Commercial and industrial composting facilities can be designed and operated using a wide spectrum of technologies, equipment and material handling strategies. The best practices for efficient operations that make sense economically and environmentally need to manage a core set of variables that requires different strategies depending on the materials being processed, the location of the facility and the scale of the operation.
Why should you be interested in commercial and industrial composting?
In 2024 the average cost per ton to dispose of organic materials in a landfill in the USA was above $60, according to the Environmental Research and Education Foundation. Meanwhile, the market value of compost per ton ranges between $30 to $70.
We can continue to spend money to dispose of organic wastes in landfills where they have no agricultural value (and a lot of environmental negatives), or we can generate wealth from those materials while reducing the environmental negatives of landfills. Would you rather spend $60 or earn $70?
Assuming you’d rather earn money than spend money, please continue reading.
But before we get into the best practices of commercial composting facilities, let’s back up and review the basics of what composting is, and why it is one of the best solutions for converting organic waste into valuable compost that enables regenerative and sustainable agriculture and closes the loop between organic waste and food production.
All life on Earth is “carbon-based,” meaning that all plants and animals are composed primarily of carbon-based compounds. This carbon, and other elements that organic waste consists of, will naturally decompose into nutrients that continue the cycle of life on the planet.
Over the years human civilization has learned that when organic waste streams are left to rot in a pile or dumped in an open pit, landfill or water source, that there are many negative impacts on the local environment including odors, greenhouse gases, ground water and surface water contamination, flies, pests and disease.
We have also learned that when organic waste streams are managed with an aerobic composting process, these negatives are eliminated or minimized. The natural heat generated by aerobic composting kills pathogens and eliminates many other potential contaminants in the material. When proper oxygen and moisture levels are maintained in a composting process, odors are also dramatically reduced or even completely eliminated.
Composting has emerged as perhaps the best solution to converting these waste streams into valuable inputs for the soils that our agriculture is based on. Composting is a natural process, driven by microbial activity, that breaks down the material into a stable product known as compost, which can be re-introduced into various life-generating cycles of agriculture.
The composting process can be accelerated and enhanced by managing a short list of key variables related to the material being processed.
The microbes that create a composting process are referred to as aerobic microbes. Aerobic means the microbes require oxygen in order to thrive. These microbes also need water, and food, like any other living organism.
When oxygen is not available, a different category of microbes, known as anaerobic microbes, take over the decomposition process. Anaerobic microbes generate a different set of outputs, including odors commonly associated with the “rotting” process, which also attract flies and pests. Other outputs of anaerobic microbes include nitrous oxide, hydrogen sulfide and methane, gases that come with odors and other negatives including greenhouse gas effects. (methane can also be captured and burned as a natural gas fuel source with Anaerobic Digester systems used to process organic waste streams).
When oxygen and water are available in proper levels, the composting microbes are able to thrive and consume their food, which is the organic materials (carbon etc) in the compost-feedstocks. Compost feedstocks can be virtually any organic material.
The key variables for aerobic composting are:
- “Browns and Greens” The ratio of carbon to nitrogen within the feedstock materials being composted needs to be within the range of 20:1 to 40:1. This means the mass of carbon within the material needs to be 20 times to 40 times the mass of nitrogen in the material. A proper feedstock blend consists of a balance of “Brown” high carbon materials such as wood chips and shredded yard waste combined with “Green” high nitrogen materials such as food waste or manure.
- Oxygen levels within the material: the aerobic microbes require 12% or more of the air in their environment to be oxygen (normal air on Earth is 21% oxygen).
- Moisture levels within the material need to be between 40% to 60% of the mass within the feedstock. Below that level the microbes start to decline. Above that level they start to drown.
- Bulk density: if the compost feedstocks are too dense, airflow and oxygen levels will be restricted, creating an anaerobic environment. If the material is too light and fluffy, lack of structure in the material prevents the microbes from building a “home” and moisture loss will starve the microbes of water.
- Temperature of the material being composted: For effective destruction of pathogens and to ensure proper aerobic microbial activity, the temperatures of the composting materials need to be above 135F during the initial composting stage. Aerobic microbes can produce pile temperatures above 170F or higher, which comes with the risk of “spontaneous combustion” at certain moisture levels. If pile temperatures grow above 150F, the material will be losing excess carbon that you want to remain in the finished compost, while also depressing the growth of certain beneficial fungal elements that are part of high value compost. Managing pile temperatures within the optimum range of 135F to 145F is a key aspect of creating high value compost quickly and efficiently.
- Odors: any composting facility will need a system and process to control and capture odors. Maintaining proper feedstock recipe standards and proper oxygen levels are the most important factors to minimize odors, but additional methods are also required in most cases. Odor control can be achieved with use of a “bio cover” of shredded high carbon material placed on top of the compost feedstock in a positively aerated system, or with a “bio filter” in which the exhaust from a negatively aeration system or a fully enclosed indoor sytem is vented into a mass of wet wood chips. Fabric membrane cover systems can also be used to cover the compost in an aerated system, or the composting process can be fully contained in an enclosed building or an In Vessel system, with ventilation exhausted into a bio-filter.
- Your business plan is ultimately the most important variable to manage: you will need to develop a real business plan for your facility. You need to understand what your revenue streams will be, what materials you will want to handle and where they’ll come from, what you’ll be paid to receive those materials, what it will cost you to convert those materials into compost products, and who your end customers will be for your finished products. Commercial and industrial composting is not just about getting paid to receive organic waste streams and converting them into products that have market value. It is also about managing a business, including your overall facility, your employees, inventory, equipment, real estate and your relationships with clients and regulators.
The best practices of commercial and industrial composting are designed to enable efficient management of these key variables. Once the feedstock “recipes” are understood (C to N ratio, moisture levels and bulk density), the key operating variable in any composting system is the oxygen level. Moisture levels also need to be managed throughout the composting process, since the heat of the process causes water loss to evaporation.
There are several established methods to provide oxygen to the aerobic microbes of a commercial composting facility, including:
- Agitation and mixing the material to expose the microbes to oxygen. This can be done with a “windrow turner” or other heavy equipment. This method can be effective, however it requires significant energy and time, not to mention the cost of the heavy equipment and fuel. Turned windrow composting facilities typically turn the material once per week over a period of 12 to 16 weeks. The downside with turned windrow composting is that within 24 hours of the material being turned, oxygen levels in the core of the pile usually drop below 10%. This encourages anaerobic microbes to take over the environment, while the aerobic microbe colonies will collapse, resulting in a stalled composting process that also creates odor and emissions problems that become especially evident upon the next turn of the pile.
- Aerated Static Pile (ASP) composting: perforated pipes or aeration channels are positioned on the ASP pad, with the compost feedstocks loaded on top. A blower or fan moves fresh air through the pile, either on a timer or with a data-based control system. This keeps a consistent supply of oxygen in the material, accelerating the natural aerobic process and preventing anaerobic microbes (and their associated odors and emissions) from growing. Typically an ASP system will cycle on and off in 30 minute increments throughout the day, with different air flow volumes depending on each stage of the composting process. Modern ASP systems usually include data-based feedback and automated controls that modulate air flow levels to keep the compost pile temperatures in the ideal range (135-145F). Pile temperature data can be used as a proxy to indicate adequate or inadequate oxygen levels. A typical ASP system will convert fresh feedstocks into “ready to cure compost” with just 6 weeks of aeration and minimal material handling costs, compared to a 12 to 16 week timeline for turned windrow processing.
- Turned Aerated Pile (TAP): this approach combines a controlled aeration system with regular mechanical turning, typically using a windrow turner twice per week. This is the fastest way to make compost at a large scale with the most space efficiency. TAP composting can produce “ready to cure” compost in under 30 days.
- In Vessel Composting: this approach uses a fully enclosed container, sometimes meaning a fully enclosed building, with aeration built into the floor and automatic mechanical agitation and mixing built into the system. There are many different styles of In Vessel composting systems, including rotary drums, modified shipping containers or roll-off dumpsters, or custom fabricated vessels that include mixing systems and mechanical methods of ejecting the finished compost automatically. The primary advantages of In Vessel systems include odor control, moisture retention and rapid automated processing with minimal labor required. In Vessel systems can produce ready to cure compost in two to three weeks.
These four primary processing types each come with trade offs and various pros and cons. In most commercial and industrial composting facilities, 50% to 75% of the operating costs are related to labor and equipment used. In general, a higher up front investment in efficient technology and infrastructure will pay for itself over time via reduced operating costs.
Summary of pros and cons of each category of commercial composting facility type:
- Turned windrow processing: lower up front costs, simple facility design and operation, high operational costs, low space efficiency, poor odor control, high VOC emissions. Turned windrow composting is simple in that you require primarily two pieces of heavy equipment (a tractor with a bucket loader and a tractor-towed windrow turner, or a front end loader and a self-propelled windrow turner). Total equipment costs could be as low as $100,000 for a small scale operation under 5000 tons per year, or in excess of $1 million for a large scale operation above 50,000 tons per year. Combine these tools with an open gravel pad or field and you can start making compost without any construction or much other infrastructure. The downsides of turned windrow composting include the lack of odor control (every time you turn the pile, significant odors are released because the material has had high levels of anaerobic microbes present since the last time it was turned), along with the cost and time required to produce the compost (12 to 16 turns over a 12 to 16 week period, and lots of space required). Water has to be added to the material as it is turned, typically every 2 weeks, as the heat of the composting process typically causes significant evaporation.
- ASP composting requires significant investments in infrastructure and technology, sometimes requiring an engineered facility to be designed, permitted and built, including infrastructure to capture leachate and stormwater. You still need a bucket loader or tractor to mix materials and load them onto the ASP pad. Material still has to be mechanically turned occasionally, typically every 2 weeks, including the addition of water to the material. ASP systems are usually designed with concrete or asphalt aeration floors, and in many cases a roof covering or a fabric cover system is required to prevent rain or snow from disrupting the composting process. Total infrastructure and equipment costs for an ASP facility can range between $150,000 to $250,000 for a 5,000 ton per year facility or $2 million to $5+ million for a 50,000 ton per year facility, depending on the facility design details. These investments in infrastructure pay off with reduced material handling costs, faster production of the final product and reduced odors and emissions, compared to turned windrow composting.
- TAP composting requires the highest up front capital investment, since the facility will require engineered aeration infrastructure along with advanced heavy equipment for space efficiency and efficient mechanical turning of the material. However, a well designed TAP system can process nearly twice the volume of material per year per acre of land compared to a typical ASP system (with more than 5X the volume of material throughput per acre compared to a typical turned windrow facility). TAP systems make the most financial sense where the cost of land, construction and labor is high, because the operational efficiency and space efficiency of the facility will offset these costs.
- In Vessel composting systems require the highest up front investment per ton of annual processing capacity of any of these approaches, and are typically recommended for facilities that are under 5,000 tons per year in volume where odor-controlled on-site composting can eliminate the cost of transporting organic wastes offsite for processing. In Vessel systems also are typically chosen where odor control is a top priority, and for facilities that require minimal operational labor and equipment on site. In Vessel systems are often chosen for urban, institutional or corporate campus and resort environments or for remote locations where composting infrastructure is limited and landfill hauling costs are high. In Vessel systems are sometimes the only solution for locations that have extreme climate conditions such as extreme winters or severe heat, because the contained process can retain essential moisture and manage temperature levels of the composting material regardless of environmental conditions. The primary “down sides” of In Vessel systems are the relatively high up front cost and the cost of maintenance of the mechanical system to ensure the investment has a long term payback period.
The final category of Best Practices that I’d like to point out is this: if you’re interested in developing a commercial or industrial composting facility, you need to recognize that you will need help, and that it will take you some time to find the help that is best for you.
There are many types of consultants, facility design engineers and suppliers of equipment and technology that offer great solutions. But you need to make sure that the solutions you are getting from third parties are the right solutions for your needs and requirements. This includes understanding what the local permitting requirements and regulations are that apply to you, and understanding what it will cost you to meet those requirements.
About the author:
Gaelan Brown works primarily as a consultant for Green Mountain Technologies, a Seattle based composting technology and engineering company.
He began his work in composting in 2008 when he founded the non profit Compost Power Network in Vermont in partnership with Highfields Center for Composting and several universities to develop best practices for heat-recovery from composting systems, including several successful compost-heated greenhouse projects. He taught composting workshops for Yestermorrow Design/Build School in Vermont for several years, and wrote The Compost Powered Water Heater book for WW Norton publishing company in 2013. He has also authored several articles about composting technology and other renewable energy topics in BioCycle Magazine, Green Energy Times and other publications. He has worked as a freelance consultant and freelance writer since 2013 including many clients that are established category leaders in the composting technology industry. In his free time he enjoys all forms of outdoor recreation and quality time with his family.
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Email: gaelanb@gmail.com
