Study of the biodegradation and fertility of the co-composting produced from sewage sludge and green waste and its effects on the speciation of heavy metals

This study aims to determine the agronomic value of sewage sludge and green waste compost and the evolution of bioavailability of heavy metals in the course of composting. In this study (60 %) of sewage sludge and (40 %) of crushed green waste were mixed. The mixture of these organic wastes was put in a wooden cubic composter having a volume of (1.5 m 3 ) for a period of 90 days. The aeration of the mixture was made by manually turning the compost. The results show that electrolytic conductivity (EC) of the compost was 1.8 mS cm -1 , pH 7.6 and C/N ratio of 15.4. The total concentrations of Zn, Cr, Cu, Ni and Pb as mg/kg dry compost were 202.1, 98.4, 54.2, 23.2 and 5.4 respectively. They were reduced and agree with the standards of the Canadian limits indicating the maturity of the end product. It has been also observed by Fourier transform infra-red (FTIR) spectroscopic that the final compost improved the concentration of aromatic compounds with respect to the initial state of matter with a decrease of aliphatic groups and a reduction of components easily inhalated by microflors acting during the biological process.