February 10, 2011
A few decades ago, the United States was thought to have an endless supply of phosphorous; however in 2007 we began importing this nutrient. Current estimates place the supply at 1,200 million tons per year and the possibility exists that we could deplete that supply in 25 years.
Phosphorous is both a blessing and a curse. It is one of the key mineral nutrients necessary for plant growth. It stimulates root growth, flower bloom, and seed development. It is an essential component of DNA, RNA, cell membranes, sugars, and carbohydrates. Without phosphorus plants just don’t grow and there is no substitute for it.
On the flip side, too much phosphorous in a body of water stimulates the growth of suspended algae, or phytoplankton. Ever see a nasty, algea-ladened golf course or farm pond? The most likely cause is too much phosphorous.
Wastewater treatment plants receive tremendous amounts of phosphorous in the influent and they are generally required to remove most either biologically or through chemical treatment. Until recently, however, the phosphorous was never ‘recovered’.
Not long ago I was in charge of constructing a design/build pilot plant to test a process called ‘Phosphorous Adsorption’. The results were promising; the levels of phosphorous in the wastewater stream after treatment were virtually undetectable (<.001 mg/l), with the nutrient being recovered as a saleable product for farmers.
The process was fascinating, albeit quite complicated, so a simple explanation will suffice. If you have ever had a water softener you probably know that there are resin beads in the softener tank. These beads hold an opposite charge from the iron in the water. The iron ions cling to the beads, but are released upon a salt water backwash. The Phosphorous Adsorption process is quite similar but instead of the phosphorous ions being washed away and lost, the nutrient is recovered in a filter press. The product can be sold and used as an income stream for treatment plants to defray the costs of the recovery system.
There are always driving forces for new technology. For this to be a viable and economical solution, the nutrient limit regulations must be very low and the cost of phosphorous must be high. I see both occurring in the near future.
