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Why Positive ASP Composting Is the Future of Organics: For the Environment and for the Economy

Two of the biggest issues faced by commercial composting operators are emissions (odor and VOCs) and moisture management. Odors and Volatile Organic Compound (VOC) emissions from compost facilities can be highly variable and are influenced by factors such as composting technology, feedstock mix, and operational parameters (initial grind, porosity, saturation, aeration, etc.). Moisture management issues are also complex, ranging from the moisture in the compost to managing the leachate and stormwater runoff, and are also influenced by feedstock mix and many of the same operational parameters.

Miramar Greenery, San Diego, CA

Limiting VOC Emissions

Over the last 20 years, the regulations set under the Clean Air Act of 1970 have driven innovation in waste management and composting methods. Aerated Static Pile (ASP) composting was first introduced in the 1970s using negative aeration to accelerate and manage the composting process with a much lower risk of VOC emissions. This method also eliminated the need for turning the pile by using negative aeration and simple timer controls.

Air pollution has been addressed on the local level, especially in the State of California where it went the extra mile in addressing its unique air pollution problems. California is now split into 35 air districts, each one facing its own challenges ranging from traffic-related smog in Los Angeles to greenhouse gases in the enclosed San Joaquin Valley caused by nitrogen compounds combined with dust particles from farming.

These issues are obviously not limited to California, as we see VOC emission controls coming up in legislation proposals in many other states due to urban sprawl and the proximity of housing to many organic processing sites. The composting technology you choose for your site should meet the needs and regulatory demands of your locality, which includes being a good neighbor controlling fugitive odor emissions as well as quantitative compound emission control including total non-methane non-ethane organic carbon (total VOCs), ammonia, and speciated organic compounds.

MidValley Disposal Compost Facility in Kerman, CA. (Learn More about MidValley in the Project Profile)

Moisture Management

Similar to the specific issues faced in California on air pollution, Florida has focused its efforts on cleaning up local waterways. The Florida Clean Waterways Act (FCWA), signed into law in 2020, requires local governments to take swift action to reduce polluting impacts on Florida’s water resources. The act addresses numerous environmental issues, including several components related to stormwater management within composting operations.

The Florida bill (SB 712) supports the FCWA and demands stricter regulations to abate nutrient impacts on Florida’s water resources. This includes evaluating and revising stormwater management systems related to site runoff into Florida’s tributaries.

The application of these regulations to the organic waste management industry is clear. Each compost pile requires protections from contaminating waterways and groundwater by clearly separating and managing leachate and preventing storm water from washing contaminants downstream.

VOC Emissions Testing at West Valley Compost Facility in Fontana, CA.

Recommended Solutions

Covered Aerated Static Pile (CASP) composting systems offer the best solution to address the primary environmental concerns of air and water pollution. CASP is a forced air composting method that uses either positive (pushing) or negative (pulling) air movement that assists in the compost process, reducing the time to create a finished product.

Negative aeration systems rely on capturing air pollutants by drawing air through the pile under negative pressure from an external blower and exhausting the air through an end of pipe air pollution control device, such as a biofilter. This requires the aeration blowers to also handle hot corrosive exhaust air plus condensate, instead of handling clean air, through an additional odor control process such as a biofilter. While the initial capture efficiency can be greater than 90 percent control, these systems require maintenance and constant monitoring. Over time the capture efficiency has been shown to decrease to 60 to 65 percent of pile surface emissions, a significant reduction.

Positive aeration systems are also encapsulated, using a blower with motor controls to manage the air input and oxygen levels through a plenum system underneath the pile. Since the air is handled inside a closed system and underneath the pile, the covered system can be more flexible in size and materials. The more advanced positive CASP systems use the blowers alongside temperature, moisture, and oxygen monitors to finely tune the composting process for the desired quality end product. Positive CASP systems are ideal for all types of feedstock including food waste, green waste, biosolids, and source separated organics.

Covered positive CASP systems typically use a compost biolayer, or synthetic covers including polyethylene (PE) tarps, flexible vinyl fabrics, PE fleece blankets and expanded polytetrafluoroethylene. The flexibility and affordability of these cover options allow the system to be scalable, portable, and highly effective.

Sustainable Generation's Advanced Composting Systems use a GORE® Cover - uniquely offering a semi-permeable, waterproof material technology to encapsulate the compost, with results that offer an advantage over other composting systems, including:

  1. Sequestering VOCs to meet or exceed local regulations by reducing emissions by more than 90 percent during covered and uncovered phases of the process

  2. Maintaining the proper pile temperature to produce Class A compost at 55oC (131oF) or higher for a minimum of three days

  3. Reusing leachate within the system to maintain the optimal levels of moisture content

  4. Keeping the ideal amount of free air space (FAS) in the pile to promote the growth of oxygen-consuming bacteria

Balancing the cost/performance ratio with the lowest total cost of ownership requiring energy consumption during composting phase of ≤ 2 kWh/ton input material and only requiring one operator per 20,000 tons per year of additional annual capacity.

By efficiently reducing greenhouse gases resulting from organic waste, and providing a protective barrier from stormwater and leachate runoff, these types of systems have a long track record of success in California, Florida, and around the world.

Using blowers alongside temperature, moisture, and oxygen monitors to finely tune the composting process, positive CASP systems are ideal for all types of feedstock, including food waste, green waste, biosolids, and source separated organics.

Optimal Conditions

Strong environmental awareness and aggressive climate goals linked to grant funding provide optimal conditions for the use of such technology which meets or exceeds many state and federal environmental regulation requirements.

Originally written by Scott Woods, Founder/CEO of Sustainable Generation and published by Waste Advantage Magazine May 29, 2022:


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