Management of the excess sludge production resulting from biological wastewater treatment is one of the most important economic and environmental issues for the next decade. Due to the intensification of wastewater treatment, a large increase in sludge production from biological processes must be anticipated. Moreover, sludge agricultural valorisation and landfilling, which are the main solutions adopted for final sludge disposal, are debated and sludge incineration cannot be a systematic solution. So, new stringent regulations regarding sludge treatment and disposal imposed in several countries as well as social and environmental concerns, have resulted in an increasing interest in emergent processes aimed at the reduction or minimization of excess sludge production. Following a 5 years on-going research program, Ondeo-Degrémont has developed a new set of processes designed to reduce sludge production inherent to biological wastewater treatment: Biolysis. The results presented in this paper relate to two case studies aimed at assessing the effect of Biolysis O and Biolysis E associated with an activated sludge process. This paper highlights results concerning reduction of sludge production and provides a comprehensive and accurate set of results dealing with the influence of Biolysis processes on the remaining sludge and effluent characteristics. An economical evaluation of the Biolysis technologies is also provided.