Phosphorus recovery: new approaches developed in Vancouver could save the world



In a May 2011 workshop sponsored by the Department of Energy, phosphorus was considered alongside lithium, neodynium, and rare earth metals as a potentially strategically important element.

Phosphorus, a key element in plant growth (and thus in agriculture), is nonrenewable, obtained for commercial fertilizers from phosphate rock that is mined in a comparatively limited number of sites around the world.

Debate swirls around the possibility that viable supplies of this rock will ultimately be exhausted, creating shortages that could devastate global agricultural output and lead to widespread hunger.

Yet the threat posed by phosphorus scarcity contrasts sharply with the current environmental problems created by excessive amounts of the stuff in many places. As a nutrient, this element contributes significantly to algal blooms in waters fed by fertilizer and wastewater runoff. Several new technologies are exploring solutions to limit this impact through recovery or recycling.

Capitalizing on Struvite

One of those technologies emerged from some complementary consulting work that University of British Columbia civil engineering professor Don Mavinic carried out for a pair of firms in 2000.

Metro Vancouver, which operates several wastewater treatment plants in this coastal city, was coping with the buildup of sludge in its pipes. This was not just any sludge, but a concrete-like mass composed of ammonium magnesium phosphate, a mineral that goes by the name struvite. Such deposits, which have been confronted by sewer operators since medieval times, can seriously impede water flow.

Just as Metro Vancouver was asking Mavinic for help, so too did BC Hydro, the power utility that manages dams throughout the mountainous British Columbia interior. The company turned out to have its own interest in struvite, which could replace the commercial product then being used to replenish the nutrient-deficient reservoirs behind those dams.

That nutrient compensates for the reservoirs' reduced populations of fish, whose bodies and wastes provide natural fertilizer to sustain healthy plant growth in lake and river ecosystems.

Mavinic and his colleagues met Metro Vancouver's request with a reactor that processes wastewater on its way to a biosolids digester. Within a cone-shaped chamber, fine crystals of struvite in the water combine with ammonium, phosphate, and magnesium reagents, growing into particles large enough to capture with a filter.

Those particles are the basis for a cost-effective fertilizer that could enable BC Hydro and other dam operators to maintain the environmental integrity of waterways affected by their installations.

Government authorities overseeing those waterways, in turn, can ensure that operators sustain the vibrant quality of these settings, which could otherwise turn into biological dead zones.

Recovering and recycling phosphorus in the form of struvite that would otherwise be discarded offers economic as well as environmental incentives.

The technology developed through the University of British Columbia inspired a spin-off company, Ostara Nutrient Recovery Technologies, Inc.

Based in Vancouver, the firm installs facilities to harvest struvite from wastewater streams, marketing their output as a slow-release fertilizer called Crystal Green®. (Editor's Note: Ostara was the winner of a GLOBE Award for Environmental Excellence. See GLOBE Foundation Awards Canada's Best Environmental Leaders)

The equipment has been installed at wastewater treatment plants in Edmonton, Alberta; Portland, Oregon; and York, Pennsylvania. In 2009, the technology began moving to the other side of the Atlantic, as Ostara inked deals with water authorities in the United Kingdom and the Netherlands.

Companies that run municipal wastewater plants have good reason to consider what Ostara has to offer. Their pipes regularly become clogged with struvite, most of it generated by human urine, which is rich in phosphorus.

There is money to be saved in the form of reduced plant maintenance, and money to be made through sales of struvite-based fertilizer. Moreover, in parts of the world where phosphates are in short supply and fertilizers must be imported, this technology could create a domestic source.

Some of the most ambitious struvite recovery targets are being set in Sweden, where the government would like to see 60% of the phosphorus compounds present in the country's wastewater streams diverted for agricultural use by 2015.

This will not only keep those compounds from draining into lakes and rivers, where they could promote eutrophication, but will also reduce the amount of fertilizer that must be produced or imported.

At the same time, Swedish researchers point out that such strategies need not be limited to the sophisticated wastewater treatment infrastructure of the developed world. The impact could improve human health and economic advantage in many countries around the world.

One study considered the United Nations Millennium Development Goals in terms of the cash equivalences of recovering nitrogen and phosphorus from human excreta-in other words, how much money could be saved by recovering phosphorus from local waste streams.

By this analysis, East Asia could retain an annual potential commercial value for these two elements-based on regional costs for fertilizers-totaling more than US$625 million. Similarly, in sub-Saharan Africa this total comes to almost $800 million.

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