The ultrasonic pretreatment was better than alkali and thermal for to increase the solubilization of wasted activated sludge.

Ultrasonic-alkali pretreatment was the most efficient treatment in terms of matter solubilization (85 %) and biodegradability (65 %).

After anaerobic digestion of wasted activated sludge pretreated for ultrasound-alkali, side so there was a reactivation of fecal coliforms.

Although the combination of ultrasound alkali seems to be the most favorable and suggests a good biodegradability is important to look the combination sequence of treatments to prevent the training Maillard reactive.

We identified the need to consider the time storage prior to disposal of biosolids, due to reactivation of pathogens.