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 zeolite containing expanded clay aggregate filtermedia (Filtralite ZL). The filter removed ammonium from domestic wastewater by a combination of nitrification and ion exchange. An identical filter material, but without sorptive capacity with respect to ammonium, was used as a reference (Filtralite). The experiments demonstrated that Filtralite ZL removed more ammonium at high 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 demonstrated in experiments with constant ammonium loading for periods up to 10 days and as well as in experiments with daily variations in ammonium loading rate. No chemical regeneration was necessary in addition to the biological regeneration during the experimental period of four months.</jats:p

The influence of carrier size and shape in the moving bed biofilm process

The moving bed biofilm process is based on plastic carriers on which biomass attaches and grows. The original Kaldnes carrier was made of high-density polyethylene (density 0.95 gcm−1) that could be used in filling fractions (volume of carriers in empty reactor) up to 70% that gives a specific area of 350 m2m−3. Lately there has been an interest in the use of larger carrier elements, especially when using the process for upgrading of activated sludge plants. This paper analyses the influence of the carrier size and shape on performance, especially related to highly loaded plants working on municipal wastewater. The results demonstrate that moving bed biofilm reactors should be designed based on surface area loading rate (g COD/m2d) and that shape and size of the carrier do not seem to be significant as long as the effective surface area is the same. The results indicate that very high organic loads can be used in order to remove soluble COD but that the settleability of the sludge is negatively influenced at high loading rates.</jats:p

Enhanced removal of ammonium by combined nitrification/adsorption in expanded clay aggregate filters

Long-term experiments were carried out on a nitrifying biofilter with a zeolite-containing expanded clay aggregate filter media (Filtralite ZL) receiving daily peak loads of ammonia. The filter removed ammonium from domestic wastewater by a combination of nitrification and sorption of ammonium. The filter was biologically regenerated continuously and there was no deterioration in performance after 10 months of continuous experiments. Isotherm experiments confirmed that the Filtralite ZL granules that had been used for more than 8 months had about the same capacity as the unused material. Desorption experiments that were carried out indicated that desorption of ammonium from the filter material was mainly caused by an exchange of cations from the wastewater even at low cation concentrations.</jats:p