By using technology and equipment designed specifically for each step in the composting process, any size operation can save time and money.
By Todd Dunderdale
The purpose of composting is to decompose organic matter as efficiently as possible in order to create a high-quality product. Many companies have spent years working intensively with scientists and agriculture specialists to design a process to guarantee maximum ecological and economical efficiency. Each process step is designed with that end goal in mind.
Shredding to the Right Size
Shredding green waste and organics is the first step in the composting process. With a low-speed high torque shredder, you can create a fractured product with greater surface area, best for the composting process. This is contrary to the belief that you need to start the composting process with the smallest product possible. The advantage to shredding with a low speed shredder is that it creates more porosity, or airflow, in the windrow. This is an important factor as larger material allows for more oxygen, leading to better and faster composting times as well as minimizing odors. In addition, with a low speed shredder you can also mix and shred at the same time, removing the need to purchase a separate mixer. A low speed shredder is also able to handle contaminates like rock and metal with very low operation and maintenance costs unlike a high-speed grinder. Shredders can be designed with reversing shafts that prevents wrapping of fibrous material such as palm and cedar. A high-speed grinder’s mill often gets jammed with this material resulting in lost production. Lastly, low speed shredders can be designed to keep plastic contamination larger so it is easier to remove on the back end. The larger the plastic film can stay through the shredding process, the more effective the separation process will be.
Windrow Composting
Windrow composting allows the operator to manage individual rows and make necessary adjustments relatively easily and quickly. Creating a tall peaked windrow is integral for the composting process. Some windrow turners are designed specifically for that goal. With the right system, it can leave behind a perfect windrow with increased porosity creating the desired chimney effect for the fastest composting times. Faster composting means increased site capacity and reduction of processing costs.
The large diameter rotor works to mix the row from the outside to the inside to ensure that the row is completely turned. Additionally, choosing a turner equipped with a scraper bar, can assure that the complete pile is turned, minimizing odors. Many turners cannot get that bottom layer from the windrow pile and exposing this aerobic layer during turning causes a release of odors. Adding water to the top of the pile usually only reaches the top area of the pile, or in other cases it can create spots that go anaerobic. Since water will take the path of least resistance, often water will just drain off the top of the windrow to the lowest point on the pad creating a leachate problem. Effective windrow turners were designed with a watering solution in mind, with a built-in watering device to infuse up to 286 gallons of water per minute into the center of the windrow while turning. This not only conserves water, but it also places the water directly where it is needed to further enhance the composting process. In addition, if space is a concern for windrow composting, certain turners allow for windrows to overlap up to a foot.
Screening Options
Most often, to achieve a high-quality uniform end product, it is necessary to screen the compost. For this process you can use a drum screen or a star screen. Each screen was designed for a specific application. The trommel or drum screen was born out of the dirt and topsoil market; whereas the star screen was built to process organics. A heavy-duty trommel is built to withstand the heavy rock and abrasive material found in topsoil. This type of material is not as well suited for a star screen.
Trommel screens are cleaned manually with cleaning brushes; however, some star screens have a self-cleaning system. Drum screens’ rotating action do a better job of breaking up the clods of dirt and rock, and adding the prescreening grizzly option allows for the separation of large rocks. If multiple product sizes are required, a trommel is limited by how costly and easily it is to move between screen sizes.
The biggest advantage of a star screen is its production. A star screen will typically produce twice as much as a trommel screen and up to three times as much as a deck screen. Star screens have the ultimate flexibility in determining output product sizes. This is because the product size is infinitely adjustable depending on the speed of the stars. The organic market often requires multiple products at multiple sizes. The star screen becomes much more cost-effective for this application—you can change output size at the touch of a button. The other big requirement in screening organics is the ability to process wet material. Star screens are specifically designed to handle wet material that often blind up the drums of a trommel screen and the decks of a deck screen. Star screens also have the added ability to incorporate wind sifting technology, on both the middles and overs fractions. The advantage is lower operating and equipment costs as you can screen and separate contaminants in one step. The high production of a star screen coupled with its flexibility is unrivaled.
Separation Technology
The last step in the compost process is separating out contaminants. If contaminants are not removed, it can further contaminate your finished product. By removing the contaminates, you can reintroduce the overs into the composting process and avoid the costs associated with disposal. Most composting operations have some form of contamination from incoming material, usually film plastics and/or rocks. This contamination is best removed from the end of the screening process for the highest quality final product. There are three different types of separation machines that can be built with hybrid technology and compatible with most mobile screening units. First, is a mobile wind sifter whose primary function is to remove film plastics from overs material, however, it can also remove some rocks and metal.
Second, is a mobile stone separator developed to remove stones and rocks from compost and biomass at a high efficiency rate, yet will also remove some light plastics. Finally, a separation machine can be built with a wind sifter and stone separator in order to be able to handle both contaminates. Separation machines can efficiently help any compost producer create a higher quality product.
Save Time and Money
The goal of successful composting is to turn waste into a valuable product while conserving resources. Using technology and equipment designed specifically for each step in the composting process, any size operation can save time and money.
Todd Dunderdale is Senior Area Sales Manager for Komptech Americas (Westminster, CO). With 18 years of industry experience Todd often acts as a consultant on matters relating to composting and organics recycling. He can be reached at (720) 890-9090 or via e-mail at [email protected].