A cost-effective method for controlling compost air emissions

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Courtesy of Engineered Compost Systems

In October 2007, ECS began conducting trials at California State University Fresno (CSUF) to explore using the new patent pending AC Composter (ACC) covered aerated static pile system to manage dairy manure solids and comply with airquality standards. A two-zone portable pilot system was delivered by ECS and installed at the CSUF research dairy. This research is being conducted under a Phase I USDA CSREES Small Business Innovative Research grant. The goal is to determine how well the ACC (Figure 1) can meet the operational and economic demands of manure management at a dairy and provide adequate capture and control to limit air emissions for compliance with California regulations.

Composting is a proven technique to process organic wastes into a more stable and valuable form. On-site composting of dairy manure allows a dairy to recycle manure solids into a safe bedding material and sell finished product. Recycling to create bedding reduces the expense of importing straw or other materials, and exporting compost creates a means to manage excess nutrients. However, increasingly stringent air emissions regulations have made open windrow composting less tenable.

One of the key goals of this research has been to quantify the ability of the ACC to capture and control air emissions. During the composting trials air emissions samples were collected by a CSUF team under the direction of Dr. Charles Krauter. Samples were taken from the exhaust duct, the surface of the biofilter, and the surface of the covered piles. Samples were analyzed using a real-time photoacoustic gas analyzer (LumaSense INNOVA 1314). Sampling from a tap in the exhaust, along with flow measurements at the same point, were used to determine the actual air emissions flux in the duct. Samples at the biofilter and pile surfaces were taken using Surface Isolation Flux Chambers. These chambers are placed over the surface to be measured and charged with clean air at a known rate to measure gas emissions flux emanating from the enclosed surface (Radian, 1986).

Initial data for air emissions from the system are summarized in Tables 1 and 2. The data shows that the capture rate for the ACC is 100%. It also shows that the biofilter control rates are significantly higher than BACT. The high control rate is largely due to the low loading rate of the biofilter (i.e. a longer retention time). Because the ACC makes low aeration rates feasible, it becomes cost-effective to have a biofilter with a low loading rate.

ECS has applied for a Phase II USDA CSREES SBIR grant to continue this research and collect more comprehensive emissions data from a larger prototype system operating at a large commercial dairy. Phase II research is scheduled to begin in September of 2008.

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