By Sara Jerome,
Researchers say a breakthrough in nutrient removal processes will make it easier to get nitrogen and phosphorus out of water.
“The new method makes it possible to separate 99 percent of the nitrogen and up to 99 percent of phosphorus in wastewater. These nutrients are used to make granular ammonium sulphate (NH4)2SO4 and phosphorus precipitate suitable for fertilizers,” The Science Times reported.
The new process makes it easier to reuse nitrogen and phosphorus once it is out of wastewater.
“Extracting nutrients from communities' wastewater will make it possible to supplement about one-tenth of phosphorus and 6 percent of the industrially produced ammoniac nitrogen that is used for fertilizers,” the report said.
The key is that this process is less energy-intensive than conventional processes, the researchers claim.
“Traditionally, the fertiliser nitrogen needed for ammonium sulphate has been made using the Haber-Bosch method, a process developed by German scientists one hundred years ago that converts atmospheric nitrogen into ammonia. The process requires high temperatures and pressures, and is thus quite a glutton for energy: the manufacture of fertiliser nitrogen accounts for an estimated two percent of global energy consumption,” according to a statement from Aalto University.
Researchers from Aalto University made the discovery. The new method raises the pH value of wastewater using calcium hydroxide, converting ammoniacal nitrogen to gaseous ammonia. The ammonia is then separated out through a membrane and dissolved into sulphuric acid, creating ammonium sulphate. Once it is precipitated with calcium salts, it can be used as fertilizer.
"As calcium is, alongside nitrogen and phosphorus, the most important nutrient required for growing crops in the acid soil of Finland, using calcium-derived substances to elevate pH levels does not increase costs because it just winds up being a part of the end product," researcher Anna Mikola said.
So far, the results are promising.
“Experiments have managed to separate up to 99 percent of the nitrogen and 90 to 99 percent of the phosphorus in urine, even though the method consumes considerably less energy and chemicals than the commonly employed nitrification-denitrification wastewater treatment process,” the university said in a statement.
The research team will begin constructing a pilot project before summer. A patent application for the technology has been filed.
Resource recovery is a hot issue for towns and cities aiming to become more sustainable. Some cities have adopted a “zero waste” model to promote the cause. Seattle Public Utilities, for instance, uses the following language in its definition of zero waste: “Zero Waste means designing and managing products and processes to systematically avoid and eliminate the volume and toxicity of waste and materials, conserve and recover all resources, and not burn or bury them.”
For similar stories visit Water Online’s Nutrient Removal Solutions Center.