When denitrification is followed by a physically separated nitrification step, the nitrates formed during nitrification must be recirculated. The nitrates are pumped back into the denitrification step, where the anoxic process splits the nitrate molecules into nitrogen and oxygen. This frees the nitrogen into the air. This application is best served by submersible recirculation pump types ABS XRCP and RCP, the submersible mixed flow column pump type ABS AFLX and the submersible propeller pump type ABS VUPX.

Treated wastewater may occasionally require further treatment. Local discharge rules may pose strict limits that cannot be fulfilled by even the most effective process, or a higher quality of effluent may be requested for its reuse. When tertiary treatment is needed, various levels of filtration can be applied, including very fine filtration. Often, however, a final step of mixing and aeration is sufficient to achieve the target. When this is the case, Sulzer's submersible mixer types ABS XRW and RW can be used, along with submersible aerator type ABS TA–TAK and disc diffuser system types ABS PIK, DS and Sucoflow.