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Quality assessment of digested sludges produced by advanced stabilization processes


The European Union (EU) Project Routes aimed to discover new routes in sludge stabilization treatments leading to high-quality digested sludge, suitable for land application. In order to investigate the impact of different enhanced sludge stabilization processes such as (a) thermophilic digestion integrated with thermal hydrolysis pretreatment (TT), (b) sonication before mesophilic/thermophilic digestion (UMT), and (c) sequential anaerobic/aerobic digestion (AA) on digested sludge quality, a broad class of conventional and emerging organic micropollutants as well as ecotoxicity was analyzed, extending the assessment beyond the parameters typically considered (i.e., stability index and heavy metals). The stability index was improved by adding aerobic posttreatment or by operating dual-stage process but not by pretreatment integration. Filterability was worsened by thermophilic digestion, either alone (TT) or coupled with mesophilic digestion (UMT). The concentrations of heavy metals, present in ranking order Zn > Cu > Pb > Cr ~ Ni > Cd > Hg, were always below the current legal requirements for use on land and were not removed during the processes. Removals of conventional and emerging organic pollutants were greatly enhanced by performing double-stage digestion (UMT and AA treatment) compared to a single-stage process as TT; the same trend was found as regards toxicity reduction. Overall, all the digested sludges exhibited toxicity to the soil bacterium Arthrobacter globiformis at concentrations about factor 100 higher than the usual application rate of sludge to soil in Europe. For earthworms, a safety margin of factor 30 was generally achieved for all the digested samples.

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This work was supported by the EU ROUTES project funded from the European Union’s Seventh Programme for research, technological development, and demonstration under grant agreement no. 265156. Giuseppe Bagnuolo, Ruggero Ciannarella and Vito Locaputo (IRSA-CNR, Bari, Italy) are acknowledged for carrying out determinations of conventional organic micropollutants. Björn Jacobs and Lennart Lörke (BfG, Koblenz, Germany) are thanked for their help during the analysis of emerging organic pollutants.

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Correspondence to C. M. Braguglia.

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Braguglia, C.M., Coors, A., Gallipoli, A. et al. Quality assessment of digested sludges produced by advanced stabilization processes. Environ Sci Pollut Res 22, 7216–7235 (2015). https://doi.org/10.1007/s11356-014-3090-6

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  • Sewage sludge
  • Agriculture
  • Enhanced stabilization processes
  • Organic pollutants
  • Heavy metals
  • Ecotoxicity