Master thesis

Eduardo Bernardo da Silva (2016)
Use of soil column tests in bench scale for assessing the feasibility of a soil aquifer treatment (SAT) with river water and secondary effluent of a wastewater treatment plant in João Pessoa, Paraíba (Brazil). Master thesis, Technische Universität Dresden, August 2016

Abstract

This thesis presents the results of a soil column experiment conducted in the Laboratory of Hydraulics of the Federal University of Paraíba (UFPB), in João Pessoa, Brazil. Aiming at assessing the feasibility of a Soil Aquifer Treatment (SAT) fed with secondary treated wastewater, 4 soil columns of 65 cm height were used to evaluate the efficiency in the removal of a set of parameters when moving through the unsaturated zone. As a whole, 9 parameters were investigated during one month and a half: total suspended solids (TSS), total dissolved solids (TDS), dissolved organic carbon (DOC), chemical oxygen demand (COD), biochemical oxygen demand (BOD), sulfate, phosphate, ammonium-nitrogen and coliforms (total, thermotolerants and E.coli). Soil characterization tests were also carried out, for determining water content, total porosity, grain size distribution and hydraulic conductivity. The results have shown that the analysed soil samples have both high permeability (10-3 cm/s), correspondent to sandy media, what was found to be in line with the results of the grain size distribution. As for the outcomes of the chemical and the pathogens analyses, the results were revealed to be very irregular, showing great errors. The interpretation of them has led to the conclusion that several factors actually have contributed to the inconsistency of the results, such as the chosen packing way (undisturbed), the columns set-up, the variable flow adopted and the way the collected wastewater was stored. After all, even with these aforementioned problems, a few parameters could be effectively removed, such as dissolved organic carbon (up to 83% of removal), BOD (up to 94%), phosphate (up to 96%) and ammonium-nitrogen (up to 100% of removal). The removal rates all find equivalents in the scientific literature. In spite of that, the results could not lead to a conclusion upon the feasibility of the analysed soils for SAT purpose, not only because of the lack of statistical consistency from the derived data, but also due to the whole period of the experiment, considered too short for drawing any relevant conclusion.