Enhancing the removal of ammonia in nitrifying biofilters by the use of a zeolite containing expanded clay aggregate filtermedia

Pilot plant experiments were carried out on a nitrifying biofilter with a z eolite containing expanded clay aggregate filtermedia (Filtralite ZL). The filter removed ammonium from domestic wastewater by a combination of nitrif ication and ion exchange. An identical filter material, but without sorptiv e capacity with respect to ammonium, was used as a reference (Filtralite). The experiments demonstrated that Filtralite ZL removed more ammonium at hi gh ammonium loading rates than Filtralite. This was caused by ion exchange of ammonium in addition to nitrification. Under low ammonium loading rates, nitrification of already sorbed ammonium took place. This combined effect of ion exchange and nitrification of ammonium in Filtralite ZL was demonstr ated in experiments with constant ammonium loading for periods up to 10 day s and as well as in experiments with daily variations in ammonium loading r ate. No chemical regeneration was necessary in addition to the biological r egeneration during the experimental period of four months.