When selecting a composting system, the first question to answer is what is your waste stream? Followed by how steady is the waste flow? How much waste do you have? How hard is it to compost? How near are your neighbors? How much land do you have available?
By Robert Winn
It seems counterintuitive that organic waste, especially waste food, would be a large problem. It would seem logical that it could be used to feed the needy, or easily processed to make energy, compost or animal feeds. This is not always the case. In fact, certain organic wastes are hard to work with and therefore it is just ‘easier’ to send it to the landfill. With the awareness of the amount of organic wastes going to landfills, the filling of landfills, and regulations being passed to eliminate the organic waste going to a landfill, there is much interest in finding another method of disposing of this waste.
The use of organic food waste for feeding the needy and feeding animals should occur if it is possible. I would like to examine the option of composting the organics, to include food waste when these options are not an alternative and wastewater treatment plant (WWTP) bio-solids. Although energy systems are something many people are interested in, it requires a large facility, with a large capital input and much infrastructure to accomplish. Composting can be done on a much smaller scale and at a much reduced cost. As we compare composting systems below, some are considered somewhat costly; however, this cost is minimal compared to anaerobic systems used to manufacture energy from waste. When selecting a composting system, there are several things involved. The first questions to answer are what is your waste stream? Followed by how steady is the waste flow? How much waste do you have? How hard is it to compost? How near are your neighbors? How much land do you have available?
Composting Methods
Larger companies with a large amount of food waste or communities with a large amount of bio-solids are sometimes able to find a compost yard that is willing to take their waste for an acceptable tipping fee. However, smaller entities (schools, colleges, restaurants, prisons and small WWTPs) may have a problem in finding an affordable alternative due to increased hauling costs of smaller loads, even if the tipping fee is the same. Some states allow composting of organic waste, generated within the business, onsite without any permitting. However, you would not be able to take in wastes from your neighboring businesses. The curing stage generally may occur at other locations if space is at a premium.
Chart courtesy of Robert Winn.
One method smaller waste producers are considering is in-house composting of the organic waste. There are several problems that quickly become apparent. There is a fairly large investment required for installing static pile and In-Vessel compost systems. There is a fairly large space requirement for windrow and static pile compost systems. There is a requirement for some fairly expensive equipment and a larger work force for turning the composting material in static pile and windrow systems. The requirements for containing runoff and storm water is much greater for static pile and windrow systems as compared to In-Vessel systems. Odor control and vector and varmint control are a large problem with both the static pile and windrow systems making it imperative to have an isolated area to implement them. Again, this generally will require more hauling and more expense. Time involved in the composting system varies considerably also. In-vessel compost systems require three to five days to meet the requirements of EPA for compost. Static pile systems require four to six weeks, and windrow operations require four to six months. Each state also has a “curing or stabilization” time required of all systems following the composting requirements. The range of the variations I am aware of range from zero days for Texas to 50 days for New York. There is no differentiation between composting systems for the amount of time required for curing and stabilization. Chart 1 shows differences between the three systems.
Feedstock
We have looked somewhat at the different systems for their pluses and minuses. Next let’s take a look at the feedstock handled best by the different systems. First, what is the stability of the waste stream input? Windrow systems are great for variable input times and amounts. For example, if there is a storm and a lot of trees are knocked down, or a lot of paper goods become wet and must be disposed of, then windrow systems are probably the method of choice. Static pile is also able to take variable amounts at inconsistent times, but the formation and covering of the piles and the air input system all have to be considered when new, large amounts of feedstocks are available. An In-Vessel system would not be able to take this large amount of sudden input. In-Vessel systems are fixed sizes and, therefore, work best with somewhat steady input of feedstock.
Second, what is the feedstock? Basically, the physical size of the feedstock from large to medium to small, works best in windrow—large, static pile—medium; and In-Vessel—small. The solubility of the feedstock follows a similar matching. Low soluble feedstock such as yard waste, tree limbs, and paper goods are best treated in a static pile or windrow system. Medium soluble feedstuffs like some agricultural plant wastes and waste from energy generation systems are best done in static pile or In-Vessel systems. Soluble products equivalent to food wastes, animal mortalities and bio-solids are best handled in In-Vessel systems, and in some cases static pile systems
Some smaller entities that have adopted an In-Vessel system for their operation include:
• Davidson College, NC
• Clemson, SC
• Lockheed Martin, Owego NY
• U.S. Fed Prison—Federal Correction Installation McCreary; Pine Knot, KY
• Washington State Correction Facilities
• Toyota Manufacturing, KY
The feedstock for each of these include food waste, but most also use yard waste as a carbon source. The finished product is used on the facility grounds. Some places have opted to give the compost away to employees or customers.
Static pile operations are used in several different operations:
• The County of Santa Clara
• The Greenery
• City of San Diego
• Atlas Organics Compost Facility
An example of windrow application may be seen in:
• San Francisco, CA
• Miami, Dade County, FL
Work with a Partner
Once you have made the original assessment of the type of system that may work for your operation, it would be best to work with someone in that area who can give you advice and information in making your final decision.
There are several engineers/consultants that work primarily with windrow operations. Also the equipment manufacturers can give you some information and ideas. If they do not have someone on staff to help you, they can point you toward an engineer/consultant in your area that should be able to help you through the planning, setup and regulatory process.
The static pile option requires someone with an engineering background to help you set up, unless you work with the companies who design and install these systems. There is much to be planned and the mechanics of the process must all work together to end up with a functioning system. Try to find an engineer/consultant with experience in this field due to the complexities of air flow combined with size, covers and turning requirements.
When working with an In-Vessel unit, there are several things to look for in a manufacturer. First, find someone in the business with machinery that has withstood the test of time. Second, look for units that are made to fit your needs, size wise. Third, you will want a unit that can control odors. Fourth, look at labor requirements and area needed. Most manufacturers of In-Vessel units can help you with set up and training for operation. This will be important, especially for the novice composter.
In conclusion, the compost system that is the best fit for your use is determined by the amount of waste to be handled, the type of waste being composted, the cost of moving the waste from your facility to the compost facility (if it is separate), the availability of customers/users for your compost, the proximity of neighbors, regulations in your state and the cost of the space needed to do the composting. For small businesses in urban areas, the idea of composting their waste, then donating it to the community and the advertisements gained by being a green, community concerned business is a consideration. Study Chart 1 and it should help you decide which system is best for you.
Robert T. Winn, DVM, is a Doctor of Veterinary Medicine for Organic Resource Company, LLC (Big Sandy, TX). Trained as a nutritionist and a veterinarian, Dr. Winn has a wide area of interest. In his effort to help the dairymen and cattlemen in the Northeast Texas area, he developed a line of enzyme products to help manipulate the rumen microbes and improve fiber digestion. In the last few years he has been working to understand the microbiota of the compost ecology and its effect on plants and animals. He feels that this is the next big innovation in feeding our growing population. Dr. Winn can be reached at (903) 720-9542, e-mail [email protected] or visit www.myorcgroup.com.
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