Life-cycle greenhouse gas emissions and energy balances of sugarcane ethanol production in Mexico

The purpose of this work was to estimate GHG emissions and energy balances for the future expansion of sugarcane ethanol fuel production in Mexico with one current and four possible future modalities. We used the life cycle methodology that is recommended by the European Renewable Energy Directive (RED), which distinguished the following five system phases: direct Land Use Change (LUC); crop production; biomass transport to industry; industrial processing; and ethanol transport to admixture plants. Key variables affecting total GHG emissions and fossil energy used in ethanol production were LUC emissions, crop fertilization rates, the proportion of sugarcane areas that are burned to facilitate harvest, fossil fuels used in the industrial phase, and the method for allocation of emissions to co-products. The lower emissions and higher energy ratios that were observed in the present Brazilian case were mainly due to the lesser amount of fertilizers applied, also were due to the shorter distance of sugarcane transport, and to the smaller proportion of sugarcane areas that were burned to facilitate manual harvest. The resulting modality with the lowest emissions of equivalent carbon dioxide (CO_2e) was ethanol produced from direct juice and generating surplus electricity with 36.8 kgCO_2e/GJ_ethanol. This was achieved using bagasse as the only fuel source to satisfy industrial phase needs for electricity and steam. Mexican emissions were higher than those calculated for Brazil (27.5 kgCO_2e/GJ_ethanol) among all modalities. The Mexican modality with the highest ratio of renewable/fossil energy was also ethanol from sugarcane juice generating surplus electricity with 4.8 GJ_ethanol/GJ_fossil.     

Dual-injection: The flexible,bi-fuel concept for spark-ignition engines fuelled with various gasoline and biofuel blends

Dual-injection strategies in spark-ignition engines allow the in-cylinder blending of two different fuels at any blend ratio, when simultaneously combining port fuel injection (PFI) and direct-injection (DI). Either fuel can be used as the main fuel, depending on the engine demand and the fuel availability. This paper presents the preliminary investigation of such a flexible, bi-fuel concept using a single cylinder spark-ignition research engine. Gasoline has been used as the PFI fuel, while various mass fractions of gasoline, ethanol and 2,5-dimethylfuran (DMF) have been used in DI. The control of the excess air ratio during the in-cylinder mixing of two different fuels was realized using the cross-over theory of the carbon monoxide and oxygen emissions concentrations. The dual-injection results showed how the volumetric air flow rate, total input energy and indicated mean effective pressure (IMEP) increases with deceasing PFI mass fraction, regardless of the DI fuel. The indicated efficiency increases when using any ethanol fraction in DI and results in higher combustion and fuel conversion efficiencies compared to gasoline. Increasing the DMF mass fraction in DI reduces the combustion duration more significantly than with increased fractions of ethanol or gasoline in DI. The hydrocarbon (HC), oxides of nitrogen (NO_x) and carbon dioxide (CO₂) emissions mostly reduce when using any gasoline or ethanol fraction in DI. When using DMF, the HC emissions reduce, but the NO_x and CO₂ emissions increase.     

Biofuel Production: Utilizing Stakeholders’ Perspectives

Abstract

The use of biofuels as a replacement for fossil fuels is growing in the United States and other countries in part because of economic and environmental concerns. One of the technologies for biofuels production is fast pyrolysis; however, to increase manufacturing of fast pyrolysis units, a better understanding of stakeholders’ requirements and perspectives is needed. This is a complex decision problem. Due to the diversity of perspectives, each group of stakeholders has their own unique requirements, which in total will determine the right manufacturing approach. Previous studies either investigated optimal sizing from a single viewpoint or have combined a subset of perspectives. This study applies multiple tools to develop a more comprehensive view of stakeholders’ perspectives. Individual subject matter experts were asked to review and prioritize a set of requirements that reflected different stakeholders’ perspectives, including economic, environmental, technical, social, and legal. The perspectives were then used to analyze multiple fast pyrolysis units to determine which size was the most effective in meeting the perspectives in total. The analysis indicated that the smallest unit, able to process an average of 50 tons per day, is the best alternative when viewed from the economic, technical, social, and legal perspectives. However, when viewed from the environmental perspective, a medium-sized unit, able to process in the range of 200–500 tons per day, is the best alternative. This work provides the basis for further discussions about the individual perspectives, including the economic and environmental perspectives of biofuel production. Potential avenues for further work in assessment of stakeholders’ requirements are also noted.     

OXYGEN LIMITATION IN MICROFLUIDIC BIOFUEL CELLS

Biofuel cells are devices that use biocatalysts (enzymes or microbes) to convert biochemical energy directly into electrical energy. Microfluidic biofuel cells exploit the lack of active mixing at microscale dimensions to eliminate the use of proton exchange membranes that separate anolyte and catholyte streams. Simulation of this system, by solving the governing 3-D conservation equations (flow, species transport), reveals that oxygen availability limits the performance of the cathode. An exponential decay in the availability of oxygen at the cathode is observed along the length of the microchannel, indicating that increasing the number of electrode pairs reduces the overall current density. This conclusion is consistent with experimental observations. Increasing electrolyte flow rates can reduce the mass transport limitations by decreasing the diffusion boundary-layer thickness, but disparity between the flow rates of the anolyte and catholyte can induce wastage of dissolved oxygen.     

Cob biomass supply for combined heat and power and biofuel in the north central USA

Corn (Zea mays L.) cobs are being evaluated as a potential bioenergy feedstock for combined heat and power generation (CHP) and conversion into a biofuel. The objective of this study was to determine corn cob availability in north central United States (Minnesota, North Dakota, and South Dakota) using existing corn grain ethanol plants as a proxy for possible future co-located cellulosic ethanol plants. Cob production estimates averaged 6.04 Tg and 8.87 Tg using a 40 km radius area and 80 km radius area, respectively, from existing corn grain ethanol plants. The use of CHP from cobs reduces overall GHG emissions by 60%–65% from existing dry mill ethanol plants. An integrated biorefinery further reduces corn grain ethanol GHG emissions with estimated ranges from 13.9 g CO₂ equiv MJ⁻¹ to 17.4 g CO₂ equiv MJ⁻¹. Significant radius area overlap (53% overlap for 40 km radius and 86% overlap for 80 km radius) exists for cob availability between current corn grain ethanol plants in this region suggesting possible cob supply constraints for a mature biofuel industry. A multi-feedstock approach will likely be required to meet multiple end user renewable energy requirements for the north central United States. Economic and feedstock logistics models need to account for possible supply constraints under a mature biofuel industry.     

Comparison of Lipid Extraction from Microalgae and Soybeans with Aqueous Isopropanol

The extraction efficiency of microalgae lipids with aqueous isopropanol (IPA) was investigated and compared with the extraction of oil from full-fat soy flour. The effects of the type of microalgae (Scenedesmus sp. and Schizochytrium limacinum), cell rupture, and IPA concentration on the yield of oil and non-lipid biomass were determined. The oil yield from intact cells of Scenedesmus was 86–93 % with 70, 88, or 95 % (by wt) IPA. Ultrasonic cell rupture prior to oil extraction decreased the oil yield of Scenedesmus to 74 % when extracting with 70 % IPA. The oil yield from intact cells of S. limacinum was <23 % regardless of the IPA concentration, but ruptured cells gave a 94–96 % oil yield with 88 or 95 % IPA. The different response of the two microalgae to extraction with IPA is possibly caused by differences in the cell wall structure and type and amount of polar lipids. The oil yield from soy flour with 88 and 95 % IPA was 93–95 %, which was significantly greater than yields with 50 and 70 % IPA. Cell rupture had no effect on soy flour extraction. In general, the oil yield from the ruptured cells of both microalgae and soy flour increased with increasing IPA concentration.     

Energy harvesting by implantable abiotically catalyzed glucose fuel cells

Implantable glucose fuel cells are a promising approach to realize an autonomous energy supply for medical implants that solely relies on the electrochemical reaction of oxygen and glucose. Key advantage over conventional batteries is the abundant availability of both reactants in body fluids, rendering the need for regular replacement or external recharging mechanisms obsolete. Implantable glucose fuel cells, based on abiotic catalysts such as noble metals and activated carbon, have already been developed as power supply for cardiac pacemakers in the late-1960s. Whereas, in vitro and preliminary in vivo studies demonstrated their long-term stability, the performance of these fuel cells is limited to the μW-range. Consequently, no further developments have been reported since high-capacity lithium iodine batteries for cardiac pacemakers became available in the mid-1970s. In recent years research has been focused on enzymatically catalyzed glucose fuel cells. They offer higher power densities than their abiotically catalyzed counterparts, but the limited enzyme stability impedes long-term application. In this context, the trend towards increasingly energy-efficient low power MEMS (micro-electro-mechanical systems) implants has revived the interest in abiotic catalysts as a long-term stable alternative. This review covers the state-of-the-art in implantable abiotically catalyzed glucose fuel cells and their development since the 1960s. Different embodiment concepts are presented and the historical achievements of academic and industrial research groups are critically reviewed. Special regard is given to the applicability of the concept as sustainable micro-power generator for implantable devices.     

Dark and acidic conditions for fermentative hydrogen production

Bacterial consortium capable of producing hydrogen in low pH (LpH) range of 3.3–4.3 is reported in this study. This operational pH is two full units below that of previously reported hydrogen producing organisms. Low pH inocula were derived from a batch biohydrogen reactor inoculated with heat treated compost (∼120 °C, 2 h), which was allowed to accumulate biogas to reach three atmospheres of equivalent headspace pressure and system pH of 3.0. Acclimation effect had positive influence on H₂ production and LpH inocula were passed sequentially into more than 15 generations to achieve consistent conversion efficiency and hydrogen composition, further tested in 23 other culture cycles. With hydrogen composition in the headspace ranging from 50% to 60%, conversion efficiency of ∼43% achieved in LpH systems is comparable to that of other buffered systems. Feasibility of hydrogen production in LpH systems is demonstrated in unbuffered reactors under intermittent pressure release conditions and in absence of initial pH adjustment and stirring. Conversion efficiencies, however, decreased by ∼1-fold for each 3 °C drop below the optimum temperature of 22 °C.     

Microfluidic fuel cells: A review

A microfluidic fuel cell is defined as a fuel cell with fluid delivery and removal, reaction sites and electrode structures all confined to a microfluidic channel. Microfluidic fuel cells typically operate in a co-laminar flow configuration without a physical barrier, such as a membrane, to separate the anode and the cathode. This review article summarizes the development of microfluidic fuel cell technology, from the invention in 2002 until present, with emphasis on theory, fabrication, unit cell development, performance achievements, design considerations, and scale-up options. The main challenges associated with the current status of the technology are provided along with suggested directions for further research and development. Moreover, microfluidic fuel cell architectures show great potential for integration with biofuel cell technology. This review therefore includes microfluidic biofuel cell developments to date and presents opportunities for future work in this multi-disciplinary field.     

Simultaneous antibiotic degradation,nitrogen removal and power generation in a microalgae-bacteria powered biofuel cell designed for aquaculture wastewater treatment and energy recovery

A novel microalgae-bacteria powered biofuel cell (MBBFC) is designed for aquaculture wastewater treatment and energy recovery, in which algal-bacterial cooperation coupling with cathodic bioelectrochemiccal process for efficient nitrogen removal while simultaneously driving anodic bioelectrochemical degradation of antibiotic florfenicol (FLO) with instantaneous electrons uptake from co-substrate. 100 mg/L of ammonia nitrogen is removed completely within 90 h in the algal-bacterial biocathode of MBBFC, mainly attributed to the activity of ammonia oxidizers in the presence of photosynthetic oxygen and the resultant nitrate/nitrite are acceleratively removed by the cathodic bioelectrochemical denitrification. The antibacterial activity of FLO is eliminated through anodic bioelectrochemical enhanced co-metabolic reductive dehalogenation. The feeding 0.5 mg/L of FLO to the anode promotes the growth of Pseudomonas species, which results in a 3.2-fold increase in power output. FLO diffused from the anode to the cathode can exert a selection pressure to the cathodic bacterial community and thereby affecting the nitrogen removal performance of the microalgal-bacterial cathode. The MBBFC shows a great potential for aquaculture wastewater treatment with simultaneously bioelectrical energy recovery.