Previous evaluations of the technologies investigated were conducted in a batch mode of testing. This program was conducted to demonstrate the viability of the technologies investigated to significantly reduce phosphorus when operated in a continuous mode, pulling manure directly from a deep pit swine operation without agitating the pit. Additionally, this demonstration also explored the ability of several dewatering technologies to produce a stackable product containing the high phosphorus recovered in the form of amorphous calcium phosphate. Considerable data on this final product was collected from multiple off-site takers expressing interest in the final product. Figure 1 is a picture of the pilot setup.
What Did We Do?
Mobile test units were employed at a swine operation representative of a typical operation in Mercer County, OH. Manure was directly pulled from the deep pit at the host farm, and after initial dewatering, it was treated under conditions consistent with a detailed program conducted under sponsorship from Ohio Farm Bureau in summer 2019. Treated manure was then sent to multiple dewatering options including passive dewatering (geotextile bags) and mechanical separation. The demonstration program ran for six months and a total of 110,000 gallons of manure was treated continuously with multiple samples collected for analysis at third-party certified labs.
Twenty cubic yards of the initial manure solids were collected for use by a Cleveland off-site taker to investigate its viability as a composting foundational ingredient, while several different off-site takers were sent samples of the final dewatered material containing the recovered phosphorus. An additional three tons of stackable final product were sent to several off-site takers in Allen County, IN for use and evaluation, an additional 20 cubic yards of the geobag containing product were sent to a local farmer for application in a 40 acre wheat field and the remainder of the material (both manure solids and geobag material) were land applied by the host farm.
Figure 2 is a picture of the dewatered manure solids collected.
Figure 3 is a picture of the recovered phosphorus product.
What Have We Learned?
We were able to confirm that the technologies demonstrated performed as expected when operating in a continuous mode. An average initial dewatered manure cake of 20.8% solids was obtained without the use of polymers and a consistent stackable product of 24.4% was obtained with the mechanical dewatering equipment used. An average of 96.1% recovery of total phosphorus was obtained during the pilot. This value compares to the average total phosphorus reduction of 95.5% measured at the batch mode operation in summer 2019. Limitations of the equipment used limited operation to approximately 7gpm but with properly sized pumps, this could be increased.
The operating cost of treatment averaged out to $0.0063/gallon (measured at $0.0064 in summer 2019). To dewater the product to stackable form varied depending on the equipment used, but costs of close to $0.01/gallon have been estimated. For the application demonstrated, the use of a geobag for final dewatering was not considered a viable option due to high costs (approximately $0.15/gallon treated) and the space required.
The Maumee Valley Authority was awarded an USDA Conservation Grant in partnership with Allen / Adams County of Indiana and Applied Environmental Solutions to further demonstrate continuous flow operation over an extended duration at a deep pit swine, dairy and mixed manure lagoon operation. A major focus of this effort will be in establishing the value and path to market for co-product streams produced. Additionally, efforts are underway to design and build a portable unit capable of treating 500,000 gpd of manure over a 3-5 day period. This would allow for treatment at smaller farms without the need for capital outlay by the individual farms. One purchaser of this design has already been identified for delivery in 2023.
In addition to the above, initial testing of a companion technology for the recovery of ammonia is also under investigation. Ammonia can be recovered in any number of ammonium salts (such as ammonium sulfate) and represents another opportunity to maximize the resource recovery from agricultural streams.
Rick Johnson, Director of Commercial Development, Applied Environmental Solutions
Theresa Dirksen, Agriculture & Natural Resources Director, Mercer County (OH)
Corresponding author email address
- Ohio Water Development Authority
- Mercer County Board of Commissioners
- Ivo & Linda Post, Host Farm
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