An arrangement for aftertreatment of exhaust gas for lean-burn internal combustion engines such as diesel engines and Otto engines with direct injection has a NOx storage catalyzer installed in the exhaust gas train for reducing nitrogen oxides and at which nitrogen oxides are stored in lean operating phases and these stored nitrogen oxides are reduced in rich operating phases. A security module is inserted in the plug-in socket. A floating wave attenuator comprising: a wall having an exterior surface and an interior surface; a flange associated with the wall and extending from at least one of the exterior surface and the interior surface of the wall; and an air chamber in the interior of the wall, the air chamber being filled with air to adjust the buoyancy of the attenuator. The orthogonal blade set preferably includes straight blades and orthogonal blades, each having a spring or frictional member for frictionally engaging a respective portion of a friction bar.