ANALYSIS OF SEWAGE SLUDGE THERMAL TREATMENT METHODS IN THE CONTEXT OF CIRCULAR ECONOMY

Abstract

As of now, the most common applications of sewage sludge treatment and disposal methods globally are in agriculture and deposition in landfills. In particular, landfill disposal causes problems associated with environmental pollution, as well as problems caused by the loss of the chance to recover energy and nutrients out of the sewage sludge. The critical content of hazardous substances in the sewage sludge makes its use in agriculture as fertilizer questionable. Thermal treatment methods offer a solution to these problems because energy can be recovered and used, some hazardous materials can be destroyed or removed, and valuable nutrients such as phosphorus can be utilized in the generated products or recovered from these products. In a first step, the objective and scope of the study and especially the important characteristics of the circular economy when considering sewage sludge treatment possibilities is described. Based on these characteristics for the three investigated thermal treatment methods – incineration, gasification and pyrolysis – a comparative analysis on the basis of a suggested set of criteria (1. cost, 2. energy efficiency, 3. nutrient recovery, 4. product market value and 5. flexibility) was carried out. In the result, incineration of sewage sludge performs best in terms of treatment costs, energy efficiency, nutrient recovery, and flexibility concerning feedstock dry matter content. Pyrolysis performs best in terms of market value of the generated products and flexibility regarding plant size.