Better Living Through Organics

Organic Waste Sources

Where does the organic waste used as feedstock for composting operations come from? According to the EPA, Americans throw away 4.5 pounds of trash per capita daily. This adds up to about 0.8 tons per person per year. Of this total 51% gets sent directly to the landfill for disposal, 13% gets incinerated to generate electricity, 27% gets recycled, and only 9% gets composted (source: “Advancing Sustainable Materials Management: 2015 Fact Sheet” US EPA, July 2018). America as a whole generates about 262 million tons of waste, of which 23 million tons are composted.

So why the relatively small percentage (but by itself a substantial amount) of composted waste? It is mostly the result of the composition of the overall wastestream which only has limited amounts of material that can be composted in the first place.

Waste is either organic (derived from living materials like wood, vegetation and plant fibers) or inorganic (made from glass and metal). According to the US EPA, there are six categories of waste: organics (yard waste—13%, food waste—14%, and wood waste—7%; 34% total), paper (27%), plastics (13%), metals (ferrous and non-ferrous, 9%), glass (clear, amber, brown 5%), and textiles/miscellaneous (12%). Paper and textiles are potentially compostable but require further and more expensive processing. So, with about 34% of the total wastestream being organic and only 26% of that (9% of the total wastestream) being recovered for composting, there would appear to be considerable potential for expansion. However, that is driven by external economic factors such as transport costs.

Organic waste production is as highly variable as it is heterogeneous. Seasonal factors impact the amount and kinds of organic waste being produced. Fall brings the harvest as well as agricultural waste. Meanwhile, homeowners are raking leaves off of their lawns while park services are doing the same. Spring/summer is a steadier production season from vegetation punctuated by increases from construction, while winter sees an almost complete drop off in natural organic waste production. Providing a baseline of organic waste production is the generation of food waste and the waste byproducts from sawmills and furniture manufacturing.

These differences in types and time present serious difficulties to the efficient and effective collection of organic waste. So, the scale of the amount of organic waste generated affects the organic waste collection and composting as much as timing and type of waste. Large-scale operations (forestry, landscaping, construction) allow for easier collection than does intermittent small-scale sources like restaurant kitchens. Households present a particular challenge since source separation of organic waste by homeowners is not a widespread practice, and neither is separate collection of organic waste by refuse collection and hauling companies. Unfortunately, a significant portion of the organic wastestream is divided up among small hard to reach niche sources. With organic waste collection and composting, size is everything with bulk sources of organic waste being more economic to collect and compost.

Despite all of these obstacles, the composting industry continues to grow apace. Forty years ago, there were no significant amounts of organic waste being composted aside from individual niche efforts. By the 1990s, organic waste composting had jumped over four million tons with another quadrupling to more than 16 million tons a decade later. The last decade has seen strong increases to well over 25 million tons annually. That is essentially exponential growth over forty years with no signs of slowing down. And these numbers only count the big operations and not the local markets or individual composting efforts. For the most part, apart from kit suppliers for homeowners (a small but enthusiastic niche market), the composting equipment industry is focused on large-scale industrial operations.

These large-scale operations rely on curbside pick-up by communities devoted to organic waste collection and transport to centralized processing centers. Pick-up operations have increased by over 200% in the past decade to cover almost three million homes and over 200 cities and towns. These efforts run parallel with a similar increase in composting operations at the receiving end (a 71% increase across 44 states, Biocycle 2014 report). Greater opportunity is there with the potential for 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 which can be diverted from landfills to composting (Institute for Local Self-Reliance, ISLR). And with this growth comes jobs, with composting providing four times as many jobs per ton of waste than landfilling, according to the ISLR).

Transporting Organic Wastes

Though organic waste has many sources, there is one cardinal rule for the transport of organic waste the trucks doing the hauling cannot leak. Organic waste often comes with a high water/liquid content and much food or agricultural waste can be corrosive. All aluminum truck beds and tanks are often preferred, providing strengths, lightweight and corrosion resistance. Tight-fitting and secure waterproof tarps are a necessity for open-top trucks.

Loading and offloading operations are also a concern. Self-loading and off-loading designs are standard with remotely operated aluminum buckets having significant lift capacity. Clean-out is made simpler with the use of pressurized water hose attachments. Containment doors and hatches require high-quality rubber or neoprene seals to prevent loss of moisture. This is of regulatory importance as well as an operational necessity since many states consider any water that comes into contact with any MSW to be leachate subject to strict environmental regulations and even fines.

The types of trucks used vary with each type having advantages and disadvantages. Trailer maneuver better, but could jackknife with potentially hazardous and environmentally damaging consequences. Straight trucks with front-end loaders are also preferred given their safer pertain and simplicity of loading which does not require the operator to leave the cab. Modification can be made for specific types of organic waste and unique collection points. For example, big city restaurants (fancy or otherwise) have back-alley containers for front end or rear end lading. Large-scale agricultural waste operations may rely on compost piles or waste rows that are loaded into the truck by a dedicated front-end loader.

According to Richard Moffitt, Vice President of Sales & Marketing, Hallco Industries, Inc., three primary concerns come up when transporting compostable organics: site volume generation, moisture content, and bulk density (weight). Hallco Live Floors equipped trailers allow for the circular transportation of raw materials to and compost away from composting facilities.

The feedstock sources for compostable raw materials are important for two main concerns: volume and type of vehicle required for transport. A small restaurant in the inner city will produce smaller volumes than a farmer pulling crop residuals off their fields or tree trimmers after a storm. The volume also creates concerns with the size of the vehicle needed for the removal of the organic material. Transfer stations collecting organics will generally have the real estate needed to maneuver larger transfer trailers around the facility. A typical household in the larger cities needs a smaller collection truck, nimble enough to navigate the city streets collecting multiple households before emptying into a larger vessel. This collection of smaller household organics will then be transferred directly to the composter or to a collection site at a transfer station where a transfer trailer, such as those equipped with Hallco Live Floors®, can be utilized to transport both feedstocks and finished compost.

Another major concern is the level of moisture in the feedstocks. Moisture is measured as a percentage of water in the raw materials. This measure varies greatly with consideration not only to the type of organic, but also the time of year it is collected. Fresh cut grass from a suburban community in the early spring or kitchen food scraps will have a much higher moisture content than raked leaves in the fall from the same area. The higher the moisture level of the materials, the heavier they are to transport. With organic feedstocks for compost, moisture of 45-65% and the accompanying extra weight of that moisture, will create compression of liquid in the bottom of a large transfer trailer. Hallco’s floor systems are capable of handling organic loads from 15-45 tons. The liquid created from compression will require a leak-resistant or leak-proof design in the floor system to keep from dripping onto roads, ferries, and scales. Smaller volumes of wetter materials such as waste food from hotels, restaurants, prisons, and convention centers can be accommodated in roll-off containers and then transported to a collection site such as a transfer station or compost site.

Bulk density is the measure of weight for a given volume. Waste organic materials with a higher bulk density will require a large vehicle to move it from generation to compost facility. Smaller vehicles may be used but would require move frequent and costly trips. A transfer trailer would be the best option for the generators of large amounts of organic waste. Feedstock will have a much higher bulk density than finished compost for most producers.

Composted Waste Storage Facilities and Related Structures

Though temporary storage of organic waste is typically required before pickup and after delivery, this is usually accomplished with small-scale individual sourced storage bins. Delivered organic waste is often placed in open-air stockpiles or directly fed into the composting process upon arrival. Long-term storage of composted materials after final processing but before final sale and delivery is a different matter. Often, the storage facility is where the composting process is performed.

Long-term bulk storage of compost presents certain challenges, so care must be taken in the design and operation of storage facilities with a key question being of the compost needs to be stored over the winter. Required storage time is a function of production versus application/use. Excess production needs to be stored until utilized or shipped to another site, and if not properly stored, compost can go bad. Its nutrients can be lost or leached from the compost, the compost pile itself can start rotting and excessive fungi growth can result. All of this can be avoided with proper storage.

In addition to ensuring a good quality product, the United States Department of Agriculture (USDA) Natural resources and Conservation Service (NRCS) has established a standard for long-term compost storage. The regulatory goals of these standards are to ensure that the storage facility: reduces water pollution potential; conserves energy by reducing mass and improving handling characteristics of organic waste solids; reuses organic waste as animal bedding and transforms organic waste into a soil amendment that improves soil health, provides slow-release plant-available nutrients, and suppresses plant disease.

The storage facility’s plan must conform to all applicable Federal, State, and local laws and regulations. The landowner is required to obtain all necessary permits for project installation before construction. Composting and storage facilities must be sited outside of a 100-year floodplain, not cause water diversion that impacts nearby structures, be at least 50 feet from wells and other sources of water such as streams and ponds, have a floor at least 2 feet higher than the local seasonal high groundwater table (which can be lowered with the use of underground drainage pipes), have design features that prevent the leaching of contaminants into local groundwater, and ensure all-weather access.

The Composting Process and Its Equipment

There are two main types of composting: aerobic and anaerobic. Anaerobic, referred to as cool composting, is performed in the complete absence of oxygen and usually in contained vessels called digesters that are sealed off from the outside atmosphere. This can be a long process (more than six months), typically managing small batches (1 cubic yard or less), and requiring expensive upfront capital costs. For these reasons, large bulk composting is usually performed with the aerobic (a.k.a. hot) composting process.

Aerobic bulk composting (more than 1 cy volume) is typically performed wither in windrows or aerated static piles. Aerobic composting is a process where organic materials are decomposed by micro-organisms 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.

A low-cost (and therefore popular) option for aerobic composting is the windrow method. These are long piles of composting material with a triangular cross-section and about 6 to 8 feet in height. During the composting process, which can take 2 to 6 months, the windrows are regularly turned either by front-end loaders or specialized windrow turning equipment. A more complicated windrow design incorporates force air pipelines installed under the windrow along its length. A blower applies negative pressure to the pipeline, pulling air (and odors) down into the windrow pile. This allows for faster processing while requiring less mechanical turning. The windrows can also be piled higher (10 to 12 feet) allowing for more efficient use of the available area.

Major Suppliers

Hallco Industries, Inc. has been producing leak-resistant and leak-proof Live Floors systems for nearly half a century. 

For the transport of high moisture feedstocks, Hallco employs its front-mounted Brute leak-proof Hallco Live Floors systems. These have hydraulics on the outside of the nose of the trailer. This allows for the connection of the floor slats to be sealed and positioned outside of the rising liquids inside the trailers. The aluminum floor slats are mounted on raised subdeck, allowing for a sealed floor in the trailers.

As more communities begin to mandate the recycling/non-landfilling of household organics, the need to transport them properly will become more vital to the success of these programs. Curbside pickup of organics is conducted in most states in North America. However, these organics programs are largely focused on yard waste, which is generally low in moisture and bulk density. Many communities are expanding these mandates to include food waste which is much higher on both these scales. To combat the high moisture created by food waste, transfer stations are utilizing leak-proof Hallco Live Floors to eliminate the leaking of organic liquid during transportation.

For over 40 years, ClearSpan has manufactured and installed fabric buildings designed for the storage of organic composting materials. These customized buildings, designed to owner specifications can be used by farms, numerous industrial applications, and large commercial composting facilities. Their standard designs provide turnkey design, delivery and installation in one, low price and custom options. These buildings create a controlled environment that maximizes the end product's quality. ClearSpan makes compost storage structures for sorting, shredding, screening, curing operations.

A ClearSpan compost storage building can improve efficiency by creating an all-weather facility that minimizes or eliminates many of the environmental risks that accompany composting. These structures allow for high nutrient retention and protect against the extremes of the sun, wind and rain, which can all adversely affect the balance of manure piles and other organic wastes. By maximizing ventilation, ClearSpan structures can improve air quality and a superior composting and handling environment.

Brown Bear Corporation manufactures both attachment machines and complete machines for windrow composting, bioremediation and stabilization, sludge drying and land application for liquids, sludge cakes and compost.

They offer a wide range of sizes starting with small compact units for skid loaders, agricultural tractors, Self-Contained aerators for articulated loaders, and their line of Carrier units ranging from 130-375 hp. All the units provide for maximum exposure of the material to the air, sun, and wind with flail-type rotors. The paddle-type flail aerators have adjustable speed control, and an optional spray additive system is available for the incorporation of water, reagents, odor control chemicals and nutrients at the aerator rotor. The self-propelled units are four-wheel drive, four-wheel steer with environmental cabins for operator comfort.

The horizontal aerator provides an economical mechanical solution for dewatering sludge in beds, building windrows, blending bulking agents or additives, pulverizing and aerating or water mixing for aerobic composting. The rapid handling rate exposes 100% of the material to oxygen immediately so that noxious odors can be absorbed.

The Brown aerator works directly into the material forming it into a windrow. Windrows can be formed from piles of nearly any size. Alleyways are not required with this machine, so there is a great reduction in space requirements.

Bob Wubben owner of Blooming Prairie Nursery described his company’s use of the Brown Bear Compost Turner: We purchased and received our turner on August 15, 2015. With our turner, we can process wood chips, leaves, blend high-quality soils, soil for bio-cells, with results that exceed engineers' spec. for blending materials for different projects. How much material varies with each process, wood chips up to 500 cubic yards per hour, leaves about 1,000 cubic yards, soils 350–400 cubic yards bio-cells 350–400 cubic yards. The process and setting up windrows help efficiency the most, also the area to properly distribute the windrows after grinding. The machine is capable of grinding materials 30 inches high, 3 to 6 feet wide depending on dry or wet materials. How does Brown Bear Turner benefit our operations? 1. Provide high-quality products that our customers demand. 2. Allows us to be a mobile operation for multiple job applications. 3. The multiple uses of the turner allow us a great return on our investment."

Roto-Mix is a supplier of compost/organics trailers and wagons to public and private customers ranging from small farmers to large towns and cities. The City of Missoula Montana owns and operates a 78,500 CY/year extended aerated static pile biosolids and green waste composting facility next to their wastewater treatment plant (purchased from EKO Compost in 2016). They used to bucket-blend their feedstocks to mix, then switched to using a windrow turner. Jason Duffin, Plant Manager for the City explained, "We tried to use the turner, although the volume of product we needed to do it correctly was too large for the machine we were using, and it took more space and time than we had available. Also, the wetter biosolids would stay more in the middle and the lighter fluffier green waste organics would be on the outer edge."

The City purchased a Roto-Mix 3410 horizontal mechanical mixer in July 2017 (Figure 2). “The acquisition of the Roto-Mix into our process has improved things here greatly,” Duffin said. “Now a pile that took 20 minutes to build and fluff takes only 8 to 12 minutes. Bear in mind the reason it even takes that long is the front-end loader has to move the material to the mixer. The consistency of the mix is much more thorough and we have no concerns of pockets that aren’t mixed in anymore.” Because the City handles a lot of abrasive land-clearing debris in its green wastestream, Duffin decided to purchase a second set of augers and have them made from abrasion-resistant (AR) steel. They now plan to swap out the first set before they are worn and replace the flights with AR steel. Duffin estimates the cost of mixing at $4.45 to run a single 28-CY batch, noting that the mixing process reduces the batch volume to 25 CY or a unit cost of $0.18/CY to mix.

We are actively working with Roto-Mix on the wear we are having