How The Phosphorus Cycle Works

Eighty percent of the phosphorus in swine feed can be found in their manure. This disproportionately large phosphorous component of swine (and other animal) waste typically exceeds the permitted discharge levels. Martin C. Van Loosdrecht of Kluyver Institute of Biotechnology reports in his Role of Biological Processes in Phosphate Recovery (2003) Natural History Museum that 80% of the phosphate found in municipal wastewater originates from urine. (34)

Adding calcium carbonate, or dolomitic limestone (a natural blend of calcium and magnesium carbonate with a small amount of zinc oxide), in a finely ground slurry is an inexpensive, safe option to bind soluble phase phosphate, particularly if the receiving soil is acidic. Phosphate accumulating bacteria, such as Agrobacterium (a plant pathogen), Propionibacterium and Acinetobacter sp. can use the calcium to assist in this binding process and can also accumulate phosphate under aerobic conditons.

limestone + water + sodium phosphate yields calcium phosphate + sodium bicarbonate + water + carbon dioxide

Under anaerobic conditions with limited phosphate in the water, phosphate accumulating bacteria use their accumulated phosphate for growth. Once these bacteria die, however, any unused accumulated phosphate is released again to the water, reducing the value of these particular bacteria in lakes and ponds as compared to wastewater treatment. In the presence of ferric phosphate and reduced sulfur compounds, Starkeya novella creates ferrous iron and releases phosphate back to the water column. Similar phosphate release has been observed from some strains of Bacillus thuringiensis and Bacillus cereus. The released phosphate can be utilized for heterotrophic growth by these same strains, under aerobic condtions.

The addition of alum, a popular waste treatment flocculent, is an alternative method of binding the phosphate out of solution. Alken-Murray does not recommend this option because of its potential impact on the food chain when applied in fertilizer. An excess of dietary aluminum has been suspected of causing decreased human fertility and various other deleterious effects.

Another recent option utilized by some remediation companies, is the addition of calcium, magnesium or strontium peroxide to a water body to tie up excess phosphate as insoluble calcium phosphate, magnesium phosphate or strontium phosphate. All three OXIDIZERS are air and moisture sensitive, are listed by NPFA and HMIS with a health rating of "2" and reactivity rating of "1", and are rated as hazardous by OSHA. All three are listed as incompatible with organic material, finely powdered metals and reducing agents. Calcium peroxide often contains lead, arsenic, strontium and calcium hydroxide. Calcium peroxide also drastically increases the pH when added to a water-body, so that must be considered as well. Magnesium peroxide often contains magnesium hydroxide and magnesiium oxide, but is less of a problem for pH increase than the other two, and is also the least reactive of the three. In our opinion, the hazards must be carefully weighed against their value for remediation before being used.

Phosphorous Discharge Standards

a . Total Phosphorous for discharge less than 100 micrograms/L

b. Where a stream enters lake less than 50 micrograms/L

c. Discharge into a lake less than 25 micrograms/L

d. Algae blooms are encouraged by levels of phosphate greater than 25 micrograms/L

e. Phosphate phosphorous: greater than 100 micrograms/L may interfere with coagulation processes in water treatment plant

For Diagram of Phosphorus Cycle