Nanou, P., Pels, J.R., Sebastiani, F., van der Meijden, C.M., Kuipers, H., Driessen, W., Vogelaar, J., TNO, The Netherlands(free)
Sewage sludge is a waste stream produced at urban wastewater treatment plants (WWTP) and is largely being disposed of by truck transportation and incineration. With existing technologies sewage sludge can be dewatered up to 23% DM and therefore makes current method of disposal inefficient and unsustainable. ECN part of TNO has developed a hydrothermal treatment technology (TORWASH®) which is capable of improving the dewatering and the quality of sewage sludge as a fuel without the use of flocculants. Also, the mild thermal treatment conditions render the effluent digestible.
A continuous, 50-L/h TORWASH® pilot plant was constructed and commissioned at the urban WWTP of Almere, The Netherlands, where tests were successfully realized with sewage sludge, containing 36% DM. The sewage sludge after TORWASH® treatment was pressed into a solid cake containing 5065% DM. This proves that the sewage sludge waste stream can be reduced by 80-85%. The chemical oxygen demand (COD) of the water stream could be converted by 60-70% and the dewatered cake was pressed into pellets with a calorific value of 16-18 MJ/kg. These results show that wastewater treatment can become cheaper for citizens, and that WWTP’s can become more sustainable by generating their own bio-based energy.