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On the Fate of Xenobiotic Compounds during Alternative Methods of Municipal Sludge Treatment

Gerasimos Lyberatos, Katerina Stamatelatou, Michael Fountoulakis, Constantina Pakou, and Michael Kornaros. Chemical Engineering, University of Patras, 1 Karatheodory st., Panepistimioupoli, Patras, Greece

The stabilization of sewage sludge is of great importance for public health and for minimization of environmental impacts. Surface active pollutants (e.g. LAS, NP, NPEO, PAE, PAHs, etc.) originally contained in the wastewaters terminate in the sludge and unless they are converted during sludge treatment they may end up with sludge disposal. Land application of treated sewage sludge, the often preferred disposal method, may then lead to groundwater and/or crop contamination with these undesired xenobiotics. The aim of this work was to assess the fate of these key xenobiotics that are oftened found in substantial quantities in municipal sludge, in alternative sludge treatment processes. All experiments were carried out in fully automated lab-scale digesters and composting reactors. A mixture of primary and secondary sludges, taken fron the Patras Sewage Treatment Plant, was formed in order to obtain representative feed material. Anaerobic mesophilic (35oC) sludge digestion was considered first. While having no impact on the process, LAS, NP/NPEO, and PAHs were not removed. The phthalate ester DEHP was removed only partially. Composting of either the raw municipal sludge or the anaerobically treated sludge proved to be effective in removing most xenobiotics to allowable discharge levels. Finally the possibility of having a brief post-aeration (1 d retention time)of anaerobically treated sludges was examined with promising results. This work reports on the findings of the project BIOWASTE funded by the European Union.