| In Spain, sewage sludge production has been increasing in the last past years and 82.6% of the sludge produced is used as an organic fertilizer in agriculture. In order to minimize the risks of addition of sludge to land, the UE is developing a new legislation regarding land application of sewage sludge in which it is introduced the concept of advanced and conventional treatments, having the advanced treated sludge fewer restrictions compared with a sludge that has been treated conventionally.;The main objective of this thesis consisted of the study of two advanced treatments described in this Proposal for a Directive, with the aim of assessing the stabilization process and sludge sanitation. The treatments were: autothermic thermophilic aerobic digestion (ATAD), and thermophilic anaerobic digestion (TAnD). Likewise, the effects of the stabilization process on sludge microbial community were assessed, and the effects of the agricultural use of an advanced treated sludge compared to a conventional sludge on soil and plants, were evaluated.;The ATAD system resulted in a suitable technology for sludge stabilization with a high organic loading rate (2.7 kg VS m-3 d-1) and a short sludge retention time (14.6 days). The content of human pathogens was significantly reduced, achieving the complete removal of Salmonella spp., and Escherichia coli and decreasing Clostridium perfringens spores. The TAnD system operated at higher OLRs (1.5 to 2.5 kg VS m-3 d-1) and shorter SRTs (16 to 28 days) than the anaerobic mesophilic digester with a similar volatile solids destruction (>40%) and biogas (0.64 Nm3 kg-1 VS-1 fed) and methane production (62%). It also eradicated Salmonella spp., and E. coli and reduced the content of C. perfringens spores.;This thesis proposes a 2-stage mesophilic anaerobic-thermophilic sludge digestion (either aerobic or anaerobic) to achieve an utterly sanitized sludge.;Sludge stabilization process determined sludge chemical properties as well as shaped sludge microbial community. Sludge application altered soil microbial community structure and activity, and plant growth and performance in a different manner depending on the stabilization process. Therefore, it stands out as a pivotal agent determining the feasibility of the final by-product as an organic amendment. |
