Chemical oxidation and adsorption for wastewater treatment
- Autores: Bruno Domenjoud
- Directores de la Tesis: Santiago Esplugas Vidal (dir. tes.)
- Lectura: En la Universitat de Barcelona ( España ) en 2012
- Idioma: español
- Tribunal Calificador de la Tesis: J. Giménez Farreras (presid.), Montserrat Perez Moya (secret.), Michel Roustan (voc.)
- Materias:
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- Resumen
This work deals with the tests of advanced treatment processes applied to sewage wastewaters aiming to control both their content in micropollutants in order to strongly reduce their release in the environment and their potential of fouling caused by the presence of dissolved organic matter in order to make the membrane technologies more economically viable.
The tested processes were selected according to a detailed bibliographic study. For both purposes, control of the release of synthetic contaminants and reduction of membrane fouling, ozonation, ozonation combined with the addition of hydrogen peroxide, a process that belongs to the so-called category of the advanced oxidation processes, and activated carbon adsorption processes were shown to be the good alternative treatment candidates. The strategy adopted to carry out the full study was based on chemical engineering and economic aspects.
A broad range of analytical tools was employed, covering conventional analysis used for wastewater characterization, advanced organic matter characterization methods, high resolution spectroscopy-based methods, filtration, toxicity tests. On one hand, they made possible to study the impact of the processes on different mechanisms involved in the membrane fouling phenomenon and to connect these changes with the modifications observed in the effluent characteristics. On the other hand, they permit to assess the possible limitation of micropollutant removal induced by competitive ozone reactions.
A first preliminary study was addressed to evaluate the processes¿ performances on the bulk of organic matter. On the basis of the results obtained, ozonation and activated carbon adsorption were selected to assess their impacts as membrane pretreatment and micropollutant content control. Simultaneous addition of hydrogen peroxide during ozonation was discarded because it did only present a kinetic advantage that was also to the detriment of the oxidation efficiency. The ozone doses to study the ozonation as membrane pretreatment and for the control of specific organic contaminants were chosen to match with the first transition stage of oxidation during which the kinetics of COD oxidation slows down above 5 times.
According to the membrane fouling issue, ozonation and activated carbon filtration displayed largely different effects. The filtration tests demonstrated the positive impact of ozone on the filtration flow and on all the blocking mechanisms identified, notably, the cake filtration. The improvements of the filtration performances achieved by the ozone application are directly linked with the breakdown of solids and high molecular weight molecules. Moreover, the strong loss of effluent aromaticity and hydrophobicity during the first oxidation stage suggests that the deposition of organic matter through hydrophobic interactions onto the membrane should be greatly reduced during operation. The results obtained with the activated carbon are less conclusive. After adsorption the filtration flow remains slightly equal or get worse. Although activated carbon adsorbs the major part of the organic matter, it is not able to remove the organic matter fraction that mainly controls the organic fouling, that is to say the high molecular weight substances. A possible leakage fine activated carbon particles from the activated carbon column may also contribute to the low flow conservation during the filtration tests.
According to the specific organics contaminant issue, activated carbon filtration as well as ozone treatments are really effective. Most of the quantified organic micropollutants, and among them the priority and priority hazardous substances listed in the European Water Framework Directive (WFD 2008/105/EC), are removed during the first oxidation stage as well as after adsorption. Nevertheless, not all the compounds can be efficiently removed as cyclohexane family compounds (ozone) or volatile solvents (activated carbon). It is also relevant noting that significant limitations of micropollutants removal could not be evidenced despite the differences in quality of the treated sewage effluents.
On the basis of the results obtained ozonation technology provides an interesting answer to the continuous release of deleterious compounds from municipal wastewater treatment plants (WWTP) and also as membrane pretreatment. Although activated carbon application as pure adsorbent for the removal of contaminants is very effective, the economic study shows that ozonation is more suitable. In addition, the good performances of ozone independently from the wastewater quality lead us to wonder whether ozone must be confined to the category of advanced treatment or it can be integrated to the conventional primary and secondary treatments? In all cases, its next implementation in municipal WWTP, at least as advanced treatment, would contribute to the preservation or recovery of the good status of all natural resources water and also to the ecosystem worldwide.
