Biofuel Production Using Charcoal and CO2 to Transform Animal Fats

The need for renewable fuels is increasing as the fossil fuel crisis becomes more severe.  Animal fats, an inexpensive source of triglyceride, are a potential cost-effective feedstock for biodiesel production (Kwon et al. 2012).  However, animal fats, which contain up to 6 wt% of free fatty acids (FFA’s), must be pre-treated before undergoing conventional catalytic processes (Crabbe et al. 2001; Naik et al. 2008).  Without pretreatment steps, impurities in the feedstock will react with the catalysts and limit the biofuel yield by producing soap.  Kwon et al. aim to prove that an efficient non-catalytic biodiesel conversion using only charcoal and CO2is possible.  They determined the optimal conditions for this conversion, including temperature, pressure, and feeding ratio of raw materials.  Previous studies on non-catalytic conversion suggest an optimal temperature of 250 °C, a pressure of 10MPa or higher, and a methanol-to-oil molar ratio of 6:1.  In the present study, Kwon et al. determined optimal operating conditions for the conversion of animal fats to biodiesel to be at a temperature of 350500 °C under ambient pressure, and volumetric flow rates of extracted lipid and methanol (MeOH) to be 10 and 3 ml min1, respectively. Shelby Long
Kwon, E. et al., 2012. Transforming animal fats into biodiesel using charcoal and
CO2. Green Chemistry 14, 1799–1804.

                  Kwon et al. analyzed the production process of biodiesel by transforming animal fat into biodiesel using charcoal and CO2.  They obtained cooking oil from a local restaurant, beef tallow and lard from the local slaughterhouse, charcoal from the local market, and MgOCaO/Al2O3 that was generated from magnesium slag from a magnesium-smelting factory.  They determined the acid value (AV), an indicator of oil quality, with the following equation: AV = A x c x 56.11/m (A = volume of KOH solution use to titrate sample; c = concentrations of KOH solution; m = sample mass).  They first examined the non-catalytic biodiesel conversion of used cooking oil to biodiesel using a pressure reactor.  For this experiment they used MgOCaO/Al2O3 as a catalyst.  Kwon et al. carried out the experiment at a temperature of 130–250 °C and maintained pressure by filling the reactor with nitrogen (N2) and CO2.  To further examine the effect of temperature on the conversion process they replicated the previous experiment but varied the temperature from 250–500 °C.  Kwon et al. replicated the same experiment a third time, but added a virgin catalyst, activated Al2O3, in order to examine the catalytic element effect of MgO–CaO on the transesterification reaction.  For their main experiment, Kwon et al. tested the conversion of beef tallow and lard into biodiesel using charcoal.  They packed charcoal into an airtight reactor and maintained the temperature at 250–500 °C while oil feedstock, MeOH, and CO2 reaction medium were continuously added into the reactor.  The mixture was allowed to settle for 2 hours after the reaction before the contents were analyzed.
Kwon et al. achieved an approximately 98% biodiesel conversion rate of used cooking oil after 30 minutes.  This high conversion rate suggests that CO2 can enhance transesterification.  CO2 is believed to enhance the efficiency of the transesterification process by accelerating bond dissociations, also known as thermal cracking (Kwon et al. 2009).  By examining the biodiesel conversion of used cooking oil, Kwon et al. determined that the conversion rate is more responsive to changes in temperature than to pressure.  They also found that non-catalytic biodiesel conversion can be completed using porous materials. The pores, such as those in charcoal, act as small reactors, while the high temperature drives the transesterification reaction.  One of the main findings Kwon et al. observed was that under atmospheric pressure and a relatively high temperature, the conversion cost can be decreased by almost 70%, compared to standard commercial processes.
                  The researchers suggest that the mass decay of lard they observed at the comparatively low temperatures of 120–140 °C may be due to low molecular lipids and moisture in the lard.  Also, the thermal decomposition of lard was observed to be lower than that of beef tallow, which may be attributed to its lower amount of saturated fat.  In addition, they also found that the thermal degradation pattern for animal fats is similar to that of vegetable oil.  The biodiesel conversion efficiency of lard and beef tallow was almost identical at 400 °C.  There was no evidence of thermal cracking taking place in the experiment.
                  Kwon et al. achieved a conversion efficiency of beef tallow and lard into biodiesel of 98.5 (+ 0.5) % under ambient pressure and at temperatures higher than 350 °C.  They determined these to be the optimal operating conditions.  Based on their observations, the researchers assert that the production of biodiesel using charcoal and CO2 has the potential to be a highly cost-effective biofuel conversion process.
Other Sources
Crabbe, E., et al., 2001. Biodiesel production from crude palm oil and evaluation of butanol extraction and fuel properties. Process Biochemistry 37, 65–71.
Naik, M., et al., 2008. Production of biodiesel from high free fatty acid Karanja (Pongamia pinnata) oil. Biomass Bioenergy 32, 354–357.
Kwon, E., et al., 2009.  ASME Conference Proceedings, 231–236. 

The Use of Coffee Grounds for the Production of Biodiesel

In recent decades, the production and consumption of coffee has increased.  As a result of the increased consumption of coffee there is a need for waste management of the spent coffee grounds (SCG).  Spent coffee grounds have a very complex chemical composition, which makes them useful for a variety of applications.  SCG have a 1020 wt% of oil content, and, therefore, they are viable feedstocks for the production of biofuels.  The high amount of sugars in SCG can be used to produce bioethanol through fermentation.  In addition, bioethanol can be used along with lipid fraction extracted from SCG to produce biodiesel through transesterification (Caetano, 2011).  Caetano et al. aims to investigate the use of SCG for the production of biofuels, as well as characterize SCG, the oil they contain, and the biofuels they produce.  They also identify the optimal operating conditions in order to extract oil from SCG, to perform oil transesterification to biodiesel, and to assess the biodiesel quality (Caetano et al. 2012).  Shelby Long
Caetano, N. et al., 2012. Valorization of Coffee Grounds for Biodiesel Production. Chemical Engineering Transactions 26.

Caetano et al. examined the use of SCG for the production of biofuels.  They obtained spent coffee grounds from a local coffee shop and allowed them to air dry for several days.  The SCG then underwent repeated cycles of oven drying at 105 + 5 °C followed by cooling in a desiccator.  The grounds were then weighed, and levels of total carbon (TC), total nitrogen (TN), protein content, ash content, cellulose content, and insoluble and soluble lignin content were taken.  In order to characterize and extract oil from the SCG researchers tested different solvents to determine which would be most effective for the extraction process.  For each treatment, 10 g of oven dried SCG and 200 mL of solvent were placed in a Soxhlet extractor for 2.5 to 9.5 hours.  When three consecutive measurements of the solvent refraction index were constant and close to the pure solvent’s value the extraction process was stopped.  The oil extraction rate was determined.  The oil extracted from the SCG were measured for solvent recoverability for hexane, isopropanol, heptane, octane, ethanol.  In order to recover the oil from the extracting solvent researchers used a rotary evaporator and a vacuum pump.  The extracted oil was characterized and assessed based on its quality.  The iodine number, acid value, water content, kinematic viscosity, density, and higher heating value (HHV) were measured.  In order to produce biodiesel, several esterification steps were performed in an orbital acclimatized shaker.  Researchers monitored the acid value of the product throughout the process and at specific steps added 40% methanol and H2SO4to perform the esterification process.  1% NaOH was used as a catalyst.  The biodiesel was then separated from the glycerol phase and washed with distilled water to achieve a neutral pH.  In order to characterize the biodiesel Caetano et al. accounted for the importance of compliance with standards for the use of biodiesel in vehicles engines.  Therefore, they assessed the biofuel density at 15 ˚C, the kinematic viscosity at 40 ˚C, the acid value, the iodine value, and the methyl esters content, which should all be in accordance with EN biofuel standards.
                  The results of Caetano et al.’s study somewhat differ from what previous studies report.  The moisture content is substantially higher, the higher heating value is lower, and the cellulose content differs from what other studies have indicated (Lago et al. 2001; Bizzo 2003; Mussatto et al. 2011b).  The present study suggests these differences may be due to different coffee extraction procedures, different storage conditions of the grounds, and the use of different types of coffee for the experiment.  The solvent that allowed for the highest oil recovery was octane.  Ethanol and hexane allowed for lower oil recovery.  Hexane had one of the higher recover rates, while ethanol exhibited a lower recovery rate.  Isopropanol had a strong capacity of oil extraction and solvent recovery.  The mixture of hexane and isopropanol at a ratio of 50:50 allowed for high oil extraction, but lower solvent recovery.
                  The extracted coffee oil had iodine values that were too low, too high viscosity to be used in direct combustion engines, and too high acidity to be directly converted into biodiesel without undergoing pre-treatment.  However, the high HHV indicates that the oil extracted may be used for direct combustion.  The biodiesel produced was also characterized, and researchers found that the acid value and viscosity were too high to comply with biofuel EN standards.  They suggest that the high water content in the oil and the high acid value may have hindered the completion of the reaction.  Caetano et al. indicate that more improvements in the SCG biofuel production process must be made in order to improve the quality of biodiesel to meet the EN standards.  Some of these improvements include obtaining a higher methyl ester content by drying the oil, removing water between esterifications, neutralizing excess acid before transesterification, and using different methanol-to-oil molar ratios. 

Effect of Increased Corn Ethanol Production on Food Export and Land Use Changes

The global production of biofuel has greatly increased due to energy security concerns.  Over the past two decades, ethanol production in the United States has grown 15–20% per year to meet the increased demand for renewable fuels (U.S. Energy Information Administration 2011).  The majority of ethanol produced within the United States comes from corn sugars.  Approximately 3% of the corn harvest was needed to meet ethanol demand in 1990, but this percentage grew to 37% by 2010.  Due to the increased demand for more renewable energy sources to replace environmentally harmful fossil fuels, policies have been enacted to promote the increased production of biofuel.  One of these policies is the U.S. Renewable Fuel Standard, which aims to increase biofuel production to 36 billion gallons by 2022.  It has been suggested that not only direct effects, but also indirect effects, of biofuel production should be taken into account (Melillo et al. 2009).  The direct effects of biofuel production include greenhouse gas (GHG) emission reductions, while indirect effects may be evident in land use changes.  It has also been argued that an increase in corn ethanol production will lead to a reduction in food exports and deforestation in other nations (Searchinger et al. 2008).  Due to the increase in the availability of U.S. agricultural data, researchers no longer have to rely on theoretical evidence; rather, now researchers can use real agricultural data to determine the effects of increases in ethanol production.  However, these data may not be sufficient enough to fully assess indirect land use changes in the United States (Wallington et al. 2012).  Shelby Long
Wallington, T. et al., 2012. Corn Ethanol Production, Food Exports, and Indirect Land
Use Change. Environmental Science and Technology 46, 6379–6384.

Wallington et al. analyzed the direct and indirect effects of the United States’ recent increase in biofuel production using available agricultural data through 2010.  They examined data on the global production, import, and export of agricultural commodities published by the United States Department of Agriculture Foreign Agricultural Service (USDA-FAS).  They also analyzed monthly data on energy statistics and production of fuel ethanol published by the United States Energy Information Administration (EIA).  Both sources of information were used by Wallington et al. to gain insight on the history of ethanol production and agriculture exports dating as far back as 1960.  Researchers examined agricultural productivity, corn ethanol production, and agricultural exports of the Unites States.  They acknowledge that between 2000 and 2010 the increase in use of corn for ethanol was accompanied by an increase in corn harvest.  However, researchers do not suggest that the increase in harvest was necessarily due to the increase in corn ethanol production. 
Wallington et al. recommend that future models need to account for increased yields in the United States and other countries due to agriculture technology improvements.  They suggest that these improvements are the result of increased biofuel production in the United States.  If this is the case, then researchers suggest decreases in land use outside of the U.S. would result, therefore, translating into a negative, favorable land use change burden.  In the long term, increases in demand for ethanol could lead to lower costs and higher yields.  In the short run, more intensive land use, investment in new production equipment, weather variability, movement of corn onto the better land, and increases in rotation of higher yielding crops (soy and corn) may take place. 
                  Wallington et al. determined that where there was an increase in ethanol production there were no obvious changes in corn and wheat exports in the past decade.  On the other hand, soybean, chicken, and pork exports have increased significantly over the past decade.  Annual corn exports showed no changes, as they remained at approximately 50 million tonnes.  There has also been a large increase in production and exports of distiller’s dry grains (DDG) over the past 10–15 years.  DDG is a co-product of ethanol production and is used as an animal feed.  Therefore, a reduction in demand for animal feed produced outside of the U.S. could be the result of increased biofuel demand in the U.S.  This reduction in demand for animal feed would lead to a negative indirect land use change.  The corn harvest has exhibited an upward trend over the past 50 years, increasing by about 2% per year.  Along with other factors taking place, the increase in harvest over the past 10 years was accompanied by an increase in use of corn ethanol.  There is no trend in the total harvested area of crops such as corn, soy, wheat, oats, and barley.  This may also indicate that there was no increase in the land devoted to the cultivation of these crops.  There is no significant correlation between U.S. ethanol production and corn exports in the past two decades.  Even if there was a correlation it could not be determined for certain whether one was the cause of the other.  Similarly, data on exports of meat and grains do not support the idea that corn ethanol production affects food exports. 
                  A past study predicted that a 56 billion liter increase in corn ethanol production would lead to a decline in corn, wheat, soybean, pork, and chicken exports by 62%, 31%, 28%, 18%, and 12% (5).  However, these levels of decline in exports were not seen as a result of the 43 billion liter increase in production over the past decade.  Another recent study proposed a model on indirect land use changes associated with an increase in corn ethanol production (Hertel et al. 2010).   The modeled increases in ethanol production were very close to the increase that took place between 2000 and 2010.  The model also predicted a net increase of 0.41% in coarse grain yield and a 17% decrease in coarse grain exports due to increases in ethanol production.  However, the historical 15% increase in ethanol production was 40x greater than the predicted 0.41% increase in yield of corn. 
                  The increases in ethanol production over the past decade have been accompanied by increases in harvest.  These increases in harvest are largely the result of improved yield per acre, increased acreage use, genetic improvements/hybrid plant breeding, and improved crop management (22).  There are two main arguments related to the effect of increased biofuel production on agricultural yields.  The first argument is that the increased market for corn ethanol production has not led to increases in agricultural yields.  This argument may be somewhat supported by the historical trend of corn yields over the past decade, which shows no change.  However, there are many other factors, such as population growth, dietary trends, economic growth, energy price fluctuation, and international export/import policy changes that may have been the cause of any changes in corn yields and demand.  Any changes are not necessarily due to the increases in ethanol production.  The other argument is that increases in demand for corn for ethanol production has made some contribution to changes in agricultural yields.  This argument is plausible because increases in demand and supply for corn, and interest in research and development of hybrid plants and improved agricultural practices are likely to lead to increases in corn yields.  Approximately 12 billion gallons of ethanol are made annually, which requires approximately 100 million tonnes of corn.  Approximately 30 million tonnes of DDG are produced as a result, and 1 tonne of DDG displaces approximately 1.2 tonnes of corn as animal feed (Arora et al. 2010).  If biofuel production does not contribute to increased corn yields, then there would be an indirect land use change due to increased corn ethanol production in the United States.  On the other hand, if biofuel production is responsible for all of the increased corn yields in the U.S., but none of the increased yields observed in the rest of the world, then there would be a small indirect land use change.  If biofuel production was responsible for all of the increases in U.S. corn yields and some of the increased yields in the rest of the world, then there would be negative indirect land use change due to corn ethanol production in the U.S.
                  Such large differences in corn yields of the U.S. and the rest of the world indicate that improved agricultural practices should be adopted by other countries, such as improved soil management, irrigation, fertilizer use, and farm machinery.  Due to the detailed agricultural data now available to researchers, new perspectives can be gained about crop yield changes and their effects.  However, further investigation must be conducted in order to gain a better understanding of the land use changes that may take place as a result of increased ethanol production.  In order to decrease the indirect land use changes in other countries as a result of higher biofuel production in the U.S., intensification of agricultural activities outside of the U.S. should be promoted.  Wallington et al. maintains that further investigation must take place concerning indirect land use changes resulting from ethanol production in order to determine what steps must be taken to decrease the impacts.         
Other Sources
U.S. Energy Information Administration, Monthly Energy Review, 2011.
Melillo, J. et al., 2009.  Science 326, 13971399.
Searchinger, T. et al., 2008.  Use of U.S. croplands for biofuels increases greenhouse
gases through emissions from land-use change.  Science 319, 1238–1240.
Hertel, T. et al., 2010.  Bioscience 60, 223–231.
Arora, S. et al., 2010. Estimated displaced products and ratios of distillers’ co-
products from corn ethanol plants and the implications of lifecycle analysis..  Biofuels 1, 911–922.

Economic Benefits of Biofuel Production in Thailand

Biofuel production requires approximately 100 times more workers per joule of energy produced than fossil fuel production (Worldwatch Institute 2007).  Biofuel is not only a viable option in the renewable fuel industry due to its lack of harmful emissions, but the production process also creates vast amounts of new jobs within developing countries.  Ultimately, this increase in demand for workers leads to an increase in overall economic activity and serves as an income generator for the workers who fill these jobs.  Increases in ethanol production are estimated to increase employment by 238,700382,400 people, and GDP by 150 million dollars by year 2022.  Biofuel policies aimed to promote production in Thailand are likely to improve the country’s agricultural sector, develop rural areas, and enhance energy security (Silalertruksa 2012).  In the United States, it is estimated that every 3.785 cubic hecta-meters of ethanol production create 10,00020,000 jobs (Kammen 2011).  Similarly, in South Africa, it has been determined that 350,000 jobs would be created if 15% of gasoline and biodiesel demand were replaced by ethanol and biodiesel production.  However, other aspects of the industry must be investigated, such as work conditions and labor laws.  The demand for biofuels in Thailand is expected to increase, and, therefore, the costs and benefits of increased production need to be taken into consideration.  Researchers expect the increase in biofuel production to have a strong effect on employment rates, GDP, trade balance, and overall socio-economic development (Silalertruksa 2012). Shelby Long
Silalertruksa, T. et al., 2012.  Biofuels and employment effects:  Implications for
socioeconomic development in Thailand.  Biomass and Bioenergy 46, 409
418.

Silalertruksa et al. assessed the benefits of biofuel production increases on the socio-economic development of Thailand.  They examined palm biodiesel as well as ethanol production from cassava, molasses, and sugarcane.  Researchers analyzed the employment effects of biofuel production in Thailand using a “hybrid method” with an analytical approach at the micro level and an input-output model at the macro level.  In order to determine the effect on direct employment due to increases in production they used a production process analysis of the expenditures for labor in land preparation, feedstock plantation, treatment, and harvesting, along with annual wage data (Duer and Christensen 2010).  The following equation was used to estimate the potential direct employment that can be achieved based on labor costs and average annual working hours in Thailand’s agricultural sector: Employmentagr =(PCfeedstock x Laborshare)/AWGagr (Employmentagris agricultural employment in agriculture; PCfeedstockis the production costs of feedstock; Laborshare is the share of labor cost in feedstock production costs; and AWGagr is the average annual wage per employed person in Thailand’s agricultural sector).  Data on the number of employees and production capacity were obtained from 5 sugar mills, 5 dried-chip floors, 10 ethanol plants, 4 palm biodiesel plants, and 17 palm oil mills.  This information was used to determine the effect increases in biofuel production would have on direct employment in the feedstock processing sector.  The impact of increased biofuel production on indirect employment was also examined.  Indirect employment includes the sectors that process intermediate goods that are delivered to the biofuel processing sector.  Researchers used economic input-output tables from 2005 that were compiled and published in an 180 x 180 format, which they then formatted into 50 x 50 input-output table.  They then categorized the final demand for molasses ethanol, cassava ethanol, sugarcane ethanol, and palm biodiesel by organizing their production costs.  These production costs were then assigned to sectors in the input-output table in order to determine indirect employment. 
                  It was determined that the largest amount of employment based on volume of biofuel produced would be created by an increase in palm biodiesel production.  The second, third, and fourth largest amount of employment increases were from sugarcane ethanol, cassava ethanol, and molasses ethanol.  However, based on energy content produced, the greatest effects were in ethanol production, with biodiesel production from palm oil being the lowest.  Researchers determined that significant increases in employment due to direct and indirect employment opportunities would lead to rural development in Thailand.  However, those employed in the biofuel industry are likely to work on a temporary basis, and, therefore, those who work in these industries are not as well-protected by laws for working conditions or other policies. Silalertruksa et al. suggest that policies and laws for working conditions, fair wages, and other labor rights must be considered in order to help small scale farmers, biofuel industry workers, and unpaid family workers secure more rights.  With improved standards for safety risks, safety procedures, child labor, working conditions, and other worker rights the biofuel industry and production can be improved for the future. 
Researchers suggest that further survey and analysis practices need to be adopted in order to determine the overall need for changes in policy because current indicators, such as the Global Bioenergy Partnership (GBEP), cannot be used as a representative of the whole country.  Researchers examined four scenarios for increasing feedstock production.  Scenario 1 would expand the cultivation areas for cassava and sugarcane, Scenario 2 would include machines to help cultivate cassava and sugarcane, Scenario 3 requires a 50% increase in labor for the production of feedstock, and Scenario 4 requires labor that increases at the same rate as yield production.  In order to produce 9 cubic decimeters per day of ethanol by 2022, it was calculated that a range of 238,700–382,360 persons would be needed.  The lowest number of workers would be required in Scenario 2 because many of the workers would be replaced by mechanization. 
Increases in the biofuel sector would spark national development through increases in GDP due to increases in investment in the biofuel sector and improvement in the trade balance and energy security.  Researchers calculated the total impact of different types of biofuels in Thailand on GDP.  They determined that producing 1 million liters of cassava, molasses, and sugarcane ethanol and palm biodiesel would contribute to GDP by 499, 411, 604 and 632 k$.  Feedstock, the most costly aspect of biofuel production, affects GDP by approximately 62–73% directly or 29–55% in total impacts.  However, an increase in the production of biofuel will also lead to a decrease in the production of petroleum, and, therefore, a decrease in GDP by around 90%.  The decrease in GDP due to reduced petroleum fuel production offsets some, but not all, of the increase in GDP due to increases in biofuel production.   This rise in GDP also implies a rise in the incomes of workers.  Also, an increase in production by 1 TJ of cassava ethanol, molasses ethanol, sugarcane ethanol, and palm biodiesel will result in an increase in total imports by approximately 29, 18, 49, and 15 k$.  However, by replacing petroleum fuels with biofuels imports could decrease by 10–41 k$ TJ—1 of ethanol and 46 k$ TJ—1 of biodiesel.  The indirect impact of chemicals used in the biofuels conversion stage and from energy consumed contribute largely to imports.  The total imports of chemicals for biofuel production account for approximately 25–68% of total imports; therefore, if ethanol production reaches a level of 9 cubic decimeters per day by 2022 then ethanol production could help reduce imports by 2547 M$ per year.  Researchers determined that in order to improve security of feedstock supply for long-term ethanol production, cassava and sugarcane yields must be improved to 50 t and 125 t ha—1 by 2022 (Silalertruksa and Gheewala 2010).  In order to achieve these levels, Silalertruksa et al. recommend that more research be done to develop high yield varieties of cassava and sugarcane and to promote good agricultural practices (GAP) to improve yields.  Increased biofuel production could also have adverse effects, such as decreased access to food for poor families, permanent farm labor of young workers, and the loss of small-scale farmers’ access to land.  Therefore, policies must be formed in order to alleviate these potential problems.
Silalertruksa et al. assert that biofuel production results in many positive externalities to the Thai economy.  It is estimated that 1720 more workers are needed for biofuel production than gasoline production, and biodiesel production would produce 10 times more workers than diesel production.  They suggest that not only does biofuel production increase the need for workers, but it also leads to a decrease in ethanol and biodiesel imports and an increase in GDP by up to $60 k per dam3 of biofuels produced.  These socio-economic benefits could make biofuels more price competitive in comparison with petroleum fuels as well.  Also, increases in biofuel production through community-based plans are also expected to help raise the living standards of rural communities as people learn to derive biodiesel from cooking oil or other oil plants from their land.  This could make energy cheaper and more available to rural communities.  
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United States senate committee on environment and public works.
Silalertruksa, T. and Gheewala, S.H., 2010. Security of feedstocks supply for future
bio-ethanol production in Thailand. Energy Policy 38, 74767486.
Worldwatch Institute, 2007. Biofuels for transport: global protential and
implications for sustainable energy and agriculture.

Increase in Efficiency of Cattle Manure Biogas Production Due to the Addition of Palm Oil Effluent

Fifty-eight million tons of palm oil mill effluent (POME) is produced each year in Malaysian palm oil mills.  This effluent can be used for biogas production, an especially viable renewable energy source in India, China, Malaysia, Thailand, Indonesia and the Philippines where palm residue is in high abundance (Renewable Cogen Asia).  Typically, biogas is produced from industrial, municipal, and agricultural waste, such as cow manure.  Raw palm oil contains high levels of fatty acids and oil, and, therefore, a high oxygen demand, which makes it necessary to treat in oxidation ponds where it can also be used to support bacterial growth (Alias and Tan 2005, Zakaria et al. 2008).  This form of anaerobic digestion not only is a form of waste treatment, but it is also used for the production of biogas in the absence of oxygen (Santibanez 2011).  Therefore, scientists expect that palm oil effluent can also be used as a beneficial additive in the treatment of cattle manure for biogas production (Nasir et al. 2012).  Shelby Long
Nasir, L.M., 2012.  Palm oil mill effluent as an additive with cattle manure in biogas
production. Procedia Engineering 50, 904912

Nasir et al. investigated the benefits of using palm oil effluent as an additive in cattle manure biogas production.  Researchers created an anaerobic environment in a jacketed fermenter from which they sampled the products of the cattle manure and palm oil effluent digestion daily.  They used a 10 L fermenter to conduct two treatments.  In the first treatment they placed 500g of fresh cattle manure and 1.5L of POME in the fermenter.  In the second treatment they only added 500g of cattle manure and added distilled water in order to achieve a solid content of 9%.  For both treatments, they carried out a batch mode for the first ten days and a semi-continuous mode for the remainder of the experiment.  In batch mode they added the contents to the fermenter and allowed it to digest for ten days.  In semi-continuous mode they removed digested cattle manure daily and replaced it with the same volume of fresh cattle manure.  For both treatments, they maintained a temperature of 53˚C in the digester, and they controlled the pH by adding 1 N HCl and 1 N NaOH as needed.  The contents were stirred at a constant speed of about 150 rpm.  In order to maintain the anaerobic environment in the sealed digester nitrogen gas was added to purge the oxygen.  Researchers removed samples on a daily basis and analyzed the total solids (TS), volatile solids (VS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), ammonia nitrogen content, and methane content.  They used a gas chromatograph to analyze the methane content and a spectrophotometer to measure the methane content.  In order to measure the biogas produced in the digester, researchers used the water displacement method.  
            Nasir et al. observed that biogas production in the first treatment, with cattle manure and POME, was continuous in the batch operation but declined after the sixth day.  However, the production increased at a constant rate during the semi-continuous mode.  The biogas production was more rapid for the first half of the digestion period and the methane content fluctuated between 5255% through the course of the experiment.  In the second treatment, with no POME, biogas production began on day 2 and peaked after four days.  The biogas production only achieved a methane content of 20%.  The level of biogas production in the first treatment (0.346 m3kg-1VS) was almost three times greater than the biogas production in the second treatment.  Researchers determined that the increase in biogas potential of the cattle manure is most likely caused by microbial degradation of organic matter because of anaerobic bacteria in the POME additive (Zakaria 2007).  
The ammonia nitrogen NH3-N content observed in the cattle manure and POME treatment seemed to stabilize throughout the experiment, only fluctuating between 400 and 600 mg/L, while the NH3-N content in the cattle manure treatment fluctuated in large amounts, between 400 and 800 mg/L.  The stabilization of ammonia nitrogen content within the cattle manure and POME treatment suggests that the nitrogen ammonia did not inhibit the digestion process with POME present, which ultimately led to a higher biogas and methane production.  Conversely, the high fluctuations in NH3-N in the cattle manure treatment suggest that the accumulation of ammonia nitrogen led to a lower amount of biogas production because of an inhibition on microorganisms.  After three days, the volatile solids content in both treatments began to decrease more rapidly, which was most likely due to the ideal pH and temperature and adaptation of the microorganisms present (Dubrovskis et al. 2009).  Overall, more VS were removed from both treatments during the semi-continuous period than in the batch period. 
The chemical oxygen demand concentration decreased most rapidly for both treatments within the first ten days, which is most likely due to hydrolysis of the cattle waste.  The fluctuations in the COD during the semi-continuous operation was likely due to the continuous adaptation of the microbial population to the changing environment within the digester (Muhammad 2011).  The substrate concentrations sampled from both treatments throughout the experiment suggest that the reduction in TS, VS, and COD can be significantly improved by two-fold using POME additive during cattle manure biogas production.  Nasir et al. recommend the use of POME as an effective additive in the biogas production from cattle manure through anaerobic digestion.  They suggest that not only would the POME considerably improve the removal of TS, VS, COD, and ammonia nitrogen in cattle manure digestion, but the process would also create a use for the palm oil waste from mills.          
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        Alias Z. and Tan, I.K.P., 2005.  Isolation of palm oil-utilising, polyhydroxyalkanoate (PHA)-producing bacteria by an enrichment technique.  BioresourceTechnology 96, 1229–1234.
         
Dubrovskis V. et al., 2009.  Investigation of biogas production from mink and cow
manure. In Proceedings of the 8th International Scientific Conference, Engineering for rural development.
Muhammad, N.I., 2011. Anaerobic digestion of cattle manure with Palm Oil Mill
Effluent as inoculum for biogas production.  Department of Chemical and Environmental Engineering Universiti Putra Malaysia.
               
Renewable Cogen Asia. Biogas Power Asia.  http://www.rcogenasia.com/biogas-
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Santibanez, C. et al., 2011.  Residual glycerol from biodiesel manufacturing, waste or
potential source of bioenergy: A review.  Chilean Journal of Agricultural Research 71, 469–475.
Zakaria, M.R., 2007. Biogas production and determination of methanogens from
digester-treated palm oil mill effluent. Master Thesis 2007; Department of Biological Sciences, Universiti Putra Malaysia.
         
Zakaria M.R. et al., 2008.  Comamonassp. EB 172 isolated from digester treating
palm oil mill effluent as potential polyhydroxyalkanoate (PHA) producer.  African Journal of Biotechnology 7, 4118–4121.

Renewable Energy for Marine Vessels

Marine transportation remains one of the most important sources of cargo transportation on Earth; however, it has been estimated that 60,000 premature deaths each year can be attributed to ship emissions (Hiricko 2008).  Marine vessels, which run on petroleum-derived diesel, are one of the largest contributors to air pollution, global warming, and premature deaths.  In order to reduce the high amount of greenhouse gas contribution and premature deaths Lin (2013) emphasizes the need to replace marine fuels, which contain sulfur, asphalt, and other environmentally harmful components, with a more environmentally friendly fuel (Lin and Lin 2006).  As a renewable and clean fuel, biodiesel has the potential to become the new leading energy source in the marine transportation sector; however, without large steps being taken to formulate marine biodiesel blends, reduce manufacturing costs, increase subsidies, and improve marine biofuel technology this potential will not be met. —Shelby Long
Lin, C.Y., 2013.  Strategies for promoting biodiesel use in marine vessels.  Marine
Policy 40, 8490.

Cherng-Yuan Lin of the National Taiwan Ocean University investigated the necessary development of biodiesel for the marine transportation sector.  He analyzed current emission limit requirements for marine vessels, environmental impacts of biodiesel, the biodiesel life cycle, obstacles for biofuel use in marine vessels, and strategies to overcome the obstacles.  Current and proposed emission limits for sulfur oxide and nitrogen oxide have been set by the International Convention for the Prevention of Pollution from Ships (MARPOL).  Biodiesel contains fatty acids and other contents that do not produce harmful emissions like petroleum diesels do when combusted, such as sulfur oxides.  Research shows that as the proportion of biodiesel blended into liquid fuel increases, the nitrogen oxide emissions decrease (Qi et al. 2011).  When analyzing the life cycle of biodiesel there are five stages that are taken into account:  feedstock production, transportation of feedstock, production of the fuel, distribution, and use of the fuel (National Biodiesel Board 2005).  Past studies have shown conflicting results over whether the total production of biodiesel requires more energy than it produces.  More specifically, a study by Pimentel and Patzek suggests that 118% and 27% more fossil fuel energy was used to produce sunflower and soybean oil biodiesel than total biodiesel oil was produced (Pimentel and Patzek 2005).  However, a more recent study by the National Renewable Energy Laboratory found that 320% of biodiesel energy is produced for every unit of fossil energy input during soybean biodiesel production (Sheehan et al. 1998).  These conflicting results can be accounted for by the lack of a precise definition for energy input and varying methods for calculating energy use within the biodiesel life cycle (National Biodiesel Board 2005).  An obstacle that remains for biodiesel use in marine vessels is the lack of a marine-grade biodiesel specification.  There are specifications for biodiesel use in land vehicles; however, marine vessels are very different in that they contain copper and other metal components which are susceptible to deterioration by biodiesel (Nayyar 2010).  Another obstacle is the large amount of farmland needed to grow the vast amount of feedstock required for the production of the biodiesel.  Lastly, Lin examines the low-temperature fluidity of biodiesel, which is a problem for marine vessels operating in colder climates.  As the surrounding temperatures decrease, crystals form in the biodiesel, which can plug the fuel lines.  
Lin suggests strategies to combat the various obstacles inhibiting the use of biodiesel in marine vessels.  In order to establish a marine biodiesel specification, he recommends that field tests must be conducted to determine the optimal mix of biodiesel and marine fuel using current ASTM biodiesel specifications and marine heavy fuel oil standards for density, viscosity, flash point, etc.  He recommends government subsidies, tax cuts, tax exemption, and fuel tariffs be made for marine-grade biodiesel to make it more price-competitive and to promote the long-term development of renewable marine biodiesels.  Previous studies have shown that an increase in the proportion of biodiesel to marine diesel results in decreased emissions from fishing boats (Lin and Huang 2012).  Therefore, if the amount of biodiesel were to be increased it would not only result in the decrease in the price of biodiesel due to economies of scale, but it would also reduce overall emissions.  Also, Lin suggests that storage tanks that are susceptible to deterioration from oxides reacting with biodiesel must be substituted with carbon steel, aluminum, fiberglass, or stainless steel tanks. 
In order to improve the fluidity of biodiesel in colder temperatures various combinations of biodiesel feedstocks must be tested.  Certain biodiesel types have a higher saturated fatty acid content, which creates a higher temperature at which crystals form and clog fuel lines; therefore, different feedstocks can be mixed in varying proportions to create an optimal blend that can withstand a desired temperature.  Lastly, Lin suggests that glycerol, a byproduct of the transesterification process of biodiesel production, can be purified and sold to the pharmaceutical, cosmetic, and other lucrative industries.  The selling of this glycerol surplus can be used to lower the price of biodiesel production and to decrease the environmental harm untreated glycerol can cause.  Although there are various obstacles that must be overcome in order to create a widely-used marine-grade biodiesel, these obstacles have feasible solutions.  Lin maintains that if these solutions are achieved and the renewable and clean biodiesel energy is used in the marine transportation sector, worldwide emissions will be reduced, thereby decreasing global warming and protecting people’s well-being.
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        Lin, B. and Lin, C.Y. 2006.  Compliance with international emission regulations: reducing the air pollution from merchant vessels. Marine Policy, 30, 220–225.
        Lin, C.Y. and Huang, T.H. 2012. Cost–benefit evaluation of using biodiesel as an alternative fuel for fishing boats in Taiwan. Marine Policy 36, 103–107.
National Biodiesel Board. 2005. Response to David Pimentel biodiesel life cycle
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Nayyar, P. 2010. The use of biodiesel fuels in the U.S. marine. Report for the U.S.
Maritime Administration (MARAD).
        Pimentel, D. and Patzek, T.W. 2005. Ethanol production using corn, switchgrass, and wood; biodiesel production using soybean and sunflower. Natural Resources Research, 14, 65–76.
        Qi, D. et al. 2011. Effect of EGR and injection timing on combustion and emission characteristics of split injection strategy DI-diesel engine fueled with biodiesel. Fuel 90, 1884–1891.
Sheehan J. et al. 1998. Life cycle inventory of biodiesel and petroleum diesel for use
in an urban bus, final report. National Renewable Energy Laboratory, NREL/SR-580-24089 UC Category 1503.

Effects of Biofuel Production on Biodiversity

Production of biofuel is expected to increase to 135 million cubic meters by 2022, which would require about 100,000,000 ha of land to grow the necessary feedstock (Perlack et al. 2005).  Such a large amount of land committed to biofuel feedstock production is likely to have a significant negative effect on local and surrounding biodiversity as crop diversity decreases and pest arthropods proliferate (Cook et al. 1991).  Insects are the largest group of organisms on Earth, comprising approximately 1 million described species (Anonymous 2011).  Plants and moths have a mutual reliance on one another.  Moths rely on plants for food and breeding purposes, and plants rely on moths as their pollinators. (Reynolds et al. 2009; Yoder et al. 2010).  In addition, adult moths are an important source of food within the food chain, and, therefore, any decline in their numbers or diversity could lead to further problems within the ecosystem (Whitfield & Wagner 1991).  As the growing production of biofuel disrupts biodiversity, Harrison and Berenbaum (2012) aim to determine the impact of non-corn feedstock production on the diversity of moths.  One of their main concerns is that the increased feedstock production will decrease the abundance and diversity of native prairie plants in Illinois, thereby decreasing the diversity and population of arthropods. Shelby Long
Harrison, T., Berenbaum, M., 2012.  Moth diversity in three biofuel crops and native
prairie in Illinois.  Insect Science. DOI: 10.1111/j.1744-7917.2012.01530.x

Harrison and Berenbaum of the University of Illinois at Urbana-Champagne investigated the impact of non-corn feedstock production on moth species diversity.  They planted 7 sites in Illinois, each site varying in size and shape.  Each site supported plant species adapted to live in the mesic prairie.  The University of Illinois site south of Savoy included 6 of each type of plot of switchgrass, miscanthus, mixed miscanthus, vetch, and corn.  At the University of Illinois Energy Biosciences Institute (EBI) Energy Farm site they planted four plots of each treatment of switchgrass, miscanthus, corn, and mixed prairie.  At the Agricultural Centers of DeKalb, Dixon Springs, Fairfield, Brownstown, and Orr they planted 8 alternating plots of miscanthus and switchgrass, which were both adjacent to large cornfields.  In order to collect samples, researchers used an 18.9-L bucket trap with an 8-watt ultraviolet light, placing the traps in the center of each plot.  Researchers identified moth species by sight and genital dissection.  Collections were taken from one of each plot type on the same night within the sites.  Samples were collected from the Savoy site ten different nights in 2007, two nights in 2008 and one night in 2009 at the EBI Energy Farm site, and one night from the Agricultural Centers of DeKalb, Dixon Springs, Fairfield, Brownstown, and Orr in 2009.  In order to determine the alpha diversity within the crops they used the Shannon-Wiener index and to determine the beta diversity researchers used the Sorenson’s index.  Alpha diversity refers to the diversity of species within a local habitat, in this case within the plots, and beta diversity compares the diversity of species between different habitats, in this case between the plots. 

Over the course of Harrison and Berenbaum’s (2012) study, 5,411 total moths, 252 species, and 25 families were collected.  Based on 2007 data collection, researchers determined that alpha diversities were similar among all crops and beta diversities were low.  After analyzing the 2008 collections they determined that alpha diversity of moths was high within the prairie and low within miscanthus and corn.  Beta diversity was lowest in praire x switchgrass and miscanthus x switchgrass and highest in corn x miscanthus.  In 2009, researchers calculated alpha diversity to be highest in prairie and switchgrass.  Overall, Harrison and Berenbaum (2012) found in 2008 and 2009 the highest level of moth diversity to be in prairie plants, second highest in the switchgrass, and lowest in the corn and miscanthus.  Therefore, their results are consistent with previous studies showing that more diverse native prairie plant abundance leads to a higher diversity of arthropods than in monocultures of annual plants such as soybeans and corn (Bianchi et al. 2006).  Harrison and Berenbaum indicated that their data are generally consistent with the previous studies; however, they suggest that any inconsistencies present are a result of the small sampling size, close proximity of the plots, and low species counts, which tend to skew the calculations. Harrison and Berenbaum recommend that further research be done in order to determine the most efficient methods to manage agricultural fields being used for biofuel feedstock production.       

Future Energy Sources of India: Algae as a Promising Contributor

India is the fourth largest consumer of petroleum energy and the fifth largest overall energy consumer in the world.  In order to meet the country’s high demand for energy, India’s government is in search of sustainable energy sources that both meet these needs and do not contribute significantly to global warming.  While 93% of urban areas in India have electricity, 47% of populations in rural areas lack it (IEA 2009).  Therefore, it is necessary for India’s government to find ways to not only meet the growing demand of the nation, but also find sources of energy that can provide and sustain energy in the rural areas.  India’s dependence on fossil fuels is so strong that any price increases or decreases in oil imports would have a significantly negative impact on India’s economy.  Hemaiswarya et al. (2012) suggest that in order for India to minimize negative impacts on the environment and maintain stability in regards to their energy sources they must efficiently utilize already-existent fuel resources.  They also suggest that India must consider alternative and more diversified energy sources, such as microalgae.  In order to investigate alternative energy sources Hemaiswarya et al. examine the positive and negative externalities of six renewable energy sources. Shelby Long

Hemaiswarya et al., 2012.  An Indian scenario on renewable and sustainable energy
sources with emphasis on algae. Applied Microbiology and Biotechnology 96, 11251135.
Hemaiswarya et al. analyzed biomass, biogas, biohydrogen, bioethanol, biodiesel, and microalgae in order to determine which would be the most efficient and least environmentally harmful energy sources for India.  Biomass refers to both dry fuel sources, such as wood, and wet sources, such as agricultural or industrial waste, wastewater, and slurries.  The smoke that results when coal and biomass are burned within households can cause respiratory infections, lung cancer, and other fatal illnesses (World Health Organization 2009).  Therefore, Hemaiswarya et al. suggest that biomass materials, such as bagasse, rice husk, coffee waste, and sawdust, should be used in gasification systems which will not create this harmful smoke and will harness the biomass for energy and thermal purposes.  The second energy source they investigated was biogas, which is a renewable fuel produced by the anaerobic digestion of the organic animal, agricultural, and industrial waste.  The high amount of methane present in biogas makes it an especially effective source of energy.  Biohydrogen was also analyzed by Hemaiswarya et al. as a viable energy source for India’s growing need for renewable and economically-stable energy sources.  The use of biohydrogen as a renewable energy source is not highly developed in India; however, biohydrogen energy is extremely useful for a variety of energy needs and does not contribute to greenhouse gases.  An obstacle in harnessing biohydrogen energy is that the necessary hydrogen must be split from H2O with the help of enzymes that can only work under specific conditions.  Hemaiswarya et al. recognize that India has made advances towards being able to harness H2 fuels, yet challenges such as availability of feedstock types and identification of ideal conditions for the hydrogen production have not been perfected.  Both bioethanol, created when sugar-containing materials ferment, and biodiesel, produced from fatty acid of ethyl and methyl ester from virgin and used vegetable oils, were also viable energy sources examined by the researchers.  The main crop in India used for the production of ethanol is sugarcane, and with the current 330 distilleries in India they estimated that about 1.5 million liters of fuel ethanol could be produced.   However, ethanol is not a main priority in the current economy; therefore, this estimate is not being met.  On the other hand, biodiesel produced from plants, such as Jatropha, has the potential to be a major contributor to India’s renewable energy needs.  Hemaiswarya et al. propose that India use degraded lands and forests, railway tracks, irrigation canals, and other public places to grow the plants (Kumar and Ram Mohan 2005).  However, obstacles that inhibit the increased production of biodiesel are lack of feedstock and increases in wage rates.  Lastly, Hemaiswarya et al. examined the use of microalgae in the production of biofuels.  They determined that microalgae can potentially be harnessed to produce high amounts of biodiesel due to its high growth rate, adaptability, and photosynthetic efficiency.  
All six of the renewable energy sources Hemaiswarya et al. considered are possible sources of energy for India in the coming years; however, some are more developed and viable for use on a mass scale in the near future than others.  Biomass, biogas, and biohydrogen are already being used as energy sources in India on a smaller scale, yet there is potential to expand production after further research and development of the industries.  Hemaiswarya et al. indicated that in order for bioethanol fuel to become a leading renewable energy source in India, current potentials for sugarcane ethanol must be met by increasing the production of the necessary raw materials.  Likewise, similar steps must be taken in order to increase and fulfill the potential levels of production of biodiesel.  They suggest that wastelands and other undesirable land in India should be used for the production of biodiesel feedstock.  Researchers estimate that one hectare of Jatropha plantation (about 4,400 plants) can supply about 1,500 liters of oil; therefore, about three million hectares of Jatropha could account for about 10% of current fossil diesel demand (TERI (The Energy and Resources Institute) 2004). 
Hemaiswarya et al. also determined microalgae to be a highly feasible option in helping India meet its energy needs because of its high growth rates, adaptability to different aquatic environmental conditions, and high oil yield.  In addition, Hemaiswarya et al. suggest that biodiesel would be a suitable energy source for India because of current easily-attainable technologies, such as the process of transesterification and photobioreactors, that can be used in the growing of and conversion of microalgae into biodiesel.  However, there are still developments and research that must be achieved in order produce microalgae biodiesel on a mass scale, including the selection of microalgae that are high in lipid content, water chemistries, determining nutrient requirements, and perfecting methods for conversion of microalgae into biofuel.  Hemaiswarya et al. maintain that in order for India to insulate itself from the often-unstable global fossil fuel economy it must harness alternative energy sources and especially look into the benefits of microalgae biodiesels.  Many of these possible sources do not contribute to global warming like fossil fuels do and can be produced by harnessing various aspects of India’s unique natural environment.  Hemaiswarya et al. argue that India should commit more resources to the development of alternative energy sources because not enough research is being devoted to finding solutions for the imminent energy crisis. 
Other Sources:
IEA (2009) World energy outlook. International Energy Agency, Paris
Kumar L, Ram Mohan MP (2005) Biofuels:the key to India’s sustainable energy
needs. Proceedings of the RISO International Energy Conference, RISO, Denmark, RISO-R-1517(EN), pp 423–438
TERI (The Energy and Resources Institute) (2004) Livelihood improvement through
biomass energy in rural areas. TERI, New Delhi
World Health Organization (2009) Global health risks: mortality and burden of
diseases attributable to selected major risks. World Health Organization, Geneva.<http://www.who.int/healthinfo/global_burden_disease/global_health_risks/en/index.html>

Biofuel Production: Climate Change Mitigation Does Not Outweigh the Global Phosphorus Reserve Depletion

The global production of biofuel, an energy source harnessed from different types of agricultural crops, has nearly quadrupled from 17 thousand million liters in 2000 (Balat 2007) to 65 thousand million liters in 2008 (Biofuels Platform 2010).  Many governments around the world are aiming to transfer much of their dependence on fossil fuels over to the more renewable biofuel in the hopes that CO2 emissions from fossil fuels may be reduced.  However, the crops that are necessary for the production of biofuel require inorganic phosphorous fertilizer, which is also necessary for global food production and has a limited supply here on Earth.  Today, global biofuel production utilizes about 2% of inorganic phosphorus fertilizer production.  As governments aim for even higher productions of biofuel than ever before, Hein et al. (2012) aim to answer the question of whether the mitigation of CO2 emissions should be chosen at the expense of depleting Earth’s precious phosphorus supply.  The depletion of the phosphorus supply for biofuel production will negatively affect future food supply by raising food prices and exhausting the necessary phosphorus fertilizers for food crops.  With more informed knowledge about how phosphorus is mined, used in agriculture, and ways in which it can be recycled, more efficient ways to combat the depletion of global phosphorus reserves can be developed. —Shelby Long
Hein, L., Leemans, R., 2012. The Impact of First-Generation Biofuels on the Depletion
of the Global Phosphorus Reserve.  AMBIO 41(4), 341–349.

Hein et al. examined the current uses of phosphorus fertilizers in the production of biofuel using statistics from FAOSTAT, crop data, and fertilizer data from the International Fertilizer Industry Association.  They analyzed how the amount of phosphorus depletion compares to the avoided CO2 emissions from fossil fuels in order to determine whether the shift in energy supply towards biofuel is ultimately more favorable.  They focused on the seven main crops used for biofuel production—sugarcane, corn, rapeseed, soybean, wheat, sugarbeat, and palmoil (Balat and Balat 2009).  The production of biofuel also results in co-products, such as corn gluten feed, rape meal, soy meal palm kernel.  Many of these co-products are used for animal feed or other economically-valuable purposes.  In order to determine the amount of phosphorus that is used in biofuel production Hein et al. adjusted for the share of phosphorus that contributed to the production of co-products as opposed to the biofuel.  They calculated the proportion of phosphorus used in biofuel production by dividing the value of biofuel production by the value of the total production.  They then calculated how much phosphorus is required to produce 1 gigajoule (GJ) of biofuel energy and how much CO2emissions could be avoided per GJ of biofuel energy.   Hein et al. compared these amounts to the level of CO2 that is acceptable to emit while still maintaining a less than 2˚, 3˚, and 4˚C increase in global temperatures.  They also took into account that the exact size of the global phosphorus reserve is uncertain, so they used a low and high estimate of 16 thousand million ton (Jasinski 2010) and 65 thousand million ton rock phosphate (Jasinski 2011).  Hein et al. then compared the amount of phosphorus required to produce 1 GJ of biofuel energy to the high and low estimated values of the global phosphorus reserve.
Using the calculated values of phosphorus amounts used to produce 1 GJ of biofuel energy and amounts of avoided CO2 emissions per GJ due to biofuel production, Hein et al. were able to compare the effects of biofuel versus fossil fuel production. They took into account the high and low estimates of the global phosphorus reserve when comparing the avoided CO2 emissions to the amount of phosphorus reserve depletion during biofuel production.  Hein et al. found that in each case, except for the scenario with the 2˚C temperature change threshold in conjunction with the high reserve estimate (65 thousand million ton rock phosphate), the phosphorus depletion exceeds the CO2emissions avoided.  In the 2˚C exception, sugarcane was the only crop out of the seven taken into consideration that exhibited phosphorus depletion, positively outweighing the level of climate change mitigation.  These results are important in forming future policy on energy production because they illustrate the wide range of factors that must be taken into account when evaluating the pros and cons of various energy sources.  Climate change mitigation is not the sole factor when determining levels of biofuel production because phosphorus reserve depletion can be similarly devastating to life on Earth. 
Phosphorus is lost through erosion in agricultural fields, inadequate storage and transport, and most especially during refining steps where much of the biofuel production waste becomes liquid that is difficult and expensive to recycle.  As governments continue to set even higher target levels for biofuel production, we must take into account the tradeoffs taking place between the exhaustion of precious and limited phosphorus reserves and climate change mitigation.  In order to prevent the future threats against food security, policy must be enacted to increase the efficient use of phosphorus (Ometto et al. 2009).  Although exact values of phosphorus reserve size and acceptable temperature increases are uncertain, it is clear through the research of Hein et al. that in most cases the depletion of the global phosphorus reserve does not positively outweigh the resulting climate change mitigation.  
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Balat, M., and H. Balat. 2009. Recent trends in global production and utilization of
bio-ethanol fuel. Applied Energy 86: 2273–2282.
Balat, M. 2007. Global bio-fuel processing and production trends. Energy Exploration
and Exploitation 25: 195–218.
Biofuels Platform. 2010. Production of Biofuel in the EU. Biofuels Platform,
Lausanne.
Jasinski, S. 2010. Mineral commodity summary. Reston: U.S. Geological Survey.
Jasinski, S. 2011. Mineral commodity summary. Reston: U.S. Geological Survey.
Ometto, R.A., M. Zwicky Hauschild, and W.N. Lopes Roma. 2009. Lifecycle   
assessment of fuel ethanol from sugarcane in Brazil. The International Journal of Life Cycle Assessment14: 236–247