The Green Machine Interim Design Report Duncan Pfeifer, Dallace Sevier, John Boyd, Robin Peterson, Kyle Artrip Composter@uidaho.edu 1
TABLE OF CONTENTS Section Page Number Executive Summary...3 Background.4 Problem Definition...5 Concepts Considered..8 Concept Selection. 16 Selected Design.20 Future Work.23 References.25 Appendix A.26 Appendix B-Budget to Date...27 2
EXECUTIVE SUMMARY The University of Idaho s President recently made a proclamation to create a more sustainable University, working towards the goal of a zero carbon footprint by 2030. Research done by two prior projects identified, categorized, and quantified the amount of waste that the University of Idaho produces as well as identifying possible areas of improvement. The University of Idaho needs to reduce the costs of transporting biodegradable waste to the local landfill and a way to take care of the mortalities created by the various animal units on campus. A composting system will reduce cost of disposing the food wastes and other biodegradable as well as creating a product of bedding material for the University s Dairy that will alleviate the need to purchase it from other sources. Many universities have turned to composting operations as sustainable and long-term solutions to their waste problems. Several different systems are currently in use at other composting sites that the University could incorporate into its own system design. Composting system design is dependent on a variety of factors including site requirements, waste stream type and volume, weather, and the type of bulking materials available. The design recommended for the University of Idaho s particular site is a combination of an aerated static pile and an aerated bin system. The major costs for the project include the purchase of a mixer and site preparations, both of which are necessary to create a suitable product. The total cost of this system is estimated to be about $85,000, not including the cost of a full time operator and costs involved with operating the blower and front-end loader. 3
BACKGROUND Student research completed by Tom Nagawiecki in spring 2009[1] and a further food waste sampling project from 2007-2008 completed by Jerrod Loveland [2] showed that the University of Idaho creates nearly 1500 tons of waste every year in the form of food waste, animal carcasses, and other various waste streams. Campus Dining alone generates an estimated 100 tons of compostable food waste every year [2]. The University of Idaho Dairy and Vandal Meats formerly disposed of animal carcasses and slaughter offal through a rendering service in Spokane. This year the company announced it will no longer provide this service to the University [1]. The Dairy produces approximately six full bovine carcasses per year, while the beef unit fills a 60-gallon drum every two months with offal. The sheep unit also needs to dispose of additional carcasses. In his 9/16 letter to the University of Idaho Community, President M. Duane Nellis outlined the University s need for an active commitment toward sustainability by prioritizing eight Strategic Innovation Initiatives. One of these initiatives is waste minimization working toward a zero carbon footprint for the campus by 2030. Another issue of note is that the University spends a large amount of money dealing with its own waste production. Therefore, it has set the goal to reduce the waste generated by 20% and the amount of waste recycled increased to 60% by 2013. These current issues facing our campus represent a unique opportunity to provide a sustainable solution to formerly costly waste disposal procedures while applying classroom engineering knowledge. Several University departments including Campus Dining, the Dairy, and the University of Idaho Sustainability Center have already invested time and money into the generation of a composting facility to reach these goals. The proposed system will need to incorporate the entire food, animal carcass, and dairy waste streams at a composting site near the University of Idaho Dairy. This system would not only 4
reduce the total amount of waste produced by the University, but would allay the considerable disposal costs from these sources. Additionally the composting system would produce bedding material for the dairy, which is currently purchased and transported from Washington State University. The facility would also provide research and study opportunities for students from a variety of courses and departments. PROBLEM DEFINITION Specific Needs The purpose of the project is to design and implement a composting system for the University of Idaho. This system will: Utilize 100% of compostable food waste from Campus Dining Utilize all dairy, beef, and sheep mortalities Be robust and expandable Strive for a low capital cost Have a low daily operations cost Be accompanied by instructional material for use Campus Dining generates estimated 100 tons of sorted compostable food waste every year. Adjusting for an eight month school year the volume of waste produced on a typical busy weekday is a maximum of 900 pounds. This food waste will be accompanied by 6-7 full bovine carcasses and a 60 gallon drum of slaughter offal every other month. Manure is available on-site for mixing. Composting Considerations The composting process takes advantage of the natural breakdown of waste materials by microorganisms through the optimization of the conditions under which they metabolize organic material. The decomposed material can then be used as livestock bedding material or fertilizer to improve soil structure and nutritional content depending on its final Carbon to Nitrogen (C:N) ratio. The 5
starting material for compost can be anything from food waste and garden cuttings to livestock manure and animal mortalities. The process requirements are dependent on the amounts and types of these starting materials. The flowchart provided outlines the basic steps involved in composting operations. This report will address mainly steps 2, 3, and 5. Sorted food waste will be delivered to the facility from Campus Dining on weekdays. The food waste can either be immediately mixed a loaded into the composting bins, or it can be piled and covered with straw or woodchips to prevent animal interference. Mixing is essential in order to begin the process with a mixture homogenous in content and particle size, and will also help to shorten the total composting time. Firgure 1 The major component of the source material is food waste, so C: N ratio and moisture content of the pile will be adjusted around the characteristics of the food waste. The calculations from this adjustment using woodchips and cow manure put the mixing ratio of 1:.28:.68 (food waste: manure: 6
woodchips) by weight. For every pound of food waste, there will be.28 pounds of manure and.68 pounds of woodchips added. This will make the total amount of material needing to be composted every day during the week will be 1700 pounds. [5,6] The active composting step depends on several control parameters including the pile moisture content, the amount of oxygen moving through the pile, its temperature, and the overall carbon to nitrogen (C: N) ratio of the material. Maintaining moisture content between 30% and 60% is necessary. At levels below 30% the dust limit is reached and excessive pile drying will occur, slowing microbial metabolism. At levels greater than 60%, oxygen flow is severely depleted and anaerobic conditions can occur. Under anaerobic conditions composting time will sharply increase and foul odors will be released. Carbon and Nitrogen Content of Common Compost Ingredients* Material % Carbon %Nitrogen Fresh manure, cow 12-20 0.6-1.0 Fresh manure, horse 20-35 0.5-1.0 Grass clippings, fresh 10-15 1-2 Fallen leaves 20-35 0.4-1.0 Newspaper or cardboard, dry 40 0.1 Wood chips or sawdust 25-50 0.1 Kitchen scraps 10-20 1-2 Weeds, fresh 10-20 1-4 * average; based on fresh weight Table 1: Numbers taken from Organic Gardening [4] Food waste and fresh manure both have high moisture contents (near 85%), so wood chips or straw will need to be added to bulk the mixture and preserve porosity in the piles at a ratio of 1:.28:.68 (food waste: manure: woodchips) by weight. This mixture results in 1700 pounds per day to be treated, or a volume of 42.8 cubic feet. Air can be pushed through the piles (positive aeration) or sucked through (negative aeration) in order to provide adequate oxygen. During the first few days of active composting, the pile will not be aerated in order to achieve the high temperatures (140-170 F) required to destroy pathogens and weed seeds in the mix. The heat 7
generated by the organisms is developed during the oxidation of carbon into CO 2 or the conversion of CH 4 (ammonia) to CO 2 based on the type of composting being used [3]. Once pathogens are destroyed by sustained high temperatures, aeration will commence and the pile temperature fall slightly. The aeration cycle will depend on pile temperature, and can be manually or automatically controlled. Once the active composting cycle is complete (3-5 weeks) the material will be piled again and allowed to cure for 3-7 weeks to stabilize. Finished compost can also be piled on top of new mixture going into the composter to preserve heat and protect it from vermin and weather. CONCEPTS CONSIDERED Rectangular Agitated Bed Composting The idea of composting food and animal waste using a rectangular agitated bed was strongly considered during the project learning phase. Rectangular agitated bed composting uses the combination of controlled aeration and periodic turning to compost food and animal wastes. Research was conducted on the equipment and materials needed the construction of a rectangular agitated bed composter. The design involved constructing three 8x30 foot composting beds out of ecology blocks placed on top of a concrete slab. The slab would contain recessed aeration piping, which would then be attached to a blower. The ecology blocks would support a rail systems so that a motor/mixer platform could roll freely down the composter beds, similar to the below design. 8
Figure 2 (On-Farm Composting Handbook) The benefits of using the rectangular agitated bed composting system is that composting time is shortened and the area needed for the system is relatively small. The biggest drawback is that the capital costs can be high and the time involved in designing the motor and rail system is unrealistic for the scope of this project. After discussing the pros and cons of the system and calculating the estimated cost and time involved with developing a functioning rectangular agitated bed composter, the decision was made to not go with the rectangular agitated composter. The project research that was involved in learning about this system proved to be beneficial for the final design selection for the composter. The composting bin layout and size from the rectangular aerated bed was preserved along with the use of ecology blocks. Windrow Composting Windrow composting involves forming mixed compost into parallel rows. Aeration occurs by natural, passive air movement over the piles. Periodic turning is required, usually 2-5 times per week based on pile height, contributing to significant labor demand. Turning releases trapped gases and heat, as well as further reducing particle size. Turning windrows requires specialized equipment that may either be pulled behind a tractor or operate as a standalone vehicle. This equipment ranges in cost from $30,000 for pull behind equipment to $250,000 for standalone vehicles. Windrow composting requires a large area to pile out compost mix since contact with moving air is required. This technique typically takes 5-6 weeks for active composting, but weather factors may lengthen the process since there is no enclosure or ventilation. While windrow composting produces a high quality uniform finished product, its high equipment cost, extensive labor requirements, and lack of process control make it unsuitable under our considerations. 9
Aerated Static Pile Composting Another method of composting is the aerated static pile. Aerated static piles utilize blowers to either draw air into (negative aeration) or force air through (positive aeration) piles of material to be composted. This aeration not only provides oxygen to microorganisms, but provides a means of temperature control. Blowers can either be time based or temperature based. Time based systems regulate the pile s environment by using a set schedule of turning the blowers on and off. On/off period lengths are set by the temperature of the pile. Periods are set to balance the pile temperature at the desired ranges. Temperature base control systems use electronic controls to control blower operation. Controls of this type can either be implemented by the blower being turned on and off, or by the application of baffles being opened and closed. Aerated static piles added environmental controls help to process the compost more efficiently, leading to shortened compost times. General compost time for an aerated static pile is between 3-5 weeks. Building an aerated static pile begins first with the blower and piping. Many of the specifications for these components are dependent on the amount and type of material being composted. Centrifugal axial-blade blowers are generally used in compost situations. Sizes for the blowers are dependent on the application; temperature-based systems have larger blower requirements then time-based ones. Blowers need to be large enough to maintain an air velocity of 2000 feet per minute in the pile and piping system. Aeration for multiple piles can be handled by the application of one central blower of a high capacity or by several smaller ones. Like the blowers, piping specifications are based on application. The piping involved in an aerated static pile is often made from plastic, but can be made of metal as well. Plastic tends to be cheaper and more resistant to corrosion. The thickness of the pipe wall needs to be large enough to support the weight of the compost material as well as to be durable enough to support the application. 10
For example, some piping systems are designed for one-time use, while others are strong enough to be used for many years. To protect their longevity, pipes can be recessed into the ground with some sort of filter media (perforated grating or gravel) above them. To assist with air circulation, the pipes in aerated static piles are perforated. If the pipes are recessed, the void space around them needs to be cleaned or maintained regularly to prevent uneven air circulation. Holes are generally drilled at regular increments, and the spacing between each hole is dependent upon the diameter and length of the pipe as well as the size of the holes. Holes should be drilled at the 5 o clock and 7 o clock positions to help prevent blockage. Maximum pipe length depends on what type of system is being implemented (time- or temperature-based). Time-based systems can be up to 75 feet long, while temperature-based systems allow for pipe lengths of up to 50 feet. If the pipes are above ground, they need to be covered with some sort of porous media to facilitate better air diffusion through the pile. The porous media must not extend to the edges of the pile or else the bulk of the air will not be directed through the compost material. The porous media may be made of wood chips, bark or gravel. The most important step in building an aerated static pile is proper mixing of feed stocks and bulking material. The more homogeneous the mixture, the better the aeration will be within the pile. If the material is not properly mixed channeling can occur. Channeling is the preferential movement of air through larger pore spaces. Channeling causes uneven composting, and may require the pile to be remixed and/or rebuilt. This is especially important in static piles because they will not be turned. Bulking materials provide structure to the pile to prevent the loss of porosity over time. They generally have higher carbon content, and can be used to create an ideal starting Carbon to Nitrogen ratio. Examples of bulking materials include but are not limited to wood chips, bark, sawdust, recycled compost, leaves, shellfish shells, waste paper, shredded tires, and straw. Caution must be taken with 11
bulking materials such as straw and paper because they will break down over time, causing the piles to collapse. Inversely, some materials, such as shellfish shells and tires, will not break down and so may need to be screened out from the final compost product. Oftentimes screened bulking material can be reused as a bulking agent to build new composting piles. There are several ways of building composting piles, but generally there are two main types of forms: individual piles and extended piles. Individual piles, as the name implies, are single piles and are built between 5 and 8 feet tall. They can be rounded or of a pyramidal shape. The taller the pile, the more heat will be held inside. This is an especially important factor in northern latitudes where the cold conditions of winter can slow composting dramatically. Pile height is also dictated by the power of the chosen blower; the height must not exceed the capacity of the blower to be able to move air and/or heat through the pile. Pile width should generally be equivalent to the pile height. This allows for even air flow throughout the pile. Composting pile length is dependent on pipe length (which is dependent on the situation), but may be longer than the pipe. Pipe length can be defined by the length of the pile minus two times the pile s height. Oftentimes the surface of the pile that is exposed to the environment will not compost as fast as the rest of the pile. To help alleviate this issue, piles are often covered in a layer of finished compost. This layer not only helps to keep heat in, but helps to prevent the attraction of pests such as birds, mice, and coyotes. Extended piles are similar to individual ones, except that in this case new piles are built in contact with older piles. Each of these adjacent piles are called cells, and each cell is its own batch of compostable material. This arrangement allows for a larger volume of material to be processed within a smaller space and also helps to maintain temperature levels in colder environments. Extended piles are best used in situations in which large amounts of similar material come in for processing daily and when 12
composting batches do not need to be segregated. Materials that take longer to compost than others already in the pile (ex: carcasses vs. manure) should not be introduced into an extended pile. Variations in composting time can make removal of the final product difficult. In extended pile systems, cells are often separated by a layer of finished compost that serves as a barrier to prevent mixing of compost at different stages. Each individual cell requires its own line of aeration (one blower per cell or a single large blower that moves air through multiple pipes). When removing finished material from an extended pile, caution must be taken to minimize disturbance to the adjacent unfinished cells. Aerated static piles can produce offensive odors, but the amount of odors is typically less than in other systems (most notably windrows). Positive aeration systems tend to generate more odors than negative aeration systems. This is because air from negative aeration systems can be processed through a filter to remove some of the offending smell. Filters can be made of activated carbon or finished compost. The high carbon to nitrogen ratios within these filters help to adsorb the offending compounds and prevent them from being released into the air. Biological activity can also help to break down malodorous compounds. This is especially true when using finished compost as the filter media. The volume of filter media depends on the blower s capabilities and the amount of odor that is acceptable to be released. Another thing to be considered when choosing between positive or negative aeration systems is moisture management. In a negative aeration system, because the blower is pulling air through the pile, moisture is also pulled out. To prevent this moisture from damaging the blower, some form of a moisture trap must be employed. In either a positive or a negative aeration system, moisture content needs to be maintained between 40 and 65 percent. A reduction in moisture content can be accomplished through the establishment of good drainage parameters and/or the use of low-moisture 13
bulking materials. If a pile becomes too dry, an increase in moisture can be achieved by manually applying water to the piles. In-Vessel Composting With the land size available for use in this process, in-vessel composting was researched as this would give us the smallest amount of land space. In-vessel composting refers to any composting technologies that confine the composting materials within a building, container, or vessel. In-vessel methods rely on a variety of forced aeration and mechanical turning. The big advantage of this system over all other composting methods, is that it takes what works best for each system and combines them into a very efficient method. The drawback is the very high capital costs and technical knowledge required to run the process on a daily basis. Several in-vessel companies were found and contacted such as Green Mountain Technologies that produces EarthTub. The EarthTub works by rotating a mechanical auger around a large tub. The lid enclosing the tub is what contains the mechanically turned auger. For the daily requirement of food waste that we would receive, it would be necessary to purchase three EarthTubs together at a cost of $38,000. Figure 3 14
Another company we contacted was BW Organics in Sulphur Springs, Texas. They use a rotary drum as their in-vessel method. The quote they gave us was $56,000 which included the rotary drum (Figure 3), conveyor belt to load rotary drum, mixer, electrical costs and delivery. Figure 4 The last company contacted was Biosystem Solutions, based out of Connecticut. They use what they call a biochamber (see figure below). The quote received was for $150-175 thousand dollars which includes a mixer, the biochamber, and computer system to automate the process. This price was half of what they normally charge because they wanted to do a partnership with the University and to use this as a possible research center. Figure 5 15
MIXER With the constraints of the project being the available land space and budget, we decided that the best compost process would be an aerated static pile. This would require a mixer to mix the material prior to placement of compost material onto the static piles. To ensure that we fight under budget, new and used mixers were searched. A wide range of mixers were found a New Holland Tub Grinder to a new heavy duty mixer from H.C. Davis. The price ranged from $995.00 for the New Holland Tub Grinder from the 1960 s to a brand new heavy duty mixer from H.C. Davis costing $16,807.00. CONCEPT SELECTION Once all of the alternatives were researched, the group decided on the use of a non-dimensional scaling technique combined with an additive weighted decision matrix to help decide which system would best fit the requirements. Four researched composting alternatives were selected. They include wind rows, aerated static pile, in vessel, and aerated Bed. Attributes deemed important to the decision were compiled as well (see table *-2). The attributes for each alternative were discussed until a consensus was made. Because there are many different ways that these alternatives could be implemented, specific values were not always applied. Instead, general headings such as low or high were used to describe typical values. Values for initial cost were selected from the lowest calculated cost for each option. Initial cost estimates did not take into account items that would be needed by all of the alternatives (such as the cost of a pads construction). The length of composting, and curing time numeric values again were reflective of typical composting situations found in project learning. Values given to all attributes can be found in table *-2. Values definitions can be found in table *-3. 16
Table -2: Attribute Values to Selected Alternatives. Alternatives Attributes Wind Rows Aerated Static Pile In Vessel Agitated Bed Initial Cost $ 30,000 $ 15,441 $ 56,050 $ 19,700 Space Requirement High Medium Low Medium Odor High Low Low Low Maintenance Costs Low Medium High Medium Weekly Management High Medium Low Medium Animal Carcasses No Yes No No Length of Composting Time (days) 60 28 21 21 Curing Time (days) 46.5 46.5 62 62 Environmental Control Low Medium High Medium Table *-3: Attribute Value Definitions. Attributes Hierarchy Numeric Values Initial Cost Lower is Better N/A Space Requirement Lower is Better High = 0, Medium = 1, Low =2 Odor Lower is Better High = 0, Medium = 1, Low =2 Maintenance Costs Lower is Better High = 0, Medium = 1, Low =2 Weekly Management Lower is Better High = 0, Medium = 1, Low =2 Animal Carcasses Yes > No Yes = 1, No =0 Length of Composting Time (typical) Lower is Better N/A Curing Time Lower is Better N/A Environmental Control Higher is Better High = 2, Medium = 1, Low =0 17
The attributed values were the scaled between zero and one. These results are found in table -4. ND Scaling and Summation Wind Rows Table **-4: Non-Dimensional Scaling and Summation Scaled Value Aerated Static Pile Alternatives Scaled Value In Vessel Scaled Value Aerated Bed Initial Cost $ 30,000 0.64 $ 15,441 1.00 $ 56,050 0.00 $ 19,700 0.90 Space Requirement 0 0.00 1 0.50 2 1.00 1 0.50 Odor 0 0.00 2 1.00 2 1.00 2 1.00 Scaled Value Maintenance Costs 2 1.00 1 0.50 0 0.00 1 0.50 Weekly Management 0 0.00 1 0.50 2 1.00 1 0.50 Animal Carcasses 0 0.00 1 1.00 0 0.00 0 0.00 Length of Composting (days) 60 0.00 28 0.82 21 1.00 21 1.00 Curing Time (days) 46.5 1.00 46.5 1.00 62 0.00 62 0.00 Environmental Control 0 0.00 1 0.50 2 1.00 1 0.50 Sum 2.64 6.82 5.00 4.90 While non-dimensional scaling gives perspective on the decision, it does not take into account the fact that not all of these attributes are considered equal. This is why the group decided to further process the attribute values by multiplying the value by a weight factor. This was accomplished by a pair wise comparison of each attribute. Once all of the attributes had been compared a sum of the winning judgments was compiled. To create the weight factor each of the winning values was divided by the total number of comparisons. The pair wise comparison calculations can be found in appendix**. Table -5 shows the number of challenges won (i.e. the hierarchy of attributes) and the corresponding weight factor. 18
Table **-5: Results of Pair Wise Comparison of Attributes with Corresponding Weight Factors Hierarchy Weight Factor Initial Cost 8 0.22 Space Requirement 7 0.19 Length of Composting 6 0.17 Maintenance Costs 5 0.14 Animal Carcasses 4 0.11 Curing Time 3 0.08 Environmental Control 2 0.06 Weekly Management 1 0.03 Odor 0 0.00 Sum 36 The final result is given as a value between one and zero for each alternative (Table **- 5). The results showed that the aerated static pile was the best alternative for our project. Table **-6: Additive Weight Analysis of Compost System Alternatives Additive Weighting Chart Wind Rows Weighted Value Aerated Static Pile Weighted Alternatives Weighted Value In Vessel Weighted Value Aerated Bed Weighted Value Initial Cost 0.64 0.14 1.00 0.22 0.00 0.00 0.90 0.20 Space Requirement 0.00 0.00 0.50 0.10 1.00 0.19 0.50 0.10 Odor 0.00 0.00 1.00 0.17 1.00 0.17 1.00 0.17 Maintenance Costs 1.00 0.14 0.50 0.07 0.00 0.00 0.50 0.07 Weekly Management 0.00 0.00 0.50 0.06 1.00 0.11 0.50 0.06 Animal Carcasses 0.00 0.00 1.00 0.08 0.00 0.00 0.00 0.00 Length of Composting (days) 0.00 0.00 0.82 0.05 1.00 0.06 1.00 0.06 Curing Time (days) 1.00 0.03 1.00 0.03 0.00 0.00 0.00 0.00 Environmental Control 0.00 0.00 0.50 0.00 1.00 0.00 0.50 0.00 Sum 0.31 0.77 0.53 0.64 19
SELECTED DESIGN Our selected design will modify an aerated static pile system to operate in a series of bins. Appendix A contains schematic diagrams of the proposed design. With the aerated static pile system selected, comparisons of the various materials involved were made. These included: Flooring, blower, mixer, and control style. Options under these components can be found in table**- 7. Table **-7: Components Considered For Aerated Static Pile Flooring Blower Mixer Control Steel Decking One Larger Batch Manual Concrete Multiple PTO Automatic Asphalt None None Gravel Each option s positives and negatives were listed as well as estimated prices. One option from each column was selected based on the group s overall decision. The following tables are a compiled comparison of each of the options. Table **- 8: Blower Comparison Number of Blowers Cost Estimates Positives Negatives One $3,000-$5,000 (Granger) Fewer Moving Parts, Simpler Filter Design Cost to Upgrade, If it breaks down the whole operation stops Multiple $3,000-$5,000 (Granger) Simpler Control Scheme, Energy Saving, Easy to Expand Control Difficulty, Increased Housing Cost, Complication of Filter 20
Table **- 9: Flooring Material Comparison Material Cost Estimates Positives Negatives Steel Decking Free, provided Affordable, Easy to Install without outside help Possible Drainage Issues, Lifespan, Flexible Concrete $5,000-7,000 (Concrete Network 30 x38 x8 Slab) Long Life Span, Rigid construction, Pipe/Drainage Control, Aesthetics Cost, Labor Intensive Asphalt $22,000 (Poe Asphalt see appendix **) Long Life Span, Pipe/Drainage Control Cost, Flexible Gravel $**** Inexpensive Shorter life span, Possible Drainage Problems Mixer After the client meeting, we were given a new direction in producing the best compost process for the lowest amount of money. H.C. Davis was the lowest priced mixer that would fit our daily volume needs. An H.C. Davis sales representative recommended that with the bulk density of the material that we were going to be composting and the type of material, we use a super duty mixer with paddle mixers. This would give us the even mixing that is required due to the varying particle sizes we would encounter in our food waste. Control System The use of an electrical control system to control the composting system blowers for aeration can be very effective when done properly. Washington State University s compost facility uses a control system for its blowers and has had success. The control system will regulate the airflow in each composting bed by controlling the blowers used for negative aeration. This will be done by placing up to 21
four thermocouples within each compost pile and then wiring the thermocouples to a programmable logic controller (PLC) located at the blowers. By using the 3-4 thermocouples in each pile, a temperature average can be computed by the PLC. The average temperature calculation of the compost pile will help alleviate erroneous inputs to the logic controller, which would otherwise result in a false reading for the aeration requirement of the compost. The logic controller can also be programmed to discard temperature inputs that do not fall within a reasonably accepted range in addition to averaging the temperatures, thus further eliminating erroneous input data to the PLC. Prior to set-up of the control system the logic controller will need to be programmed using code written in either National Instruments Labview or Rockwell System Ladder Logic. These two software programs are being considered due to their availability and ease of use by the group members. Testing will need to be done to determine which software is more suitable for the composting system. Finally a small computer terminal or touch screen monitor will need to be housed with the PLC to display the temperature and airflow information to the composter system operator. The greatest benefit to using a control system is that automation of the aeration control would reduce the amount time needed by the system operator to manually adjust the airflow whenever a temperature changes occur. It will also increase the efficiency of the system by reducing overall compost time and labor required. The greatest limitation to using a control system is correctly coding the logic controller so that it performs accurately enough to be beneficial to using it in the system design. Control system failure due to faulty components and/or operator error is also possible. To prevent this, the control system must be durable and require only basic computer skills to operate. 22
Table ** - 10: Control Scheme Comparison Control Method Cost Estimates Positives Negatives Manual Time Cost, Less Power Requirements Increased Labor and Composting Time, Limited Control Automatic <$1,000 Less Management, Faster Compost Time Cost, Increased Operator Knowledge FUTURE WORK There are several milestones before the University can implement the recommended design. We will test the feed stocks in January for an average C: N ratio, moisture content, and density. This will be a main priority in order to confirm that the initial calculations for the given various parameters, which were based off other research and composting systems, are comparable to our own feed stocks. This step is critical for sizing our system so we can redesign our system if need be to accommodate different system parameters. Another immediate priority is selecting the ground cover for our system. This requirement is dependent on funding and what the University and the Dairy deem acceptable. We will also select the blowers for the system in this first month. Once we have finalized a design, we will begin material acquisition as soon as possible to allow time for building and final testing of the system. This step needs to be underway in February. The final assembly and testing of the design will not be able to be completed until the ground unfreezes so most of the materials for the composting system will be stored on site until the weather permits its use. During this period we will begin testing the various components including the temperature probes for accuracy and work out any design flaws before implementing them into the final system starting in April. Once the ground pad is in place, we can begin building a conceptual design, building one section of the 23
composting system for a proof of concept. Once this step has proven successful, we will complete the system and finish writing up an operator s manual on it. The system should be delivered in its final form to the University of Idaho by the beginning of May. 24
REFERENCES [1] Nagawiecki, T. (2009, June). University of Idaho Waste Characterization. Moscow, ID: University of Idaho. [2] Loveland, J. (2009, June). Waste Stream Management for the University of Idaho [Excel document, powerpoint]. (2009, fall semester). [3] Biology & Chemistry, Compost Fundamentals, Washington State University Whatcom County Extension, 2009. [Online]. Available: http://whatcom.wsu.edu/ag/compost/fundamentals/index.htm. [Accessed: Nov 5, 2009]. [4] The Carbon/Nitrogen Ratio, Organic Gardening, Rodale Inc., 2009 [Online]. Available: http://www.organicgardening.com/feature/0,7518,s1-5-21-112-2-1-2,00.html. [Accessed: Nov 2, 2009]. [5] Leege, Philip B. and Thompson, Wayne H.1997. Test Methods for the Examination of Composting and Compost. 1st Edition. Bethesda, MD. The US Composting Council. [6] Haug, Roger T. 1993. The Practical Handbook of Compost Engineering. 2 nd Edition. Lewis Publishers. Boca Raton, FL. [7] Recycled Organics Unit. 2007. Food Organics Processing Options for New South Wales. 2 nd Edition. University of New South Wales. Sydney, Australia. [8] Renewable Carbon Management, LLC. Available at: http://composter.com/. Accessed 20 October 2009. [9] Green mountain Technologies. In-Vessel Systems. Available at: http://www.compostingtechnology.com/. Accessed 20 October 2009. [10] Rynk. Robert. Northeast Regional Agricultural Engineering Service. Ithaca, NY. On-Farm Composting. Rectangular Agitated Beds. Ch 4. pg.37 25
APPENDIX A Figure 1: Conceptual Bin Design [Courtesy of The Green Machine Senior Design Team] Figure 2: Site layout [Courtesy of The Green Machine Senior Design Team] 26
Appendix B: Budget To-Date Match 1. Equipment/capital expenditure total equipment 0 2. Travel total travel 0 3. Other direct costs a. Material Removal UI Dairy, Equipment Use $140 b. Site Prep UI Dairy, Equipment Use $560 c. Yearly equipment cost, PREEC $5824 total other directs $6524 4. Personnel a. Material Removal UI Dairy, Labor b. Site Prep UI Dairy, Labor c. Temp. Composting Mats, PREEC labor d. Yearly PREEC labor $930 $602 $218 $3775 total salaries $5525 5. Other Contributions $12,000 a. Project Startup, Campus Dining $8000 b. Waste Transport from dining facilities/yr total other contributions $20,000 6. Totals $32,049.00 These costs represent contributions in labor, equipment, and time already made by the UI Dairy or budgeted for yearly contribution as well as the original project startup budget pledged by Campus Dining. 27