Phytotoxicity of biosolids for soil application: Influence of conventional and advanced anaerobic digestion with sequential pre-treatment

The aim of this study was to evaluate the influence of different anaerobic digestion processes on the phytotoxicity of biosolids (BS) for soil application. Three different plants species, Lactuca sativa, Raphanus sativus, and Triticum aestivum, were subjected to seven treatments consisting of different amounts of BS (5-1000 g/kg). In this case, the biosolid samples came from the stabilization of sewage sludge (SS) and were obtained by using conventional anaerobic digestion (CAD) or advanced anaerobic digestion (AAD), which includes a sequential ultrasound pre-treatment and a low-temperature thermal process. To evaluate the phytotoxicity, the germination inhibition percentages, root and sprout growth, germination index (GI), and EC50 were determined. The results showed that the application of SS with a concentration of 250 g/kg inhibited the germination of L sativa, R. sativus and T. aestivum, with percentages that varied between 50%-100%. This study concludes that the application of 100 g/kg BS shows either beneficial effects (GI >= 100) or no presence of phytotoxicity (100 > GI >= 80). These results were corroborated by EC(50)averages of 164 g/kg and 159 g/kg obtained at endpoints from plants treated with BS after CAD and AAD, respectively. (C) 2019 Elsevier B.V. All rights reserved.