Phosphorus (P) is a chemical element and exists almost entirely in the form of phosphate (PO4 3-).
For millennia, geology has allowed phosphate to slowly accumulate in ancient seabed formations in just a few lucky locations around the world. P is essential to all life, including plants—such as agricultural crops. So, without phosphate, the breadbasket of America would be empty.
The Green Revolution, the major mid-20th-century expansion of global food production, relies in large part on fertilizer, to the tune of approximately 20 million metric tons of P in fertilizers applied in 2012 worldwide. Without it, agricultural productivity would have to get by with phosphorus that gets into soil by natural weathering of P from Earth’s rocks, which would only yield about 10 percent of what’s currently used—and would be wholly incapable of supporting our current population, much less the 2 billion to 4 billion additional humans expected for 2050.
Where does all this phosphorus for fertilizer come from? From mining operations focused mostly on ancient P-rich geological deposits that are concentrated in just a handful of countries, with Morocco having the lion’s share—about 75 percent at last report. China, in second place, has only 5.5 percent, and the United States trails in seventh with about 2 percent.
The best opportunity for lowering our demand for mined P is to recover and reuse P from agricultural and human wastes.
Animal manures, food-processing wastes, and human sewage constitute about half of the P on the conveyor belt to the environment. These waste streams offer the most immediate route to recovery and reuse because most of the P is in slurries of organic solids that also contain high amounts of energy. Anaerobic digestion, in which specialized microbes chew up organic matter in the absence of oxygen while producing methane gas, or microbial electrolysis cells, in which bacteria generate an electrical current that leads to hydrogen gas, are excellent means to convert the organic materials into highly valuable energy outputs. These microbial processes release the P as phosphate, which can be captured in clean, concentrated, and convenient forms for reuse in agriculture. Using microorganisms this way would give us three valuable things: renewable energy, concentrated P, and water with most of its pollution removed.