Fourier-Transform Infrared (FTIR) spectroscopy analysis of seven wisconsin biosolids

Our research explores the use of Fourier-transform infrared (FTIR) spectroscopy to better understand the phosphorus (P) characteristics of biosolids and how these characteristics can affect agricultural production. Our question was whether FTIR spectra can differentiate between the organic and inorganic species of phosphorus in biosolids by showing shifts in the peaks that indicate species of phosphorus. We obtained biosolids from five Wisconsin wastewater treatment plants (Madison, Delafield, East Troy, Mukwonago, and Fort Atkinson). From the Madison location, we obtained several samples from different parts of the treatment process — cake, final liquid (labeled as Metrogro), and composted biosolids. We compared the FTIR spectra from these samples to P standards, aiming to identify the dominant P species in each biosolid. We employed several FTIR methods: attenuated total reflectance (ATR), sodium chloride (NaCl) salt plates with mineral oil, and pressed potassium bromide (KBr) pellets. We found that the FTIR method that best shows P species differences in the biosolids was the pressed KBr pellet method. Additionally, the P standards indicated two critical wavelength regions in which the inorganic species’ FTIR peaks are shifted to a higher wavenumber than those of the organic species. This work indicated that we can use KBr pellet FTIR as a simple and rapid method to start characterizing P species in biosolids. These research findings could provide farmers useful information about P availability to crops and risk of P loss in runoff when applying biosolids to their fields.