The objective of this study was to evaluate the effect of clay content on sewage sludge decomposition in soil and to propose mathematical models with clay dependent parameters. Soils with contrasting textures from the same sample matrix allowed better relationships to be derived between clay content, microbial biomass, organic carbon and CO2 production then those usually obtained in the literature. Clay effect was noticed only in the first week (R² = 0.59**). Kinetic models were proposed to model sludge decomposition in soils with different textures. Double phase first order models with non-simultaneous time scales were fitted to the data. Model parameters were correlated to clay content, emphasizing the clay effect on sewage sludge decomposition and providing a model for prediction of CO2 production.
anaerobic sludge; clay content; soil respirometry; microbial activity; organic carbon
