Assessment of pre-treatments to mesophilic-thermophilic anaerobic digestion

摘要

The legislative standards in many European countries and in the USA on sludge use inagriculture require effective removal of pathogens during stabilization processes. Greatattention is also paid nowadays to organic micropollutants like PCBs, surfactants (LAS),hydrocarbons, polynuclear aromatic hydrocarbons (PAH), halorganics (AOX) andpharmaceuticals whose removal is not effective in conventional sludge processing.Anaerobic thermophilic digestion was considered suitable for producing class A biosolidssince 30 years (Rimkus et al. 1982) considering that more effective removal of pathogensseems to be attained in thermophilic digestion in comparison with mesophilic conventional.A research project was funded in 2011 under FP7 by the European Commission with theacronym ROUTES (Novel processing routes for effective sewage sludge management) toassess whether innovative techniques might be useful for producing a sludge of very goodquality introducing also in Europe the concept of biosolids instead of sludge (undesirablewaste to be disposed as soon as possible).In this paper the preliminary results of this research project are presented together with abenchmarking of two innovative techniques, in term of the energy balance, in comparisonwith a conventional one. This study evidenced that the energy balance (energy productionenergyrequirement) is hardly achieved by a conventional scheme while separate processingof primary and secondary sludge might increase such chances. Secondary sludge processingby thermal disintegration + thermophilic digestion seems better than sonication, andmesophilic + thermophilic digestion. However, in the former case an additional heat sourcewould be required.