The maturity tests during the composting of municipal solid wastes

This study investigated at first the evolution of co-composting process of municipal solid waste and sewage sludge under Tunisian pedo-climatic conditions.Results showed that the temperature profiles established in the system revealed three classical steps, the mesophilic phase during the first 25 days, the thermophilic phase between 30 and 130 days and the cooling phase began after the 14th week in the two windrows W1 (100% of municipal solid wastes) and W2 (60% of municipal solid wastes and 40% of dried sewage sludge). Potential toxic heavy metal content appeared generally more important in W2 than W1, and both finished products of compost obtained in this study satisfied most parts of the recommended norms of agronomical use. The presence or absence of nitrifying activity allowed determining that the compost W1 was more mature than the compost W2.Composting cannot only transform waste by reducing its harmful effect but also corrects when added to soil, the deficit in organic matter. The nature of the raw material used in composting may affect the quality of the final product. There is a significant need for the amendment of soils by compost. The quality of the amendment may have a significant impact on environment.

► As composting proceeded, NH4-N levels generally declined, with NO3-N increasing substantially in a few late samples.
► The dehydrogenase activity generally showed an appreciable increase during the thermophilic phase of the composting process.
► The BC/BN ratio represents the biological activity balance of the compost and a high BC/BN ratio is equivalent to a high microbial heterogeneity.
► The organic carbon mineralization decreased in parallel to the progress of the composting process.
► Nitrates are formed as a consequence of microbial oxidation of ammonia by nitrifier microorganisms of which the presence and the activity are indicators of the compost maturity.