Fluorescence analysis of humic-like substances extracted from composts: influence of composting time and fractionation

Humic-like acids (HLA0, HLA70, HLA130, HLA730) were extracted from composts obtained from sewage sludges and trimmings after 0, 70, 130 and 730 days of composting, respectively. In addition, HLA130 was fractionated using SEC-PAGE set-up. Fluorescence spectroscopy revealed that HLA0 was the only sample to contain emission bands characteristic of protein-like compounds (kexc/kem: 280/350) and chlorophyll (kexc/kem: 420/660). Emission intensities above 400 nm and HIX both varied in the order: HLA70[HLA130[HLA730[HLA0 and increased as the fraction molecular size decreased. Thus, the formation of long wavelength emitting fluorophores during composting is connected to the humification process. These fluorophores are mainly concentrated in the low molecular size fraction obtained by SEC-PAGE fractionation of composts