Energy use of biogas hampered by the presence of siloxanes

Siloxanes are widely used in industrial processes and consumer products. Some of them reach the wastewater. Siloxanes are not decomposed in the activated sludge process and partly concentrate in the sludge. During anaerobic digestion of the sludge, they volatilise into the formed biogas. Combustion of silicon containing gases, e.g., when producing electricity, produces, however, the abrasive microcrystalline silica that has chemical and physical properties similar to those of glass and causes serious damage to gas engines, heat exchangers and catalytic exhaust gas treatment systems. The growing consumption of silicones and siloxanes and the subsequent increased concentration in wastewater, together with the increasing interest in the production of biogas and 'green energy' in sewage treatment plants, has created significant concern about the presence of siloxanes and the related damage (fouling etc.) in the biogas beneficiation equipment. The present paper, therefore, reviews the fundamentals of siloxanes and the current problems of the associated fouling. Moreover, it summarizes the useable methods for siloxane abatement from biogas and makes some recommendations towards preventive actions