Influence de la température sur l'élimination du carbone organique biodégradable

Influence of temperature on the removal of biodegradable organic carbon

SAGEP - Eau de Paris 9, rue Schoelcher, 75074 Paris - France

Résumé

Le suivi du carbone organique dissous et de sa fraction biodégradable a été effectué à différentes températures allant de 5 à 15°C sur une chaîne de traitement comportant plusieurs étapes biologiques.

L'efficacité d'élimination du carbone organique dissous biodégradable (CODB) entre la filtration lente et la filtration sur charbon actif en grains (CAG) a été comparée.

L'optimum d'efficacité de la filtration lente, dans nos expériences, est atteint pour une température supérieure ou égale à 15°C alors que celui du CAG est atteint dès 10°C. A 15°C, l'efficacité de la filtration lente pour l'abattement du CODB est supérieure à celle de la filtration sur charbon actif en grains.

Pour des températures plus froides de 5°C, l'efficacité est comparable. Pour des températures de 10°C, le CAG semble plus efficace.

Abstract

The removal of BDOC has been studied at every step of treatment. The influence of temperature is very important, particularly for biological steps: slow sand filtration and GAC filtration. The efficiency of slow sand filtration is very good at 15°C with a removal of 76% of BDOC. Nevertheless, at this temperature, the concentration of BDOC of water at the outlet of slow sand filters is higher than at lower temperatures.

The biological action of slow sand filters produces BDOC. At colder temperatures (5°C), efficiency of slow sand filtration is not very good (20%) and the optimum of temperature for a good efficiency must be more than 10°C.

Results on GAC seem very different: at cold temperature (8°C), the removal is 35% and we have observed a maximal removal of 55% at a temperature of 9°C.

GAC must be regenerated because it works as a biological contactor and not as an adsorption reactor. Nevertheless, at high temperatures (15°C), efficiency of slow sand filters is better than GAC filters.

During ozonation step, we observe always an increase in BDOC. But this increase depends on temperature and on applied ozone dose. Four different parts have been differentiated on the BDOC of ozonated water: BDOC released by slow sand filters, particular BDOC redissolved, BDOC released by refractory DOC with ozonation and the ground level always released by slow sand filters whatever the temperature. We have observed an increase of BDOC released by slow sand filters, an increase of particular BDOC released by ozonation with the temperature and a decrease of BDOC from refractory compounds.

The removal of BDOC on GAC does not exceed 60% at the temperature of 15°C and it seems that for a temperature of 5°C, efficiency of these two steps is comparable (20-30%). At 10° C, GAC seems more efficient than slow sand filters.

We have attempted to differentiate some parts od BDOC in ozonated water. We have observed an increase of BDOC released by slow sand filters with temperature and a decrease of BDOC produced by refractory compounds with ozonation.