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Multivariate analysis of near infrared reflectance spectroscopy (NIRS) spectra of sewage sludges and green wastes can be used to monitor the composting process, say researchers in France. Their findings could improve the quality sewage-derived compost for agricultural use. Remy Albrecht, Raphaël Gros, Jean Le Petit, Gérard Terrom, and Claude Périssol of the Paul Cézanne University in Aix-Marseille and Richard Joffre of the Centre for Functional and Evolutionary Ecology in Montpellier point out that sewage compost has many benefits not only as a fertiliser but in improving soil quality, reducing erosion, and inhibiting soil pathogens. Compost quality for land application must be monitored and controlled closely and there are many physical, chemical and biological methods for assessing maturity and stability. However, a consistent quality assessment is not currently possible. It is known that compost maturity is often associated with the degree of humification, while stability is reflected in the presence of decomposed and so more stable organic compounds. Albrecht and colleagues have now recruited the power and speed of NIRS to take the chemical fingerprints of compost derived from biological waste, which they explain can provide important biochemical information about the character and number of functional groups present, such as -CH, -OH, and -NH chemical bonds. They tested NIRS using 426 samples representative of the six stages of composting at 8, 20, 35, 75, 135, and 180 days. Maturity was assessed by carbon to nitrogen ratio and various multivariate analytical methods were applied to the spectra at 200 wavelengths. Initially, they derived a descriptive approach that revealed how the compost changes with time. They then developed a calibrated model at each stage of composting based on carbon and nitrogen content and the ratio of the two using partial least-squares regression. The technique proved both sensitive and accurate, the researchers say. The results "show the efficiency of NIRS to predict chemical changes and the stage of transformation of organic matter during the composting process," the team says. "NIRS is a highly reproducible technique able to draw a precise chemical fingerprint of an organic material, moreover it is rapid and makes it possible to analyse a large number of samples in a practical and timely manner," Albrecht told SpectroscopyNOW, "Control of maturation can be easily simplified with good calibrations and a reference data bank." Related links:
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