Monitoring composting process of olive oil solid waste using FT-NIR spectroscopy

FT-NIR (Fourier Transform-Near Infrared) spectroscopy has been used for the prediction of properties of various materials. Olive oil solid waste compost (OSWC) can be a good and available source for soil organic matter in Mediterranean countries. This study was aimed at developing a fast and nondestructive method for determining compost carbon to nitrogen (C/N) ratio, total nitrogen (TN), inorganic nitrogen, total carbon (C), pH and electrical conductivity (EC) using FT-NIR spectroscopy. Composts were sampled weekly and some chemical analyses were performed on the samples using standard methods. Also, reflectance spectra of the same compost were acquired using FT-NIR spectroscopy right after the standard measurements. Organic matter functional groups of OSW and OSWC were compared using C-13-NMR spectroscopy. Calibration models between the standard measurements and the spectral measurements performed on samples were established applying Partial Least Squares (PLS) method. According to prediction models following determination coefficients (R-2) of 0.86, 0.82, 0.81, 0.77, 0.75, 0.65 and 0.51 were obtained respectively for nitrate (NO3-), pH, ammonium (NH4+), total N, C/N ratio, total C and EC. With this study, it was shown that FT-NIR spectroscopy has the potential of sensing OSWC parameters nondestructively.