Phosphate Recovery

Phosphates and nutrition

A vital contributor to human growth and metabolism

The human skeleton is composed mainly of calcium phosphate. Phosphorus accounts for 11 to 12 g per kg body weight. 85% of this phosphorus occurs in bones and teeth. Phosphorus plays an important role in several functions:

The transfer of energy;
The synthetic of amino acids and proteins;
The contribution to the generation of vitamins;
The maintenance of bones and teeth.

Examples of P content in food
(expressed as % of fresh weight)

Wheat 1.2%
Peas 0.1%
Peanuts 0.4%
Fish and meat 0.2%
Milk 0.1%
Fruit 0.015%

Daily phosphorus requirements for man

Children 0.5 g/day
Adults 0.8 g/day
(During pregnancy and lactation 1.2 g/day)

Animal feed phosphates

Phosphorus is one of the essential elements needed for animal growth and milk production.
It has many vital functions:

The participation in metabolic processes in soft tissues;
The maintenance of stable conditions for biological reactions;
The maintenance of appetite, optimal growth, fertility and bone development;
The prevention of bone disease, such as rachitis.

By far the greatest proportion of phosphorus is used for building up and maintaining the skeleton. A constant exchange of phosphorus occurs between bones and blood.
Since animals also need a wide range of other elements including calcium, magnesium and sodium, inorganic feed phosphates are usually supplied as mixtures of these essential elements.
Phosphorus nutritional requirements for most farm animals are well documented (dairy cattle 85-95 g/day, beef cattle 35-40 g/day). The phosphorus content of natural feed varies from one plant species to another. For example, grass contains only a few grams of phosphorus per kilogram dry weight. The phosphorus content of feed grains such as barley, maize and oats is also very low. Feeds which contain high amounts of phosphorus include rape seed meal, by-products from the milling industry and especially animal products like fish and bone meal. Only a small part of the phosphorus in this material is digested by the animals.
The mechanisms of phosphorus digestion and metabolism differ substantially between ruminant and monogastric animals. The former can utilise the organically bound phosphate (phytates) found in grains while monogastrics can not. Diets which contain a high proportion of roughage with a low phosphorus content can be considerably improved by the use of feed supplement.
To provide the daily requirement for phosphorus, phosphates are used in the form of compound feed or as separate mineral supplements. Phosphate supplements are manufactured in many chemical and physical forms to suit different feeding and handling practices.

Consumption of main mineral feed
phosphates in Western Europe

Dicalcium phosphate 60%
Mono-dicalcium phosphate 10%
Monocalcium phosphate 18%
Magnesium phosphate 6%
of the market

Whilst some of the dietary phosphate is retained in the skeleton, a proportion is used in metabolic processes and excreted or simply passed through the digestive tract, unused. The resulting manure should be recycled efficiently on agricultural land.

By designing feeds to maximise the level of dietary availability of phosphorus, feed producers have to significantly increase digestable feed phosphate.
Further, a combination of feed phosphates and enzymes can bring additional improvement in use of feedstuffs by animals and reduce excreted phosphates.

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