Nature’s Own

How much compostable material is out there? And how much is it worth? Begin with the fact that Americans throw away on average about 4.5 pounds of municipal solid waste per person each day. This is equivalent to about 3/4 of a ton each year. Of this amount, about 2.3 pounds of MSW per person go to the landfill for disposal, 0.6 pounds are sent to combustion to produce steam heat and electricity, 1.2 pounds are recycled, and only 0.4 pounds are composted (source: “Advancing Sustainable Materials Management: 2015 Fact Sheet” US EPA, July 2018). In 2015, America as a whole generated about 262.4 million tons of waste. Of this amount, we recycled 67.7 million tons (25.8%) and composted 23.3 million tons (8.9%).

The reason for this relatively small amount of composting has more to do with the nature of the wastestream itself. MSW is a heterogeneous mix of various types of materials, each with its unique material characteristics (organic or inorganic, large objects and small particles, differing shapes and weights, variable densities and moisture contents, electromagnetic properties, and color). Each of these factors affect how easy it is to extract the material from the wastestream for recycling and composting, and what its potential end-use market would be for these reused materials. There are six broad categories of waste materials, each constituting a different percentage of the wastestream by weight: organics (yard waste—13%, food waste—14%, and wood waste—7%, 34% total), paper (27%), plastics (13%), metals (ferrous and nonferrous, 9%), glass (amber, brown, clear—5%), and textiles/miscellaneous (12%).

It is the first category of organic waste that is the prime candidate for composting. By strict definition, organic waste is any waste derived from animals or plants, from slaughterhouse renderings to autumn leaves.

However, the production of organic waste can be highly variable with some forms of waste being much harder to extract for composting than others. Certain operations that produce organic waste (manufacturing using wood feedstock, meat process, etc.) occur year-round. Vegetation-derived waste from yards, forests, and farms is highly seasonal with the amount of waste often doubling during the autumn and summer seasons. Composting is not just a matter of timing; it is also a matter of scale. Oddly enough, widespread sources of organic wastes (yards and forests) are easier to extract compared to concentrated—but isolated—sources (home kitchens and restaurants).

What about paper and cardboard­—why aren’t they composted? They are, but not at the same large quantities as plant-based organics. There are several reasons for this. Paper includes colored paper and glossy magazines which may contain toxic heavy metals. While cardboard, newsprint, and office paper are suitable for compositing, they create a high carbon to nitrogen ratio that slows down the composting process. Paper and cardboard also require a great deal of physical processing, shredding the material down to fluff or small particles. And as with food waste, paper waste is typically intermingled with the general wastestream and can be hard to extract. In contrast, vegetative organic wastes are typically required to be segregated from MSW with separate bagging and pickup operations.

US EPA data breaks down waste generating, recycling, and composting rates for all categories of waste materials. As of 2015, the US produced 262.43 million tons of MSW of all types. Of this amount, approximately 70% (almost 184 million tons) consisted of non-compostable waste materials (paper and paper boards, glass, metals, plastic, rubber, textiles, etc.). The remaining 30% (78.44 million tons) consists of compostable organic waste divided into the three categories of food waste (15%, 39.73 million tons), yard waste (13%, 34.72 million tons), and miscellaneous organic wastes (2%, 3.99 million tons). A closer look at the organic waste categories shows major differences in composting rates: food waste (5.3% of the amount of waste generated, 2.10 million tons), yard waste (61.3% of the amount of waste generated, 21.29 million tons), with no significant amounts of miscellaneous organic wastes being composted. In total, 29.8% (23.39 million tons) of all organic waste is composted. By comparison, 13.8% is combusted to generate electricity with the remaining 56.4% being disposed of in landfills. These numbers indicate that there remains significant potential for increasing the amount of organic waste reutilized by composting.

And the amount of organic waste being composted has been steadily increasing. As of 1980, there were no significant quantities of composted waste. A decade later, the amount of composted waste had jumped to 4.2 million tons with another four-fold increase to 16.5 million tons by 2000. Fifteen years of steady increases gave us the current (2015) figure of 23.4 million tons of composted organic waste, equivalent to an average annual growth rate of 2.36%. The above numbers are only for large commercial composting operations that have been recorded by the US EPA and do not include small-scale backyard composting efforts by individual homeowners and small businesses.

And this scale difference defines the two broad categories of composting: small-scale home composting run by individuals and commercial scale operations run by either large businesses or municipalities. Home composting is performed by individuals who take their own food and yard waste to composting bins collocated at their residence. It is a small but enthusiastic niche market with practitioners either selling the composts at local markets or using the compost themselves on their own gardens.

Commercial- and municipal-scale composting operations involve community curbside collection programs, transport to a composting facility, composting in bulk quantities, and bagging and shipping of the final product for sale. This industry has kept pace with the growth of composting itself with the number of homes served by specific compost pickup growing by 239% between 2007 and 2012 to over 2.55 million homes in more than 200 communities.

Major businesses are also involved in composting, and for many it is a significant source of cost savings. Composting companies, and subsidiaries of mainstream MSW collection and disposal companies, bid on and win community and business contracts. Greenfield sites are established for composting or areas of existing landfills are set aside for composting operations. Compost is bought and sold as mulch, soil amendment, and fertilizers with a secondary market in ancillary equipment such as bins, liner, windrow turners, and monitoring instruments. And these businesses have only begun to tap the potential of this market. Previous studies (Biocycle, 2014) showed that 71% of composting operations across 44 states only processed yard trimmings. The composting industry has the potential to diversify further into biosolids, food waste, paper, and wood scraps. According to the Institute for Local Self-Reliance (ILSR), 35 million tons of food scraps, 14 million tons of yard trimmings, 13 million tons of soiled paper, and 13 million tons of wood waste can be diverted from combustion or landfilling into composting.

And then there are the jobs generated by composting. According to the US EPA, the composting and recycling industries generate 757,000 jobs, $36.6 million in wages, and $6.7 million in tax revenues. As a rule of thumb, over 1.5 jobs are created by every 1,000 tons of recycled and composted materials. The ISLR estimates that composting created four times as many jobs per ton of waste compared to sending that waste to a landfill.

Current market values for compost depend on its end usage. Most commonly used as top dressing or as a soil amendment, compost runs about $15 per cubic yard, delivered. At a typical density of 0.40 tons per cubic yard (800 pounds per cubic yard), this is equivalent to an average price of $37.50 per ton. However, this price can vary widely with season, location, and application. As a rough estimate, the total compost market would be valued at $877.5 million dollars per year. Given the amount of untapped composting resources available, this figure has the potential to double.

Traditional Composting Methods and Equipment
Composting is defined as the “biological decomposition of organic constituents of wastes under controlled conditions” (“Composting, A Study of the Process and its Principles,” Golueke, 1972). There are two main composting processes, aerobic and anaerobic, as well as three primary composting techniques: windrows, aerated static pile, and in-vessel composting. Each is uniquely affected by environmental factors and utilize different operational and control techniques to manage the composting process.

Aerobic composting is a process where organic materials are decomposed by microorganisms that require oxygen. The air voids within the organic material’s mass are identical to that of the atmosphere, with large amounts of oxygen. This oxygen supply allows for decomposition by aerobic (oxygen using) bacteria. The aerobic bacteria subject the organic constituents to both hydrolysis (chemical reactions with moisture and water presenting the waste mass that result in the breakdown of complex organic molecules such as carbohydrates into simpler ones such as sugar) and aerobic degradation. This process generates heat, raising the organic material’s temperature. This high temperature results in a relatively rapid decomposition with the absence of significant odors.

In contrast, anaerobic composting is a decomposition process performed by microorganisms that are poisoned by oxygen. It therefore largely occurs within enclosed vessels or containers (referred to as “digesters”) that keep out atmospheric oxygen. This process results in the production of methane in its final stage as well as odorous products in the interim stages of the process. The anaerobic process occurs at low temperatures and has a slow rate of decomposition. Hydrolysis by anaerobic bacteria is actually a form of fermentation that produces organic acids, hydrogen, carbon dioxide, water vapor, ammonia, and nitrogen. Sulfur reducing bacteria produce hydrogen sulfide with its “rotten egg” smell. Anaerobic decomposition is a process that requires the addition of heat energy and the temperature of the organic waste usually falls.

Anaerobic composting is the opposite of aerobic composting in almost every way. Referred to as “cool” composting, anaerobic composting is fueled by bacteria and moisture in the complete absence of oxygen. It requires greater upfront capital investment in equipment but less oversight by the operator who does not need to turn or otherwise mechanically manipulate the organic waste mass. It can be used to process small batch quantities (less than 1 cubic yard) but can take an extended period of time (more than six months) to accomplish. And care must be taken that the process does not spread dangerous pathogens or promote the growth of weeds.

In summary, the aerobic composting process is relatively simple and straightforward. Organic matter (that includes its own supply of carbon, chemical energy, protein, and nitrogen) is mixed in large piles or pits with minerals, other nutrients, water, and natural aerobic microorganisms. The mixture emits water, heat, and carbon dioxide and produces finished compost material. The volume of the finished compost is typically half that of the initial organic waste. A version of this process utilizes an enclosed composting vessel fed by a forced air supply. This results in better control of the process and allows for treatment of the exhaust air. The final compost product is cured and screened prior to being bagged for shipment and sales distribution.

In-vessel composting is required for anaerobic processes. Anaerobic composting is a more complicated process that involves the delivery of organic waste to a specially designed facility. After passing through a grinder/mixing tank, the material is sent to a pre-heat tank and then to the anaerobic digester. Cut off from atmospheric oxygen, anaerobic bacteria proceed with decomposition in a controlled environment at 55–60°C. The biogas (methane and carbon dioxide) is removed and sent to storage and purification as fuel and the digestate created by the composting process gets sent to a solids separation tank where solid organic compost is separated from liquid organic fertilizer. Final composting is achieved in as little as 1 week. Given the need for intervals of anaerobic digestion, this is a batch process instead of a continuous flow operation. These processes tend to be proprietary and more expensive, but yield higher production rates, better quality control, and useful byproducts such as liquid fertilizer.

With all methods, post-production processing is required. This involves size reduction of the final compost by use of grinders. Separation of different sized compost particles is accomplished with screeners. If originally separated from a general MSW wastestream, magnetic separation may be required to completely remove any leftover impurities. Lastly, there is the curing of the compost. Curing makes the compost fit for use by maintaining the pile of finished compost in conditions that allow the compost microbes to maximize their growth rate and effectiveness. This last point is necessary because the same high heat that eliminated pathogens also destroys beneficial microbes. Lastly, the cured compost is ready for shipping and sale after it has been weighed, bagged and loaded for transport.

Advances in Composting and Future Potential
Increases in the amount of organic waste being processed have also resulted in improvements in composting methods and advances in compost quality. These advances are not just limited to newer technology; advances are occurring in the related fields of process management and quality control.

Odor Control. One key advance has been in the often-overlooked issue of odor control. Composting facilities until recently were for the most part sited out in rural areas where odors would have less impact. But the need for composting operation nearer to the sources of organic waste and potential resale markets has required facilities closer to urban areas, making odor a major concern. One new technique is the encasing of windrows in materials such as permeable geotextiles and semi-permeable fleece fabrics that act as shields against ultraviolet light. To augment these active measures, secondary odors controls such as neutralizing sprays, perfumes used to mask odors, air cleaning filters, and scrubbers are used along with flaring off of combustible gases.

Control Integration. Another development is the use of essentially turnkey operations that put the entire composting process under one roof. These completely closed dynamic systems rely on embedded sensors and probes are used to gather data on heat and other physical characteristics during the composting process. This data is tied to computers to track these changes while adjusting automatic controls that regulate the process. The result is a complete integration of moisture control temperature management, input of organic waste, output of compost, shredding, screening, and curing. The use of air and wastewater filters regulates the output of emissions throughout the process.

Customization. While traditional compositing technology produced a basic compost material with little variation, these new control methods allow the operator to tinker with the process and produce more customized compost products. Scale can also be customized. Composting processes can be tailor-made to suit the size and location of both organic waste sources and compost end-users. Companies now specialize in composting equipment designed for individual households, apartment complexes, small communities, and major cities.

Better Management. Computer modeling allows better design management by engineers and technicians to ensure maximization of airflow, minimization of emissions, right-sizing the dimension of windrows and piles to match local environments, and adjusting moisture content. Data gathering from temperature and emission sensors allows for better day-to-day management of the composting process. Communications and public relations management can reduce customer complaints (especially concerning odors) by improving customer feedback and management response.

As for the future, the sky is nearly the limit. As noted above, there is still a great deal of untapped potential in the compost market and the utilization of organic waste. Less than a third of all organic waste (not even including paper and board waste) is currently being composted. The market quite literally has the potential to triple in size if given the right regulatory incentives and technological advances. More aggressive municipal requirements requiring curbside segregation of organic waste for separate pickup and processing will allow for greater exploitation of this resource. More advanced separation technologies at materials recovery facilities (MRFs) will allow direct composting of the food waste and paper and board waste that makes up a significant percentage of the wastestream. Hydro-pulping used at advanced MRFs uses streams of high-pressure water to shred and pulp paper and other organic waste into materials that can later be used as feedstock for anaerobic digesters or direct composting once it is properly dried.

Major Suppliers
Continental Biomass Industries has recently introduced its 6800CT Horizontal Grinders, which have been engineered to improve on the older 6800BT’s advanced design. Improvements include a 15% larger screening area that wraps more than 190 degrees around the rotor on the 6800CT, allowing production rates to surge beyond 200 tons an hour. Supported by a larger shaft and bearings and an optional 1200-hp CAT C32, the engine powers the forged drum rotor through the toughest materials. Built to process land clearing debris, pallets, clean industrial waste, stumps, logs, mulch, bark, shingles, and whole trees as fast as it can be loaded, the 6800CTs can devour entire trees and stack the desired end-products. The newly available TSC 80T Stacking Conveyor is used in conjunction with these grinders to optimize their operational productivity. The 7544 Flail & Disc Chipper combo is designed to debark logs and produce a pile of premium quality chips. CBI’s 6400 Horizontal Grinder has the ability to process railroad ties contaminated with metal.

Ecoverse Environmental Solutions composting equipment includes its EcoSift 4000 screener and the EcoStack conveyor. The EcoSift is capable of handling the separation of four different-sized factions. Simultaneously, it allows the operator to decontaminate the material stream while removing impurities from the organic waste, or conversely to extract organic waste from an overs pile. EcoSift is the solution to the continuous buildup of plastics and other inorganics, or the loss of potential revenue from the loss of organics in a general material stream. By matching the EcoSift with the EcoStack conveyor system, an operator can further improve overall material handling efficiency. This system comes in custom sizes, with either tracks or wheels, up to 100-foot length, and 48-inch width.

For more than 25 years, Green Mountain Technologies provides a whole system approach to compost management. These services include facility design, three-dimensional modeling, operator training, feedstock evaluation, and odor studies. GMT has more than 30 municipal and commercial compost facilities ranging from 3,000 to 200,000 tons per year that have been efficiently composting curbside collected yard debris, food waste, biosolids, and agricultural wastes. Their design staff has over 100 years of combined industry experience in the composting industry. This design effort includes the presentation of 3D models that ensure proper fit and placement of all of the composting facility components. These displays allow for quick permitting of proposed facilities. Their Compost Feedstock Evaluation service allows an operator to develop a smart composting process for your organic waste. This is especially valuable for feedstocks with unique characteristics such as agricultural or industrial waste products, biosolids, and animal manures. GMT also provides site analysis and remedial plans for sites experiencing odor complaints. The services include dilution to threshold (D/T) sampling and VOC, ammonia, and methane sampling. With more than a combined 50 years of experience operating and supporting compost operations, the GMT staff is approved for onsite training for state required operator training courses. They are active in the development and implementation of the US Composting Council and the Washington Organic Recycling Council’s operator training programs.

Komptech Americas is a North American technology supplier of machinery and systems for the mechanical and mechanical-biological treatment of compost, solid waste, and for the treatment of biomass as a renewable energy source. Their product line includes over 30 different types of machines that cover all key process steps in modern waste handling
—shredding, windrow turning, screening, separation, and biological treatment. The Komptech Topturn X Series line of windrow turners comes equipped with a large diameter rotor driven by the high-torque, hydrostatic drive that produces a very tall peaked windrow with great porosity. These machines are designed for the windrow composting of manure, green waste, food waste, or any organic material. The Komptech Topturn uses its robust plows to allow one windrow to overlap the next by over a foot. This overlapping results in an increased site capacity of over 50%. “If you’re not doing a good job turning, you’re going to have trouble making good compost,” says Farrel Crowder, owner/CEO of Humalfa, an organic fertilizer producer in Colorado. “I’d buy another Komptech [turner] in a heartbeat. It’s just good engineering.” Komptech has spent over 25%2