ABSTRACT
This Doctoral Thesis has been focused on the application of Advanced Oxidation Processes (AOPs) at circum-neutral conditions for elimination of chemical (emerging pollutants) and biological (zebra mussel larvae) pollutants in natural waters by solar heterogeneous photocatalysis (TiO2) and photo-Fenton process at neutral pH.
Oxidation treatments applied to emerging pollutants have been made in a solar simulator and pilot plant and their degradation was followed by employing different analytical techniques such as UHPLC, GC-MS, spectroscopy (COD, DQO); moreover, a study of toxicity evolution (Vibrio fischeri)  has been made during each process. 
Titanium dioxide studies in solar simulator are able to remove the totality of pollutants in less than 240 minutes, with an increase of the toxicity to 50% at 120 minutes of the treatment, which practically disappears at the end of treatment. When the process is scaled to pilot plant slower degradations were perceived due to differences between spectrums (solar and solar simulator) in the region of 280-300 nm.
In this work it is important to emphasize that photo-Fenton reactions yield at circum-neutral medium is acceptable for its application and is strongly influenced by initial concentrations of pollutants and humic acids present in the medium, which oppose its function of stabilizing iron in solution, its potential role as internal filter and scavenger action of active species. Moreover, toxicological assays show fluctuations during the treatment time due to a generation of toxic reaction intermediates, having identified the main ones by GC-MS. In addition, a mechanistic study has been made to hydroxyl radical role in the process, being lower in neutral than acid medium. The secondary clarifier effluent has been treated to remove emerging pollutant traces, which have reached to detection limit concentration and disinfection effluent by coliform bacteria removal.
The effectiveness of photocatalytic processes in the elimination of zebra mussel larvae (Dreissena polymorpha) has been evaluated by polarized light microscope. Among all the treatments were carried out, the solar photocatalysis treatments (TiO2) and photo-Fenton process at neutral pH seem to be the most appropiate. The heterogeneous photocatalysis has the added problem due to the need of coupling a clarifier stage, therefore the photo-Fenton processes are those the best prospects; the slightly acid (pH=5.5) offers the possibility of use as irrigation water and makes possible a treatment that improves the effectiveness in relation to neutral conditions. Neutral pH treatments in the Ebro´s waters also show effectiveness due to the presence of humic substances, which are capable of stabilizing the necessary minimal quantity of iron for the photodegradation. The pilot plant application at pH=7 with reagents dosification (Fe2+ and H2O2) produces 90% dead larvae at 170 minutes of t30W.