Evaluation of the organic matter composition of raw and composted municipal wastes

Abstract

The organic matter contained in ten municipal wastes (7 raw residues and 3 composts) was evaluated by studying chemical parameters. The structural-chemical composition of organic matter was also studied by pyrolysis-gas chromatography (Py-GC) and the qualitative properties of organic matter were investigated by isoelectric focusing (IEF). The chemical indices employed (biodegradability index and water soluble C/total N ratio) were found to be useful for distinguishing raw organic matter from composted one, although they did not enable to differentiate between organic matter derived from municipal solid wastes (MSW) and that from aerobic sewage sludges (SS), The structural chemical composition of the organic matter extracted from the wastes differed depending on the groups studied (raw MSW, raw SS, and composts) when the most aliphatic pyrolytic compounds (acetic acid and furfural) were considered; these were less abundant in the composts, as acetic acid predominated in sewage sludges and furfural in fresh MSW. The mineralization index: acetic acid/pyrrole, showed that the least mineralizable organic matter was present in the composts and the most mineralizable one in raw sewage sludge. IEF was found to be a useful technique for distinguishing between organic matter extracted from wastes; the spectra obtained by this technique were in agreement with the data obtained from the pyrolysis mineralization index and with those obtained from chemical parameters.