Background The treatment and disposal of sludge contaminated by heavy metals, microorganisms and several organic compounds is an increasing problem. Its disposal on farm land creates a potential risk for human health and the environment. However, alternative solutions, such as thermal treatment, are becoming more important in Europe. In Germany, already around half of all municipal sludge is thermally treated, mainly in large centralised incineration or co-incineration plants such as cement kilns and coal-fired power plants. Both disposal methods, however, have ecological and economical drawbacks. As sludge transportation routes are frequently very long, the sludge is either dewatered – thus 70-75% water is transported – or dried prior to transport (normally by using fossil fuels). Objectives The aim of the SLUDGE2ENERGY project was to demonstrate the decentralised reuse of sewage sludge in an efficient small-scale heat and power generation plant on the premises of the wastewater treatment plant (WWTP). The innovative sludge processing technique was intended for market introduction. The energy self-sufficient plant would reduce the amount of sewage sludge for disposal to 1/8 of the dewatered sludge. Amounts of sludge are increasing and disposal routes are limited, but this technique offers an environmentally sound alternative for sludge management. The residues of the process are an ideal resource for phosphorous recycling. Results The project created the SLUDGE2ENERGY system, a decentralised combination of sewage sludge drying followed by mono-incineration and power generation by means of a gas turbine. The main system components are a belt dryer, a micro gas turbine and a grate stoker furnace for dried sludge. The project sewage sludge treatment system that was developed allows sludge to be reused directly at the point of origin, i.e. on the premises of the WWTP. Transport is thus avoided and the energy content of the sludge can efficiently be used on a local scale, e.g. for drying. In addition useful heat is available from the dryer by recovering the heat from condensation. The project demonstrated a decentralised solution, which is both technically feasible and economically viable. The plant has shown that the concept is suitable for WWTPs throughout Europe with a size of greater than 150 000 PE (population equivalent). The theoretical potential for Germany is about 170 plants. The plant is designed for an annual processing capacity of up to 3 000 tonnes of dry substance and a maximum electric capacity of 100 kWe. During its implementation, however, the project suffered two major setbacks: legal and political barriers were encountered to implementing the project at the Straubing wastewater treatment plant, and unexpected technical problems occurred in the construction of the designed system. But close co-operation with all team members resulted in the development of appropriate solutions. Thus, despite a substantial delay, the project was closed successfully following promising results of the first test operations performed in September 2011. Long-term plant operation was scheduled to begin early 2012. The contractual agreement between the project beneficiary, Huber and the municipality of Straubing includes a half-year period of additional test runs followed by a half-year monitoring phase to be performed by Huber. Support for the idea that energy self-sufficient sewage sludge incineration can be achieved at Straubing was a result of the project. A substantial approach to saving energy is the energetic optimisation of the belt dryer and best possible utilisation of the incineration exhaust heat. The long-term social benefits are related to the safe use of sludge in terms of health and the prevention of unpredictable risks linked to the agricultural use. The method was also shown to be economically viable thanks to stable disposal costs. Co-firing additional municipal biomass residues (such as screenings, grass clipping, bush and tree cuttings, composting residues) also reduces costs. Moreover, the project results can be used to manufacture modular units for implementing the concept in other European WWTPs without any additional development costs. The transfer of the validated concept to other application fields – e.g. small-scale biomass fired Combined Heat and Power (CHP) plants – will enhance the exploitation of renewable energy sources and thus contribute to the reduction of greenhouse gas emissions in line with climate change commitments. Further information on the project can be found in the project's layman report (see "Read more" section).