B. Capdeville

Dextran blue colorant as a reliable tracer in submerged filters

Abstract A reliable method to evaluate residence time distribution in submerged filters is presented. This method is useful even when using a porous packing. The tracer employed is Dextran blue, which is better detected in the u.v.-zone (220 nm). The advantage of this colorant is that it avoids the tailing phenomenon, allowing accurate mean retention time evaluation. The tailing phenomenon is explained using the diffusion theory.

The effect of air superficial velocity on biofilm accumulation in a three-phase fluidized-bed reactor

Abstract The aim of this investigation was to evaluate the effect of air superficial velocity ( U G ) on biofilm growth in an aerobic three-phase fluidized-bed reactor. Spherical shape polymer particles (2.7 mm diameter and density of 1180 kg·m −3 ) were used as support material. The reactor influent was a synthetic wastewater, mainly composed of glucose, glycerine and meat extract (COD of about 180 mg·l −1 ) and reactor operation was carried out at an organic load of about 8 kg COD·m −3 ·d −1 . The results indicate that biofilm accumulation decreases when gas superficial velocity increases in the range of 0–20 m·h −1 . However, COD removal efficiencies were practically independent of U G , whereas biofilm characteristics were significantly affected by air superficial velocity.

Selected dyes for residence time distribution evaluation in bioreactors

A selection of dyes for tracer studies in bioreactors, specially for wastewater treatment, is presented. Substances that showed no adsorption on air or biomass, stability in time, good solubility and no color change between pH 6.5 to 8.5, were: bromocresol green, bromophenol blue, dextran blue, eosin Y and mordant violet. Consequently they seem to be adequate for common biochemical engineering processes. In addition, dyes that showed some limitations, but may be employed in special cases, were: bromophenol red and phenol red (color change between pH 5.0 to 6.8 and 6.8 to 8.4 respectively) and methylene violet Bernsthen (low spectrophotometric response).

Kinetic behaviors of nitrifying biofblm growth in wastewater nitrification process

Abstract A conventional laboratory scale annular reactor was employed to investigate the growth dynamics of nitrifying biofilm. A dense and thin nitrifying biofilm was developed in the reactor. It was found that the feed concentration (So) has a significant effect on the performance of the nitrifying biofilm reactor. It was demonstrated that the biological constants are strongly dependent on So. The same is true for the volumetric removal rate of substrate (kov), which shows that the process always depends on the reaction. The results indicated that thinner biofilms ranging from 15 to 20μm have a higher specific nitrification rate, that is, the biological reaction of ammonium nitrogen probably occurs at the biofilm‐liquid interface. It is preferable to use thin biofilm for an attached culture. Meanwhile, it was shown that in this system high nitrification capacities could be reached.. It was expected to have promising possibilities to develop a new biological process specialized in wastewater nitrification.

Some observations on free ammonia inhibition to Nitrobacter in nitrifying biofilm reactor

SummaryFree ammonia inhibition to Nitrobacter population in a nitrifying biofilm was investigated. It was found that when the tree ammonia concentration is greater than 0.1 mgN/l the oxidative activity of Nitrobacter was significantly inhibited, and resulting in a transient accumulation of nitrite ions. The results show that Nitrobacter population is capable of rapidly recovering its lost metabolic activity once the free ammonia concentration becomes less than 0.1 mgN/l, and a complete oxidation of nitrite to nitrate was achieved.

Oxygenation par le peroxyde d'hydrogene des biomasses fixees utilisees en traitement biologique des eaux

Because of their advantages as compared to flocculated biomass processes, there is now a revival of interest in fixed biomass processes: no mishaps due to bad flocculation, particularly with filamentous organisms (bulking) compact equipment owing to the ability to obtain greater biomass concentrations (several g l−1), which is impossible in flocculated biomass. In this paper, we will consider mainly bio-discs and submerged fixed bed filters. In bio-disc investigations, Hoehn and Rays (1973), Kornegay and Andrews (1968) now classical results showed that the bacterial film only acts on the surface, over a thickness which, at best, does not exceed 150 μm. At the same time, Bungays (1969) very accurate measurements showed that the film active thickness coincides with the depth where the oxygen concentration in the film is higher than the critical oxygen concentration. In submerged filters, Elmaleh (1976) and Grasmicks (1978) theoretical studies permit one to define a Useful Column Height (UCH) which corresponds to the active part of the reactor and which is superposed on the height where oxygen concentration is higher than the critical oxygen concentration. In classical devices, the UCH is relatively low: approx. 0.50-1 m. In both cases, the system is provided with oxygen through an exchange between the air and the effluent to be treated, at a gas-liquid interface. This procedure limits the O2 concentration to about 9 mg O2 l−1, at the ambient temperature. Therefore, to increase the UCH of a submerged reactor or the active thickness of a bio-disc film by increasing the oxygen penetrating depth, the oxygen partial pressure in the gas phase should be increased by either using pure oxygen or increasing total gas phase pressure. These two methods are somewhat difficult to use and we prefer to use another method: bringing dissolved oxygen directly into the liquid phase without the exchange at the gas-liquid interface. This is feasible by using an oxygen liberating labile chemical reagent i.e. hydrogen peroxide. We consider two types of fixed biomasses: the bio-discs and the submerged filters. Bio-discs. The apparatus used is shown in Fig. 1. The utilization of H2O2 resulted in a very sharp increase in the substrate removal efficiency. It is observed that the substrate removal efficiency (Figs 5 and 6) and the reduced pollution flux (Figs 4 and 7) show a maximum when these are plotted as a function of the ratio: equivalent quantity of O2 given by H2O2/O2 demanded by the effluent and as a function of dissolved oxygen in the liquid phase. Moreover, these curves suggest that oxygen acts as an inhibitor and different attempts at modeling, based on standard models of inhibiting effects, lead to the exponential model giving the lowest deviation (Fig. 8). Submerged packed reactors. The apparatus used is shown in Fig. 3. This unit is fed by urban effluents and the oxygenation in the reactor is carried out by using diluted H2O2 (0.5-1.5 N).

IMPROVEMENT OF THE ANAEROBIC DIGESTION OF DILUTED WHEY IN A FLUIDIZED BED BY NUTRIENT ADDITIONS

Abstract Anaerobic digestion of diluted whey was performed in two different fluidteed bed pilot reactors of 40 1 and 250 1 respective volume. Different operating conditions were tested. Without nutrient addition there is a maximum COD removal rate which is directly proportional to the packing medium volume. The corresponding specific maximum COD removal rate is of about 6 kg COD degraded. m‐3 packed bed volume. d‐3. Suitable nutrient additions, consisting mainly of iron, nickel and cobalt salts and of dried yeasts, allow a dramatic increase of this maximum rate up to about 40 kg COD degraded m‐3 packed volume. day‐1. This increase of COD removal rate is mainly due to higher biomass accumulation inside the reactor.

Response pattern of nitrifying biofilm reactor to shock loading

The effects of shock loading on the performance of a nitrifying biofilm reactor were investigated over a wide range of conditions by varying the feed concentration of ammonium (SO) and dilution rate (D) respectively. It was found that variation in the effluent ammonium concentration as SO or D changes was subject to a semi-U shaped curve. The response patterns of the nitrifying biofilm reactor to one-step change in SO at a constant dilution rate, and to one-step change in D with keeping constant SO have no significant difference.