A number of Idaho dairies use flushing systems that result in large amounts of liquid manure that are applied via irrigation systems to adjacent crop-land during the growing season. Solids and nutrients found in liquid dairy manure pose challenges to manure handling processes. Separating solids and nutrients from liquid dairy manure is a critical step to improve nutrient use efficiency and reduce manure handling costs. To better address issues related to solid/nutrients separation, a critical question needs to be answered: what are liquid dairy manure solid and nutrient distributions? Identifying solid particle distribution and associated nutrients in liquid dairy manure is necessary for designing settling ponds, choosing suitable separation technologies/equipment, and making better manure nutrient management practices.
What did we do?
Liquid dairy manure samples were collected from a flushing receiving pit on each of three dairies (Dairy SF, Dairy DD, and Dairy SE) in Southern Idaho. Triplicate samples were analyzed for solid content, particle density, particle size distribution, total nitrogen (TN), and total phosphorus (TP). Solid content was analyzed based on Method 2540B (APHA, 2015). Particle density was analyzed based on the method ASTM D1217-15 (Weindorf and Wittie, 2003) using a pycnometer with a methanol medium for particle sizes of 4, 2, 0.5, 0.25, 0.125, 0.063, and <0.063 mm. Particle size distribution was determined using a set of 6 sieves (4, 2, 0.5, 0.25, 0.125, and 0.063 mm) combined with the hydrometer method ASTM D7928-17 (Days, 2002) for particle sizes less than 0.063mm. Nutrient parameters (TN and TP) were analyzed using a Hach spectrometer (DR 5000) based on Hach methods (Hach, 2005). The Pipette Methods ASTM D6913/D6913M-17 (Hellman and McKelvey, 1941) was used in conjunction with ASTM D7928-17 to extract liquid manure samples for analyzing the nutrient parameters. The apparatuses used for the test are shown in Figures 1, 2, and 3.
What we have learned?
The particle densities of three dairies (Figure 4) were found to be similar ranging from 1.32 g/cm3 for particle sizes larger than 4 mm to 2.20 g/cm3 for particles less than 0.063 mm. The particle densities which are smaller than commonly used soil particle density of 2.65 g/cm3 need to be considered during design of dairy flushing water settling basins.
Flushing liquid dairy manure solid particle distributions of three dairies are shown in Figure 5. It was noticed that high bedding fibers were presented in the liquid manure from Dairy DD which resulted in a 32.6% of solids with particle sizes larger than 4 mm. For both Dairy SF and Dairy SE, the percentages of solids (dry weight basis) with particle sizes larger than 4 mm were 8% and 17.2%, respectively.
Flushing liquid dairy manure total nitrogen (TN) and total phosphorus (TP) associated with different particle groups are shown in Figures 6 and 7. There were 58.3 g (or 33.6%) and 52.1 g (or 43.9%) of TN associating with particles larger than 0.5 mm in 100 liters of flushing manure for Dairy SF and Dairy SE, respectively. There was 9.1 g (or 6.5%) of TN attaching to particles larger than 0.5 mm in 100 liters of flushing manure for Dairy DD. Most TP was attached to fine particles with sizes less than 0.5 mm for the three dairies. In order to separate more TP out of liquid stream, advanced separation methods beyond inclined screens are needed.
The test results showed:
- flushing dairy manure particle densities ranged from 1.32 g/cm3 to 2.20 g/cm3;
- Most TP were associated with fine particles that cannot be screened out by screens;
- Advanced separation technologies are needed to capture more TP from flushing liquid dairy manure.
Future plans
We will hold workshops and field days to communicate the results with producers and promote on-farm adoption of advanced separation equipment such as centrifuge.
Authors
Lide Chen, Department of Soil and Water Systems, University of Idaho; email: lchen@uidaho.edu.
Kevin Kruger, Department of Soil and Water Systems, University of Idaho.
Howard Neibling, Department of Soil and Water Systems, University of Idaho.
Additional information
APHA. (2015). Standard Methods for the Examination of Water and Wastewater. Washington D.C. : American Public Heath Assosiation., Pp. 216-217
Das, B. M. (2002). Soil Mechanics Laboratory Manual (6th ed.). New York, NY: Oxford University Press. website: site.iugaza.edu.ps/dsafi/files/2015/02/Soil-Laboratory-Manual-Das.pdf
DR5000 Spectrophotometer: Procedures manual. (2005). Germany: Hach Company
Hellman, H. H., & McKelvey, V. E. (1941). A Hydrometer Method-Pipette Method for Mechanical Analysis. Journal of Sedimentary Petrology, 11(1), P. 3-9.
Weindorf, D. C., & Wittie, R. (2003). Determining Particle Density in Dairy Manure Compost. The Texas Journal of Agriculture and Natural Resource, volume 16, Pp.60-63.
Acknowledgements
This study is supported by the USDA NIFA via WSARE project SW18-015.
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