Project Number: RWT-1001 Methane Creation from Anaerobic Digestion An Interactive Qualifying Project Report Submitted to the Faculty of the WWOORRCCEESSTTEERR PPOOLLYYTTEECCHHNNIICC IINNSSTTIITTUUTTEE in partial fulfillment of the requirements for the Degree of Bachelor of Science in Civil Engineering by Date: April 29, 2010 Approved: Professor Robert W. Thompson, Advisor i Abstract Anaerobic digestion is the process in which organic material decays in an oxygen free or low oxygen environment. The process releases heat and biogas, which contains methane, carbon dioxide and traces of other gases. The first known use of anaerobic digestion was located in India, in 1859. Today, anaerobic digestion is commonly used for animal waste from farms, food waste from restaurants or food processing plants and wastewater at wastewater treatment plants. Biogas generated from anaerobic digesters can be used to generate thermal or electrical energy, which also reduces methane emissions. Anaerobic digestion can be used in many more parts of the world. The parameters that affect it’s usage is the size of the plant or farm, amount of manure being produced, initial capital investment, frequent maintenance, and obeying the land use law and utility companies. ii Acknowledgements We would like to thank Professor Robert Thompson for all of his help with this project. We would also like to thank Nadia Caines and Charles Tyler from the Deer Island Waste Water Treatment Plant, Bert Waybright from Mason Dixon Farms, Debra LaVergne from the Upper Blackstone Water Pollution Abatement District and Joe Ramirez from White Energy for their time and help in the completion of this project. iii Table of Contents Abstract ................................................................................................................................. i Acknowledgements ............................................................................................................. ii 1.0 Introduction ............................................................................................................... 1 2.0 Background ............................................................................................................... 3 2.1 Anaerobic Digestion ..................................................................................................... 3 2.2 Methane and Biogas ..................................................................................................... 9 2.3 Wastewater in the US ................................................................................................. 10 2.4 Dairy Farm Costs ....................................................................................................... 10 3.0 Case Studies ............................................................................................................ 13 3.1 Deer Island ................................................................................................................. 13 3.2 Point Loma Wastewater Treatment Plant .................................................................. 19 3.3 Mason Dixon Farm ..................................................................................................... 23 3.4 The South Shropshire Biodigester .............................................................................. 27 3.5 Vermont Studies .......................................................................................................... 28 4.0 Possible Places ........................................................................................................ 30 4.1 Upper Blackstone Water Pollution Abatement District ............................................. 30 4.2 Hereford, TX ............................................................................................................... 33 5.0 Discussion ............................................................................................................... 41 5.1 Pros and Cons of Anaerobic Digestion ...................................................................... 41 5.2 Other Applications of Anaerobic Digestion ............................................................... 42 5.3 Other Waste to Energy Methods ................................................................................. 43 5.3.1 Pyrolysis .................................................................................................................. 44 5.3.2 Gasification ............................................................................................................. 45 6.0 Conclusions ............................................................................................................. 48 Appendices………………………………………………………………………………A1 A.1 Average Residential Electricity Costs in the United States (2008)……………………….A1 A.2 Operational Agricultural Anaerobic Digesters in the United States……………………..A3 iv Table of Figures Figure 1-1:US Electric Power Industry Net Generation in 2007 .................................................... 1 Figure 2-1: Anaerobic Digestion Phases......................................................................................... 4 Figure 2-2: Biogas Production by Feedstock .................................................................................. 6 Figure 2-3: Livestock Farms with Anaerobic Digesters ................................................................. 8 Figure 2-4: Methane Molecule........................................................................................................ 9 Figure 2-5: Estimated Capital Cost ............................................................................................... 12 Figure 2-6: Estimated Capital Cost Per Cow ................................................................................ 12 Figure 3-1: Deer Island Water Treatment Plant, Boston, MA ...................................................... 14 Figure 3-2: Aerial View of Deer Island Wastewater Treatment Plant Digesters ......................... 16 Figure 3-3: Deer Island Wastewater Treatment Plant Process…………………………………. 17 Figure 3-4: Point Loma Wastewater Treatment Plant Treatment Process .................................... 21 Figure 3-5: Aerial View of Point Loma Wastewater Treatment Plant in San Diego, CA ............ 22 Figure 3-6: US Average Residential Electricity Retail Price in 2007 .......................................... 24 Figure 3-7: Aerial View of Mason Dixon Farms in Gettysburg, PA ............................................ 26 Figure 4-1: Aerial view of the Upper Blackstone Water Pollution Abatement District in Millbury, MA .............................................................................................................................................. 32 Figure 4-2: Panda Energy International Facility in Hereford, TX ............................................... 35 Figure 5-1: Pyrolysis of Solid Municipal Waste........................................................................... 45 Figure 5-2: Schematic of MSW Gasification and Power Generation Plant.................................. 46 1 1.0 Introduction Throughout history, mankind has been using fuel to generate energy. Today, electricity is one of the most heavily relied upon energies in industrialized nations. In 2007, approximately 4.2 billion kilowatt-hours of electricity were generated in the United States.1 Figure 1-1 illustrates the breakdown of fuels that were used to generate electricity. Figure 1-1:US Electric Power Industry Net Generation in 2007 (Source:http://media.photobucket.com/image/us.gif) Approximately 72% of electricity generated in 2007 was produced by coal, natural gas, and oil. These are the leading energy sources used today. These fuels are known as fossil fuels. Since a quarter of the Earth’s known coal resources are located in the United States, coal is the most common fuel in the United States. 1 EIA, Form EIA-923, “Power Plant Operations Report,” www.eia.gov, 04/10/10. 2 Fossil fuels are formed when organic materials, such was plants or animals, decay underground near an underground heat source. The combination of heat and pressure over millions of years creates fossil fuels, such as coal, oil and natural gas. Fossil fuels are used because they can produce relatively high levels of net energy, when compared to other fuels.2 Fossil fuels take millions of years to replenish and the world is using fossil fuels at a rate far greater rate than they are being replenished. Different alternatives must be sought to conserve fossil fuels and construct a much cleaner energy source to produce electricity. In figure 1-1, only 8.3% of electricity being produced in the U.S. was used by renewable energy. The main advantage of fossil fuels is their high efficiency. But recent findings about their environmental impact have raised many new concerns. Burning fossil fuels produces sulfur- dioxide, nitric-oxide and other pollutants, which either causes air pollution or requires expensive scrubbers. Even with proper pollution controls, waste material such as ash, carbon dioxide and other gases are produced. Many of the gases produced are released into the atmosphere where they can cause acid rain or act as greenhouse gases. Burning pure natural gas produces no solid waste material and releases less carbon dioxide than petroleum or coal2. With growing concern for the environment and sustainability the government is pushing for renewable alternative sources for energy. Reducing the amount of carbon emissions will greatly reduce the impact that global warming has on the environment. The use of renewable resources will also ensure a reliable energy source as fossil fuel supplies dwindle. Renewable resources will also help the US to diversify their energy sources so they do not become reliant on one single source, which can prove disastrous if that source becomes compromised. 2 Commission, California Energy. (2006). Energy Story- Fossil Fuels. Retrieved December 15, 2009, from Energy Quest: http://www.energyquest.ca.gov/story/chapter08.html 3 2.0 Background This chapter will discuss all the background information that was deemed important to this project. Information in this section will serve as a knowledge base for the other sections in this paper. The background will cover the anaerobic digestion process, the products and waste production in the United States. 2.1 Anaerobic Digestion Anaerobic digestion was practiced in the 10th Century for heating baths in Assyria by biogas, gas produced by the breakdown of organic matter. In the 17th century, Jan Baptita Van Helmont of Belgium discovered that decaying organic matter produces flammable gas. In 1808, the British chemist Sir Humphry Davy discovered that methane gas was present in cow manure. The first known plant to use anaerobic digesters built in a leper colony in Bombay, India in 1859.3 Today, Germany converts half of their biogas generated from sewage sludge digestion to fuel cars. However, the most common use for anaerobic digestion is on farms and in waste water treatment plants. Anaerobic digestion occurs when organic material decays in an oxygen-free or low oxygen environment. Anaerobic methane recovery occurs in bio-digesters, where organic matter is digested, and produces a fuel called biogas. This process conserves nutrients and reduces pathogens in organic matter. David House states in his book, 1000 lbs of human waste can produce 0.6 cubic meters of biogas.4 3 Penn State University. (2010). A short history of AD: Penn State University. Retrieved December 15, 2010, from Penn State Univeristy: http://www.biogas.psu.edu/pdfs/ShortHistoryAD.pdf 4 House, D. (2006). The Biogas Handbook. Aurora: House Press. 4 Anaerobic digestion occurs when organic material is broken down by bacteria in four major processes: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Hydrolysis is the process in which carbohydrates, proteins, fats are converted to sugars, fatty acids, and amino acids. Acidogenesis is the process in which the sugars, fatty acids, and amino acids are converted to carbon dioxide, ammonia, and carbonic acids. Acetogensis is the process which creates acetic acid and carbon dioxide. The final process, methanogenesis, is when biogas is formed. Biogas contains a mixture methane and carbon dioxide gases. The extracted methane can provide a fuel for heat and electricity.5 Figure 2-1: Anaerobic Digestion Phases (Source: University of Strathcylde, 2010) shows a summary the anaerobic digestion processes. Hydrolysis Acidogenesis Methanogenesis Bacterial Cells Protiens Amino Acids (Digestate) Volatile Fatty Acids (Acetates) Carbohydrates Simple Sugars Methane CO and 2 Hydrogen CO and Fats Fatty Acids 2 Hydrogen Figure 2-1: Anaerobic Digestion Phases (Source: University of Strathcylde, 2010) There are two common types of digesters used for anaerobic treatment: batch and continuous. Batch digesters are the simpler of the two because the material is loaded in the digester and then allowed to digest. Once the digestion is complete, the effluent is removed and the process is repeated. 5 Anaerobic Digestion.Com. (2010). Advantages and Disadvantages: Anaerobic Digestion DotCom. Retrieved November 13, 2009, from Anaerobic Digestion DotCom: http://www.anaerobic- digestion.com/html/pros___cons.html 5 In a continuous digester, organic material is regularly fed into the digester with the constant loading and unloading of effluent. The material moves through the digester either mechanically or by the force of the new feed pushing out digested material. There are three types of continuous digesters: vertical tank systems, horizontal tank or plug-flow systems. Continuous digesters are most common for large-scale operations.6 Temperature is carefully controlled in anaerobic digestion systems. There are two common environments for anaerobic digesters: thermophilic and mesophilic. The difference between the two environments is the temperature at which the organic material, or sludge, is digested. Thermophilic digestion operates around 50 to 60 °C (120 to 140 °F). The quick breakdown of sludge allows digester volume to be small, relative to mesophilic systems. The average digestion time is approximately three to five days. Thermophilic digestion require more insulation and more heat energy and are more sensitive to incoming materials and temperature changes, compared to the mesophilic digestion system. 7 Mesophilic digestion operates around 35 to 40 degrees °C (95 to 105 °F). The average digestion time is 15 to 20 days. Mesophilic is more common in wastewater treatment plants because thermophilic treatment due to cost and more energy is required to have more sophisticated control & instrumentation, as a thermophilic system would need.8 6 U.S. Department of Energy. Anaerobic Digestion Types and Designs. 2010. http://www.energysavers.gov/your_workplace/farms_ranches/index.cfm/mytopic=30004 (accessed December 2, 2009). 7Industrial Gas Plants DotCom. (n.d.). Biogas Plant: Industrial Gas Plants DotCom. Retrieved November 19, 2009, from Industrial Gas Plants DotCom: http://www.industrialgasplants.com/biogas-plant.html 8 Industrial Gas Plants DotCom. (n.d.). Biogas Plant: Industrial Gas Plants DotCom. Retrieved November 19, 2009, from Industrial Gas Plants DotCom: http://www.industrialgasplants.com/biogas-plant.html