Use of sewage sludges for CO2 removal

Sewage sludge from the Turin water purification system (SMAT; TO) is first anaerobically digested for biogas production and then used as filter material. Filter material for the purification of biogas produced by anaerobic digestion. The digested sludge must be appropriately treated. The case study was focused on the technical feasibility of the process. These samples were adopted for the removal of carbon dioxide from a biogas mixture. A sensitivity analysis was performed considering the main process parameters (temperature, residence time, activation agent, heating rate and activation flow rate). The sludge is characterised by its irregular shape and size, ranging from 1 mm to approximately 2 cm in equivalent diameter. Activation of the ground sludge was carried out in a tubular stainless steel reactor 57 cm long and 3.4 cm in outside diameter. A cylindrical electric furnace was adopted for the pyrogasification process, using N2, CO2 or air as the activating agent. A temperature control regulator, ranging from 200 to 600 °C, was adopted. These lower values compared to the literature are related to the coupling of SOFC discharges as possible agents for char production. Temperature and residence time are the most relevant parameters for char production with the pyrogasification process from sewage sludge. Temperature is the parameter that most influences the char production value. The biogas mixture (CH4/CO2=1.5) was considered. The untreated material shows an adsorption capacity of 4 mg/g, while the physically activated material shows a maximum value of about 102.5 mg/g. Future work will focus on the chemical activation of this sludge to investigate its gas-cleaning potential.