As a result of the significant need to solve environmental problems through composting, over the years many organizations have made attempts to provide commercially viable solutions.  Batch systems were the first introduced to the market.  These systems often required staging of waste until the previous mass was completely composted.   Continuous flow systems were later introduced.   However, this term is often misused.  For a system to be truly continuous flow, material should be able to be added to the system on a constant basis without requiring staging.   Some manufactures use this term to describe a batch process that has enough capacity to take in more waste.  The two are not the same. 

Only a small number of companies have developed fully automated continuous-flow systems.  Even fewer have been able to do so with great efficiency.

Listed below are summary descriptions of each process followed by general detail about their cost and processing efficiencies and effectiveness as compared to in-vessel continuous-flow solutions.   


Aerobic Composting

  Open Windrows and Static Piles

Windrow composting typically involves the 6 ft. -8 ft. high rows of biodegradable waste spread along a large plot of land.  Precipitation is the primary source of hydrating the composting mass.  In very dry regions, these piles are manually misted to keep wild fires from erupting.  To control aeration, which also has an impact on temperature, the windrows are turned periodically with a front loader or specialized compost turner.  A static pile is similar to windrow composting with the exception that the material is not aerated by turning, rather by forced air that comes from devices such as a perforated pipe laid under the pile.  This aeration method does not aerate the pile uniformly.

Disadvantages:

Inefficient due to the inherent batch process
Prone to negative odor and dust impacts on the surrounding community
Requires a large land area for processing
Due to lack of process controls, an inferior and inconsistent end-product is produced
Long processing and retention times can take up to a year to fully stabilize waste
Subject to fire
No leach ate control. Toxic runoff seeps into the earth and causes water pollution.  
Dependant on nature, which can’t be controlled. 
Expensive when land, waste transportation, and labor costs are all taken into account
Numerous multi-million dollar facilities have been closed due to odor impacts on surrounding communities

Agitated Beds

This process is similar to open windrow composting except for the fact that these processes occur in an enclosed area.  Agitated beds typically are comprised of 6 ft. – 8 ft. deep concrete lanes filled with biodegradable waste.  The lanes are protected from the environment by a roof and often four walls; however in some cases the walls are open.  A compost turner travels up and down the concrete lanes or travels from a suspension mechanism from the ceiling to periodically turn the material. This system is more controlled than open air windrows and static piles, and therefore should produce less odor as opposed to those processes.

Disadvantages:

Inefficient due to the inherent batch process
Requires a large land area for processing
High maintenance costs of the compost turne
Longer processing and retention time due to inferior process controls
Workers are often exposed to gasses given off by the pile

 Rotating Drums

Similar to an aerated container, this process occurs in a large drum.   Rotating the drum slowly provides agitation and aeration.  Although this method can be termed “in-vessel”, this is not a continuous-flow system.
Disadvantages when compared to products from BioSystem Solutions:

Inefficient due to the inherent batch process
Short retention time of 3-5 days does not stabilize the mass before it is discharged
Prone to attracting vectors and releasing odors
Not scalable for large-scale facilities
Rotation tends to clump the material and does not provide uniform air flow
Large land area required for compost curing process 

 Aerated Containers

This process is similar to a static piles except that they are housed within a sealed container.  Temperature is controlled through forced air.  Often, biofilters are used for odor control.  This process does not include agitation or turning of waste material during processing.  Although this method can be termed “in-vessel”, this is not a continuous-flow system.

Disadvantages:

Inefficient due to the inherent batch process
Labor intensive to load, move, and unload each container
No agitation (mixing) after material is inside the container
Not cost-effective for large-scale composting facilities
Longer waste retention times due to static process without agitation

 In-Vessel Continuous Flow

This process eliminates all of deficiencies of the preceding processes and therefore is the most efficient.   Biodegradable waste is typically shredded and mixed before entering the vessel.   Once inside the vessel various variables, such as humidity, temperature and oxygen levels are controlled.   The mixture is automatically agitated when appropriate.   This process provides the most control of the thermophilic processes and therefore is capable of producing superior and consistent compost.   Key differences exist amongst the top in-vessel manufactures.   These differences can be found in the design philosophy and may have a significant impact on acquisition cost and total cost of ownership.  
The following should be considered when choosing an in-vessel system:

Footprint
Power and water consumption
Life cycle and maintenance requirements
Labor requirements
Level of automation
Conveyance mechanism
Automation of regulatory reporting
Remote control and monitoring
Modular and scalable customizable 
Corrosion proof construction
Robust control of composting variables consistently across the composting mass
Ability to recycle 100% of leachate for beneficial reuse

 Vermicomposting

Vermicomposting harnesses a high concentration of earthworms to accelerate the decomposition and stabilization of biodegradable matter. After the worms ingest the biodegradable food source, they excrete a premium organic soil supplement called wormcastings.  
Only one company has completely automated this process.  



Worm Beds
This method of vermicomposting is similar to that of an agitated bed.   This process usually occurs in long 12 in. - 18 in. high rows in which worms eat their way up to the top and excrete castings.

Disadvantages:

Inefficient due to the inherent batch process
Labor intensive due to lack of automation
Cumbersome worm casting harvesting process
Extremely long processing and retention times
Requires large land area for processing

It is clear that the state-of-the-art scalable products BioSystem Solutions has designed are the most advanced, cost-efficient, smallest footprint per ton, scalable, automated, in-vessel composting systems in the industry.  In addition, BioSystem Solutions is the only company that offers comprehensive automated in-vessel thermophilic and vermi-composting systems.