How does the industrial composting process work?

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Ever wondered what happens once you drop off your food scraps at your local composting facility? The industrial composting process can be much more intensive than your average backyard bin depending on the method. Let’s break them down!

Types of industrial composting:

According to the mapping project of the Sustainable Packaging Coalition, a small percentage of composting facilities in the US actually accept all compostable products including bioplastics. This variation in material acceptance is partly due to the type of commercial composting that these facilities use. 

There are four different methods including vermicomposting, windrow composting, static pile composting, and in-vessel composting as stated by the EPA. 

Vermicomposting

worm composting, vermicomposting

This process is mainly practiced on a smaller, individual scale because it revolves around the incorporation of red worms. These worms easily digest this organic material producing high-quality compost called casting which becomes usable within three to four months. Nevertheless, this technique can be scaled up in order to meet industrial demands. One pound of adult worms is able to consume around half a pound of compost in a single day. However, this approach only allows for food scraps, paper, and yard trimmings to be compost due to the consumption limitations of these worms.

Windrow composting

This composting method relies on the creation of four to eight feet high by 14 to 16 feet wide piles of organic material called windrows. Maintaining these specific dimensions allow for the piles to produce enough heat and retain a certain temperature range while also granting oxygen the ability to flow through the core. This process produces large amounts of fertilizer in approximately four months.

Static pile composting 

static pile compost pile at Farmer Pirates
Farmer Pirates

The static pile composting technique entails mixing loose, bulking materials like wood or paper into the layer of the organic material. The loose matter creates air pockets that flow from the bottom to the top of the pile. In some cases, a system of pipes is incorporated into the various layers of the compost in order to ensure that there is oxygen to feed the micro-organisms. However, animal bioproducts and grease are an issue for this approach because they break down at a slower rate than the rest of the material. Thus, additional sorting is required before processing. Pictured above is our composting partner Farmer Pirates for Borderland Music Festival.

In-vessel composting

XACT Systems Composting

This operation of composting requires the organic material to be loaded into a drum, silo, concrete-lined trench, or other similar equipment. This container allows for the temperature, moisture, and airflow to be controlled within the enclosed space. Within a few weeks compost will be produced, but it will not be usable until a few weeks or months after its initial processing. This delay is because the microbes still need to balance the soil while also allowing it to cool.

Touring an industrial static pile composting facility:

Recently, I had the opportunity to tour the McGill composting facility in Waverly, Virginia. I learned about their version of the static pile method and how they utilize it to degrade all of their organic matter and bioplastics.

McGill-Waverly exterior

McGill’s version of the static pile technique consists of mixing wood and yard products into their organic material in order to create air pockets. This, along with their aeration system, ensures that there is enough oxygen to feed the working micro-organisms.

1. Off-Loading:

The compost is unloaded into an indoor, concrete bunker that is organized into two piles: the dry feedstock pile (wood and yard products) and the wet feedstock pile. This bunker is where the organic material starts to heat up and decompose with the help of some naturally produced carbon and nitrogen. The ideal carbon to nitrogen ratio is 30 parts carbon to 1 part nitrogen. If there is too much carbon, the decomposition of the organic matter will slow down. If there is too much nitrogen, the plant will have an odor issue. Therefore, McGill closely regulates their gas production to ensure stable conditions.

2. Blending:

Once ready to be transported into the bays, a ratio of wet and dry feedstock is mixed together with a backhoe truck bucket. 

3. Encapsulation Bays:

Encapsulation bays are concrete chambers that possess special aeration systems, located in the floors, walls, and ceilings. This aeration system provides the microbes with a source of oxygen and removes some of the heat produced by the organisms feeding actions. In addition, industrial fans regulate the temperature of the isolated bays. These fans pull excess air away from the work zone, process it into a biofilter, and release it back into the atmosphere. The astonishing part is that all of this can be controlled from a computer system! This system also informs the facility when the compost is ready for filtering. 

4. Screening One:

This material is then filtered through a fine screen. All of the material caught by the screen is taken back to the off-loading dock to be reprocessed.  

5. Break:

The compost is then placed in an outside area where it sits for a few weeks to ensure that all of the organic matter has completely broken down. 

6. Screening Two: 

The material is filtered through an even finer screen to ensure its quality. 

After all of this, you have beautiful, nutrient-filled organic matter ready for use.

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