The implementation of the bioaugmentation technology in the Heraklion city WWTP commenced in August of 2015. Heraklion WWTP, receives wastewater from the Municipality of Heraklion, the fourth most populated city of Greece and biggest city of the island of Crete (app. 180.000 habitants) resulting in a yearly sewage sludge production of 12.000-14.000 tn. By applying the bioaugmentation process, the plant managed to reduce its yearly sewage sludge production volume by more than 70%, retaining its high-quality final effluent. In addition, a significant reduction of odors within the different parts of the process was succeeded and biogas production of more than 1000 m3/d has been constantly achieved.