Nitrification of waste waters with circulating floating bed reactors

The Circulating Floating Bed Reactor (CFBR) presents some peculiar characte ristics as wastewater treatment system. This system is an airlift reactor w ith rectangular section, easy to operate and design, and uses a rough granu lar product of plastic in which the biofilm grow take place. The density of the support was 890 kg/m(3). The three-phase separator, which is required to separate the treated wastewater from the biofilms is located at the bott om of the system, this being a special characteristic of the system, compar ed with other bioreactors io which is more common to use a gravity settler. The main objective of this research was to study the evolution of the bioma ss and nitrifying capacity of a CFBR, which was fed with an autotrophic med ium with 50 mg N-NH4+/L and was operated with 1 h HRT. During the operation , the ammonia removal percentage was comprehended between 90 and 97% and th e volumetric nitrification rate was 1.1 kg N-NH4+/m(3.)d. During a first st age, first 60 operating days, accumulation of nitrite in the system ocurred , the accumulation being result of two factors: Q inhibition of nitrite oxi dation to nitrate by free ammonia accumulation, during the first 15 operati ng days. ii) A pseudo-stationary state of the system on biomass concentrati on (days 20-60) which limited the nitrite oxidising capacity of the biofilm . Nitrite accumulation ceased when ammonia was replaced by nitrite in the f eeding medium during 10 days, which caused an increase of the nitrite oxidi sing capacity of the biofilm. Nitrifying biomass growth took place in pores and cavities of the plastic s upport. The growth of biomass was not observed onto the external surface of the support in which the shear stress is stronger. Both, the nitrite and a mmonia specific oxidation rate were determined. Ammonia specific oxidation rate was 0.57,1.42 and 1.97 g N-NH4+/g-proteine(.)d and nitrite specific ox idation rate was 1.21, 2.84 and 4.59 g N-NO2/g-proteine(.)d at temperatures of 10, 20 and 30 degreesC.