Etienne Paul

Determination of carbon dioxide evolution rate using on-line gas analysis during dynamic biodegradation experiments

Respirometry is a precious tool for determining the activity of microbial populations. The measurement of oxygen uptake rate is commonly used but cannot be applied in anoxic or anaerobic conditions or for insoluble substrate. Carbon dioxide production can be measured accurately by gas balance techniques, especially with an on-line infrared analyzer. Unfortunately, in dynamic systems, and hence in the case of short-term batch experiments, chemical and physical transfer limitations for carbon dioxide can be sufficient to make the observed carbon dioxide evolution rate (OCER) deduced from direct gas analysis very different from the biological carbon dioxide evolution rate (CER).To take these transfer phenomena into account and calculate the real CER, a mathematical model based on mass balance equations is proposed. In this work, the chemical equilibrium involving carbon dioxide and the measured pH evolution of the liquid medium are considered. The mass transfer from the liquid to the gas phase is described, and the response time of the analysis system is evaluated.Global mass transfer coefficients (K(L)a) for carbon dioxide and oxygen are determined and compared to one another, improving the choice of hydrodynamic hypotheses. The equations presented are found to give good predictions of the disturbance of gaseous responses during pH changes.Finally, the mathematical model developed associated with a laboratory-scale reactor, is used successfully to determine the CER in nonstationary conditions, during batch experiments performed with microorganisms coming from an activated sludge system.

Survival of alginate-entrapped cells of Azospirillum lipoferum during dehydration and storage in relation to water properties

Survival of alginate-entrapped cells of Azospirillum lipoferum was studied during dehydration using a dry air stream and during prolonged storage at various constant water activity values (aw). During the drying operation, the viability loss remained almost constant from the initial water content to 0.35 g water/g dry weight (DW) corresponding to a 98.5% water removal, strongly increased until a water content of 0.25 g/g DW and then stopped until the end of the drying operational (final aw 0.18). A water content of 0.25 g/g DW (aw=0.55) corresponded to the critical point of the moisture sorption isotherm curve from which water became restricted to the dry material. A high drying rate (5 g/g DW per hour) was shown to be more detrimental for cell viability than a low drying rate (1.18 g/g DW per hour). When the product was stored in a closed chamber with a regulated aw (0.23), the number of living cells decreased during a short period (less than 15 days) corresponding to the product aw stabilization, and then remained constant for more than 150 days. In addition, cell survival during storage was not affected by aw values in the range 0–0.55. Above aw=0.55, the higher the aw and the storage duration, the lower the residual survival percentage. The influence of the drying and storage conditions on the cell death rate are discussed with regard to both the mechanisms generally involved in viability loss and the hydration properties of water.

Reduction of Excess Sludge Produced by Biological Treatment Processes : Effect of Ozonation on Biomass and on Sludge

The excess sludge produced during biological treatment of wastewater can be reduced by treating this sludge with ozone in a specific reactor and recycling it to the biological facility. This increases the biodegradability of the inert fractions of the sludge without deteriorating the activity of the microorganisms. Ozone reacts only within the film zone near the gas/liquid interface: it is assumed that the size of the microflocs of active microorganisms is greater than the effective thickness of the film, thus protecting them from ozone. This coupled treatment produces treated water having satisfactory characteristics and a residual excess sludge that has an extremely high settling capability.

Nitrification in hybrid reactor with a recycled plastic support material

This work investigated the nitrification in a hybrid moving bed pilot scale reactor, which used a low density recycled plastic support material for biomass growth. The filling rate was 20% of its working volume (22L). The feeding and recirculation outflow was 45L/day. The reactor operated at a temperature of 16oC, in two phases, according to the sludge retention time (SRT): A phase was 10 days and B phase was 3 days (average values). The applied average volumetric nitrogen and organic loads were 0.16KgTKN/m3.day and 1kgCOD/m3.day, respectively. The results showed an average nitrogen removal of 95% and average COD removal of 89%, in both A and B phases. Nitrogen removal rates were independents of the SRT.

Experimental Modeling of a Biofilter for Combined Adsorption and Nitrification

Abstract Biofilters consisting of packed bed columns are efficient devices for purification of ground- or wastewater from solid and toxic components. In this work, a biofilter for nitrification is equipped with a porous bed of Manganese dioxide particles, which offers the support for the formation of a biofilm and which, in addition, adsorbs ammonium. Experiments are performed to study the distributed parameter behavior of key state variables, e.g. biomass and nitrogenous components, and a dynamic model described by partial differential equations is derived. Several unknown model parameters are estimated from measurements collected in the course of these experiments. The resulting model is in good agreement with the experimental data.

DYNAMIC MODELLING OF A BIOFILTER USED FOR NITRIFICATION OF DRINKING WATER AT LOW INFLUENT AMMONIA CONCENTRATIONS

Abstract This paper reports on the development of a mathematical model of a packed bed biofilter operating at low influent ammonia concentrations. It is initially filled with biomass-free media, the adhesion by filtration of the bacteria present in the groundwater allowing colonization of the filter. The mathematical model is intended for simulation/optimization purposes, and should describe sufficiently well the start-up phase, as well as nominal operation. Unknown model parameters are estimated using experimental data collected on pilot plants. Validation and cross-validation results are discussed.