Application: used within buildings to reduce emission of odors and gases from the building and manure storage
- Improved air quality within the building for animals.
- Potential to increase nitrogen retention in liquid.
- Separation of nitrogen and phosphorus may have benefits.
- Difficult to incorporate into an existing building.
- Two waste streams must be handled.
- Equipment sources are not well developed.
- Maintenance could be a challenge.
The manner in which manure is collected can have an impact on emissions. Systems which allow urine and feces to mix can cause higher releases of ammonia. Bacterial urease from feces promotes the breakdown of urea to ammonia, which is a more volatile form of nitrogen, so more ammonia is emitted, reducing the nitrogen content in the manure. Separating the manure into urine and feces can be challenging, especially once urine and feces have been mixed. A more effective approach is to segregate liquid and solid at the time of collection using specially designed scrapers or belts.
|Figure 1. A picture of a belt system for manure
segregation. Kroger et al (2014)
Systems typically used in swine production collect urine and feces together. The most prevalent manure systems in the USA include deep pit storage, pull plug systems, flush gutters and scrapers. Deep pit storage is simply an under-floor manure pit which stores manure for up to one year. This is the most common system in swine finishing buildings in Iowa. Pull plug systems use a flat, shallow pit to store manure for two to eight weeks and then are drained, by gravity, to an outside storage. These are used in many swine farrowing rooms and nurseries. Flush gutters use liquid to flush solids from a gutter under the slats on a daily (or more frequent) schedule.These are typically used with anaerobic lagoons and generally use recycled effluent to flush the gutter. Scraper systems use a cable and blade device to scrape manure from a gutter below the slatted floor to be deposited in an outdoor manure storage such as a slurry tank. This occurs daily or more frequently.
Most of the segregation systems utilize gravity to separate liquid and solid. There are two main strategies, belts or “V” scrapers. Belt systems, Figure 1, generally are sloped so that solids remain on the belt and liquid flows off to one side where itis collected in a slotted pipe thatruns to one end of the building of storage. The belt operates along the length of the building and periodically carries the solids to the end of the building where it is deposited in some sort of collection conveyor which deposits the solids for composting or stockpiling. “V” scrapers operate on the same principle, Figure 2. The scraper is much like a normal gutter scraper except the gutter floor is sloped to the center of the gutter width. Solids remain on the sloped floor and liquidsflow to the center where a slotted pipe allows the liquid to flow to a storage container. The scraper pushes the solids along the floor to a collection point where another conveyor or scraper may transport solids for stockpiling or composting. Both of these systems require two handling systems, one for solids and one for liquids. In some systems the solids are composted or stored for land application. Liquids are generally stored in a closed storage tank to reduce nitrogen loss. There is also a benefit due to the fact that most of the nitrogen can be found in the liquid, while most of the phosphorous remains in the solid fraction. This can have benefits when considering manure application rates.
|Figure 2. A "V" scraper sloped to the middle of the
gutter and a slot to collect liquids.
(Courtesy of Michigan State University)
Most of the evaluation studies have compared the segregation system to a pull plug or traditional scraper system. In general these comparisons have yielded a reduction of 40 to 60% in ammonia. Because deep pits have longer storage times, one would expect a greater reduction in emissions. Aarnink, et al (2013) stated that a belt system used for separation in Europe reduced emissions of ammonia, odor and methane by approximately 70% over conventional systems.
Incorporation into new construction would be most efficient. Existing buildings would be difficult to change to a urine/feces segregation system because of the concrete work required to form the pit. Incorporation of a belt system into a deep pit facility may be easier than a scrapersystem but it will still be costly. In either case, the accompanying storages would need to be constructed to handle the solids, which sometimes are composted, and the liquid, which should be confined in a covered storage or tank to avoid nitrogen loss. Ease of maintenance may also be a concern. Systems below slats are difficult to access and located in a less-than-clean environment.
Belt and “V” scraper systems are not common equipment. Facilities at Michigan State University and Iowa State University purchased scrapers from companies in Japan and Quebec.
|NH3||40 to 80%||40% compared to short term storage, 80% estimated compared to deep pits|
|H2S||80 to 90%||estimated|
|Odor||60 to 80%|
|Volatile Organic Compounds (VOC)||Unreported|
|GHG||70 to 80%*||estimated methane, CO2|
|Cost||$$ to $$$||equipment/retrofitting|
*Assuming that out-of-building storage is contained.
Cost is relatively variable depending factors such as if the project is a retrofit or new construction, and the type of outdoor storage selected for the liquid and solid fractions. Scraper systems are not commonly available and specialty manufacturers should be sought.
Aarnink, A.J.A., C.M. Groenestein,N.W.M. Ogink. 2013. Aerial pollutants in pig houses; innovative reduction systems in Europe. IN: International Symposium on Animal Environment and Welfare. Chongqing, China. pp. 90-100.
Koger, J.B., T. van Kempen, G.A. Wossink. Belt manure removal and gasification system to convert dry manure thermally to a combustible gas stream for liquid fuel recovery. Animal and Poultry Waste Management Center. North Carolina State University, Raleigh, NC. Accessed August 10, 2014.
Lachance, I., S. Godbout, S.P. Lemay, J.P. Larouche, F. Pouliot. 2005. Separation of pig manure under slats: to reduce releases in the environment. ASAE Paper 054159. ASABE, St. Joseph, MI.
Liu, Z., W. Powers, S. Mukhtar. 2014. A review of practices and technologies for odor control in swine production facilities. Applied Engineering in Agriculture 30(3): 477-492.
von Bernuth, R.D., J.D. Hill, E. Henderson, S. Godbout, D. Hamel, F. Pouliot. 2005. Efficacy of a liquid/solid isolation system for swine manure. Transactions of the ASABE 48(4): 1537-1546.