*Why Examine Solid – Liquid Manure Separation at Pig Farms?
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V-shape pit with automated manure scraper and trough |
Many US pork production operations have become large in size and more geographically concentrated, and use very similar production facilities and manure management. With the potential extreme climates and diminishing water and land base, the industry needs to further improve the production systems and conservation effort. A Missouri swine finishing barn was designed to separate manure into solid and liquid portions, reduce odor and air emissions, and provide options for nutrient and water management. There is potential to reduce overall water use, and more importantly, to more efficiently export nutrients from the farm, or conserving nutrients in either the solid or liquid portions using additional practices.
What did we do?
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Gravity draining of liquid manure |
The solid/liquid separation barn has a capacity of 1200-hd. Manure management consists of a V-shaped gutter with mechanical scrapers installed beneath slatted floor, and a central pipe that collects the liquid manure fraction. The scraped manure is mechanically conveyed out to a nearby storage shed. Liquid manure portion is gravity drained into a temporary sump pit, and pumped into a nearby anaerobic lagoon automatically. Four monthly solid portion and liquid portion samples were collected and analyzed for moisture content, total nitrogen, phosphorous, potassium, pH, total carbon, and volatile solid content. The collected samples were kept on ice during transport and then frozen until analyzed by the University of Missouri Soil and Plant Testing Laboratory. Ammonia and hydrogen sulfide concentrations of the exhaust air streams were also measured using gas detection tubes during three of the four sampling events.
What have we learned?
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Storage shed for solid manure |
The solid manure portions have relatively low moisture content (MC, 57.9% to 63.4%, averaged 60.7%), and the liquid portion still have considerable amount of solids (MC = 93.3% to 98.3%, averaged 96.1%). The average nitrogen, phosphorus, potassium were 1.72%, 0.65%, 0.75% for the solid manure samples, and were 0.40%, 0.10%, and 0.29% for the liquid manure samples, respectively.
Ammonia concentration of the center exhaust fans averaged 7.7, 7.0, and 1.8 ppm for the February (n=3), March (n=2), and May (n=2) sampling visits respectively, and only one room fan was operating during the March visit, which measured 5.0 ppm (n=1). For all the sampling visits, hydrogen sulfide never reached the minimum detection limit of 0.5 ppm.
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Stored solid manure |
The new facility design and reported findings have the potential to be adapted by new and existing production facilities, to develop new business models and management that are more flexible in nutrient management, and to improve resource conservation and reduce pollutions. It has been noted that the liquid stream can have relatively low solids from the well maintained scraper systems. If the farm continues to use the lagoon, there will be significantly less solid to be agitated and pumped. Assuming the untreated manure has a solid content of 6%, and the solid contents of the separated liquid and solid portions average about 3% and 39% respectively, the estimated contents in the solid manure are 28% and 47% of the total nitrogen and phosphorus in untreated manure, respectively. This is promising for exporting nutrients from the farm, or conserving nutrients in either the solid or liquid portions using additional practices.
Future Plans
More research is needed to systematically analyze the costs and management of the facilities, implications of water/nutrient conservations, potential byproduct production, and long-term sustainability improvement. The immediate next steps are to characterize the liquid and solid manure portions (in terms of volume and nutrient values) and barn air quality and emissions during different seasons. Effort should also include identification of the minimal and different levels of pre-treatment and reverse osmosis onto the liquid manure, for potential fertilizer concentrate, improved manure management, and potential water recycling. The long-term goals are to improve such solid/liquid separation barn, to provide partial manure treatment and water recycling potential that can be tailored for different cases and production sites.
Authors
Teng Lim, Associate Professor, University of Missouri limt@missouri.edu
Joseph M. Zulovich, University of Missouri.
Additional information
The collaboration of the farm owner and managers are greatly appreciated.
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