Doctoral Thesis in Civil Engineering
Isabel Cristina Castanheira e Silva
University of Beira Interior, Covilhã, Portugal
Geopolymeric binders are artificial materials obtained by alkaline activation of alumino-silicate materials. In this work, several geopolymeric artificial aggregates (AGA) were initially developed, using waste mud from Panasqueira’s mines and various ratios R(P/S) and R(S/H). The mixture that present itself as the most stable in water was selected to be used as a fix-film wastewater treatment processes.
After that, the AGA’s compression strength was tested, as well as its resistance to acid attack and abrasion, for different dry conditions and water immersion conditions. Also, its physical and chemical proprieties were analysed, and it was observed that the density, the specific surface area, the resistance and the durability were close to the ones existent in another materials, commonly used as fix-film wastewater treatment processes. Therefore, those proprieties are adequate for that.
It was verified that the disintegration of samples produced under certain curing conditions, the rise of the water pH and decrease of the water resistance would be associated to an incomplete geopolymerization reaction, that might be explained by an insufficient concentracion of the activation solution, which resulted in a low Si and Al dissolution rate.
Following that, the AGA were put on a biological filter, that filtrates through submerged packed bed, in order to evaluate its efficiency in removing specific pollutants of urban residual waters. It was observed that, independently of the operating conditions, the phosphor removal occurred essentially through adsorption and that the organic matter, ammonia and nitrate removal occurred through biodegradation mechanisms. The rates and efficiency of those processes were close to the ones observed in studies where other aggregates were used.
The fed-batch tests allowed a much higher organic matter and ammonia removal than the ones operated in continuous. This may have been related to a much elevated retention time, which favored the contact between substrates and biofilm.
Hence, the development of artificial materials through alkaline activation of waste mud in order to be used as fix film in waste water treatment by filtration presents itself as viable solution to compete with the traditionally used materials.