Pyrolysis-GCMS as a Tool for Maturity Evaluation of Compost from Sewage Sludge and Green Waste

The objective of the study was to characterise co-composting dynamics and maturity of the end products of sewage sludge/ green waste mixtures. We analysed all initial substrates and co-composts, sampled at different composting times for studying (1) physicochemical parameters and (2) organic matter biodegradation and biotransformation using pyrolysis coupled to gas chromatography and mass spectrometry. Physicochemical analysis indicated compost maturity of the three co-composting mixtures after 200 days. Pyrolysis-GCMS showed that organic matter in sewage sludge generated a large number of different pyrolysis products, most of which had unspecific origin. The pyrolysis products of the three co-compost were classified according to their chemical composition (benzene derivatives, N-containing compounds, phenol derivatives, furan derivates) and according to their chemical structure (polyaromatics, aromatics compounds and aliphatic compounds). These compound classes evolved differently during composting. We suggest two new specific ratios of peak areas from pyrolysis products to describe the biodegradation and to evaluate the degree of maturity during co-composting sludge-green waste: (1) the ratio benzene, methyl (methylethenyl) /benzene, which decrease during composting, and (2) the ratio of Indene/2-methoxy-4 vinyl-phenol which increase during composting. The good correlation between these ratios and physico-chemical parameters confirms their usefulness to evaluate the co-compost maturity. [GRAPHICS] .