Emerging option for excess sewage sludge minimization and/or energy generation maximization

In many countries, in the sector of wastewater treatment the fate of excess sludge is becoming an emerging problem due to the continuous increase in sludge production. The restriction to its landfilling, set in many countries will cause a significant increase of costs. In this context, the emerging technologies aimed to the minimization of excess sludge production becomes more and more interesting. The most promising technologies available for full-scale applications and aimed to the reduction of excess sludge production, directly on-site in municipal wastewater treatment plants, are highlighted in the first part of this paper. Most of the technologies are aimed to solids solubilization and disintegration of bacterial cells. These approaches cannot put to zero the need of a final treatment. A modem approach cannot be related to landfilling as clearly pointed out in Europe. Also the use of sludge in agriculture (directly or after composting) is going to be limited in some countries for health reasons. As a consequence the sector of the thermo-chemical treatments is seen with a growing interest (thermal drying can be considered an intermediate treatment). These treatments will be discussed in the second part of this paper taking into account the overall fate of sludge.