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Turning Swine Manure Into Fertilizer: The PSF Solution

by 5m Editor
4 May 2004, at 12:00am

By Theo van Kempen, Swine Nutrition Specialist, North Carolina State University - Premium Standard Farms has started the construction of a "Next Generation" environmental system on one of its farm complexes, Valley View Farms in Northern Missouri. The objective of this project, the construction of the Crystal Peak fertilizer plant, is to convert hog manure into a high value commercial fertilizer using a process developed and patented by Premium Standard Farms and its technology partners.

Dr Theo van Kempen
Swine Nutrition Specialist

The process of developing the Crystal Peak plant began following a 1999 Consent Decree between the company and the State of Missouri. That agreement called for the company to develop "Next Generation" technology with the assistance of a State-appointed panel of experts and to invest $25 million in manure management research and technology. The Crystal Peak plant is one of their major initiatives and will cost an estimated $9 million.

Diagram of the Crystal Peak fertilizer operation

The system consists of the following steps:
  1. Manure collected from each of the barns will first be processed through an Internal Recirculation Process (IRP). This process consists of a screen to remove large solid particles, and an 8 inch wet well to allow for settling of solids. Screened and settled solids are combined to generate an 8% solids fraction. Separated liquids are acidified with sulfuric acid to minimize odor and ammonia, and will be used for flushing fresh manure out of the barn. Concentrated solids will be transferred to a digester.

  2. The digester used is an in-ground digester heated to 90°F using waste heat from the dryer. In this digester, organics in the manure are broken down, resulting in the production of methane. This methane is captured, and used later on in the process. Besides producing valuable methane, the digester will also reduce the odor of the manure, making further processing more practical. Manure will reside in this digester for a period of approximately 1 month.

  3. Effluent from the digester will be pumped to a settling basin. The settled solids gathered here will be further concentrated using a centrifuge. The liquids, both those separated in the centrifuge and those obtained directly from the settling basin, will be pumped to a holding pond where they will be stabilized using sulfuric acid, which prevents the escape of ammonia.

  4. The liquids in the holding pond will be accumulated throughout the year in three lagoons that have been converted to storage ponds. During the winter these liquids will be transferred to an area where they will be sprayed onto a pad and allowed to freeze. The freezing and subsequent thawing cause a separation of minerals in the liquid fraction because pure water freezes first and thaws last. While thawing, the liquids will flow from this pad and, based on electrical conductivity, they will be directed either to a brine pond (mineral-containing water) or to a treated water pond (clean water) for recycling. An analogy to this process is icebergs at the North pole; the icebergs, although floating in salt water, consist of fresh water.

  5. The brine pond will contain a high concentration of minerals, including nitrogen and potassium. This material will be mixed with the solids obtained after centrifugation, which is high in phosphorus. After mixing, the material will be formed into pellets, dried and charred using methane derived from the digester as an energy source. Emissions derived during this drying process will be captured using wet scrubbers and dust filters, and the captured material will be recycled in the system. The pellets will be marketed as a high-quality fertilizer with composition expected to be 12-8-8.

  6. Liquid harvested from the freeze-thaw process will be stored in a newly generated water storage cell and either used as irrigation water or further processed to produce drinking water for the pigs on site.

The Crystal Peak process is an interesting combination of technologies for solving environmental issues facing the swine industry. Emissions of ammonia from manure storage are minimized by using a cover on the digester and by acidifying subsequent material streams (acidification is very effective for lowering ammonia emission). Ammonia and possibly odor emission from the housing is also reduced through acidification of flush water. Odor from the stored manure also is minimized through the digestion process.

Energy contained in the manure is captured in the form of methane, and this methane is used to dry the harvested minerals in the production of a high-quality fertilizer. Their system avoids having to generate and market electricity, two steps that are major obstacles for conventional digesters. It also makes the energy cost of this system relatively small, especially if good separation of minerals and water can be achieved by using the freeze-thaw process powered by Mother Nature.

Another benefit of the system is that its end product, fertilizer with a composition of 12-8-8, is not a niche product and is easily marketed. Many methods of producing value-added products from animal manure target niche markets, which may work for smaller operations. But if a large portion of the swine industry were to adopt such value-added technology, the market would quickly become saturated, and the price of the end product would plummet.

Because the Crystal Peak system uses a freeze-thaw process, it will be suitable only for climatic zones were winter temperatures fluctuate from substantially below freezing to above freezing. In North Carolina, alternative methods for separating minerals from the liquid fraction would have to be applied (evaporation of the water may be a better option here). However, the system is a very intriguing solution to swine manure disposal, and it will be interesting to see how it operates in practice.

Reproduced Courtesy

Source: North Carolina State University Swine Extension - April 2004