Die Abreinigung der wässrigen Phase des thermokatalytischen Reforming (TCR®) von Klärschlamm mittels innovativer elektrochemischer Prozesstechnik und begleitender Gewinnung von Wertstoffen

The present work deals with the analysis of the chemical composition of the aqueous phase from the conversion of dried sewage sludge by means of the thermo-catalytic reforming (TCR®) process. In addition, a 3-step purification strategy is presented that allows extensive purification of this aqueous phase while recovering secondary raw materials. The aim of the investigations is the pretreatment of the aqueous phase as a prerequisite for the final purification in a wastewater treatment plant and the associated recovery of raw materials as an alternative to the currently practiced disposal in a hazardous waste incineration. The development of the purification strategy is based on the analysis of the chemical composition of the aqueous phase, taking into account the legal framework and the resulting economic consequences. The cleaning strategy, which is focused on electrooxidation by means of boron-doped diamond electrodes, allows a reduction of the organic carbon of more than 80 %. The inorganic carbon can be removed almost completely, and the ammonia contained can be removed by more than 90 %. The mentioned chemical compounds can be recovered in the form of lime or ammonium sulfate. In
addition, hydrogen can be recovered during the electrooxidative treatment of the aqueous phase. The here developed cleaning strategy has clear advantages over the disposal of the aqueous phase practiced to date. For example, the cleaning strategy developed allows the aqueous phase to be precleaned at the TCR® plant site, while at the same time recovering valuable materials. During pretreatment, an average of 307 g of lime and 160 g of ammonium sulfate per liter of aqueous phase can be recovered. In addition, approx. 15 % of the electrical energy required for the removal of the
organic carbon can be recovered in the form of hydrogen. Open questions include a possible integration of the developed cleaning strategy into the TCR® process as well as a comprehensive consideration of the economic efficiency. As soon as these questions have been clarified, the developed cleaning strategy can be tested and established on an industrial scale.