The cost of treating wastewater contaminated with nitrogen could be lowered in future. Soil scientists at the Helmholtz Centre for Environmental Research (UFZ) have developed a new mathematical model which can help determine the optimum conditions for microbiological water treatment. Using the stable natural nitrogen isotope 15N, this mathematical model, which is the most accurate to date, can for the first time calculate exactly the quantities of dinitrogen (N2) produced by the complex biochemical treatment processes anammox and denitrification and the background levels in the atmosphere, according to the researchers writing in the specialist journal Rapid Communications in Mass Spectrometry.