Thermochemical decomposition of sewage sludge - An eco-friendly solution for a sustainable energy future by using wastes

Abstract

The study aims to promote clean energy technologies that ensure the recycling and recovery of waste, namely the sewage sludge (SS), by converting it into products (e.g. oil, gas) with added value, contributing thus to reducing the negative impact on environment and health. An experimental setup was proposed in order to achieve the pyrolysis process, by varying the heating rate, (5°C/min, 10°C/min and 50°C/min). The resulted products, namely i) char - SSPyChar, ii) oil - SSPyOil and iii) gas - SSPyGas, were investigated in terms of elemental content, high heat value (HHV), low heat value (LHV) and emission factor (EF). The pyrolysis oils obtained with lower heating rate, 5°C/min and 10 °C/min, presented higher HHV, in comparison with the oils obtained at 50 °C/min, which were rich in water. These oils can have a negative impact on the environment, through their combustion due to their high content of N (6 wt%) and S (1.2 wt%), responsible for the formation of NOx and SOx. Pyrolysis gas revealed in its composition high contents of hydrocarbons (C1-C6), carbon dioxide (CO2) and hydrogen (H2). The highest HHV was obtained by using 5°C/min increment, namely 33.81 MJ/m3. Also, the pyrolysis gases had comparable energy values with natural gas, biogas or gases resulted from the plastic pyrolysis.