Preparation of carbon-based adsorbents from pyrolysis and air activation of sewage sludges

The pyrolysis of 10 sewage sludges (5 anaerobic and 5 aerobic) from the Madrid region (Spain) was carried out at 450 °C during 1 h in a vertical glass-furnace. A thorough characterisation of sewage sludges was performed in order to study the influence of their properties on the pyrolysis process. Both anaerobically and aerobically stabilized sewage sludges that lead to pyrolysed materials with higher carbon content (38.6 and 43.4 wt.%, respectively) were selected for the preparation of carbon-based adsorbents. These two materials were air-activated at 275 °C during 4 h in order to improve their properties. After that, the BET surface area of carbon-based materials increased from 16 to 102 m2/g for the aerobic sludge and from 81 to 105 m2/g for the anaerobic one. These results showed that pyrolysis of sewage sludges using lower pyrolysis temperatures and air activation could be an interesting alternative route for the inexpensive and environmentally acceptable synthesis of carbon-based adsorbents.