Using focused pulsed technology to remove siloxane from municipal sewage sludge

Siloxanes, impurities in the biogas produced from anaerobic digestion of wastewater sludges, are transformed to silica dioxide sand during combustion of the biogas, which damages the heat exchanger and engine. Decamethylcyclopenta-siloxane (D5) and octamethylcyclotetra-siloxane (D4) were added to return activated sludge (RAS) and treated using a pulsed-electric field method [focused pulsed (FP)] that makes the sludge solids more readily converted to methane. With an FP treatment intensity (TI) of 36 kWh/m3-RAS, the D4, and D5 removal efficiencies were 32±4.0 and 11±0.2%, respectively. Removals of D4 and D5 increased proportionally with TI whether TI was affected by sludge conductivity or FP pulse frequency. FP treatment of activated sludge before methanogenic batch tests lowered the amount of both siloxanes in the produced biogas, and evidence suggests that the siloxanes were biotransformed during the batch tests.