The History of Phosphorus
A German alchemist named Hennig Brand discovered phosphorus, albeit accidentally. His experimental subject was human urine. It is estimated that he processed 1,500 gallons of pee in his career. This would have required many sources, of course, and it is likely that he had to coerce dozens if not hundreds of people into donations. In our time, Brand might be behind bars, but in his time he was just another alchemist seeking the Philosopher’s Stone, a substance with magical powers believed to be able to turn base metals into gold or silver.
He was convinced that it could be produced from concentrated urine. What he discovered instead was pure Phosphorus. Shortly thereafter he also discovered that pure phosphorus burns spontaneously in air, inadvertently burning down his laboratory. It is so reactive, in fact, that it is always combined in nature, usually as phosphate, a phosphorus atom bonded with 4 oxygen atoms with the chemical formula PO43-.
The Science of Phosphorus
Phosphate compounds are present in all living organisms. In humans, the largest portion occurs in bones where, together with calcium, it forms the mineral apatite. It is also part of genetic material (DNA and RNA) and the compound adenosine tri-phosphate (ATP), the molecular unit of currency for energy transfer in cells (metabolism). The recommended daily allowance for phosphorus is about 4 g/day but varies depending on your age and condition. Excess phosphorus is processed in the kidneys and discharged in urine and feces at a rate of about 1.3 g per person per day which equates to 29 lbs. P/day, mostly in particulate form, for every 10,000 population equivalent.
Phosphates are also very important for hygiene. Phosphates sequester hardness, solubilize soil, and enhance clean rinsing making them an excellent cleaning agent, except for the undesirable effects once returned to the environment. As a result, phosphates have been removed from many consumer cleaning agents. Proctor & Gamble stopped using phosphates in laundry detergent sold in the US in the early 1990s. Even so, approximately 0.5 g P/day is estimated to enter the collection system from laundry and dishwashing detergent per person per day which equates to another 11 lbs. soluble P/day for every 10,000 population equivalent.
So that’s 40 lbs. of phosphate as P per day not counting industrial sources of which about two-thirds is particulate and about one-third is dissolved, mostly ortho-phosphate. This equates to a concentration of about 4.8 mg P/L from daily human activity using 100 gpcd. Industrial wastewater may contain a much higher proportion of P, for example, from meat-packing facilities and metal processing. However, point sources of treated municipal wastewater are not the largest source of phosphorus that is discharged to the environment.
Why Does this Matter?
Nationwide, runoff from non-point sources is the largest source of nutrients, including N and P discharged to surface water. Although phosphorus is the 11th most abundant element in the earth’s crust, most natural phosphate compounds are very insoluble, and therefore, not quickly replenished. Therefore, plant available phosphorus is only a fraction of phosphorus in the soil. To make up for the difference between what is available and what is needed, more soluble forms are created for use in commercial fertilizers. Unfortunately, this same property makes them susceptible to runoff to surface waters through field tiles, storm sewers, and non-point sources.
So, why are the treatment regulations so stringent when the main problem is in the fields? Indeed, scrutiny over HABs (harmful algae blooms - Download Hypoxia Infographic) in Lake Erie and other locations has, rightly so, been directed towards the agricultural sector. However, unlike the examples above, quantifying the amount of P in agricultural runoff is complicated (Wisconsin’s guidance on calculating P index to estimate runoff potential is 33 pages long!). Still, there are options to offset point source loads with non-point source reductions. For example, in Wisconsin adaptive management is a compliance option whereby point sources partner with land owners to restore the watershed and reduce in-stream phosphorus concentrations to water quality standards. However, for many reasons, adaptive management is not a practical alternative for many WRRFs (wastewater resource recovery facilities). Some additional treatment will be required.
Future article in this blog series will include 'Status of Phosphorus Regulation', Chemical Phosphorus Removal from Wastewater', 'Biological Phosphorus Removal from Wastewater', and 'Online Phosphorus Monitoring and Control'.
Additional Blog Posts of Interest
The Science of Phosphorus | Blog Series | 2 of 5
Monitoring Orthophosphate for Reduced Chemical Costs in Water Resource Recovery Facilities
The Phosphorus Problem: Wastewater Treatment Options and Process Monitoring Solutions
6 Steps to Reduce Total Phosphorus in Water Resource Recovery Facilities
Oregon's Tualatin River: America's Early TMDL Case Study