Background EU wastewater treatment plants (WWTPs) produce 30 000 tons (dry matter) of sludge daily. This sludge is deposited, incinerated or used as fertiliser. Sludge disposal has large negative environmental impacts and is costly. As a result of the increasing number of households with sewerage connection, the problem is increasing rapidly. The main challenge for the sustainable operation of WWTPs is to decrease these negative environmental impacts and the costs of sludge handling. State-of-the-art technologies are only economically viable for larger WWTPs, limiting actual implementation. Digestion has been introduced to reduce the amount of waste production, and at the same time produce energy, resulting in a lower environmental and carbon footprint. In the Netherlands, the present digestion technology is economically viable for WWTPs with a minimum capacity of 200 000 population equivalents. Therefore, in the Netherlands only 50% of residual sludge is digested at only 25% of the WWTPs. The current technology does not offer a viable solution to the rapidly increasing problem of sludge production at WWTPs. Therefore, there is an urgent need for innovative technologies to reduce sludge production. Objectives This LIFE+ISR project aims to demonstrate the environmental and economic benefits of two highly innovative sludge pre-treatment technologies that substantially reduce waste (i.e. sludge) production at municipal WWTPs. Both complementary technologies realise substantial sludge reduction, but are targeted at different types of WWTPs and situations. Thermocrack is an innovative technology based on thermal pre-treatment of sludge, which results in sludge and chemical reductions and enhanced biogas production. This technology will be implemented in the facilities of the Kralingseveer WWTP, which already has a digester. Optigest is a novel technology for sludge digestion, in which the hydraulic retention time and solids retention time are separated. Implementing Optigest results in sludge reduction, increased sludge volume handling capacity and enhanced biogas production. This technology will be tested in the facilities of the Tollebeek WWTP. Expected results: The demonstrated technologies together result in an annual reduction of almost 8 000 tonnes of waste production, a 900 t reduction in CO2 footprint and an increased energy production of 29.2 TJ/yr. For Optigest at WWTP Tollebeek the expected results are: Annual reduction of 4 200 t in waste production (30%); Annual reduction of 600 t (38%) of the CO2 footprint; Annual reduction of 10% of chemical usage (polyelectrolytes) for dewatering sludge; An increased energy production of 12.2 TJ/yr; and A 3-5% reduction in greenhouse gas (GHG) emissions related to sludge treatment. For Thermocrack at WWTP Kralingseveer the expected results are: Annual reduction of 3 629 t waste production (11%); Annual reduction of 3 000 kg (100%) of AntiFoam usage; Annual reduction of 7 000 kg (6%) of chemical usage (polyelectrolytes) for dewatering sludge; An annual reduction of 290 t of the CO2 footprint (8%); An increased energy production of 17 TJ/yr (33%); and A 3-5 % reduction in GHG emissions related to sludge treatment.