. Hydrogen production by HT 34 from xylose was highly pH dependant and optimum production was at pH 6.5 (circa 1.98 mol-H₂/mol-xylose) through acetate pathway. The efficiency of the strain HGN-2 at pH 6.5 was 1.92–1.94 mol-H₂/mol-xylose, and displayed both acetate and butyrate pathways. At 55 °C, very low hydrogen production was detected (less than 0.5 m mol/mol-xylose).     

Bioethanol production potential from Brazilian biodiesel co-products

One major problem facing the commercial production of cellulosic ethanol is the challenge of economically harvesting and transporting sufficient amounts of biomass as a feedstock at biorefinery plant scales. Oil extraction for biodiesel production, however, yields large quantities of biomass co-products rich in cellulose, sugar and starch, which in many cases may be sufficient to produce enough ethanol to meet the alcohol demands of the transesterification process. Soybean, castor bean, Jatropha curcas, palm kernel, sunflower and cottonseed were studied to determine ethanol production potential from cellulose found in the oil extraction co-products and also their capacity to meet transesterification alcohol demands. All crops studied were capable of producing enough ethanol for biodiesel production and, in the case of cottonseed, 470% of the transesterification demand could be met with cellulosic ethanol production from oil extraction co-products. Based on Brazilian yields of the crops studied, palm biomass has the highest potential ethanol yield of 108 m³ km⁻² followed by J. curcas with 40 m³ km⁻². A total of 3.5 hm³ could be produced from Brazilian soybean oil extraction co-products.     

Actual and putative potentials of macauba palm as feedstock for solid biofuel production from residues

The making of biofuel from source that aggregates multiple suitable raw materials is of great interest. An example of such source is macauba palm. Its fruit satisfies the demands for biodiesel production, and the solid residues resulting from its processing contain a series of potential fuel byproducts. Thus, our objective was to evaluate macauba fruit yield and the potential of this fruit to produce for solid biofuel. For this, the palm's productivity was assessed in a natural population, and two different scenarios of fruit yield and derived residues were analyzed: in scenario 1, the fruit yield average values were used without a priori information, while in scenario 2, the top 10% of plants in terms of number of bunch per plant were considered. Harvested fruits were quantified and processed. Solid residues had their chemical and physical characteristics determined. The fruit yield in scenario 2 was 98% higher than that in scenario 1, which did not exceed 2.32 Gg km⁻² y⁻¹ fresh fruit. Regarding residue characterization, the endocarp showed higher values of fixed carbon, lignin, bulk density and energy density than the other residues. The overall primary energies of the residues were 23.35 TJ km⁻² y⁻¹ and 44.39 TJ km⁻² y⁻¹ in scenarios 1 and 2, respectively. These findings indicate that macauba fruit is a promising source of primary and residual raw materials for biofuel production. Satisfactory production scale would be from a breeding program to maximize the fruit production of the plants, as mimicked by scenario 2.     

Worldwide commercial development of bioenergy with a focus on energy crop-based projects

Bioenergy consumption is greatest in countries with heavy subsidies or tax incentives, such as China, Brazil, and Sweden. Conversion of forest residues and agricultural residues to charcoal, district heat and home heating are the most common forms of bioenergy. Biomass electric generation feedstocks are predominantly forest residues (including black liquor), bagasse, and other agricultural residues. Biofuel feedstocks include sugar from sugarcane (in Brazil), starch from maize grain (in the US), and oil seeds (soy or rapeseed) for biodiesel (in the US, EU, and Brazil). Of the six large land areas of the world reviewed (China, EU, US, Brazil, Canada, Australia), total biomass energy consumptions amounts to 17.1 EJ. Short-rotation woody crops (SRWC) established in Brazil, New Zealand, and Australia over the past 25 years equal about 50,000 km². SRWC plantings in China may be in the range of 70,000–100,000 km². SRWC and other energy crops established in the US and EU amount to less than 1000 km². With some exceptions (most notably in Sweden and Brazil), the SRWC have been established for purposes other than as dedicated bioenergy feedstocks, however, portions of the crops are (or are planned to be) used for bioenergy production. New renewable energy incentives, greenhouse gas emission targets, synergism with industrial waste management projects, and oil prices exceeding 60 $ Bbl⁻¹ (in 2005) are major drivers for SRWC or energy crop based bioenergy projects.     

Energy crops in Ireland: Quantifying the potential life-cycle greenhouse gas reductions of energy-crop electricity

This study uses life-cycle assessment (LCA) to compare greenhouse gas (GHG) emissions from dominant agricultural land uses, and peat and coal electricity generation, with fuel-chains for Miscanthus and short-rotation-coppice willow (SRCW) electricity. A simple scenario was used as an example, where 30% of peat and 10% of coal electricity generation was substituted with co-fired Miscanthus and SRCW, respectively. Miscanthus and SRCW cultivation were assumed to replace sugar-beet, dairy, beef-cattle and sheep systems. GHG emissions of 1938 and 1346 kg CO₂ eq. ha⁻¹ a⁻¹ for Miscanthus and SRCW cultivation compared with between 3494 CO₂ eq. ha⁻¹ a⁻¹ for sugar-beet cultivation and 12,068 CO₂ eq. ha⁻¹ a⁻¹ for dairy systems. Miscanthus and SRCW fuel chains emitted 0.131 and 0.132 kg CO₂ eq. kWh⁻¹ electricity exported, respectively, compared with 1.150 and 0.990 kg CO₂ eq. kWh⁻¹ electricity exported for peat and coal fuel chains. 1.48 Mt CO₂ eq. a⁻¹ was saved from electricity production, and 0.42 Mt CO₂ eq. a⁻¹ was saved from displaced agriculture and soil C-sequestration. The total reduction of 1.9 Mt CO₂ eq. a⁻¹ represents 2.8% of Ireland's 2004 GHG emissions, but was calculated to require just 1.7% of agricultural land area and displace just 1.2% of the dairy herd (based on conservative Miscanthus and SRCW combustible-yield estimates of 11.7 and 8.81 t ha⁻¹ a⁻¹ dry matter, respectively). A 50% increase in cultivation emissions would still result in electricity being produced with an emission burden over 80% lower than peat and coal electricity. Lower yield assumptions had little impact on total GHG reductions for the scenario, but required substantially greater areas of land. It was concluded that energy-crop utilisation would be an efficient GHG reduction strategy for Ireland.     

Isolation of anoxygenic photosynthetic bacteria from Songkhla Lake for use in a two-staged biohydrogen production process from palm oil mill effluent

We are developing a process to produce biohydrogen from palm oil mill effluent. Part of this process will involve photohydrogen production from volatile fatty acids under low light conditions. We sought to isolate suitable bacteria for this purpose from Songkhla Lake in Southern Thailand. Enrichment for phototrophic bacteria from 34 samples was conducted providing acetate as a major carbon source and applying culturing conditions of anaerobic-low light (3000 lux) at 30 °C. Among the independent isolates from these enrichments 19 evolved hydrogen with productivities between 4 and 326 ml l⁻¹ d⁻¹. Isolate TN1 was the most efficient producer at a rate of 1.85 mol H₂ mol acetate⁻¹ with a light conversion efficiency of 1.07%. The maximum hydrogen production rate for TN1 was determined to be 43 ml l⁻¹ h⁻¹. Environmentally desirable features of photohydrogen production by TN1 included the absence of pH change in the cultures and no detectable residual CO₂.     

Evaluation of methane production from maize silage by harvest of different plant portions

Biogas production is mainly based on the anaerobic digestion of cereals silages and maize silage is the most utilized. Regarding biogas production, the most important portion of the plant is the ear. The corn ear, due to high starch content, is characterized by a higher biogas production compared to the silage of the whole plant.In this paper, we present the results of experimental field tests carried out in Northern Italy that aim to evaluate the anaerobic methane potential (BMP) of different portions of ensiled maize hybrids. The BMP production is evaluated considering the possibility of harvesting and ensiling: the whole plant; the plant cut at 75 cm of height; the ear only; the plant without the ear. For the different solutions, the results are reported as specific BMP and as average biogas production achievable per hectare. The methane production by harvesting and ensiling the whole plant (10,212 and 10,605 m³ ha⁻¹, for maize class 600 and 700, respectively) is higher than the ones achievable by the other plant portions (7961 and 7707 m³ ha⁻¹, from the ear; 9523 and 9784 m³ ha⁻¹, from the plant cut at 75 cm; 3328 and 3554 m³ ha⁻¹, from the plant without the ear, for maize class 600 and 700, respectively). The harvest of the whole plant, although it is the most productive solution, could not be the best solution under an economic and environmental point of view. Harvesting only the ear can be interesting considering the new Italian subsidy framework and for the biogas plants fed by biomass transported over long distances.     

Evaluation of annual bioenergy crops in the boreal zone for biogas and ethanol production

Three annual plant species, maize, hemp and faba bean were tested for suitability as dedicated biomass crops in Boreal conditions. Biomass yields were 10-15 t ha^-1. The crops were analyzed for their composition and tested as raw materials for conversion to methane and to fermentable sugars. The methane yield was 379 ± 16 Ndm³ kg⁻¹ VS⁻¹ from maize, 387 ± 20 Ndm³ kg⁻¹ VS⁻¹ from faba bean and 239 ± 9 Ndm³ kg⁻¹ VS⁻¹ from hemp. Based on the yield per hectare, maize proved to be the most potential raw material source for methane production. Analogous to methane production, maize was the most productive raw material also in standard hydrolysis tests, with a conversion yield of about 80% of the theoretical sugars. Based on the amount of carbohydrates, the highest theoretical yield per hectare was obtained with hemp. However, considering all parameters, including the need for weeding and fertilizers, all three crops studied proved to be attractive options for cultivation in boreal conditions as well as being used as energy crops in boreal climate.     

Energy and CO2 analysis of poplar and maize crops for biomass production in north Italy

The rising price of fossil fuel and the increasing environmental concern encourage the use of biomasses as energy sources. Aim of this study was to compare two poplar SRC and vSRC (6 and 3 years rotation cycle) with an annual crop (maize), used for biomass production in north Italy.The average of the biomass production was 13.9 Mg DM ha⁻¹ per year for the SRC and vSRC poplar and 19.2 Mg DM ha⁻¹ for the maize.The energy consumption for the poplar cultivations was about 15 GJ ha⁻¹ per year, which represented only the 6% of the energy biomass product (about 257 GJ ha⁻¹ per year).The input value of the maize was higher (26.8 GJ ha⁻¹ per year). In this case, the input value was about the 7% of the energy content in the biomass product (about 370 GJ ha⁻¹ per year).During the vSRC cultivation an amount of 8090 kg CO₂ eq ha⁻¹ was emitted, 6420 kg CO₂ eq ha⁻¹ for the SRC and 26,370 kg CO₂ eq ha⁻¹ for the maize.Compared to the maize, the poplar SRC (or vSRC) crops are interesting from an energetic point of view, while maize requires less manpower, but it has major problems related to the landscape biodiversity.     

An evaluation of cassava, sweet potato and field corn as potential carbohydrate sources for bioethanol production in Alabama and Maryland

The recent emphasis on corn production to meet the increasing demand for bioethanol has resulted in trepidation regarding the sustainability of the global food supply. To assess the potential of alternative crops as sources of bioethanol production, we grew sweet potato (Ipomoea batatas) and cassava (Manihot esculentum) at locations near Auburn, Alabama and Beltsville, Maryland in order to measure root carbohydrate (starch, sucrose, glucose) and root biomass. Averaged for both locations, sweet potato yielded the highest concentration of root carbohydrate (ca 80%), primarily in the form of starch (ca 50%) and sucrose (ca 30%); whereas cassava had root carbohydrate concentrations of (ca 55%), almost entirely as starch. For sweet potato, overall carbohydrate production was 9.4 and 12.7 Mg ha⁻¹ for the Alabama and Maryland sites, respectively. For cassava, carbohydrate production in Maryland was poor, yielding only 2.9 Mg ha⁻¹. However, in Alabama, carbohydrate production from cassava averaged 10 Mg ha⁻¹. Relative to carbohydrate production from corn in each location, sweet potato and cassava yielded approximately 1.5× and 1.6× as much carbohydrate as corn in Alabama; 2.3× and 0.5× for the Maryland site. If economical harvesting and processing techniques could be developed, these data suggest that sweet potato in Maryland, and sweet potato and cassava in Alabama, have greater potential as ethanol sources than existing corn systems, and as such, could be used to replace or offset corn as a source of biofuels.