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A Model Bioconverter MAG
The Brookhaven Township is a suburban community on the north shore of Long Island, New York. In the second half of the twentieth century, two major areas of concern have been the energy crisis and the ongoing problem of refuse disposal. Due to the rapid growth and development rate of the Long Island region, it has become increasingly difficult to find a safe, efficient solution to these problems. In addition, significant space restraints are a key limiting agent in the quest for an answer. Although Brookhaven Township, a generally middle-class sector of Suffolk County, has searched for a viable means of dealing with these issues, none has been found to date.
Investigation of the Problem
Although nearly every region of the country feels the need for improved energy sources, as well as better garbage disposal, the people of Long Island are particularly feeling the strain. An average resident of New York State generates five pounds of solid waste each day, but on Long Island, this figure rises to eight pounds per person. Traditionally, Suffolk County has relied heavily on the use of landfills for disposal of its trash. In 1992, a total of 2,084,500 tons of garbage was dealt with as follows: 54.1% landfilled, 29.6% incinerated, 14.7% recycled, and 1.6% transported out of county. These methods are merely temporary answers that cannot be depended on for the future. The Brookhaven landfill is nearly full; incineration is environmentally unsound; and transporting garbage is extremely costly. Therefore, a better method is required.
In addition to the difficulty Brookhaven faces regarding garbage disposal, residents of this area also pay some of the highest energy rates in the country. The Long Island Lighting Company (LILCO) holds a monopoly on the electricity used by Long Islanders, and is therefore able to charge what many consider to be exorbitant prices. The average national cost of power is eight cents per kilowatt hour; however, on Long Island, this figure rises to sixteen cents. This discrepancy has resulted in a demand for less expensive sources of power.
The combination of the lack of affordable energy coupled with the high expense of waste reduction has made Long Island, and especially Brookhaven, an increasingly undesirable place to live.
The Plausibility of the
Although there are several plausible solutions for the energy crisis facing Long Island, including wind power, nuclear energy and solar power, bioconversion is the only method that would also decrease the garbage problem. Bioconversion is a form of recycling in which organic waste is metamorphosed by microorganisms into usable fuel. It has been estimated that if everyone recycled organic waste, rather than throwing it out, the influx of garbage into landfills would decrease by at least forty percent. Because one of the end products of bioconversion is fuel, this process can be used to produce energy as well as dispose of solid waste. In effect, the garbage of the community can be transformed into power which is less costly than that provided by LILCO.
Specifically, the bioconversion process transforms organic wastes (or biomass), into usable methane gas and a fertilizer rich in nutrients. The bacteria naturally found in decomposing wastes will produce these products through anaerobic digestion. In an oxygen-free environment, microorganisms digest carbon and nitrogen compounds contained in the rotting materials and excrete methane, often called biogas. This process, anaerobic fermentation, results in virtually no unusable byproducts. When the methane gas is channeled into a generator, electricity can be provided to homeowners. According to the Environmental Protection Agency (EPA), daily refuse from 70% of the United States population would yield energy equivalent to that of 500,000 barrels of oil. The Department of Energy asserts that at least 28% of our nation's energy needs could easily be fulfilled by the use of bioconversion.
The bioconversion process is generally considered to have five major steps. To begin with, some sort of recycling program must be implemented in order to collect biomass from the community. At a bioconversion center, the organic waste is shredded and mixed into a slurry. This slurry is then fed into an anaerobic digester for fifteen to thirty days. The resulting methane is refined to meet standard sales specifications and bottled for consumer use. The byproducts of the bioconversion process may be used for fertilizer.
It is apparent from the definition of the bioconversion process that it could certainly be applicable to the problems facing Long Island. An intensive analysis of the pros and cons will be discussed at a later point.
In order for any new proposal to work, it must have public support. In order to determine the willingness of the Brookhaven community to participate in waste recycling, we conducted a model program in the spring of 1994. Currently, under three major community-sponsored programs, the residents of Brookhaven Township recycle glass and plastics (numbers one and two), newspaper, and regular paper products, designated days for the recyclable garbage to be collected for recycling centers. This system works fairly well, and reduces the amount of refuse shipped to landfills. Because Brookhaven Township has had a relatively high rate of success, we decided to follow their lead. We asked members of the community to separate organic waste from the rest of their garbage, and leave it by the curb for collection. We picked up the trash once a week for ten weeks from approximately 35 households, spread over an area of 60 miles. In addition, all participants were surveyed before and after the program to determine their knowledge of and thoughts on the program.
We were interested in the recycler participation rate and the weight of the refuse each household produced. From these figures, we were able to decide whether there was enough public support for bioconversion to make research and implementation worthwhile.
Recycler participation was very high, generally around 90%. This shows that once committed to the program, people were willing to continue with it until completion. We feel that this trend would be even stronger in an actual community program, as opposed to a model one. If every household in Brookhaven separated organic waste, about 20 percent of all garbage could be used for bioconversion.
Basically this indicated that our project was a success. In a final survey, 92 percent of the recyclers responded that they would be willing to participate in similar program. In addition, at the conclusion of our experiment, 69 percent felt that they had gained significant knowledge about the bioconversion process. Furthermore, these participants indicated that this knowledge made them more willing to take part in another program.
The great concern about environmental and economic issues has led us to believe that government officials need to be informed of the possibilities presented by the bioconversion process. Therefore, our proposal involves three major steps: self-education, construction and testing of a model bioconverter, and presentation of our findings to local representatives.
The University of Maine at Orono has the only running full-scale bioconverter in the country. It processes manure from the campus dairy farm, as well as all food scraps from the cafeteria. This plant has been operating since 1984. A team headed by Professor George K. Criner has done extensive research on the feasibility of bioconversion-based power and has diagrammed several designs for bioconverters. We have exhausted local resources in educating ourselves about the bioconversion process, and as a result, we propose to visit the University of Maine in order to glean more information. In addition, by having the opportunity to talk to the leading researchers in the field, we would be able to ask them questions about bioconversion, and its possible applications to Brookhaven Township.
After speaking with experts at the University of Maine, we propose to build a prototype bioconverter capable of digesting the organic waste of two families. We plan to run the anaerobic digester for approximately six to eight weeks in order to collect data. We hope to determine the amount of methane gas that can be produced per family and calculate the energy which could be produced from this gas. In addition, this will provide us with the maintenance required to keep such a system running.
Lastly, we intend to tabulate our findings and present them to government representatives from the Brookhaven area. Several representatives have already expressed a willingness to advocate further research if they feel that bioconversion would be beneficial to their district. Furthermore, New York State Assemblyman Steven EngIebright indicated a strong interest in the bioconversion process and in the information we could provide him with. We hope that by sharing our knowledge with local officials, we will incite them to take an active stance in securing funding and facilities for further research.
In building a model bioconverter, climatic conditions, space available, and type and quantity of biomass to be digested must be taken into account. Our prototype will be operating in a typical Long Island summer with no shelter from the sun; in other words, the bioconverter will be allowed to reach temperatures in excess of 100 degrees Fahrenheit as well as high humidity. Because of these circumstances, we feel that a plug flow digester will be best suited to our purposes. This is a continuous flow converter, which will allow organic matter to be added once a day. Waste will be fed into the system as a slurry consisting of 10 to 15 percent solid, and 85 to 90 percent water. Digestion will take approximately 15 days, and the low-odor effluent, which will be used as fertilizer, will be permitted to flow directly out of the digester into a holding tank. Methane gas will rise through a pipe in the top of the digester to a flexible collection vessel.
The main body of the converter will consist of a cylinder of either fiberglass or coated of glass-lined steel. The cover will be made of PVC (polyvinylchloride) or CPE (chlorinated polyethhylene) which has been coated for sunlight protection, and will have a pressure release gauge in order to maintain optimal pressure conditions. PVC is fairly inexpensive yet has an excellent resistance to chemicals and a life expectancy of five years when shielded from direct sunlight. However, when exposed to cold temperatures, it does not retain flexibility, and in direct sunlight it lasts only one year. CPE is very resistant to high temperatures, moderately priced, and easily repaired, but it is relatively low-strength. In our research, we have been unable to ascertain what type of material is desirable for pipes leading in and out of the digester. We hope that our study of the University of Maine center will provide us with answers to this and other questions.
Research on a running bioconverter has demonstrated the importance of stability within the system. The bacteria found in the organic waste yield the highest amount of methane at temperatures in the mesophilic range of 85 to 104 degrees Fahrenheit. In addition they require a fairly neutral pH, optimally between 6.6 and 7.6. Ideal pressure is defined as 0.5" water gauge or more, and it is important to keep air from entering the system, while at the same time preventing a vacuum from forming.
There are numerous benefits that can be obtained from implementing bioconversion in Brookhaven Township. Food wastes - derived from the kitchens of households, restaurants and institutions - are estimated to account for as much as 15 percent of the nation's municipal solid waste. Biogas from anaerobic digestion of organic residue is utilized in various ways: as a substitute for natural gas or liquid propane which may require scrubbing and compressing; burned directly in a boiler; or to fuel an internal combustion engine which powers an electrical generator. Nearly all power on Long Island is derived from either natural gas or oil, and a reasonable percentage of both of these commodities could be provided by the bioconversion process, while at the same time recycling organic waste. George Criner says of the Maine plant, "Our unique use of the widely accepted treatment process of anaerobic digestion is showing that it is an effective way to deal with tons of food waste. We are taking valuable organic material out of the waste system, reducing the amount of garbage to be hauled away or incinerated, while creating electricity and valuable fertilizer material as the byproducts." In addition, the National Energy Strategy states that, with successful research, liquid fuels from biomass could possibly provide 3.2 - 4.2 times 1018 joules of energy per year by 2030, and other estimates are even greater. This means biofuels could displace millions of barrels of oil, decrease our dependence on foreign oil that contributes so much to the U.S. trade deficit, and generate thousands of jobs for U.S. citizens. Biofuels represent the only existing renewable technologies capable of producing liquid transportation fuels [that would save the U.S. one million barrels of oil annually] and fuel additives that can displace conventional fossil fuels.
The bioconversion process does present several cons, but the net effect of these cons is less severe than those presented by any other method. Although the electricity that could be produced from biogas is less expensive than that currently being generated by LILCO, profits would not be apparent until approximately eight years after the plant begins operation. Therefore, a lump sum of money must be available from the outset, and would not be repayable for nearly a decade. The Maine bioconverter cost $105,000 to build, and annual repair and maintenance costs equal $1,074. In addition, the plant must be closed down for eleven days annually for cleaning, and so an alternative energy source is needed at that time.
Through extensive research and previous experimentation, we have determined that bioconversion does in fact seem to be a viable solution for the garbage and energy problems faced by Brookhaven Township. We feel that construction of a prototype bioconverter based on the full-scale plant at the University of Maine - Orono would provide the incentive to the public and local government to investigate the plausibility of opening a facility capable of serving the community in the future. u