ENVIRONMENT & SAFETY
Phosphates & the Environment
Phosphorus is one of the more common elements on earth and is essential to all living organisms. It is found combined with other elements in the earth’s crust in the form of phosphate rock. The major commercial deposits are in the United States, China, the former Soviet Union, Morocco, Finland, South Africa, and some Pacific Islands. It is estimated that there are 40 billion tons of reserves of phosphate rock or a 250-year supply at current usage. This may seem like an abundant supply, but some of this material is not accessible or of poor quality. In addition, we are using this material at an increasing rate.
Over 80% of the ore currently mined is used in fertilizer products. As pressure for greater agricultural yields intensifies, more fertilizer is applied to replenish the nutrients removed by crops. In earlier times, food was consumed near the place of production, and the animal and human wastes were returned to the land. This natural recycling loop for nutrients has been broken due to societal changes.
Sewage treatment plants are potential point sources of phosphorus for reuse. Presently, most sewage treatment facilities in Europe and North America remove phosphorus prior to further processing. This has been typically done by precipitation with iron or aluminum salts. Unfortunately, phosphorus in this particular form is not readily usable as a nutrient. There is work underway in Sweden and other countries to convert the iron salts to iron sulfide by biological processes. The phosphorus would then be released in a more soluble form.
Treatment facilities in the Netherlands have begun recovering phosphorus as a calcium salt, used further as a raw material for other phosphate products. Japan and Australia are removing phosphorus in the form of struvite, a magnesium ammonium phosphate compound, which is a valuable fertilizer containing these three nutrients. None of these options are technically or commercially feasible in every site or country, so further research is underway.
Large feedlots are another point source of recoverable nutrients. To date this resource has not been exploited to any great extent. Some hog farms in Holland are experimenting with recovery technologies. In the United Kingdom, chicken litter is incinerated for energy and the ash recycled as slow-release fertilizer. Recovery of nutrients from animal waste is an area of great potential, but much more research is required to develop a form that can be stored during non-fertilizing seasons and is economical to transport to nutrient-deficient areas.
Many industries, such as chemical processing, pharmaceutical production, metal finishing, food processing, and others, produce waste streams that could be rich sources of phosphorus. Recovery of this material in a form that is useful as a fertilizer or another feedstock is a laudable goal. As each site and process is unique, so will be the solutions.
The Phosphate Forum of the Americas has sponsored two studies to examine the economics of phosphorus recovery at sewage treatment facilities and at poultry and potato processing sites. While technically feasible, the present low cost of landfilling waste does not make recovery economically attractive.
The Centre Europeen d’Etudes des Polyphosphates (CEEP), the European Chemical Industry Council’s (CEFIC) sector group representing European producers of polyphosphates, has been instrumental in sponsoring research in the recovery and recycling of phosphates. They have sponsored two conferences on this subject.
Further information may be obtained at the following websites:
European Sustainable Phosphorus Platform: http://www.phosphorusplatform.eu
US Environmental Protection Agency study “Phosphorus Recovery from Sewage”:
http://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.abstractDetail/abstract/7345/report/0
References
Phosphorus & Potassium, Issue No. 216, July-August 1998.
Scope Newsletter, Number 41, “Phosphate Recovery: Where Do We Stand Today.”
Nutrients are compounds that the agricultural community uses to stimulate and enhance the growth of food crops and animals. Nitrogen and phosphorus are the most common nutrients with which people are familiar. Phosphates, a family of naturally occurring compounds that combine phosphorus and oxygen, are present in all living organisms, animal and vegetable. Phosphorus is an essential nutrient needed to support life.
Given their essential role in life processes, many phosphates are “Generally Recognized As Safe” as a food ingredient by Health Canada and the U.S. Food and Drug Administration
Where do phosphates come from?
Excellent sources of phosphorus-laden rock are ancient sea beds. The rock is mined, refined, and purified. The resulting phosphorus-based products are used as ingredients in fertilizers, detergents, baking powders, toothpastes, cured meats, evaporated milk, soft drinks, processed cheeses, pharmaceuticals, and water softeners.
What is eutrophication?
Nutrients such as nitrogen, phosphorus, carbon, and silicon are essential for algae to grow. Our water bodies provide an important environment for the growth of algae that provides a rich food source for fish and other animals in the aquatic food chain. These nutrients find their way into the waterways through agricultural runoff, soil erosion, and discharges from the treatment of human waste.
While nutrient enrichment is a natural process, too much enrichment can cause algae to grow uncontrollably, disturbing the balance among organisms in the food chain. Fortunately, these aquatic environments are very resilient and this over-enrichment, or eutrophication, can be managed.
What is nutrient management?
To prevent excessive amounts of nutrients from being released into our waterways, plans are put in place to manage the amount of fertilizers used in agriculture. Also, animal production operations are exploring ways to manage runoff of manure that is often rich in nutrients.
What is being done about the nutrient management problem?
Several steps to minimize excessive amounts of nutrients released to the environment have been taken. At wastewater treatment plants, several hundred million pounds of phosphorus have been eliminated annually from our rivers and streams. Phosphate detergent bans, once thought to provide a quick reduction in phosphates in the environment, were enacted by several states. However, the “efficacy of this remedy continued to be debated throughout the 1970’s and 1980’s” according to a U.S. Geological Survey Review of Phosphorus Control Measures. It is unlikely that further removal of phosphates from consumer products will have a significant impact on nutrient management efforts.
In addition, farmers are now required in most states to prepare nutrient management plans. These plans specify the appropriate amount of nitrogen and phosphorus required for individual crops without applying excessive nutrients that can migrate into our waterways.
Recovery and recycling of phosphorus from wastewater sludges and animal waste show promise. The Phosphate Forum of the Americas has sponsored research into technologies that will remove phosphorus and allow the material to be recycled. Feasibility studies have been completed for phosphate recovery and removal from municipal wastewater treatment plants, as well as potato and animal production operations. Research continues on technical and economic methods of phosphorus recovery and recycling.
References:
1Litke, David W., 1999, Review of Phosphorus Control Measures in the United States and Their Effects on Water Quality, U.S. Geological Survey, Water Resources Investigations Report 99-4007, 38 p.