 |
 |
What Human Activities Increase Phosphorus Levels?
Humans now add a great amount of phosphorus-containing compounds into the environment either directly or indirectly. Wherever there is agriculture or human settlement, the chances are that nearby waters are rich in phosphorus compounds.
Sewage
Phosphorus-containing compounds enter rivers carried in industrial or municipal sewage. This phosphorus originates with:
- poorly treated human sewage
- cottage and farm septic systems
- some dishwasher detergents
- some commercial cleaning products
- industrial anti-caking agents
- water softeners
- industrial boiler water
Each person excretes approximately 1.3 - 1.5 g of phosphorus each day. This inorganic phosphate in human waste results from breaking down protein and expelling it in urine.
Synthetic detergents can contain 12-13% monophosphates and up to 50% polyphosphates. This phosphorus washes down the drain and also enters sewage water.
Top of page
Sewage Treatment
Traditional sewage treatment plants have been the major source of increased levels of river phosphorus. Primary treatment (settling ponds) removes some phosphorus and secondary treatment (aerated bacteria) removes even more.
- The removed phosphorus-containing sludge is eventually sent to landfills, injected into farm fields as fertilizer or mixed into the giant composer operated by the City of Edmonton.
- The phosphorus that cannot be removed from the treated sewage is released back into the river.
Top-of-the-line wastewater treatment plants now use tertiary treatment (biological nutrient removal and chemical precipitation) to remove most of the phosphorus from treated sewage. The City of Calgary Bonnybrook Wastewater Treatment Plant has been recognized across North America for treatment excellence. The City of Edmonton Goldbar Wastewater Treatment Plant began tertiary improvements in the late 1990's.
Phosphorus removal is expensive and limits the amount of technology that can be purchased and used in smaller urban centers. There are solutions to this problem:
- The Capital Region Sewage Treatment Plant located just downstream of the City of Edmonton is cost effective by collecting and treating the sewage from numerous small commuter towns surrounding the provincial capital.
- In southern Alberta, the growing Town of Cochrane located just upstream of Calgary closed its' sewage treatment facility and began using a pipeline to transport waste into the larger city for treatment.
Top of page
Storm Water
Humans around the world are now using great amounts of phosphorus for fertilizer. Phosphorus in the form of diphosphorus pentoxide (P2O5) is the second percentage number listed on fertilizer bags (e.g. 10-5-5). Phosphorus fertilizers are applied directly to the soil but can enter a river if carried in melted snow or rainwater washing-off streets and farmland.
The phosphorus in storm water originates with:
- dog droppings
- human sewage that mixes with storm water
- some anti-icing road salts
- excessive fertilizer washing off crops, golf courses and lawns
- cattle feedlot runoff
- irrigation water returning from fields back into a river
A 1990 Alberta Environment report estimated the total number of cattle along the Bow River Basin of southern Alberta was 450,000 cattle; 230,000 hogs; 25,000 sheep and 250,000 chickens. Calculating waste production based on those populations suggested that 10,000 tons of phosphorus were produced each year along the Bow River.
Top of page
Phosphorus Sinks
The numerous sources of phosphorus also include phosphorus "sinks". Lake beds, ocean beds and river bottoms can act as phosphorus storage areas or sinks. As phosphorus-containing particles settle to the bottom, they are covered by sediment and thus removed from the phosphorus cycle for some time. This is a natural method that removes phosphorus from polluted water bodies.
However, the sins of past pollution can come back to haunt a river if trapped phosphorus is disturbed and once again released into the water. Phosphorus sinks can be disturbed by human or natural events - scouring currents, floods, pH changes, pipeline construction or the actions of benthic macroinvertebrates. Just when a water body seems free of phosphorus pollution, a setback can occur when a further dose is stirred up from the bottom.
- In the 1990's, the community of Pine Lake worked with Alberta Environment to clean up the agricultural sources of phosphorus surrounding their lake. They then took the unusual step of installing a pumping system to remove phosphorus contaminated water and sediments directly from the bottom of the lake.
Top of page
|
