Under typical proton exchange membrane fuel cell (PEMFC) operating conditions, temperature gradients through the porous gas diffusion layer (GDL) can result in product water condensation. As a ...result, non-uniform partial saturation of the GDL changes the local effective porosity and tortuosity encountered by oxygen diffusing to the catalyst layer. This additional transport resistance reduces the partial pressure of oxygen at the catalyst surface of an air-fed cathode. In the current work, this phenomenon is investigated in two-dimensions using limiting current experiments that define GDL boundary conditions along with simultaneous neutron imaging to measure the local water content relative to the flow field geometry. The subsequent effective diffusion coefficient vs. saturation relationship derived from this method is reported for two common GDL carbon fiber substrates. It is also shown that the land vs. channel distribution of liquid water must be accounted for to accurately predict diffusion resistance. These results represent the first time that the effect of water saturation on effective diffusion coefficient has been directly measured in situ, thus enabling accurate determination of the exponent “n” in the modified Bruggeman relationship for two commercially available gas diffusion layer materials.
Anaerobic digestion (AD) is widely considered a more sustainable food waste management method than conventional technologies, such as landfilling and incineration. To improve economic performance ...while maintaining AD system stability at commercial scale, food waste is often co-digested with animal manure, but there is increasing interest in food waste-only digestion. We investigated the stability of anaerobic digestion with mixed cafeteria food waste (CFW) as the main substrate, combined in a semi-continuous mode with acid whey, waste bread, waste energy drinks, and soiled paper napkins as co-substrates. During digestion of CFW without any co-substrates, the maximum specific methane yield (SMY) was 363 mL gVS−1d−1 at organic loading rate (OLR) of 2.8 gVSL−1d−1, and reactor failure occurred at OLR of 3.5 gVSL−1d−1. Co-substrates of acid whey, waste energy drinks, and waste bread resulted in maximum SMY of 455, 453, and 479 mL gVS−1d−1, respectively, and it was possible to achieve stable digestion at OLR as high as 4.4 gVSL−1d−1. These results offer a potential approach to high organic loading rate digestion of food waste without using animal manure. Process optimization for the use of unconventional co-substrates may help enable deployment of anaerobic digesters for food waste management in urban and institutional applications and enable increased diversion of food waste from landfills in heavily populated regions.
Food processing operations produce large amounts of waste that are rich in nutrients, and although these wastes are utilized to produce value-added products to some extent, the majority of the waste ...is discarded. This paper provides a comprehensive review of the characteristics of food processing waste for micro- and macro-nutrient composition, and utilization of these materials in alcohol production. The feasibility of producing alcohols, mainly ethanol and butanol, was investigated while identifying the research gaps and suggesting future directions for food processing waste utilization. Ethanol and 1-butanol are the most studied alcohols produced by fermentation of food processing wastes. Methanol is used to a much lesser extent as fuel and produced using chemical conversion methods. Propanol and isobutanol from fermentation of food processing waste are gaining interest more recently, and there are fewer published articles on these products. Alcohols have high market demand as fuels and industrial solvents. Effective utilization of food processing wastes in alcohol production can significantly affect the production economics by not having a need to grow crops for raw materials or acquiring biomass at a high cost. Although theoretically alcohol production from food processing waste appears to be feasible, the technology still has to overcome several constraints.
•Commercial food waste shows potential for anaerobic mono- or co-digestion.•Bio-methane potentials (BMP) ranged from 165 to 496mL CH4/g VS (13–414m3 CH4/t).•Co-digestion resulted in BMP close to ...weighted average of individual substrates.•Hydrolysis rate coefficients increased for co-digestion over individual substrates.•Macro-composition in itself is not sufficient to explain process kinetics.
Anaerobic digestion of commercial food waste is a promising alternative to landfilling commercial food waste. This study characterized 11 types of commercial food wastes and 12 co-digestion blends. Bio-methane potential, biodegradable fraction, and apparent first-order hydrolysis rate coefficients were reported based upon biochemical methane potential (BMP) assays. Food waste bio-methane potentials ranged from 165 to 496 mL CH4/g VS. Substrates high in lipids or readily degradable carbohydrates showed the highest methane production. Average bio-methane potential observed for co-digested substrates was −5% to +20% that of the bio-methane potential of the individual substrates weighted by VS content. Apparent hydrolysis rate coefficients ranged from 0.19d−1 to 0.65d−1. Co-digested substrates showed an accelerated apparent hydrolysis rate relative to the weighted average of individual substrate rates. These results provide a database of key bio-digestion parameters to advance modeling and utilization of commercial food waste in anaerobic digestion.
Many food manufacturers in the U.S. are attempting to reduce the environmental footprint of their high biological oxygen demand (BOD) effluents due to increased risk of financial surcharges from ...publically owned treatment works, water scarcity issues and changes in societal opinions about large scale biodegradable waste releases. Managers at these firms are often reluctant to consider on-site processing due to their fear of committing to unfamiliar and complex wastewater treatment processes with excessive capital expenditures. While an abundance of research has been performed on the use of biochar (i.e. charcoal intended to be used for agricultural purposes produced from organic waste feedstocks via pyrolysis) to mitigate the problem of heavy metal ions from traditional manufacturing effluents by filtration, little is known on biochar's potential to treat high BOD industrial aqueous food wastes. This paper attempts to fill this gap by gauging the environmental and financial sustainability of a vertically integrated biochar filtration system, wherein maple wood biochar is used to treat high BOD tofu whey effluent and subsequently re-utilize that material as an enriched value-added soil amendment to improve crop quality and yields in basil and lettuce. Results show whey filtered biochar significantly increased fresh weight in basil and lettuce above the no biochar and unfiltered biochar controls. This novel approach could potentially help food and beverage manufacturers sustainably reduce their carbon and water footprints by harvesting and monetizing the nutrients found in their wastewaters, while allowing farmers to close regional nutrient cycles by returning nutrient rich carbon to the soil and reduce the use of synthetic fertilizers or costly peat moss or perlite soil amendments in greenhouses.
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•A system to recycle nutrients from food processing effluents with biochar is proposed.•The system exploits biochar's ability to increase fresh weight in greenhouse crops.•Filtered biochar greatly increased yields in greenhouse grown basil and lettuce.•The maximum price biochar could be to growers of basil and lettuce was calculated.•The estimated value of biochar to growers is significantly above the average price.
The management of liquid water from either internal chemical reactions or externally humidified reactants is an important design consideration for proton exchange membrane (PEM) fuel cells because of ...the effects on both cell performance and durability. To achieve proper water management, significant effort has been devoted to developing new fuel cell materials, hardware designs, and appropriate stack operating conditions. However, water management in the region of the channel-to-manifold interfaces has received limited attention. This region covers the ends of the bipolar plate from where liquid water exits the active area to the entrance of the stack exhaust manifolds where excess reactant flows from individual cells are combined and leave the stack. For practical applications, there is a small driving force to expel liquid water in this region, especially in the anode flow field. Under severe operating conditions such as freezing temperatures, the buildup of water may cause a channel-scale blockage. In this study, hydrophilic and hydrophobic bipolar plate treatments were investigated to identify the effectiveness of water mitigation through ex-situ experiments performed using a dedicated freeze test rig. Water mitigation behavior with various locations of hydrophilic/hydrophobic coatings was characterized using measurements of differential pressure and gas flow rate. It was found that the hydrophilic coatings provide better performance, as water accumulation can be readily mitigated with less potential to cause full channel-scale blockages.
•Surface energy modifications can alter bipolar plate water accumulation behavior.•Hydrophobic and hydrophilic coatings tested on the non-active outlets region.•Hydrophilic provides greatest benefit, may be effective in simplifying start-up.
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► Feedstocks to produce bio-fuels for a solid oxide fuel cell auxiliary power unit. ► Energy and GHG emissions assessed through thermodynamic analysis and LCA. ► Optimal bio-fuel ...pathway in NY State is compressed natural gas from landfills.
A methodology that integrates life cycle assessment (LCA) with thermodynamic analysis is developed and applied to evaluate the environmental impacts of producing biofuels from waste biomass, including biodiesel from waste cooking oil, ethanol from corn stover, and compressed natural gas from municipal solid wastes. Solid oxide fuel cell-based auxiliary power units using bio-fuel as the hydrogen precursor enable generation of auxiliary electricity for idling heavy-duty trucks. Thermodynamic analysis is applied to evaluate the fuel conversion efficiency and determine the amount of fuel feedstock needed to generate a unit of electrical power. These inputs feed into an LCA that compares energy consumption and greenhouse gas emissions of different fuel pathways. Results show that compressed natural gas from municipal solid wastes is an optimal bio-fuel option for SOFC-APU applications in New York State. However, this methodology can be regionalized within the U.S. or internationally to account for different fuel feedstock options.
'Sustainable Food Waste-to-Energy Systems' assesses the utilisation of food waste in sustainable energy conversion systems. It explores all sources of waste generated in the food supply chain ...(downstream from agriculture), with coverage of industrial, commercial, institutional and residential sources. It provides a detailed analysis of the conventional pathways for food waste disposal and utilisation, including composting, incineration, landfilling and wastewater treatment.
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