The Conversation (0)
The depletion of phosphate through wastewater runoff and overconsumption has prompted a water management group to propose phosphate recycling as a way to deal with the problem.
The London, UK-based institution is raising awareness about the rate that phosphorus is being depleted through overconsumption and lack of wastewater recycling.
The group believes that recycling phosphorus from wastewater and sewage systems will “improve food security and reduce geopolitical risk.”
“[T]oday’s phosphorous mines will be exhausted by the end of the 21st century and estimates of future reserves range from 200 to 400 years (at the current rate of extraction),” notes a CIWEM policy position statement.
“The economics of extensive phosphate recovery from wastewater would be quite favourable if we viewed phosphorus as a resource, rather than … a pollutant in the environment, and mining it in mineral form to fertilise our crops,” the CIWEM states.
The CIWEM is not the first organization to sound alarm bells about the need to recycle phosphate in order to effectively manage the supply of the irreplaceable agricultural resource. Other variants of the peak phosphate thesis claim that the world could deplete its phosphate — over 80 percent of phosphate ore currently mined is used in fertilizer products — in 30 to 40 years’ time.
While the likelihood of peak phosphate has been rebuffed by numerous groups inside and outside the phosphate mining industry, the utility and feasibility of phosphate recycling could impact phosphate miners if substantial efforts to recycle phosphate materialize. For one thing, recycling could pull a portion of mined supply out of the market, putting upward pressure on phosphate prices, which have languished this year.
Industrial farmers lay down about 18 million metric tons of mined phosphorus each year, and only negligible amounts remain in the soil. The majority is either removed through harvest, washed into water bodies or leached into water tables.
Concerns about phosphate loss are arising because the phosphorus cycle is one of the slowest element cycles in the biological world. The time it takes the mineral to return from sequestration in water bodies is exponentially longer than the time it takes companies to locate, develop and produce phosphorus projects.
As pressure for greater agricultural yields intensifies, more fertilizer is applied to replenish the nutrients removed by crops. Phosphates need to be reapplied yearly to soils, except in drought years, when crops are ploughed down.
In harvesting corn, of the average 0.5 pounds of phosphate (P2O5) applied per bushel, approximately 0.4 pounds is removed. Of the amount removed during harvest, the majority is transferred into human or animal waste which can then be re-introduced into the agricultural system.
Sewage treatment plants are a potential source of phosphorus for reuse. The CIWEM notes that applying suitably treated biosolids (sewage sludge) back onto agricultural land is the best way to conserve and recycle the phosphate it contains. Currently, the US Environmental Protection Agency estimates that the rate of biosolids recycling in the US is 50 percent.
Phosphates that are flushed off the land and into rivers and lakes also make up a significant portion of recoverable phosphate resources. The CIWEM suggests that wastewater treatment could recover 95 percent of the phosphate from urban wastewater, representing one of the highest levels of waste capture.
Currently, 20 percent of the phosphate in urban wastewater in the EU is recycled, but new, economically-feasible methods of phosphate extraction are in development.
A team of researchers, including Steven Safferman, an associate professor of biosystems and agricultural engineering at Michigan State University, and colleagues at MetaMateria Technologies, based in Columbus, Ohio, is looking into cost-effective methods of recovering phosphorus so that it can be reused as fertilizer products.
“We found that a nano-media made with waste iron can efficiently absorb it, making it a solid that can be easily and efficiently removed and recovered for beneficial reuse,” Safferman said in a Science Daily article.
Safferman also suggested that retrieving phosphorus through extraction from wastewater runoff — a major contributor to eutrophication of rivers and lakes — is more cost effective than the extraction of phosphate rock.