Biomedical subjects

A Héduit

Publications and source records attributed to A Héduit.

6 recordsLinked to original sources

PubMed2005

Predicting oxygen transfer of fine bubble diffused aeration systems--model issued from dimensional analysis.

The standard oxygenation performances of fine bubble diffused aeration systems in clean water, measured in 12 cylindrical tanks (water depth from 2.4 to 6.1m), were analysed using dimensional analysis. A relationship was established to estimate the scale-up factor for oxygen transfer, the transfer number (N(T)) The transfer number, which is written as a function of the oxygen transfer coefficient (k(L)a(20)), the gas superficial velocity (U(G)), the kinematic viscosity of water (nu) and the acceleration due to gravity (g), has the same physical meaning as the specific oxygen transfer efficiency. N(T) only depends on the geometry of the tank/aeration system [the total surface of the perforated membrane (S(p)), the surface of the tank (S) or its diameter (D), the total surface of the zones covered by the diffusers ("aerated area", S(a)) and the submergence of the diffusers (h)]. This analysis allowed to better describe the mass transfer in cylindrical tanks. Within the range of the parameters considered, the oxygen transfer coefficient (k(L)a(20)) is an increasing linear function of the air flow rate. For a given air flow rate and a given tank surface area, k(L)a(20) decreases with the water depth (submergence of the diffusers). For a given water depth, k(L)a(20) increases with the number of diffusers, and, for an equal number of diffusers, with the total area of the zones covered by the diffusers. The latter result evidences the superiority of the total floor coverage over an arrangement whereby the diffusers are placed on separate grids. The specific standard oxygen transfer efficiency is independent of the air flow rate and the water depth, the drop in the k(L)a(20) being offset by the increase of the saturation concentration. For a given tank area, the impact of the total surface of the perforated membrane (S(p)) and of the aerated area (S(a)) is the same as on the oxygen transfer coefficient.

Air Movements↗

PubMed2002

Modeling acidogenic and sulfate-reducing processes for the determination of fermentable fractions in wastewater.

The biochemical acidogenic potential (BAP) of a wastewater is the maximum concentration of volatile fatty acids (VFAs) that can be measured at the end of an anaerobic fermentation test. A model was constructed to describe the acidogenic reactions occurring during BAP tests and to divide the BAP into organic fractions. The model was calibrated with a set of specific experiments highlighting the role of sulfate-reducing bacteria on acidogenic processes, which description was necessary for correct parameter identification. The model could describe acidogenic fermentation processes, with or without sulfate reduction, at 20 degrees C, for 13 wastewaters of different origin, composition, and settleability using the same optimized parameters. A simplified version of the model, without sulfate reduction, was able to describe VFA production by the adjustment of only three variables: readily fermentable organic matter (Sf), anaerobically hydrolyzable organic matter (Xf), and heterotrophic acidogenic biomass (Xha), which proved to be coherent with the experimental BAP value. The combination of the BAP test and the model developed in this study resulted in a new reliable tool to characterize wastewater under anaerobic conditions. As VFAs are the main substrates for phosphate-accumulating organisms (PAOs), the use of organic fractions VFA, Sf, Xf, and Xha in wastewater treatment plant modeling could improve the predictability and optimization of enhanced biological phosphorus removal (EBPR) processes.

Bacteria, Anaerobic↗

PubMed2002

Hydrogen peroxide (H2O2) as a source of dissolved oxygen in COD-degradation respirometric experiments.

Two different re-oxygenation techniques (aeration and hydrogen peroxide addition) were compared in respirometric experiments. As similar results were obtained in both cases, it was concluded that the addition of hydrogen peroxide does not modify the oxygen uptake rate of the biomass, under either endogenous or feeding conditions. It was hypothesized that under those experimental conditions (inhibition of nitrification with ATU), hydrogen peroxide alters neither the biomass metabolism nor the biodegradability of the tested substrates. The oxygen uptake rates obtained with the aeration system were often more scattered due to the adhesion of fine bubbles after the switch off of the aeration. Moreover, the transfer rate of oxygen to the solution is faster in the case of hydrogen peroxide addition.

Bacteria↗

PubMed2002

Operating conditions for the determination of the biochemical acidogenic potential of wastewater.

The aim of this work was to study the test conditions for the determination of the biochemical acidogenic potential (BAP) of wastewater, which should be useful to predict the performance of enhanced biological phosphorus removal (EBPR). Proposed operating conditions for a simple and reproducible BAP test in 250 ml serum bottles (equipped with black butyl stoppers and magnetic bars) are: use of either frozen or fresh water, no inoculum addition, fermentation carried out in the dark during 15 days, addition of 1 mM bromo-ethane sulfonate (BES) and 2 mM barium chloride (BaCl2), stirring speed strong enough to maintain vortex conditions, no pH control and controlled temperature of 20 degrees C.

Bioreactors↗

PubMed2001

Transfer number in fine bubble diffused aeration systems.

On the basis of full-scale data from 58 clean water tests performed in 26 activated sludge tanks equipped with fine bubble diffusers and of a theoretical approach, it can be stated that fine bubble aeration systems with total floor coverage arrangement provide higher kLa values and the lowest spiral liquid circulation. An efficiency criterion for oxygen transfer (NT) was defined on the basis of the dimensional analysis. The transfer number NT allows us to take account of the impact of vertical liquid circulation movements on oxygen transfer. The values of NT calculated from the results of full scale nonsteady-state clean water tests vary from 5.3 x 10(-5) to 9.1 x 10(-5) and are directly dependent upon the arrangement of air diffusers. It has been shown that the highest transfer numbers corresponded to the total floor coverage arrangement and the average calculated NT values is 7.7 x 10(-5), independently of the diffuser density and of the gas velocity, over the ranges studied. The lowest transfer numbers are obtained when the diffusers are located in separate grids, and the transfer number is reduced with increasing air flow rate.

Air Movements↗

PubMedDate not supplied

Specificity and potential applications of the biochemical acidogenic potential method for the anaerobic characterization of wastewater.

The biochemical acidogenic potential (BAP) test is an anaerobic characterization method for wastewater. Fermentable organic fractions are obtained through modeling BAP test results. This method was compared to more common fractionation methods such as settling, coagulation, and respirometry, but no direct relationship was found. Biochemical acidogenic potential testing was thus considered to bring new and complementary information. The settleable matter accounted for approximately 50% of the fermentable matter, with a rate comparable to that of aerobic hydrolysis, suggesting a potential assimilable carbon source that could be liberated in sewers or in anaerobic processes. It was also observed that respirometry could underestimate the amount of fermentable substrates while overestimating that of hydrolyzable matter and of heterotrophic biomass involved in anaerobic processes. The BAP fractions are related to the wastewater capacity to produce volatile fatty acids, which are the main substrates of the micro-organisms responsible for enhanced biological phosphorus removal (EBPR). The potential contribution of the BAP fractionation to assist the design, operation, and modeling of the activated-sludge EBPR processes was discussed.

Bacteria, Anaerobic↗