Innovative methodologies for the purification of polluted water

Pharmaceuticals constitute a major class of Emerging Contaminants due to their extensive global consumption, intrinsic chemical stability, and limited removal in conventional wastewater treatment plants. Their persistence and bioactivity raise considerable environmental and toxicological issues, necessitating the development of efficient, scalable, and sustainable remediation strategies. This thesis first provides a systematic review of heterocyclic pharmaceuticals, synthesizing current knowledge on their sources, environmental occurrence and fate, physicochemical persistence, transformation pathways, and documented toxicological profiles, including neurotoxicity, genotoxicity, mutagenesis, and carcinogenicity. Examples of targeted experimental studies employing Advanced Oxidation Processes and adsorptive materials are also presented. The analysis identifies substantial gaps in the understanding of long-term ecological risks and highlights pressing limitations in existing remediation technologies. Sildenafil and tadalafil are heterocyclic pharmaceuticals used to treat erectile dysfunction that, in recent years, have gained considerable attention due to their widespread legal and illegal use, including increasing recreational consumption among young people. Their high stability and environmental persistence, together with the generation of potentially hazardous phototransformation products, pose risks to human health and ecosystems. Conventional wastewater treatment plants are largely ineffective at removing these compounds, resulting in their continuous release into effluents and subsequent contamination of surface waters. This study evaluated photooxidation processes under simulated solar irradiation for removing sildenafil and its derivatives from water using three oxidants (hydrogen peroxide, peroxymonosulfate, and persulfate), as well as photocatalytic processes employing a TiO₂ catalyst. Potential transformation products were assessed and tentatively identified using liquid chromatography coupled to mass spectrometry with electrospray ionization and multiple-stage mass spectrometry. The Sunlight/peroxymonosulfate system proved most effective, achieving complete degradation in distilled water after 80 minutes and in synthetic wastewater after 130 minutes. Acute toxicity tests on Vibrio fischeri confirmed the non-toxicity of treated solutions, demonstrating the environmental compatibility of the Sunlight/peroxymonosulfate system. The global rise in depressive disorders has led to increased prescription of venlafaxine, a serotonin–norepinephrine reuptake inhibitor. Its physicochemical stability, limited biodegradability, and incomplete removal in wastewater treatment have resulted in its frequent detection in effluents and surface waters. The persistence and biological activity of venlafaxine underscore the need for effective, sustainable treatment technologies, including Electrochemical Advanced Oxidation Processes, which employ reactive species such as hydroxyl (•OH) and sulfate (SO4−•) radicals to achieve the mineralization of pollutants. While most studies employ boron-doped diamond anodes, these present practical challenges, including delamination, high cost, limited scalability, and short service life. In this thesis, platinum was used as a stable alternative for galvanostatic electrochemical degradation. Experiments conducted in 0.1 M Na2SO4 at pH 9 under a current density of 25 mA cm-2 achieved 94% degradation of 25 mg L-1 venlafaxine within 7 hours, following first-order kinetics (k = 0.0084 min-1). LC-MS (Liquid Chromatography-Mass Spectrometry) analysis identified key transformation intermediates, revealing predominant degradation pathways involving demethylation, hydroxylation, and aromatic ring modification. In silico toxicity predictions confirmed that these intermediates pose significantly lower ecological risks than the parent compound. To complement oxidative treatments, sustainable adsorption-based approaches were investigated. Activated carbons were synthesized from spent brewery grains using K2CO3 as an activating agent, with both conventional and microwave-assisted pyrolysis employed to assess the effect of thermal treatment on adsorbent properties. Microwave-assisted activated carbon exhibited higher surface areas, enhanced porosity, and improved surface functionalization, as confirmed by Scanning Electron Microscopy and BET (Brunauer-Emmett-Teller) analysis. Adsorption experiments showed that, with microwave-derived activated carbon, equilibrium was reached within 2 hours, achieving removal efficiencies of 62% ± 3% in ultrapure water and 49.5% ± 0.6% in wastewater at a dose of 50 mg L-1. Kinetic modeling indicated pseudo-second-order behavior, suggesting chemisorption as the dominant mechanism, while equilibrium isotherm fitting supported monolayer adsorption on a homogeneous surface with identical adsorption sites. The superior performance of the microwave-derived activated carbon is attributed to its enhanced porosity and improved textural properties resulting from rapid and uniform heating during microwave-assisted pyrolysis. The results support the viability of transforming agro-industrial waste into high-value adsorbents and contribute to the development of greener, circular, and robust solutions for addressing emerging pharmaceutical contaminants. The removal of sildenafil and tadalafil was similarly investigated using activated carbons and natural and organo-modified montmorillonite with didodecyldimethylammonium bromide (DDAB). Microwave-derived activated carbons achieved equilibrium in 2 hours with removal efficiencies of 90.3% ± 0.1% for sildenafil and 95% ± 2% for tadalafil at a dose of 50 mg L-1. DDAB-modified montmorillonite reached equilibrium within 60 minutes, removing 84.9% ± 0.1% of sildenafil and 91% ± 3% of tadalafil using a dose of 250 mg L-1. Isotherm analyses and kinetic modeling confirmed that chemisorption and specific interactions with active sites govern adsorption, while differences in surface heterogeneity explain variations in capacity across the different materials. Collectively, this investigation demonstrates that bio-derived activated carbons and engineered clay minerals are effective and sustainable adsorbents for removing sildenafil and tadalafil from aqueous matrices. This study advances sustainable and economically viable water-treatment strategies aligned with circular-economy principles. By evaluating technology and resource-recovery, it offers a scientific framework for designing systems that reduce waste, save energy, and encourage material reuse. The research provides a solid foundation for mitigating pharmaceutical contaminants in water, promoting ecosystem health, and resilient management practices.