The recovery of ammonium from sludge liquor using the ion exchanger loop stripping process was studied at a pilot scale plant at a municipal waste water treatment plant. The ion exchanger loop stripping process combines ion exchange and air stripping in a hybrid process and works with fixed bed columns containing natural zeolite (mainly clinoptilolite), which is alternately loaded and regenerated. The sodium hydroxide regeneration solution is simultaneously air stripped. Ammonium is recovered in a subsequent acid scrubber as concentrated ammonium sulfate solution, which is a suitable reducing agent for industrial off-gas treatment [nitrogen oxide (NOx) removal]. Pilot scale experiments demonstrated the technical feasibility of the process. The zeolite ion exchange capacity was stable over 62 loading and regeneration cycles. Ammonium removal rates of 69-94% were achieved in consecutive loading and regeneration cycles, when sludge liquor with a treatment capacity of 500 L h−1 and typical input concentrations from 500-1,500 mg NH4+ L−1 was treated.