The Use of Landfill Leachate and Waste Heat to Sustainably Grow Algae for Biodiesel. Bethann K. Parmelee

Transcription

1 The Use of Landfill Leachate and Waste Heat to Sustainably Grow Algae for Biodiesel by Bethann K. Parmelee 1

2 Clarkson University The Use of Landfill Leachate and Waste Heat to Sustainably Grow Algae for Biodiesel A Thesis Proposal by Bethann K. Parmelee Department of Civil and Environmental Engineering Mentors: Drs. Susan Powers and Michael Twiss March 10,

3 Abstract The Developmental Authority of the North Country (DANC) is currently seeking possible solutions to sustainably utilize 23.4 million BTUs of waste heat available at its landfill facility in Rodman, NY; this excess heat is created during the conversion of landfill gas into electricity via gas generators. One suggestion is to use the waste heat to grow algae for biodiesel. The landfill s leachate, another waste product, could be used for this process as algal growth requires a water source. A previous study determined that the growth of the algae Chlorella protothecoides, well-known in literature for its high lipid content, in various concentrations of leachate is possible on a lab-scale. This is likely due to the high concentrations of nutrients such as nitrogen and phosphorous in the leachate that provides for a nutritive growth media. However, further analysis is necessary on a lab-scale to determine optimal conditions for growth and lipid content, which will affect the quantity of biodiesel produced. Once the preliminary results are confirmed, scale-up to an industrial level will be developed using this data with environmental analysis. The expectation is to develop an industrial process for algal biodiesel production at the site that may be translated to facilities under similar circumstances. 3

4 INTRODUCTION The Development Authority of the North Country s (DANC) Solid Waste Management Facility located in Rodman, NY is currently employing methods to reduce its reliance on fossil fuels with the addition of a landfill gas to energy (LFGTE) process. This system converts methane gas from the decomposing waste into electricity using gas-powered generators. However, this sustainable measure has another outcome: in producing electricity from an otherwise unusable waste product, a large amount of excess heat is emitted. This heat totals approximately 23.4 million BTUs per hour, enough to power an industrial-sized process. As such, the facility desires alternatives to releasing this waste heat into the atmosphere. One possible solution is using the heat to grow microalgae for biodiesel production. Not only would this utilize a waste product, but also decrease the facility s reliance on fossil fuels, as the biodiesel may be mixed with petroleum products to make B20 (twenty percent biodiesel), which is compatible with current fossil fuel uses at the facility. The crux in this seemingly sustainable solution is that algal growth on an industrial scale will require a large source of water nearby. The DANC landfill cannot currently provide the approximated 12 million gallons of water per year required for algal growth without transportation to the site, which would represent a high cost to the facility and an unnecessary sink in the water supplies. The landfill s leachate, available in large quantity, is largely water-based with constituents picked up as it passes through the contents of the landfill. With 22 million gallons available per year, the landfill s leachate could act as a water and nutrient source for the alga. As such, the main question this research intends to answer is: Will the leachate act as a sufficient growth medium for algae in an industrial-scale algal biodiesel production process at the DANC facility? Although preliminary research has already indicated that the leachate will sustain algal growth, research is necessary to further develop the process. The ultimate objective of this research is a preliminary full-scale engineering design of an algal biodiesel production process at the DANC facility. A series of lesser goals must first be accomplished before a design is implemented. The first is the determination of optimal metabolism and growth conditions for neutral lipid production, as this is the substance of interest in biodiesel production. A preliminary quantification of the industrial-sized system s major mass and energy flows including the sizing and costs of major mechanisms will be necessary for the following objective, but will not be included in the proposed research. The environmental impacts of algal biodiesel production must also be determined at the facility using the scaled-up data as mentioned, which with iteration with the engineering design will form the final recommendation for the process s design and operation. BACKGROUND Biodiesel Biodiesel, which is fuel derived from plant or animal lipids (the fat content), is an option to potentially bolster or replace fossil fuels. These fuels have been derived from a number of different types of crops, mainly plants such as soybeans, sunflowers, and coconuts, but can also be manufactured from waste cooking oils, animal fats, or algal lipid. These feedstocks are comprised of triglycerides, a combination of glycerol and fatty acids, and are converted into mono alkyl esters via transesterification. The fatty acids react with an alcohol and a hydroxide catalyst to produce glycerin, a by-product, and esters, which are then combusted as fuel. 4

5 Algal Biodiesel Although biodiesel may be derived from a number of crops and sources, algae produce lipid more efficiently than the crops common to biodiesel production; algae require less land area to produce energy, and have a greater energy output than traditional corn- or soybean-based fuels. To fulfill fifty percent of transportation needs in the U.S., biodiesel from algae would require less than five million hectares, whereas corn-derived fuels would require over 1.5 billion hectares [1]. The growth of algae would not take up cropland required for food production. Additionally, this product is more compatible with diesel fuels than biofuels derived from other natural oils, which generally have lower volatilities and higher viscosities [2]. As such, algal biodiesel can be integrated into current fuel economies by combining it with petroleum diesel. The decreased land use and integration into current diesel use forms some of the motivation behind choosing algal biodiesel production as an option for waste heat usage. Another important consideration in the North Country is that crops cannot be grown year-round and sunlight is limited; a perennial lipid producer would allow for increased fossil fuel replacement yearround in a cold climate such as Upstate New York. Processes for producing biofuels from algae vary, as different types of fuels can be derived from the cell material. Algal cells may be converted to methane via anaerobic digestion or to hydrogen fuel through biological processes [1]. A third option is algal biodiesel. Though not currently commercialized, production occurs identically to crop-derived fuel. The processes that exist to extract plant lipids can be applied to alga. After some growth process, typically in a bioreactor or open pond, algae are dewatered, filtered, and the lipid extracted mechanically to be converted into biodiesel via transesterification [1]. The species Chlorella protothecoides has been indicated by many studies as a primary lipid producer for this purpose [1, 3, 4, 5, 6]. Productivity of algae for lipid production is highly dependent on the initial growth conditions. Although algae have been shown to yield over ten times more tons of biodiesel per acre of land used than natural oils taken from other crops [3], exact productivity is based on the variability of algal growth; the slightest change in conditions will affect how many cells can grow and their lipid content. Lighting, available water and nutrients, species of algae, and metabolic pathway all determine how quickly the cells will grow and their capacity to produce lipids. According to preliminary research on batch growth of C. protothecoides in leachate, algae can take up to a week to reach the end of exponential growth, the point in the growth phase thought to produce maximum lipid. The growth process, even in a continuous flow reactor, will be the rate limiting step of the entire process. This demonstrates how important the determination of growth conditions is; both growth rate and lipid content need to be considered for the biodiesel process to have maximum production. The most important aspect of growth conditions when considering algae for biodiesel is the metabolic pathway of the algae. This will determine the growth requirements and dictate how much lipid the algae can produce and how quickly. Although algae are generally autotrophic, requiring light and inorganic carbon for growth, some species, including C. protothecoides, can grow heterotrophically with no light and an organic carbon source. However, optimizing both growth rate and lipid content, as discussed for the maximum biodiesel production, would be difficult through the use of one metabolic pathway. The nature of each metabolic pathway can yield only one desirable as discussed in the following. As photosynthesis is the main metabolic pathway for algae, autotrophy generally results in faster growth. This is with the exception of photoinhibition, which will occur with greater than 10% 5

6 natural sunlight, creating a shadowing effect for cells throughout the culture due to the high density of cells exposed to the light and subsequently decreasing growth [4]. On the other hand, studies of the heterotrophic growth of C. protothecoides indicates optimal lipid yield for biodiesel production [5, 6]. These two desirables are the result of two different metabolic pathways, creating a challenge in experimental design. If there are acute differences in growth results under the two metabolisms, decisions will be necessary regarding favoring lipid content or quick turnover in production. Environmental Impacts One of the prime reasons for choosing algal biodiesel, or any biodiesel, is its supposed lesser environmental impact in comparison with petroleum products. Fossil fuels are known air pollutants and contributors to global warming. With such short supply and subsequent rising prices, diesel is not only undesirable environmentally, but economically as well. This is especially true when considering our dependence on foreign oil; ninety-eight percent of transportation fuel use is fulfilled with fossil fuels [7], not all of which can be provided domestically. However, there remains some doubt as to the true implications of replacing fossil fuels with biofuels, specifically algal biodiesel, due to the high energy inputs required. Doubts also remain with regards to algal biodiesel in comparison with other crop-based fuels. In comparison to petroleum products, biodiesel use generally results in decreased pollutant emissions, including fine particulates, carbon monoxide, hydrocarbons, and sulfur oxides. This is with the exception of NO x emissions, which have been shown to increase with the combustion of algal biodiesel in certain engines [4]. However, studies roughly estimate that algal biodiesel has only 80% of the energy content of fossil fuels [1], which would require more material use and energy inputs to provide the same amount of energy. As such, environmental analysis becomes crucial in determining the benefits of algal biodiesel when looking at upstream sources of materials and energy inputs. These factors will not only determine the feasibility of replacing petroleum diesel with biodiesel, but determine if the decreased energy content of biodiesel may be overcome in life-cycle analysis by total energy inputs and environmental factors. Even with such variability in algal growth and biodiesel production, life cycle analysis generally indicates less energy inputs and decreased pollutant emissions, in comparison with biodiesel from soybeans and other crops [3, 7]. Algae are approximately ten times more efficient at utilizing solar energy for lipid production than terrestrial plants commonly used for biodiesel [3]. Algae also require less land area for productivity and will not use land which could otherwise be used to grow food crops [1, 3]. When using waste heat to power the process, algal biodiesel becomes even more competitive with other crop-derived fuels with respect to total life-cycle energy consumption [7]. However, there is still some hesitation in the scientific community with regards to the fastidiousness of algal growth when productivity is concerned: studies have indicated that the life cycle analysis is crucial before implementing a process, as algae is not as temporally reliable as other crops with regards to producing lipid and may have an energy input-output ratio greater than one [8, 9]. These same studies stress the importance of analysis in all growth, production, and transportation stages in order to accurately estimate the environmental and economic costs of implementing such a process. Upstream processes must be considered, such as the production of methanol for transesterification, the manufacture of parts used in the bioreactors, and the transfer of materials, in order to account for the overall energy input to output ratio. This will form a more accurate comparison to both crop-based fuels and petroleum diesel. 6

7 The DANC Facility With regards to biodiesel production at the landfill facility itself, the use of waste products for energy production, namely the available waste heat, will enhance the sustainability of this process. A preliminary estimate indicates the 24 million BTUs per hour available for collection from the facility s four generators is sufficient for the replacement of all fossil fuels by B20 [10]. This waste heat can provide temperature control and a means for decreasing the water content of the algae. Figure 1 shows a compartmental schematic of the process s inputs and outputs. The CO 2 available from electricity conversion will also aid in algal growth, if autotrophy is found to be the optimal metabolism. Twenty two million gallons of leachate are also available per year as an algal growth medium. While there are many toxic components to the leachate, imbibed from the landfill s contents, large amounts of nitrogen and phosphorous are also available for growth processes, approximately 870 and 5 mg/l, respectively, according to permit analysis [11]. While this feasibility study is necessary to determine if this is in fact possible, the resources available at the facility are theoretically sufficient for biodiesel production; this research will determine the optimal design of a sustainable biodiesel production process at the facility based on these qualities. Figure 1: A theoretical compartmental schematic of a biodiesel production process at the DANC facility Preliminary Results Research has already begun with respect to growth conditions and metabolic pathways. Although testing is incomplete, positive growth results indicate the feasibility of algal growth in leachate and 7

8 dictate the need for further research. Initial experiments of 100 ml of algae growing in leachate solution in 250 ml polycarbonate flasks prove algal growth is possible in the leachate at any concentration. Solutions of 0.33%, 3.3%, 10%, 33%, 50%, and 100% leachate by volume in deionized water comprised the entirety of growth experimentation, and each resulted in quantifiable algal growth. The significance of this growth with respect to biodiesel production is unknown. Incomplete lipid analysis did not allow for the determination of optimal growing conditions for lipid production. While the maximum growth rate occurred in lower concentrations of leachate, the concentration of leachate for maximum lipid content is also unknown. A quick screening method for lipid content using fluorometry was developed, but needs refinement for more accurate analysis. Dilution methods other than by volume will be incorporated after later analysis, as leachate constituents are dependent upon precipitation and evaporation; drier months will result in a more concentrated solution, likely a more toxic media. The issues brought up during the completed tests will form the basis for further experimentation and design. METHODOLOGY The proposed research will take place in three iterative stages. The first, partly completed already, is the determination of optimal metabolism and growth conditions. C. protothecoides will be submitted to different growth conditions, including lighting and leachate concentrations. Once the optimal growth conditions are determined with respect to potential for lipid production, mass and energy inputs will be quantified for a preliminary engineering design; this will also provide some sizing and costs related to major components of the system such as the continuous-flow bioreactor. This design will not be included in the proposed research, but is a necessary tool for the third stage. This final stage will be a full engineering design of the plant including the scaled-up growth reactor with environmental and economic analyses. The preliminary stage includes lab experimentation of algae growth in batch cultures (no flow). Overall this preliminary research will include further growth experiments in leachate, the creation of a more accurate method of leachate dilution, and the development of a quick screening method for lipid content. Experimentation will be modeled from the previous set up. All stock cultures will be maintained in incubators at 25 C and shaken at 115 rpm. Subsequent experiments will be conducted with 250 ml of solution in 500 ml glass flasks to promote more accurate growth results, due to the higher volume of media. Since DANC needs to use the maximum amount of leachate to fulfill the water requirement, higher concentrations of leachate will be used. The first experiments will use dilutions of 10% and 33% by volume with a positive control of Bold s Basal Medium (BBM), a common growth media for C. protothecoides, with 1% leachate for comparison. Samples in each experiment will be made in triplicate and monitored for cell count and lipid content. The initial experiment will compare different metabolisms, with one set of replicates grown autotrophically and one set grown heterotrophically. The results of the metabolism testing will dictate the optimal growth conditions and the parameters for further experiments. The purpose of the cell counts is to monitor the growth process throughout lipid analysis, in order to determine when to harvest the algae for maximum lipid content and, consequently, maximum biodiesel production. Cell count methodology will utilize a Coulter Counter for determining cell concentrations in the cultures. Two-mL algae samples will be extracted every two days from the 250 ml cultures and suspended with Lugol s iodine for preservation until measurements are taken en masse on a weekly basis. Samples will be run through the Coulter Counter under the standard procedure. The goal is that the growth monitoring results 8

9 will indicate a common day in the growth cycle throughout all experiments to obtain the greatest amount of neutral lipids, which will be used for timing batches in the system s operation. In order to induce more consistent algal growth, the variation of the leachate must be normalized. Using the volumetric dilutions as in preliminary experiments will yield different growth rates and lipid content over time, as the leachate constituents are dependent on precipitation and the contents of the landfill. As such, dilutions will be based on the quantity of a pervasive parameter in the leachate, chemical oxygen demand (COD). COD in the leachate will be monitored in different samples taken over time to determine changes in the leachate throughout the year and for an initial sample over time to determine if degradation occurs. Experiments after the initial of 10% and 33% by volume will be based on the COD of the leachate. Subsequent experiments will use leachate diluted to the COD content as calculated from the volumetric dilutions. A quick screening method for lipid analysis using Nile Red solution will provide an estimate for the algae s lipid content. The pigment Nile Red has been indicated by other researchers as an indicator for neutral lipid, the material of interest in biodiesel production [12]; when added in certain concentrations, Nile Red will fluoresce in a linear fashion to the lipid content in the sample [4, 12, 13]. The results of this method will be compared with fatty acid methyl ester (FAME) content determined from gas permeation chromatography, as well as derivatization using gas chromatography-mass spectrometry (GC-MS) of the algae samples to ensure the method s accuracy. This analysis will be performed by the Center for Air Resources Engineering and Science (CARES) facility at Clarkson University. For quick screening, a TD-700 fluorometer will be calibrated for direct concentration measurements using a green lipid standard. This standard will approximate a range of the lipid content in the samples; by calibrating this standard to some value in the range to be measured, the fluorometer will register a sensitivity that should accurately quantify the lipid content of each sample around the standard. Four-mL samples of algae culture will be taken on a regular basis, every other day, throughout experimentation to measure lipid throughout the growth cycle. The creation of standard curves for lipid content in the presence of 0.1 mg/l of Nile Red will allow for a quick determination of lipid content. Some background fluorescence may occur in the leachate, which has an average oil and grease content of over 50 mg/l according to permit analysis [11]. This high concentration of oils may interfere with the fluorescence of the algal lipids, causing a greater reading for fluorescence. Even diluted leachate interferes with the emission and excitation of the Nile Red and lipids, so all samples will be filtered and re-suspended in media for fluorescence readings. This will result in a reading of solely the neutral lipid content, not the neutral lipid in combination with the oil content of the leachate. The results of this analysis will determine the approximate concentration of leachate in which the algae will best produce lipid. Once the optimal growth conditions for lipid production are determined, a preliminary engineering scale-up will begin; due to time constraints placed by the facility, the batch culture results will be expanded directly to determine the mass and energy flows required in the full-scale process, which will are essential for later environmental analysis. Although the information included in this paper design is necessary to complete this research, it will not be a part of the proposed research but rather a tool for following phases. The initial design will include not only the type of algal bioreactor based on growth conditions, but the sizing and cost of major mechanisms of the system. This will coincide with the mass and energy flows to and from the process s components. As the motivation of this research is the presence of waste heat at the facility, this quantity will be the limiting factor in design specifications, 9

10 and will determine the size of the reactor and the mass and energy balance through the system. The amount of waste heat available, including efficiencies for recovery and transfer, will dictate how much biodiesel can be produced. In order to eliminate the release of heat into the atmosphere, the facility would likely utilize the entirety of energy available. Based on commercial biodiesel production processes and thermodynamic relationships, the available heat will be distributed proportionally to the different uses within the process (see Figure 1). Available energy will dictate the amount of algae that can be grown, which in turn will quantify the inputs necessary for production and the amount of biodiesel produced for B20. Inputs for the growth process include leachate, water, heat, CO 2 (if grown autotrophically), electricity for lighting (if grown autotrophically), an organic carbon source (if grown heterotrophically), and algae as an inoculant. The inputs and growth conditions will determine the design of the growth reactors. This design will include number, size, type, and arrangement of reactors to optimize algal growth. Environmental analysis will be modeled after a previous study done at Clarkson concerning algal biodiesel production in cold climates [7]. A life-cycle assessment (LCA) will be performed on the entire process, from the manufacture of inputs to the final use of the biodiesel including the subsequent emissions. The quantification of inputs and outputs from the preliminary engineering design will form the basis of the LCA. Literature reviews will comprise the majority of analysis, as many of the manufacturing processes and reactions have already been analyzed for the components of biodiesel production. Another asset will be the Greenhouse gases, Related Emissions and Energy use in Transportation (GREET) model, a tool used for quantifying the upstream materials production and energy use in the biodiesel production process [7]. This will be a benchmark for comparison as data on other types of biodiesel already exists, and may also be modified for the purposes here. Parameters to be analyzed are as follows: Total energy consumption Fossil fuel use Land use Potable water use (for leachate dilution) Greenhouse gas emissions Other emissions o Toxins o Particulates These metrics as quantified by the LCA will be compared to current petroleum diesel use at the landfill as well as to soy biodiesel using the GREET model. If unsatisfactory with respect to sustainability, the process design will be modified accordingly. Timeline Since the project s initial funding in the summer of 2010, a number of opportunities have widened its scope beyond my own thesis. In an effort to obtain funding, this research for DANC was turned into a P3 project, a program sponsored by the EPA to fund sustainability research initiatives, and now involves students from a number of disciplines throughout Clarkson s schools. A separate budget allotment from the DANC facility also added an additional timeline for results. As such, certain parts of the project will not be included in my thesis. However, for the project to continue, preliminary design for a continuous flow bioreactor with mass and energy balances will take place in the summer of The timeline below illustrates only the parts of the research for my thesis. 10

11 Summer 10: Feasibility Study of Algal Growth in Leachate Spring 11: Fall 11: Optimal metabolism and growth conditions including lipid and COD analysis Life-cycle analysis and finalization of engineering design for entire process. Preliminary drafts of thesis Spring 12: Finalize thesis and presentation References [1] Chisti, Yusuf. "Biodiesel from microalgae," Biotechnology Advances, vol. 25, pp , [2] Biodiesel and Other Renewable Diesel Fuels, National Renewable Energy Laboratory, Golden, CO, NREL/FS , [3] A. Rengel, Promising technologies for biodiesel production from algae growth systems, in 8th European IFSA symposium, Clermont-Ferrand (France), [4] J. Sheehan et al., A Look Back at the U.S. Department of Energy s Aquatic Species Program Biodiesel from Algae, National Renewable Energy Laboratory, Golden, CO, Close-out Rep. TP , Jul [5] X. Li, H. Xu, Q. Wu, Large-scale biodiesel production from microalga Chlorella protothecoides through heterotrophic cultivation in bioreactors, Biotechnology and Bioengineering, vol. 98, no. 4, Nov [6] H. Xu, X. Miao, Q. Wu, High quality biodiesel production from a microalga Chlorella protothecoides by heterotrophic growth in fermenters, Journal of Biotechnology, vol. 126, no. 4, pp , December [7] R. Baliga and S.E. Powers, Sustainable algae biodiesel production in cold climates, International Journal of Chemical Engineering, vol. 2010, no X, Apr [8] A.F. Clarens et al., Environmental life cycle comparison of algae to other bioenergy feedstocks, Environmental Science Technology, vol. 44, no. 5, pp , Jan [9] L. Lardon et al., "Life-cycle assessment of biodiesel production from microalgae," Laboratoire de Biotechnologie de l Environnement, vol. 43, no. 17, pp , Jul [10] Jiang, G., Billuri, M., Kring, S., and Kaur, K LFGTE waste heat utilization- algae to biodiesel. Report prepared for Clarkson University Industrial Ecology class. [11] P. Chereshnoski, Environmental Coordinator, Developmental Authority of the North Country, Personal Communication, June [12] S.J. Lee et al., Rapid method for the determination of lipid from the green alga Botryococcus braunii, Biotechnology Techniques, vol. 12, no. 7, pp 553-6, July [13] F. Alonzo and P. Mayzaud, Spectrofluorometric quantification of neutral and polar lipids in zooplankton using Nile Red, Marine Chemistry, vol. 67, pp , July

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