|Abstract:||Untreated wastewater is the main source of pollution of ground and underground drinking water sources. The characteristics of wastewater are poor biodegradability, accumulation in organisms and sediments as well as toxicity for people and the environment. Among pollutants, detergents are some of the most influential as well as organic pollutants, which form adsorbable organohalogens (AOX) together with chlorine.
The purpose of this dissertation is the removal of AOX from industrial wastewaters, which also contain surfactants. We have used coagulation, a conventional physical and chemical process, to remove pollutants from wastewaters, and micellar-enhanced ultrafiltration (MeUF) to treat waters in accordance with the guidelines of sustainable development. In high concentrations, surfactants namely have the ability to form major clusters (micells), causing the solubilization of organic molecules, such as AOX, which then remain on the ultrafiltration membrane. This method of industrial wastewater treatment is much more effective than other separation processes, as it enables us to simultaneously remove a large amount of organic and inorganic pollutants using surfactants, without having to add special chemicals.
The coagulation process was carried out directly on actual wastewaters using different combinations of metal coagulants and industrial flocculants. The results show that this method can effectively treat wastewater to a certain degree. Using conventional metal coagulants, this can be a relatively low-cost process. However, a problem arises with the disposal or the possibility of reusing large quantities of precipitate that forms during the process.
Using the ultrafiltration process, the study was carried out on model and real waters, containing a certain concentration of surfactants, salt, AOX and other organic pollutants, recorded as values of Chemical Oxygen Demand (COD). We have determined the correlation between them and created a mathematical model, which sufficiently describes this correlation. Regression analysis was used to study the correlations between the mentioned measured parameters, enabling us to determine the impact of the concentrations of anionic surfactants, non-ionic surfactants and electrolytes on AOX removal. We created a correlation for each of the components, depicting AOX removal as a linear function of the concentration of individual components. The equations were validated using the analysis of variance. In the last step we created a linear model, which includes the concentrations of all three components, by successively adding the corresponding concentrations into the model.
The results have demonstrated that MeUF shows great potential for removing surfactants and particularly organic pollutants such as AOX. We have confirmed our thesis, that the efficiency of AOX removal on the membrane is a result of AOX solubilization within the surfactant micells and therefore the formation of anionic surfactants is crucial for the effective removal of AOX. Regression analysis was used to effectively confirm that the creation of anionic surfactant micells depends on numerous factors. In the linear models, created for low and high concentrations of anionic surfactants, we focused solely on two factors: the presence of non-ionic surfactants and conductivity. Both factors lower critical micelle concentration (CMC) of anionic surfactants, which makes their influence noticeable only when the concentration of anionic surfactants approaches its CMC value, thus in the model with a high concentration of surfactants. However, this is also where the differences between both models become apparent. It is therefore important to create separate models, allowing us to predict to what extent different wastewaters can be treated, as it is the initial concentration levels of anionic surfactants in the wastewater that is the most influential. |