CHARACTERIZATION AND AGRICULTURAL UTILIZATION OF A BIOSOLID FROM CHEMICAL STABILIZATION OF MUNICIPAL SEWAGE SLUDGE

The disposal of municipal sewage sludge (MSS) is a topic of great interest as this waste is produced in large amounts in the European Community (EC) (9.106 tons in the EC and about 8.105 tons in Italy, in 2006) and its production is rapidly increasing because of the great number of commissioned wastewater treatment plants and more stringent effluents treatment and discharge standards. On the other side, sewage sludge is rich in organic carbon (C, 50-60% of dry matter) nitrogen (N, about 1.5%), phosphorous (P, 3%) and other nutrients for plant growth (Laturnus et al., 2007). That’s why the agricultural utilization of MSS is an interesting way to achieve both the disposal of this material and the closure of nutrient cycle from renewable resources. However, for a more effective agronomical valorisation, MSS should be subjected, before agricultural utilization, to one ore more treatments such as drying, biological maturation, composting, anaerobic digestion or chemical stabilization in order to remove undesired compounds, such as human pathogens and xenobiotic molecules (Fernandez et al., 2009). In this way their quality should improve, in the perspective of a rational and sustainable agriculture. The result of these processes is no longer a sludge but a biosolid, that is the product of a transformation possessing all the features (maturity, stability, chemical and physical characteristics within the legislation limits) to be employed in agriculture as an amendment (NRC, 2002). As a matter of fact, the effect of organic amendments on soil quality should also be assessed, as their soil application can stimulate or inhibit microbial activity. For example the use of immature of unstable or immature product could led to N immobilization, moreover C mineralization could be affected not only by soil features but also by the source of the added product (Huang and Chen, 2009). Therefore the aim of the this work was to characterize, from chemical and physical point of view, a new biosolid (bio-sulphate product) obtained from the chemical stabilization of MSS with H2SO4 (sulphuric acid/sludge ratio 1/5 w/w) and CaO, classify it according to the current Italian legislation (D.Lgs. 75/2010) and study its behaviour as fertilizer, determining the mineralization of organic C and N, when it is applied to soil.