Speaker
Description
Urbanisation is leading to the installation of increasingly efficient wastewater treatment systems to limit discharges into the natural environment. To date, concrete biodeterioration in relation to wastewater treatment systems has been studied mainly in sewer networks, where it has been linked to biological activity in the presence of hydrogen sulphide, leading to irreversible damage. However, new types of degradation of concrete structures have been observed in wastewater treatment plants, mainly in nitrifying and denitrifying units that treat wastewater containing nitrogen compounds (ammonium and nitrate). This treatment permit to transform ammonium to nitrite and then nitrate by bacteria in aerobic condition. The second treatment permit to transform nitrate to nitrogen in anaerobic condition by bacteria. In contrast to sewer networks, the exact causes of these degradations are not yet known.
In order to understand these biodeterioration mechanisms and the durability of binders, samples of mortars based on two different binders (CEM I and CAC) were exposed in 6 different nitrogen pollution treatment basins within the SIAAP. These tanks differ in terms of process: nitrification or denitrification and the presence or absence of biomass support (free or fixed culture). The samples were monitored macroscopically (photos, mass, diameter and surface pH) for 3 years. Each 6 months, the samples were sawed and then analysed by SEM-EDS and micro-raman.
The results showed that decalcification of the cement matrix was exacerbated in the nitrification fixed culture tanks. After more 3 years of exposure, the CAC mortars are more resistant to this biological attack in the presence of nitrifying bacteria than Portland cement-based mortars.
Affiliations
Université Gustave Eiffel, MAST/CPDM, 77454 Marne La Vallée, France
| Keywords | Biodeterioration, nitrogen pollution, sewer treatment, biotreatment |
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