Landfills are physical facilities used for the disposal of residual solid wastes in the surface soils of the earth. Historically, landfills have been the most economical and environmentally acceptable method for the disposal of solid wastes, both in the United States and throughout the world. Even with the implementation of waste reduction, recycling, and transformation technologies, nearly all of the residual solid waste in the United States today is deposited in landfills. Further­more, landfills are not going to disappear, rather they will continue to be an important component of solid waste management strategy far into the twenty- first century.

Landfills produce a large amount of gas. Anaerobic decomposition of the biodegradable portion of the municipal solid waste produces methane and carbon dioxide in roughly equal amounts. These two principal components, together with atmospheric nitrogen and oxygen and trace organic compounds, comprise landfill gas, LFG. According to the Environmental Protection Agency (EPA) Landfill

Methanol Outreach Program (LMOP) statistics, each pound of organic waste biodegrades into 10 to 12 standard cubic feet of gas during its landfill residence of approximately 25 years. Modest size landfills produce one to five million standard cubic feet of landfill gas daily. By way of example, one of the largest landfills in the United States, Fresh Kills, Staten Island, NY, produces more than 30 million cubic feet of landfill gas daily. Landfill gas generation increases while the landfill is active and decays three to five percent annually beginning several years after the landfill is closed. Significant landfill gas is generated for up to 25 years after closure of the landfill.

The 1986 Clean Air Act (CAA) requires that landfills containing over 2.5 million tons of municipal solid waste be required to collect and flare the landfill gas in order to prevent methane migration and control the odor associated with the landfill. This requirement helps prevent methane migration, which contributes to local smog and global climate change. Methane will try and escape into the atmosphere from the landfill either through fissures in the lining of the landfill or through the surface cover. Landfills are the largest human-related source of methane in the United States, accounting for about 34% of all methane emissions. The amount of methane created depends on the quantity and moisture content of the waste and the design and management and environmental practices of the landfill.

In order to comply with the CAA, LFG is extracted from the landfill by an engineered system of liners, pipes, wells, wellhead monitors, and a vacuum system to move the collected gas to a metering device and then to the constant temperature flare. Significant amounts of landfill gas that are now flared could be utilized for economically viable projects. The EPA estimates that there are between 800 and 1000 domestic landfills that are currently flaring landfill gas that could be converted to energy and energy-related projects, thereby reducing dependence on fossil energy. Methane vented or flared from existing U. S. landfills was estimated by the LMOP in 2001 to equal about 5% of domestic natural gas consumption or about 1% of domestic total energy needs.

Landfill gas is similar to low-quality natural gas in that it requires the removal of the volatile organic contaminants and the CO2 to realize substantial commercial value. Landfill gas contaminants challenge separation technology because the potential contaminants can number in the hundreds of chemical compounds and various toxic species such as vinyl chloride and hydrogen sulfide. Additionally, no two landfills have the same contaminants and these contaminants are constantly changing over the gas production life of the landfill as the decomposition occurs.

The conventional uses of landfill gas to energy include electricity generation using internal combustion engines, turbines, micro turbines and fuel cells; direct use, which would include boiler, dryer, kiln, greenhouse, wastewater treatment; cogeneration, also known as combined heat, and power that enjoys the efficiency of capturing the thermal energy in addition to electricity generation; and alterna­tive fuels that include pipeline quality gas, compressed natural gas, liquefied natural gas, methanol, and hydrogen.

Landfill ownership is either public or private. Solid waste disposal firms generally own and operate the majority of the private landfills. Privately owned landfills tend to promote their gas resource and solicit buyers or users of the gas more aggressively than their public counterparts. The process of obtaining and acquiring landfill gas rights is essentially the same for either case. Such a process usually consists of the following: a review of the proposal by the owner or appropriate public officials, the negotiation of the business plan and definition of responsibilities and liabilities, and an execution of a contractual agreement gov­erning the gas rights, responsibilities of the parties, term of the agreement, price for the gas, and other details of mutual concern.

Establishing a price for landfill gas and other project considerations requires the examination and negotiation of many factors, including but not limited to the following:

• Amount of landfill gas available and the projections of future gas generation rates.

• Gas composition or gas quality.

• Environmental regulations and permits required.

• Ownership of gas collection system and responsibility for its mainte­nance.

• Competing prices for natural gas and electric in the area.

• IRS Section 29 tax credit availability.

• Building permits and access to landfill.

• Local air quality conditions and regulations.

The IRS Section 29 tax credits were an attempt to provide a financial incentive for the utilization of the landfill gas for energy projects. The IRS Code provided for a $1.05 per million BTU tax credit to a landfill gas developer if such an energy project were started prior to June 30, 1998. These tax credits will expire on December 31, 2007, and no longer provide financial incentive to promote tradi­tional landfill gas to energy projects.

Two methods have been developed for capturing the protein-rich fraction from alfalfa and separating it from the more fiber-rich fraction. From whole field-dried plant material, leaves can be separated from denser stems using shaking screens (Arinze et al., 2003; Downing et al., 2005). Fresh material can be dried using a rotary drum drier and leaves separated aerodynamically due to their lower mass and faster drying time than that of stems (Arinz et al., 2003). Wet fractionation involves mechanical maceration of fresh total herbage followed by the expression of protein-rich juice (Jorgensen and Koegel, 1988; Koegel and Straub, 1996). Approximately 20-30% of the herbage DM can be captured in the juice (Koegel and Straub, 1996). The proportion of DM that was captured in the juice was shown to decrease with increasing maturity of the herbage (Koegel and Straub, 1996). The juice contains both particulate and soluble proteins. The soluble proteins, which may have greater value, can be separated from particulate proteins by heating and centrifugation (Jorgensen and Koegel, 1988). Wet fractionation has been used successfully in small-scale experiments (see “Pretreatment of Alfalfa Fiber” below) to refine alfalfa into a high-value protein fraction and a fiber fraction that was further refined and fermented to produce ethanol (Koegel et al., 1999; Sreenath et al., 2001), lactic acid (Koegel et al., 1999), and wood adhesive (Weimer et al., 2005). Fiber can also be processed into animal feed. The deproteinized juice is a source for extracting xanthophyll and can also be used as a fertilizer (Koegel and Straub, 1996). Wet fractionation has the advantage of minimizing leaf loss and is less weather dependent than field drying. Dried material has the advantage of being lighter to transport and is easily stored for later processing and refining. The nature of the protein product will clearly impact the method of herbage harvest and processing.

In addition to protein, alfalfa also contains numerous secondary metabolites that are of interest in human nutrition and food production. In particular, alfalfa is a rich source of flavonoid antioxidants and phytoestrogens including luteolin, coumestrol, and apigenin (Hwang et al., 2001; Stochmal et al., 2001) that have possible health-promoting activities. Alfalfa foliage also contains high amounts of xanthophylls, which are added to chicken feed to pigment egg yolks and broiler skin (Koegel and Straub 1996). Thus, in a biorefinery model for alfalfa processing, ethanol would be one of several products produced with the protein component possibly the more valuable and economically important product.

Table 8.1 compares the physical properties of E85 and gasoline. The property differences that exert the most influence on vehicle performance are: octane, energy density, Reid vapor pressure, stoichiometric A/F mixture, heat of vapor­ization, and flammability limits. The effects of these different properties are described below.

Fuel Economy

The energy density on a mass basis for E85 is only about 68% of the level for gasoline. Fortunately, the specific gravity of E85 is slightly greater than that for gasoline leading to an E85 energy density of 71% of that for gasoline on a volume basis. Therefore, in order to achieve the same level of power, and assuming no change in engine efficiency, a vehicle operating on E85 would have to consume about 1.4 times as much fuel on a volume basis. This would lead directly to a 29% loss in fuel economy. However, in practice, this reduction is limited as the E85 fuel burns more cleanly, and the engine calibration is adjusted to advance the spark timing, further improving engine efficiency.

Actual test values for FFVs are published by the U. S. federal government; a portion of this is shown in Table 8.3. This data reveals an average loss of about 25% in fuel economy on both the federal highway and city tests when going from gasoline to E85 in FFVs.16 It is interesting to note that the test data reveal losses as high as 29% and as low as 20%, demonstrating the effect that proper engine

calibrations can have when using E85 with the same FFV. Other sources have suggested lower losses in fuel economy (miles per gallon) of only a 5% to 12% during real-world driving conditions.13

A dedicated E85 vehicle could perform better by taking advantage of the higher octane of E85 compared to gasoline. As shown in Table 8.1, E85 enjoys about a 10% advantage in octane rating. Studies have shown that engines could then be designed with higher compression ratios, increasing their operating effi­ciency by up to 10%.14 This efficiency, coupled with the increased power extrac­tion during the expansion stroke of the engine due to the increased volume of the combustion products results, in a total efficiency increase of up to 15% compared to gasoline engines. If vehicles were designed to take full advantage of E85, they would probably experience a fuel economy penalty of about 14% on a volume basis when compared with a gasoline powered vehicle. Although it is important to note that engine calibrations, as shown earlier, can have a dramatic impact upon this value.

In conclusion, it is important to note that the actual energy efficiency for vehicles using E85 is higher than those using gasoline; however, the fuel economy, expressed on a miles-per-gallon basis, is lower due to the lower energy density of E85 on a volumetric basis. Thus, it is environmentally beneficial to use E85 even though its use will probably result in higher fuel usage on a volumetric basis.

The bioanode of the biofuel cell is the electrode at which the fuel is utilized by enzymes to produce electrons and protons, which are then utilized by enzymes of biocathodes to reduce O2 to H2O. Alcohol-based enzymatic systems that have been chosen most frequently for the bioanode involve NAD+-dependent alcohol dehydrogenase (ADH), which oxidizes alcohols to aldehydes. This enzyme can be employed with aldehyde dehydrogenase to further oxidize the aldehyde. Lit­erature reports of alcohol biofuel cells are limited to only two alcohol-based enzymatic schemes. They are for methanol and ethanol and are shown in Figure 12.6. Methanol is oxidized to formaldehyde by alcohol dehydrogenase and then the formaldehyde is oxidized to formate by formaldehyde dehydrogenase. The formate is completely oxidized to carbon dioxide by formate dehydrogenase. The ethanol system involves oxidizing ethanol to acetaldehyde by alcohol dehydro­genase and then oxidizing the acetaldehyde to acetate by aldehyde dehydrogenase.

All of these enzymatic systems require NAD+ as a coenzyme/cofactor and the reduced form (NADH) is the hydrogen source at the electrode surface. How­ever, NADH has a high overpotential at most typical electrode surfaces (platinum, carbon, etc.), so an electrocatalyst layer is necessary to decrease the potential and increase the power output. The problem with electrocatalyst layers is that they are not as conductive as carbon or most metals and they add an extra complexity to the system that makes forming high surface area bioanodes difficult. A variety
of electrocatalysts have been used, but at this stage, there is no optimal electro­catalyst. Palmore and coworkers have employed a diaphorase/benzyl viologen system that has shown good thermodynamics properties, but poor lifetimes [13]. Minteer and coworkers have employed methylene green as the electrocatalyst layer due to its optimal electrocatatlytic properties. Poly(methylene green) pre­pared via electropolymerization has been shown to be an electrocatalyst for NADH [23].

The second problem with an NAD+-dependent bioanode is the instability of the NAD+/NADH couple in the membrane. When ethanol is oxidized to acetate, the NAD+ is converted to NADH. It is simple to electrostatically immobilize NAD+ in the bioanodes membrane, but NAD+ has a short lifetime in solution and a limited lifetime in the membrane. NAD+ is only stable in solution for a few hours, but it can be stabilized for up to 45 days in the membrane. Dehydrogenase enzymes are stable for much longer (>6 months) in the membrane, so it is necessary to employ a coenzyme that is stable for at least as long as the enzyme is stable.

Akers et al. have tested ethanol-based biofuel cells fabricated using bioanodes containing NAD+-dependent ADH immobilized in a modified Nafion® membrane as discussed above and cathodes formed from ELAT electrodes with 20% Pt on Vulcan XC-72 (E-Tek). These bioanodes can function for greater than 30 days [23]. The test cell contains an anode solution of 1.0 mM ethanol in pH 7.15 phosphate buffer and a cathode solution containing pH 7.15 phosphate buffer saturated with dissolved oxygen. The two solutions are separated by a Nafion® 117 membrane. The ethanol-based biofuel cells have had open-circuit potentials ranging from 0.61 to 0.82 V at 20°C and have maximum power densities of 1.12 mW/cm2 [23]. This is a 16-fold increase in power density versus the state-of-the — art biofuel cell developed by Heller and co-workers [24]. The milestone that was required to further develop a biofuel cell is to eliminate the need for the electro­catalyst layer, poly (methylene green). This will be done by replacing NAD+- dependent ADH with PQQ-dependent ADH.

Through the use of kelp meal and solar-evaporated sea salt as ingredients in the fish feed we make, we directly add microelements to the food we are producing. The microelements remain available to the plants since there is no leaching, as in the case with soil culture. New feed each day adds more microelements to the system and thereby maintains the availability for plants and fish alike. Different vegetables have different micronutrient signatures that are made available to us when we eat these vegetables. Providing a broad range of micronutrients to the young growing plants gives each plant the opportunity to reach its full potential micronutrient signature. For instance, it is a commonly held belief that spinach has iron in it — which it does. However, it has only 10% of the iron in it than it had in 1948. As a result, you would need to eat 10 bowls of spinach today to equal the nutritional value of 1 bowl of spinach grown in 1948 (source: Internet search, Google, “bowl of spinach”).

Given the above information — which I have witnessed personally — it is my belief that aquaponics — supported by green energy — will become a major

provider of high-micronutrient-content food, not only in northern climates, but also in more temperate regions of the world, where wintertime heating and lighting are not a factor. In short, our breathless, visionless, juvenile, and (oh, call it not rabid) love affair with petroleum will not last forever. The resource is simply not infinite. Considering our enormous dependence on petroleum, if the last barrel of oil were sold today, what would we do tomorrow?

The BCL gasifier is indirectly heated by a heat transfer mechanism as shown in Figure 2.3. Ash, char, and sand are entrained in the product gas, separated using a cyclone, and sent to a second bed where the char or additional biomass is burned in air to reheat the sand. The heat is transferred between the two beds by circulating the hot sand back to the gasification bed. This allows one to provide heat by burning some of the feed, but without the need to use oxygen, because combustion and gasification occur in separate vessels.

Because of the atmospheric pressure, the BCL gasifier produces a gas with a low CO2 content, but consequently containing a greater number of heavier hydrocarbons. Therefore, tar cracking and reforming are logical subsequent steps in order to maximize CO and H2 production. The reactor is fast fluidized allowing throughputs equal to the bubbling fluidized IGT, despite the atmospheric opera­tion. The atmospheric operation decreases cost at smaller scale, and the BCL has some commercial experience (demo in Burlington, VT (Paisley et al. 1998)). Because biomass gasification temperatures are relatively low, significant depar­tures from equilibrium are found in the product gas. Therefore, kinetic gasifier modelling is complex and different for each reactor type (Consonni et al. 1994;

Li et al. 2001). The main performance characteristics of both gasifiers are given in Table 2.1.

Corn is received at the plant and separated from the chaff, and the kernels are milled to a coarse flour. Particle sizing is a compromise between grinding fine enough to provide increased surface area (to make starch granules available for swelling and hydrolysis), yet large enough to allow separation of residual solids from the liquid. The corn meal is mixed with water, and the resulting mash is adjusted to pH 6 and then mixed with alpha-amylase. The mash is heated above 110°C in a jet cooker using direct steam. A jet cooker is in essence a pipe with a narrowing and a steam inlet directly upstream. The narrowing is carefully engineered to provide maximum mixing of the starch slurry with steam, and also to cause shearing, which aids in thinning the starch. Upon exiting the jet cooker, the corn slurry enters a holding column where the mixture is kept at 110°C for 15 minutes. From the holding column, the slurry enters a flash tank at atmospheric pressure and 80-90°C. Additional alpha-amylase is added and the mash is lique­fied for approximately 30 minutes. The jet cooking and liquefaction steps break apart the starch granules and reduce the size of the polymers. The shorter mole­cules, termed dextrins, contain approximately five to ten glucose molecules [21]. Subsequently, the liquefied mash is cooled to 32°C and the pH is lowered to 4.5-5.0 using phosphoric acid and recycled backset from the bottom of the ethanol distillation column.

Fermentation

Dry yeast is hydrated or conditioned and then added to the mash along with glucoamylase, to initiate simultaneous saccharification and fermentation (SSF). Glucoamylase cleaves the dextrins at a-1,4-glucosidic linkages, releasing glucose and maltose for yeast fermentation. The SSF process reduces the extent of micro­bial contamination because glucose is consumed by yeast as it is formed. The SSF process also reduces osmotic stress, because the yeast cells are exposed to a relatively lower sugar concentration. The dry-grind ethanol fermentation process lasts for 48 to 72 h and yields approximately 2.7 gallons of ethanol per bushel of corn.

Due to the toxic nature of butanol, the initial substrate concentration is limited to <80 gL-1 (usually 60 gL-1). A substrate concentration in excess of this results in a high residual substrate, thus resulting in inefficient sugar utilization and increased BOD (biological oxygen demand) load for wastewater treatment. How­ever, recent developments in downstream processing (recovery) of ABE have made it possible to use concentrated sugar solutions for this fermentation. During the fermentation, the toxic products are removed simultaneously, thus relieving inhibition that results in the utilization of more substrate. The details of the recovery techniques are given in the recovery section (3.1). Employing butanol removal techniques, sugar solutions containing 161 gL-1 glucose (C. beijerinckii; Ezeji et al., 2003) and 227 gL-1 lactose (C. acetobutylicum; Qureshi and Maddox, 2005) have been successfully used. Use of concentrated glucose and lactose solutions has resulted in the production of 76 and 137 gL-1 ABE, respectively. In such fermentations, fewer acids are produced, thus improving the ABE yield. In another process, 200 gL-1 lactose was successfully fermented in a batch reactor of C. acetobutylicum when integrated with product recovery by gas stripping (Maddox et al., 1995). This system resulted in the production of 70 gL-1 ABE with a productivity of 0.32 gL-1h-1 as compared to 0.07 gL-1h-1 in the control batch reactor. Studies reported in this section demonstrated that a fermentation medium containing over three times the sugar concentration as compared to a batch reactor can be successfully fermented when integrated with product removal techniques.

The following section cites selected studies aimed at optimizing the performance of DMFCs through careful variation of design, materials, and operating condi­tions. An excellent study of a wide range of experimental conditions is presented first, then issues of cathode flooding, electrolyte/electrode contact, parasitic power loss associated with fuel pumping, electrode design, and CO2 bubble formation are considered.

A systematic study by Liu and Ge varied operational parameters such as cell temperature, methanol concentration, anode flow rate, air flow rate, and cathode humidification, and showed that changing any one of the parameters has a pro­nounced effect on the performance of the DMFC [30]. However, varying cathode humidification has negligible impact on DMFC performance. The range of param­eters evaluated are listed in Table 9.4. In general, higher cell temperatures lead to better DMFC performance; however, other processes that diminish cell performance as temperature increases such as methanol crossover and water transfer from cathode to anode set a limit on optimum performance. The study found the optimal methanol solution to have a concentration between 1 and 2 M. This is in general agreement with other studies that found the optimum concen­tration to be 2.0 M [5] and 2.5 M [31] for DMFCs run under similar operating conditions. Methanol crossover from the anode to the cathode can be minimized by increasing either the cathode air flow rate or oxygen partial pressure. The work suggests that the cathode structure and operating conditions play a major role in DMFC performance. The reference by Liu and Ge contains a large amount of data, both plotted and tabulated, and is a useful resource for making comparisons of DMFC performance over a range of conditions.

For DMFCs power plants, performance degradation occurs when water builds up at the cathode. Knights et al. describe a load-cycling strategy to reduce cathode flooding [27]. By removing the load of the DMFC for 30 seconds of every 30 minutes of operation, the rate for performance degradation is shown to be 13 pV hr-1 over 2000 hr of failure-free operation, which is in the low range of the typical performance degradation rate of 10 to 25 pV hr-1.

The use of solid PEMs such as Nafion prevents electrolytes from fully envel­oping the electrode as liquid electrolyte does. This limits the reaction area to points of direct contact between membrane and electrode. To increase the reactive area, Nafion suspension is often compounded directly into the catalyst layer. Sudoh et al. use the spray method to optimize the electrochemical characteristics of the catalyst layer [37]. The spray method consists of introducing a catalyst to the electrode surface and then spraying Nafion over the catalyst. Three Nafion loadings are considered: 0.5, 1.0, and 3.5 mg cm-2. The resulting electrodes are incorporated into DMFCs and the performance measured. The cell made with catalyst layers having a Nafion loading of 1.0 mg cm-2 performed the best producing 258 mA cm-2 at 0.4 V. The cell made from electrodes with 0.5 mg cm-2 Nafion loading generated roughly half the current and the cell with the highest Nafion loading was resistive and performed poorly. The performance of the spray-coated, in-house DMFC is similar to that of commercially available ELAT® electrode with similar catalyst loading (0.5 mg cm-2). ELAT is the trademarked name of gas diffusion electrode material distributed by E-Tek, Inc. It is frequently used in PEFCs and DMFCs.

Zhang and Wang present a piezoelectric micropump design for delivering fuel to a miniaturized DMFC power source [39]. For low current densities (<100 mA cm-2) methanol concentrations between 0.5 M and 2.0 M do not significantly impact the power generated. The authors suggest their DMFC running at 40°C will have a maximum current density, or Jmax of 120 mA cm 2 at 0.35 V for a 1-W system where a 25 cm2 cell will be required. The estimated power consump­tion of their piezoelectric pump operating at 100 Hz, pushing 1 ml min-1 over the face of the cell is on the order of 70 mW, or 7% of the power produced by the cell, which compares well with other literature examples.

Typical DMFC anode structures consist of strata of a supported/unsupported catalyst bonded with a Nafion suspension over Teflon-bonded carbon black

TABLE 9.2 Survey of DMFC Performance Loading Anode Flow Ano. ((L ) ( ml ) Separator Catalyst cm2 / min f Naf. 117a Pt-Ru 1.0 1.0 Naf. 117 Pt-Ru 1.0 1.0 Naf. 117b Pt-Ru 2.0 2.0 Naf. 117 Pt-Ru 2.0 2.0 Naf. 117c Pt, Ru/C 2.0 n/a Naf. 117 Pt, Ru/C 2.0 n/a Naf. 117 PtRu 5.0 4.0 Naf. 105 PtRu 5.0 4.0 Polyaryld PtRu 5.0 4.0 Naf. 115e PtRu n/a n/a Naf. 115 PtRu n/a n/a Naf. 115 PtRu/NTf 0.4 2.0 Naf. 115 PtRu/C 0.4 2.0 Naf. 115 PtRu/NTf 0.4 2.0 Naf. 115 PtRu/C 0.4 2.0 Naf. 117 PtPu/C 2.0 3.0 sPEEK N/a n/a n/a Polymer11 N/a n/a n/a Polymer1 N/a n/a n/a Naf. 117 PtRu 3.0 6.0

Max. Power

Cath. Loading Cath. Flow Cath. I m I Press. ( ml ) Catalyst cm2 1 MPa min f Pt 1.0 0.1 75 air Pt 1.0 0.1 75 air Pt 2.0 0.1 500 O2 Pt 2.0 0.1 500 O2 Pt 2.0 0.1 n/a O2 Pt 2.0 0.1 n/a O2 Pt 6.0 0.4 1500 air Pt 6.0 0.4 1500 air Pt 6.0 0.4 1500 air Pt n/a n/a 300 O2 Pt n/a n/a 300 O2 Pt/C 0.4 0.1 80 O2 Pt/C 0.4 0.1 80 O2 Pt/C 0.4 0.3 80 O2 Pt/C 0.4 0.3 80 O2 Pt/Cg 2.0 0.2 350 O2 n/a n/a 0.3 n/a n/a n/a n/a n/a n/a n/a n/a n/a Pt 3.0 n/a 600 air

Cell T [MeOH] ImWA Potential (°С) M cm2 1 (mV) Ref. 23 1.0 2.8 180 [32] 23 1.0 0.9 160 40 2.0 36 380 [33] 40 2.0 26 100 95 2.0 82 390 [34] 95 2.0 32 360 110 1.0 120* 500 [24] 110 1.0 270* 500 110 1.0 230* 500 65 2.0 49 350 [35] 65 2.0 40 350 70 2.0 70 200 [36] 70 2.0 50 200 90 2.0 140 250 90 2.0 125 250 90 2.0 103* 400 [37] 120 n/a 140 n/a [38] 110 n/a 300 n/a 60 n/a 50 n/a 70 2.0 66 270 [30]t

a Membrane has 1-иш sputtered Pd-Ag film b Pd impregnated Nafion; 0.0214 g Pd/cm3 of Nafion c Pd sputtered membrane d Polyaryl blend of PEK, PBI, and bPSU e Nafion has 14% mass gain from polystyrene

f Multiwall carbon nanotube support with Fe — and Ni-contaminated catalyst g Cathode impregnated with 1.0 mg cm-1 Nafion ionomer h Sulfonated poly(4-phenoxybenzoyl 1,4-phenylene)

1 Sulfonated poly[bis(3-methylphenoxy) phosphazene]

j Power calculated from model based on Nafion 117 DMFC data [40] minus power needed to drive piezoelectric pump * Not necessarily maximum power. T Reference has performance data over wide range of conditions

TABLE 9.3 Survey of DMFC Performance Loading Anode Flow Loading Cath. Cath. Flow Max. Power Ano. ( ml ) Cath. Press. ( ml ) Cell T [MeOH] (mW Potential Separator Catalyst cm2 / min f Catalyst cm2 / MPa min f (°С) M cm2 1 (mV) Ref. Naf. 117 PtRu/C 1.0 12.0 Pt/C 1.0 0.1 1.0 air 90 1.0 64 300 [41] Naf. 117 PtRuk 1.0 12.0 Pt/C 1.0 0.1 1.0 air 90 1.0 58 250 Polymer1 Pt-Ru 4.0 25.0 Pt 4.0 n/a 3000 O2 80 1.0 316 722 [42] Naf. 115 Pt-Ru 4.0 25.0 Pt 4.0 n/a 3000 O2 80 1.0 309 696 Naf. 1135m-n Pt-Ru n/a n/a Pt n/a 0.08 n/a air 70 0.3 29 375 [43] Naf. 1135m-° Pt-Ru n/a n/a Pt n/a 0.08 n/a air 70 0.3 51 543 Nafionp Pt-Ru/C 2.0 n/a Pt/C 2.0 0.25 n/a O2 145 2.0 400 900 [44] Nafionp Pt-Ru/C 2.0 n/a Pt/C 2.0 0.05 n/a O2 145 2.0 200 485 Nafion Pt-Ru/C 2.0 n/a Pt/C 2.0 0.25 n/a O2 145 2.0 350 318 [45] Naf. 1154 Pt-Ru/C 1.3 1.0 Pt/C 1.0 0.2 160 O2 75 1.0 46 380 [29] Naf. 115r Pt-Ru/C 1.3 1.0 Pt/C 1.0 0.2 160 O2 75 1.0 66 560 Naf. 115s PtRu 3.0 5.0 Pt/C 3.0 0.1 250 air 80 2.0 70 507 [46] Naf. 115 PtRu 3.0 5.0 Pt/C 3.0 0.1 250 air 80 2.0 32 320 [46] Naf. 115 PtSn/C 1.3 1.0 Pt/C 1.0 0.2 n/a O2 90 1.0 17 150 [47] Naf. 115 PtRu/C 1.3 1.0 Pt/C 1.0 0.2 n/a O2 90 1.0 55 210 Naf. 115 Pt/C 2.0 1.0 Pt/C 1.0 0.2 n/a O2 90 1.0 136 335 Naf. 115 PtRu/C 1.0 2.5 Pt/TiO2/Ct 1.0v 0.27 2.5 O2 70 3.0 21 229 [48] Naf. 115 PtRu/C 1.0 2.5 Pt/TiO2/Cu 1.0v 0.27 2.5 O2 70 3.0 15 165 Naf. 115 PtRu/C 1.0 2.5 Pt/C 1.0 0.27 2.5 O2 70 3.0 12 177 Naf. 115 PtRu/C 2.0 1.0 PdPt/Cw 1.0 0.2 n/a O2 75 1.0 95 320 [49]

k Anode made from Ti mesh with electrodeposited catalyst layer 1 Membrane is 5-^m thick copolymer of TFE and ethylene

m MEAs made of half cells placed back to back so Nafion thickness between electrodes is 7 mil and potential listed for cell is iR corrected n MEA run as component of 22-cell DMFC stack for 6 months o Same cell as listed with “n” superscript prior to use in DMFC stack p 100-^m thick PEMs made from recast Nafion and 3 wt % SiO2 — PWA filler q Single-cell DMFC after 75-hour lifetime test

r Same cell as listed with superscript “q” superscript prior to 75-hour lifetime test s 1 wt % CeO2 doped cathode t Catalyst heat treated at 500°C u No heat treatment

v Listed value is Pt loading; Pt to Ti ratio of 1:1 w Ratio Pd to Pt is 3:1

x Ratio Fe to Pt is 1:1; Pt loading 1.0 mg cm-2

TABLE 9.4

Operating Conditions and Range over Which DMFC Performance is Evaluated

Parameter

Cell Temperature

Methanol Concentration

Cathode Humidification Temperature

Anode Flow Rate

Air Flow Rate

diffusion layer over carbon cloth or paper diffusion layer. This structure is an ineffectual design for the transport and release of CO2 gas produced by methanol oxidation and limits methanol transport to the anode. To remedy this problem, Scott et al. directly deposit PtRu catalyst onto a titanium mesh by electrodepo­sition and subsequent thermal decomposition and use the coated mesh as the anode [41]. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray diffraction analysis (XRD) are used to characterize the electrodes. Anodes are tested under galvanostatic control as well as in DMFCs. Galvanostatic testing shows the mesh and conventional anodes have similar electrochemical performance. This is somewhat unexpected given the very different morphologies of the strata and electrodeposits of electrode types. Tests using the anodes under working DMFC conditions mirror the performance of the anode tests. Catalysts loadings are in the range of 0.8-1.0 mg cm-2.

An often overlooked limitation in DMFC performance is CO2 bubble forma­tion in the anode. Kulikovsky developed a simple DMFC model to determine how anode channel bubble formation impacts cell performance [52]. Under con­ditions simulating typical operating conditions, the model suggests that moderate to severe bubble formation decreases the mean methanol concentration as it passes through the anode channel, limiting the current that can be drawn for the cell. Under severe bubbling conditions, the limiting current that can be drawn from the cell is diminished by as much as a factor of four. The author speculates that faster flow rates may help offset some performance losses due to bubble formation and offers some calculations to support his speculation, but he also cautions that kinetics of bubble formation are outside the scope of the model.

One greenhouse (501 x 156) will be used to house the alcohol fuel production equipment and fish feed equipment. It will be located separately from the aqua — ponic greenhouses. Site preparation has been completed for this greenhouse, as well as water supply and electric transmission lines. The water supply is from a developed artesian well, which will have its capacity expanded. The project will use bakery waste as the feedstock for alcohol since it is so plentiful locally. After packaging is removed, the production of fuel will follow these steps: A) the bakery waste is passed through a standard garden chipper-shredder, B) the shredded bakery waste is mixed with hot water in a tank, C) a liquefication enzyme is added and the mixture is boiled for about 20 minutes — this enzyme prevents the slurry from jelling, D) the mash is cooled to 140°F and a saccharification enzyme is added. It is held at this temperature for another 20 minutes. The saccharification enzyme converts starch to sugar, E) once starch conversion is complete, the mash is cooled to 90°F, adjusted for optimum yeast activity to occur (Ph and brix), and distillers yeast is added. A vapor lock is installed to eliminate contamination of the ferment by airborne putrescent bacteria. CO2 is captured at this stage, F) when yeast activity stops — from 3-5 days — the ferment is filtered to remove solids, and G) the clear liquid beer is now ready for distillation. Once distilled and denatured, it is ready for the microturbine to generate electricity and heat for the greenhouses. The solids that are generated will be mixed with other components, pelletized, and used as the base for fish feed. Packaging is sorted, compressed, and sold as scrap, or used as direct combustibles.