The final step for achieveing maximum NOx reduction is to combine ROFA and ROTAMIX with a catalyst (SCR).

The first two steps (ROFA & ROTAMIX) jointly produce reduction rates of up to 75%. When using SCR as an "ammonia killer" ROFA and ROTAMIX by itself may reduce NOx up to 90%. Together with the NOx reduction from the SCR itself, very high NOx reduction can be achieved.

Since the first two steps have significantly reduced the NOx, the catalyst can be built considerably smaller, resulting in small investment costs for the catalyst.

With the three steps combined (ROFA, ROTAMIX and SCR), NOx reduction well above 95% can be achieved.