Nitrificación de aguas residuales con reactores circulantes de lecho flotante

The Circulating Floating Bed Reactor (CFBR) presents some peculiar characteristics as wastewater treatment system. This system is an airlift reactor with rectangular section, easy to operate and design, and uses a rough granular product of plastic in which the biofilm grow take place. The density of the support was 890 kg/m³. The three-phase separator, which is required to separate the treated wastewater from the biofilms is located at the bottom of the system, this being a special characteristic of the system, compared with other bioreactors in which is more common to use a gravity settler. The main objective of this research was to study the evolution of the biomass and nitrifying capacity of a CFBR, which was fed with an autotrophic medium with 50 mg N-NH⁺₄/L and was operated with 1 h HRT. During the operation, the ammonia removal percentage was comprehended between 90 and 97% and the volumetric nitrification rate was 1.1 kg N-NH⁺₄/m³·d. During a first stage, first 60 operating days, accumulation of nitrite in the system ocurred, the accumulation being result of two factors: i) inhibition of nitrite oxidation to nitrate by free ammonia accumulation, during the first 15 operating days, ii) A pseudo-stationary state of the system on biomass concentration (days 20-60) which limited the nitrite oxidising capacity of the biofilm. Nitrite accumulation ceased when ammonia was replaced by nitrite in the feeding medium during 10 days, which caused an increase of the nitrite oxidising capacity of the biofilm. Nitrifying biomass growth took place in pores and cavities of the plastic support. 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 ammonia specific oxidation rate were determined. Ammonia specific oxidation rate was 0.57, 1.42 and 1.97 g N-NH⁺₄/g-proteine-d and nitrite specific oxidation rate was 1.21, 2.84 and 4.59 g N-NO⁺₂/g-proteine·d at temperatures of 10, 20 and 30 °C.