Revealing the ocean's hidden fertilizer

 

Press Release 15-053 Revealing the ocean's hidden fertilizer Tiny marine plants play major role in phosphorus cycle An instrument system used to collect samples from different water depths in the ocean. Credit and Larger Version May 14, 2015 Phosphorus is one of the most common substances on Earth. An essential nutrient for every living organism--humans require approximately 700 milligrams per day--we're rarely concerned about consuming enough because it is in most of the foods we eat. Despite its ubiquity and living organisms' dependence on it, we know surprisingly little about how it moves, or cycles, through the ocean environment. Scientists studying the marine phosphorous cycle have known that phosphorus was absorbed by plants and animals and released back to seawater in the form of phosphate as these plants and animals decay and die. But a growing body of research hints that microbes in the ocean transform phosphorus in ways that remain a mystery. Hidden role of ocean's microbes A new study by a research team from the Woods Hole Oceanographic Institution (WHOI) and Columbia University reveals for the first time a marine phosphorus cycle that is much more complex than previously thought. The work also highlights the important but previously hidden role that some microbial communities play in using and breaking down forms of this essential element. A paper reporting these findings is published this week in the journal Science. "A reason to be excited about this elegant study is in the paper's last sentence: 'the environmental, ecological and evolutionary controls ...remain completely unknown,'" says Don Rice, a program director in the National Science Foundation's (NSF) Division of Ocean Sciences, which funded the research through its Chemical Oceanography Program. "There's still a lot we don't know about the sea." The work is also supported by an NSF Dimensions of Biodiversity grant. "This is an exciting new discovery that closes a fundamental knowledge gap in our understanding of the marine phosphorus cycle," says the paper's lead author Ben Van Mooy, a biochemist at WHOI. Much like phosphorus-based fertilizers boost the growth of plants on land, phosphorus in the ocean promotes the production of microbes and tiny marine plants called phytoplankton, which compose the base of the marine food chain. Phosphonate mystery It's been unclear exactly how phytoplankton are using the most abundant forms of phosphorus found in the ocean--phosphates and a strange form of phosphorus called phosphonates. "Phosphonates have always been a huge mystery," Van Mooy says. "No one's been able to figure out exactly what they are, and more importantly, if they're made and consumed quickly by microbes, or if they're just lying around in the ocean." To find out more about phosphonates and how microbes metabolize them, the researchers took samples of seawater at a series of stations during a research cruise from Bermuda to Barbados. They added phosphate to the samples so they could see the microbes in action. The research team used ion chromatography onboard ship for water chemistry analyses, which allowed the scientists to observe how quickly microbes reacted to the added phosphate in the seawater. "The ion chromatograph [IC] separates out the different families of molecules," explains Van Mooy. "We added radioactive phosphate, then isolated the phosphonate to see if the samples became radioactive, too. It's the radioactive technique that let us see how fast phosphate was transformed to phosphonate." Enter the microbes The researchers found that about 5 percent of the phosphate in the shallow water samples was taken up by the microbes and changed to phosphonates. In deeper water samples, which were taken at depths of 40 and 150 meters (131 feet and 492 feet), about 15 to 20 percent of the phosphates became phosphonates. "Although evidence of the cycling of phosphonates has been mounting for nearly a decade, these results show for the first time, that microbes are producing phosphonates in the ocean, and that it is happening very quickly," says paper co-author Sonya Dyhrman of Columbia University. "An exciting aspect of this study was the application of the IC method at sea. In near-real-time, we could tell that the phosphate we added was being transformed to phosphonate." Better understanding of phosphorus cycle A better understanding of phosphorus cycling in the oceans is important, as it affects the marine food web and, therefore, the ability of the oceans to absorb atmospheric carbon dioxide. The researchers say that solving the mystery of phosphonates also reinforces the need to identify the full suite of phosphorus biochemicals being produced and metabolized by marine microbes, and what physiological roles they serve for these cells. "Such work will help us further resolve the complexities of how this critical element is cycled in the ocean," Dyhrman adds. Grants from the Simons Foundation also supported the work. -NSF-

Sustainable phosphorus recovery from wastewater

 

Wed, 05/06/2015 - 11:12am Ken Doyle, American Society of Argonomy   Wastewater treatment infrastructure, such as this anaerobic digester, can be leveraged to capture and recycle phosphorus, a limited essential nutrient. Image: Michael NorthropA new approach to wastewater treatment may be key in efforts to reduce, reuse, and recycle. Moreover, it can be profitable. Phosphorus is an essential element for human nutrition. It plays multiple roles in the human body, including the development of bones and teeth. Fertilizer with phosphorus, applied to crops or lawns, enables healthy growth. Without it, the basic cells of plants and animals, and life itself, would not exist. Typically, phosphorus is found in phosphate-containing minerals that are mined—a limited and non-renewable resource. The annual demand is rising quickly. However, once used, phosphorus is difficult to reclaim. Where does the phosphorus go? In animals (including humans), urine contains phosphorus. Surface water carry large amounts of phosphorus from fields and lawns downstream. The result is phosphorus in water discharged by wastewater treatment plants (WWTPs). "Whatever phosphorus we use and discharge into rivers and oceans is lost to the environment," says Rolf Halden, professor at the School of Sustainable Engineering and the Built Environment, and director of the Center for Environmental Security, Arizona State Univ. Additionally, accumulation of phosphorus can result in problems like algae blooms in lakes and other surface water bodies. In turn, algae blooms deplete oxygen from the water, affecting the delicate balance of aquatic life. "This problem is observed in the seasonally recurring 'dead zone' of the Gulf of Mexico," says Halden. Halden's group recently published a study in the Journal of Environmental Quality that examined methods for recovering phosphorus from wastewater using mathematical modeling. "WWTPs represent ground zero for addressing the problem of global phosphorus depletion," Halden says. WWTPs in many cities are currently implementing methods to extract phosphorus before discharging wastewater into the environment. There are two main types of phosphorus recovery methods: chemical and biological. In the chemical method, WWTP treat phosphorus dissolved in wastewater. The phosphorus then falls out of solution for easier removal. In the biological method, bacteria introduced into the water collect the phosphorus into removable sludge. A variation includes enhanced biological phosphorus removal (EBPR). This method selectively encourages bacteria that can accumulate phosphorus. Choosing a method is complicated. "The region's water quality, size of the treatment plant, and economic considerations play a role in the selection," explains the study's lead author, Arjun Venkatesan. Halden and Venkatesan's study focused on a combination approach. First, EBPR concentrated phosphorus in sludge. Next, chemical treatment helped phosphorus fall out to form struvite, a usable phosphate mineral. The study showed that a typical WWTP could reclaim approximately 490 tons of phosphorus in the form of struvite each year. Conventional methods remove only 40 to 50% of P, according to Venkatesan. The secondary treatment of sludge employed by EBPR "achieves an additional 35% mass reduction, for a total of about 90% removal," he says. EBPR helpfully avoids additional chemicals and reduces sludge production. Both these factors lower the cost of operation—a key consideration for WWTPs with limited budgets. Reclaimed phosphorus pays off for the environment with less mining for phosphorus and improved surface water health. phosphorus recovered as struvite can also generate income. The team estimates that the WWTP used in their case study could generate $150,000 in annual revenue from this two-pronged approach. A plant with existing EBFR facilities can recoup the initial expenses in as little as three years. "Nearly 367,500 tons per year of phosphorus could be generated with combined EBPR and struvite production," says Halden, in plants with treatment capacity similar to the one used in the case study. Such a payload can be a welcomed payoff for conscientious communities. Source: American Society of Argonomy