OPERATIONS AND TECHNOLOGY

This section offers factors to consider during the initial startup of a composting operation.  It also outlines six composting technologies used in today’s industries.

The initial startup of any operation takes a solid work plan and research about the industry.   Listed are some of the activities to undertake during the initial development of an industrial composting operation.

• Identify markets and strategies for feedstocks, waste management, and product(s) sales
• Set clear, concise composting project goals
• Prepare budget, including operation, equipment and labor costs
• Identify and evaluate potential sites, permit requirements and environmental factors
• Obtain necessary government approvals, permits and ordinances
• Assess potential savings in costs over current practice - market this
• Determine feedstocks, yard waste, municipal solid waste, animal manures and bedding, paper waste, biosolids, food waste, sawdust and wood chips, or sludge
• Evaluate transportation logistics for both feedstocks and products
• Evaluate equipment options
• Develop or access an operator training program
• Program monitoring and assessment; Seal of Testing Assurance Program - US Composting Council

The main focus of any composting operation is to produce a quality product that is marketable, environmental and ecological sustainable and safe for humanity.  There are key environmental parameters that must be maintained within a specific range to provide optimum outcome.

The initial process begins with collecting, processing and storing feedstock materials.  The material must be screened for contaminants such as metals and plastics, which are non-biodegradable.  Depending on the feedstock the material may need to be chipped or shredded into particles 3" to 4" that will make the decomposing process more efficient.

Then an aerobic process, which uses microorganism such as bacteria and fungi to breakdown the organic material under controlled conditions, accelerates the decomposition process, which can occur naturally or rapidly depending on the method and technology used.

The microbes require oxygen, moisture and food in order to grow and multiply.  The microbes generate heat, water vapor and carbon dioxide as they transform raw materials into a stable soil conditioner. Active composting is typically characterized by a high-temperature phase thermophilic (45°-70° C) that sanitizes the product and allows a high rate of decomposition, killing of pathogens and weed seeds, followed by a lower temperature phase mesophilic (20°-45°C) that allows for the product to stabilize while still decomposing at a lower rate. Compost can be produced from many forms of feedstock.

State and federal regulations exist to ensure that only safe and environmentally beneficial composts are marketed.

COMPOSTING TECHNOLOGIES

Windrow Composting
Aerated Static Pile
Aerated Compost Bins
Rotary Drum
Box/Tunnel Composting Systems
Vermi Composting (Worm composting)

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Windrow Composting

Organic waste is formed into rows of long piles called "windrows" and aerated by turning the pile periodically by either manual or mechanical means. The ideal pile height, which is between 4 and 8 feet, allows for a pile large enough to generate sufficient heat and maintain temperatures, yet small enough to allow oxygen to flow to the windrow's core. The ideal pile width is between 14 and 16 feet.

Aerated Windrow Composting Composting US EPA

• Long, narrow piles agitated/turned regularly
• Approximately eight feet high by 13 feet across. 
• Aeration by natural/passive air movement
• Composting time: 3-6 months
• Equipment: Front end loader or composting turning tracker 
• Process it widely use on farms

Aerated Static Pile

In aerated static pile composting, organic waste is mixed together in one large pile instead of rows. To aerate the pile, layers of loosely piled bulking agents (e.g., wood chips, shredded newspaper) are added so that air can pass from the bottom to the top of the pile. The piles also can be placed over a network of pipes that deliver air into or draw air out of the pile. Air blowers might be activated by a timer or a temperature sensor.

Aerated Static Pile Composting Composting US EPA

• Aeration provided by mechanical blowers
• Compost time: 3-4 weeks; followed by 30 days curing
• Ideal waste: biosolids and sludge

Aerated Compost Bins  

• Aeration through porous floor plates/channels
• Composting time: 2-3 weeks
• Curing time: 2 months
• Durable materials of construction
• Equipment: Front end loader
• Vector/Vermin control need with food wastes (cover with compost)
• Capacitates: 3-4 Days waste and bulking agent per bin

In-vessel composting occurs in enclosed reactors. These consist of a wide variety of electro-mechanical cinfigurations usually enclosed in a building.  In-vessel systems can be categorized into vertical bioreactors, horizontal bioreactors, biocells, bio-containers, and biotunnels.  These systems offer methods through which air flow and heat can be controlled.  One example of a type of in-vessel system is:

Rotary Drum Composter

The Rotary Drum is designed as a continuous feed, taking raw waste in one end and discharging at the other.  The material composts for  3-5 days in the insulated drum achieving 55 - 60 ^oC.  Odours are collected and biofiltered. The drum provides a solution to odourous wastes.  After the composting step in the Rotary Drum the odours generated  are greatly reduced and pathogen reduction has been achieved.   

Transform Compost Systems -- Rotary Drum Composter

• Rotation mixes, aerates compost mix                               
• Second – stage curing/composting needed
• Waste grinding & mixing with bulking agent 
  (needed prior to feeding drum)
• Recipes for drum composting (by volume)
• Food waste: 2 parts wood chips, 1 part sawdust, 
  2 parts food waste
• Seafood waste: 3 parts wood waste, 1 seafood waste

Box/Tunnel Composting Systems

• Waste grinding & mixing with bulking agent prior to loading
• Mechanically transport & aerate compost throughout process
• Computer controlled monitoring (temperature, CO2, Oxygen, moisture) 
  to meet EPA Part 503 Rules & aeration
• 11-21 days process time
• Finished compost requires 30 –90 days curing

Vermi Composting

Through this method, red worms (Eisenia foetida) not nightcrawlers or field worms found in gardens are placed in bins with organic matter in order to break it down into a high-value compost called castings. Worm bins are easy to construct (they are also commercially available) and can be adapted to accommodate the volume of food scraps generated.

Vermicomposting Composting US EPA            

• Utilizing red worms to consume and process organic
   matter into worm castings
• Worms will eat almost anything you would put in a typical compost pile
• One pound of mature worms (approximately 800-1,000 worms) 
  can eat up to half a pound of organic material a day