Activity control in nitrifying biofilms: application of respirometric tests

Nitrification is the biological oxidation of ammonia to nitrate via nitrite. These reactions are performed by aerobic autotrophic microorganisms, commonly known as nitrifiers. The nitrifiers are generally constituted of ammonia oxidizing bacteria and nitrite oxidizing bacteria. They are very sensitive to environmental factors, namely the pH, which has its optimum value in the range of 7.5 to 8.5 (Sharma end Ahlert, 1977) A simple method, the respiration rate measurement, has been extensively used in literature to characterize microbial populations in suspended cultures (Kristensen et al., 1992, Nowak and Svardal, 1993) and to monitor the nitrification performance of immobilized nitrifiers (Nakamura et al., 1995) and nitrifying activated sludge processes (Surmacz-Gorska et al., 1996). Respiration refers to reactions that use oxygen as an electron acceptor. The aim of the present study is to characterize the functional microorganism groups of a nitrifying biofilm using a simple microbial activity measurement, the respiration rate, and to use this information to identify disturbances that have an impact on process performance

Thermodynamically stable noncomposite vortices in mesoscopic two-gap superconductors

In mesoscopic two-gap superconductors with sizes of the order of the coherence length noncomposite vortices are found to be thermodynamically stable in a large domain of the $T - H$ phase diagram. In these phases the vortex cores of one condensate are spatially separated from the other condensate ones, and their respective distributions can adopt distinct symmetries. The appearance of these vortex phases is caused by a non-negligible effect of the boundary of the sample on the superconducting order parameter and represents therefore a genuine mesoscopic effect. For low values of interband Josephson coupling vortex patterns with $L_1 \neq L_2$ can arise in addition to the phases with $L_1 =L_2$, where $L_1$ and $L_2$ are total vorticities in the two condensates. The calculations show that noncomposite vortices could be observed in thin mesoscopic samples of MgB$_{2}$.Comment: 5 pages, 3 figures, to be published in Europhysics Letter

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

The influence of dissolved oxygen concentration on the nitrification 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 effluent as feed water. The nitrifi- 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 diffusion-reaction model applied to porous catalysts. When oxygen was the rate limiting substrate, the nitrification rate was close to a half order function of the oxygen concentration. The average oxygen diffusion coefficient estimated by fitting 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 fication kinetics. The latter occurred for an oxygen to ammonia concentration ratio below 1.5-2 gO2/gN-NH4+ for both laboratory and pilot scale reactors. The volumetric oxygen mass transfer coefficient (kLa) determined in the laboratory scale reactor was 0.017 sˉ¹ for a superficial air velocity of 0.02 m sˉ¹, and the one determined in the pilot scale reactor was 0.040 sˉ¹ for a superficial air velocity of 0.031 m sˉ¹. The kLa for the pilot scale reactor did not change significantly after biofilm development, compared to the value measured without biofilm.Fundação para a Ciência e a Tecnologia (FCT) - PRAXIS XXI, project 2/2.1/Bio/37/94.INTERREG

Behavior of Eucalyptus grandis and E. cloeziana seedlings grown in arsenic-contaminated soil.

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Avaliação da atividade celulásica e quitinásica de estirpes de Bacillus thuringiensis ativas contra Spodoptera frugiperda, Anticarsia gemmatalis e Anthonomus grandis.

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