FLUORESCENCE SPECTROSCOPY APPLIED TO THE CHARACTERIZATION OF DIGESTATES OBTAINED FROM DIFFERENT ORGANIC SUBSTRATES

Fluorescence spectroscopy was applied to the characterization of a number of digestates obtained by various mixtures of organic waste. Different results were obtained for digestates produced by anaerobic digestion of a 1:1 mixture of the organic fraction of municipal solid waste and sewage sludge under mesophilic and thermophilic conditions. Under thermophilic condition emission maxima located at higher ? than those obtained under mesophilic conditions were observed. In general, higher fluorescence intensity (FI) were obtained in emission spectra of digestates as compared to their corresponding substrates, whereas FI of digestates under thermophilic condition were lower than those of digestates under mesophilic conditions. Digestates obtained by energy crops, poultry manure, stomach residue and others agro-industrial residue sampled in different sections of the digestion plant exhibited an increase of FI values of the peak at highest ? in synchronous-scan spectra from the first digester to the storage tank. Excitation emission matrix (EEM) of all digestates revealed a typical peak characterized by very low excitation ? (250-265) and relatively high ? (410-442) which could not be included in the classification of EEM peaks reported in literature for natural organic matter and therefore it was referred to as peak E. Our results indicated that this peak can be used to identify and characterize digestates with respect to other different samples of natural OM.