A new patented process design has re-invented thermal hydrolysis in sludge treatment. The first plant from Cambi for hydrolysis of sewage sludge was built in 1995 at the HIAS WwTP, Hamar, Norway for a design capacity of 3500 Mg DS/year. The sludge is directly heated by injection of live steam. During internal recycling of steam a low energy consumption is secured. Predewatering raw sludge upstream hydrolysis and a changed viscosity of the hydrolysate enables HIAS to feed the conventional digester with 11 % DS for stabilisation and odour reduction. The conversion rate of volatile matters (VM) is 57 %. The reduction of sludge tonnage is over 93 % from thickener to final dewatering. The guaranteed desinfected sludge cake is mainly used in agriculture. It stacks very well and is easy to spread.