TechnologytSolutions Closing the phosphorus loop
Florida Institute of Phosphate Rese arch
investigation potentially can recover 90% of phosphorus, compared with 40–50% recovery for the CSH Sources of high-grade phosphate ore calcium silicate hydrates (CSHs), process, Weidler notes. The disaddeposits could disappear within the which are byproducts of the buildvantage is that chemical or cheminext 100 years at current use rates, ing material industry, to remove cal–thermal treatment steps are analysts say. In the hunt for alternaphosphorus through crystallizarequired to redissolve the phostives to mining this nonrenewable, tion. It’s a simple, one-step process phorus to separate it out. These adunique resource, researchers have that removes phosphorus directly ditional steps translate into higher found one possible surprising new from the wastewater stream and chemical and energy costs and largsource: sewage treatment plants. recovers it without the addition of er initial volumes of sludge. About 90% of the phosphate “The optimal recovery methdug out of the ground goes od is still an open question,” into fertilizer; the remainder says Christian Schaum of Techis used in products including nische Universität Darmstadt food additives, glues, flame re(Germany), and will depend on tardants, and detergents, aclocal requirements for sludge cording to Chris Thornton of disposal. Both Germany and the Centre Européen d’Etudes Sweden have announced nades Polyphosphates (CEEP), the tional objectives for phosphorus phosphate industry research recovery from recycled sewage, association housed at the Eurobut recovery rates have not yet pean Chemical Industry Counbeen set. cil. “If it runs out, then there’s The uncertainty remains no more agriculture as we know partly because none of the reBecause of growing world demand for fertilizers, it,” Thornton points out. “The covery options is as yet technihigh-grade phosphate ore deposits, such as this one amount that can be reasoncally or commercially feasible at in Florida, could run out within the next 100 years. ably recycled from sewage is every sewage treatment plant, not a huge percentage of the toThornton says. The main probtal amount being used, but it’s still further chemicals, says Ute Berg, a lem is economic: phosphate prices significant.” geoecologist with the water and geoon the world market still fall beMost wastewater facilities in Eutechnology division of the Institute low the costs of any of the recovery rope and North America remove for Technical Chemistry at the Karls methods currently used at sewage phosphorus to prevent algal blooms ruhe Research Center (Germany). treatment plants. “The economic in receiving waters. Biological and The hydrates do not require predriver is less the actual value of the chemical treatment methods contreatment steps that other crystallifertilizer you recover but more the centrate the phosphorus into a residzation methods under development money you save in having to dispose ual sludge that is typically applied need, such as major pH adjustments of” the sludge, Thornton explains, to agricultural fields as a fertilizer. and later removal of CO2, Berg exbecause all the recovery methods reBut around big cities, particularly plains. “We just add this starting duce the amount of leftover sludge. in Europe, less and less farmland is material and have ready precipitaOn an industrial timescale, dwinavailable for spreading the sludge. tion of calcium phosphate,” she says. dling phosphate reserves “are not of Concerns over contaminants, such In this way, Berg and her colleagues immediate concern to us,” Thornton as heavy metals, hormones, and have been able to produce a secadmits, but CEEP nonetheless has pharmaceutical residues, contained ondary phosphate rock containing sponsored research in recycling the in the sludge have led to more of it 12–13% phosphorus. “We’re nearly phosphorus recovered from sewage. being placed in landfills or incinat the 13–15% levels that raw, high“We used to be using ores that were erated. The demand for other disquality phosphate ores contain,” 18% phosphorus, and now we’re posal outlets has led researchers to adds Peter Weidler, chief physicist at down to 15%. If we can move to uspursue technologies to recover the the Karlsruhe Research Center. ing recycled phosphate rather than a phosphorus contained in sewage in Other research projects focus on raw material from nature, then that’s a form that can be recycled by the the recovery of phosphorus from a move toward sustainable developphosphate and fertilizer industries. sewage-sludge ashes and from the ment,” he says. One of these technologies uses sludge itself. The processes under —KRIS CHRISTEN 2078 n Environmental Science & Technology / APRIL 1, 2007
© 2007 American Chemical Society
