Influence of dissolved oxygen on the nitrification kinetics in a circulating bed biofilm reactor

Abstract

The in¯uence of dissolved oxygen concentration on the nitri®cation kinetics was studied in the circulating bed reactor (CBR). The study was partly performed at laboratory scale with synthetic water, and partly at pilot scale with secondary ef¯uent as feed water. The nitri®-cation kinetics of the laboratory CBR as a function of the oxygen concentration can be described according to the half order and zero order rate equations of the diffusionreaction model applied to porous catalysts. When oxygen was the rate limiting substrate, the nitri®cation rate was close to a half order function of the oxygen concentration. The average oxygen diffusion coef®cient estimated by ®t-ting the diffusion-reaction model to the experimental results was around 66% of the respective value in water. The experimental results showed that either the ammonia or the oxygen concentration could be limiting for the nitri®cation kinetics. The latter occurred for an oxygen to ammonia concentration ratio below 1.5±2 gO 2 /gN-NH 4for both laboratory and pilot scale reactors. The volumetric oxygen mass transfer coef®cient (k L a) determined in the laboratory scale reactor was 0.017 s A1 for a super®cial air velocity of 0.02 m s A1 , and the one determined in the pilot scale reactor was 0.040 s A1 for a super®cial air velocity of 0.031 m s A1 . The k L a for the pilot scale reactor did not change signi®cantly after bio®lm development, compared to the value measured without bio®lm. List of symbols

Nitrification in fixed-bed reactors treating saline wastewater

“…Attached growth on surfaces of support materials has many advantages as compared to suspended growth in flocs or granules, for instance a long sludge retention time, prevention of washout of biomass and better process tability in terms of withstanding shock loadings or short-term inhibitory effects (Fitch et al 1998, Nogueira et al 1998). …”

Effect of wall growth on the kinetic modeling of nitrite oxidation in a CSTR

“…Therefore, biofilm growth is not limited by the concentration of DO, even at the highest dilution rates of CSTR operation. Nogueira et al (1998) have also concluded that the nitrification rate is not affected for a biofilm thickness of 179 mm and DO concentrations in the bulk liquid above 3.5 mg O 2 /L (for uncontrolled pH) and 5.3 mg O 2 /L (for controlled pH). Moreover, the maximum active thickness of the biofilm (L max ), calculated by Equation (10) for zero DO concentration on the wall barrier, is 237 mm, which is in close agreement with the reported values of average oxygen penetration depth in biofilms that are around 100-200 mm (De Beer et al, 1993).…”

“…Considering dissolved oxygen (DO) as the only limiting substrate of biofilm growth, the minimum DO concentration at the wall barrier of a biofilm with maximum active thickness L max ¼ 48 mm can be calculated using Equation (10) with ''S'' denoting the DO concentration. Taking the value 0.01512 dm 2 /d for the oxygen diffusion coefficient (D s ), as reported by Nogueira et al (1998) for a nitrifying biofilm, and the growth yield coefficient of oxygen Y O 2 ¼ 0:67 mg biomass=mg À O 2 (IAWPRC, 1987), the minimum DO concentration on the wall barrier is found to be 7.1 mg O 2 /L. Therefore, biofilm growth is not limited by the concentration of DO, even at the highest dilution rates of CSTR operation.…”

Addition of sodium nitrite and biofilm in a Litopenaeus vannamei biofloc culture system

“…When suspended, microorganisms move freely in the water, providing direct contact between bacterial cells and the water mass. When attached, microorganisms grow on a layer adhered to a solid surface, which can be artificial or natural depending on the rearing system that is used (Fitch et al, 1998;Nogueira et al, 1998). In the biofloc culture systems, both the microbial community that is formed suspended in the water (bioflocs) and the biofilm (formed on the artificial substrates) can contribute to the metabolism of the nitrogen compounds generated within the culture (Schveitzer et al, 2013;Viau et al, 2013).…”