Some Idaho dairies use liquid manure handling systems that result in large amounts of manure applied via irrigation systems to adjacent cropland during the growing season. Solids and nutrients presented in liquid dairy manure pose challenges to manure handling. Separating solids and nutrients from liquid dairy manure is a critical step to improve nutrient use efficiency and reduce manure handling costs. Most Idaho dairies have primary screens that separate coarse particles from their liquid streams. A few dairies have incorporated secondary solid separation technologies (centrifuge and secondary screen) into their manure handling systems to achieve higher solids and nutrient removal rates. Idaho dairymen want to know more information about solid and nutrient separation efficiencies by centrifuges and screens to make informed decisions on upgrading their solid/nutrient separation technologies. The objectives of this study were to evaluate centrifuges and screens in terms of removing solids and nutrients from liquid dairy manure and affecting ammonia emissions from the treated liquid dairy manure.
What Did We Do?
A year-long evaluation of on-farm centrifuges and screens on removing solids and nutrients and affecting ammonia emissions from centrifuge- and screen-separated liquid dairy manure was conducted. Triplicate fresh liquid dairy manure samples were collected monthly from before and after screens and centrifuges on a commercial dairy meanwhile triplicate screen- and centrifuge separated solids were collected from the same dairy. Figure 1 shows the dairy’s liquid manure flow diagram and locations where the liquid and solid manure samples were collected. The collected solids were analyzed for nitrogen (N), phosphorus (P), and potassium (K) concentrations by a certified commercial laboratory. The collected liquid samples were analyzed for total and suspended solids based on Methods 2540B and D (APHA, 2012) in the Waste Management Laboratory at the UI Twin Falls Research and Extension Center. Ammonia emissions from the monthly collected liquid dairy manure were evaluated using Ogawa ammonia passive samplers outside the Waste Management Lab for a year. Ammonia emission rate was calculated based on the duration and NH4-N concentrations from the Ogawa ammonia passive sampler tests. Ogawa passive ammonia sampler and Quickchem 8500 analysis system are shown in Figures 2 and 3.
What Have We Learned?
Centrifuge can further remove finer particles than cannot be removed by primary screens. Figure 4 shows both the screen- and centrifuge separated solids.
Total nitrogen, phosphorus, and potassium in screen- and centrifuge separated solids are shown in Figures 5, 6, and 7. It was noticed that centrifuge separated solids had significantly (P<0.05) higher N, P, and K than that in screen separated solids. Yearlong averages of 9.2 lb/ton of total nitrogen, 8.0 lb/ton of P2O5, and 7.2 lb/ton of K2O were in the centrifuge separated solids while yearlong averages of 5.4 lb/ton of total nitrogen, 2.0 lb/ton of P2O5, and 4.4 lb/ton of K2O were in the screen separated solids.
Liquid dairy manure total solids and suspended solids are shown in Figures 8 and 9. Both the total solids and suspended solids in the liquid stream were significantly (P<0.05) reduced after the screen and centrifuge treatment.
It was found that there was no significant difference (p≥0.05) between treatments for the ammonia emission rate in Figure 10 Which indicates that further treatment is needed to reduce ammonia emissions.
In Figure 11 a correlation was determined between ammonia emission rate and suspended solids. As suspended solids were reduced within liquid dairy manure the ammonia emission rate increased among the treatments.
In Figure 12 a correlation was determined between ammonia emission rate and ambient temperature. As the ambient temperature increased, so did the ammonia emission rate among the treatments.
The test results showed:
- Centrifuge can further remove finer particles that can’t be removed by primary screens.
- Centrifuge separated solids contained higher N, P, and K contents, especially P (at an average of 8 lb/ton of P2O5 in centrifuge separated solids vs. 2 lb/ton of P2O5 in screen separated solids).
- Ammonia emissions from raw liquid manure, screen- and centrifuge separated liquid manure did not show significant differences.
- The most influential factors for ammonia emissions from liquid dairy manure were ambient temperatures and suspended solids within the liquid dairy manure.
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.
Lide Chen, Waste Management Engineer, Department of Soil and Water Systems, University of Idaho
Corresponding author email address
Kevin Kruger, Scientific Aide, Department of Soil and Water Systems, University of Idaho.
APHA. (2012). Standard Methods for the Examination of Water and Wastewater. Washington D.C. : American Public Heath Association., Pp. 2-64 and Pp. 2-66
USDA NIFA WSARE financially supported this study. Thanks also go to Scientists at USDA ARS Kimberly Station for their help with analyzing ammonia emission samples.
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