RESPONSE TO PH CHANGES OF FLUORESCENCE SPECTRA OF DIGESTATES FROM MUNICIPAL SOLID WASTE AND SEWAGE SLUDGE UNDER MESOPHILIC AND THERMOPHILIC CONDITIONS

The wide range of fluorophore responses to pH available in the literature reflects the complex nature and heterogeneous composition of natural organic matter so that the study of fluorescence spectra to pH changes is not an easy task. However, since early 80’s it is well known that humic substances tend to have a linear structure at high pH and coil up when pH decreases so that changes in fluorescence intensity and/or wavelength values with changing pH can be attributed to conformational changes in the molecules hiding or exposing fluorescing parts. In general, more rigid structures provide better fluorescent yields since a spherocolloidal configuration could mask some fluorophores inside their structure. Here the response to pH changes (4, 6, 8, 10) of fluorescence spectra of 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 was studied. Our results showed that emission spectra of digestates exhibited a shift to higher values and a general increase of FI up to pH 8 and a more or less slight decrease of FI from pH 8 to pH 10. The response to pH modifications of synchronous-scan spectra was more complex and articulated.