Medici, Antonio (2025) Study of urban and industrial wastewater for the removal of organic pollutants, in order to reuse the treated waters. [Tesi di dottorato]

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Abstract

The increasing presence of emerging contaminants and the complexity of industrial effluents represent one of the most pressing challenges in the field of sustainable water management and environmental protection. Different oxidation/disinfection processes were studied, such as chlorination (currently one of the most widely used) but also innovative advanced oxidation processes (AOP) from a chemical and ecotoxicological point of view. The research mainly focused on the study of by-products generated by the oxidation of various model emerging pollutants generally found in wastewater. Two different organic molecules used in sunscreens to absorb harmful UV rays, namely Ethylhexyl triazone and Octocrylene, were studied, which, following classical treatment with hypochlorite, showed the formation of even more toxic by-products, demonstrating how the process with hypochlorite, although necessary to reduce the bacterial load in the effluent, can lead to the generation of by-products that are extremely more toxic than the starting molecules. Subsequently, other model molecules such as sartans, Losartan, Irbesartan, Valsartan, were studied, investigating different processes, both classical and advanced oxidation through Fenton processes, with oxidants such as peroxymonosulphate and percarbonate catalytically activated by iron. It was shown how these advanced processes lead to the formation of by-products that are in any case toxic to the species tested, except for the Fenton-like process with Fe(II)-activated peroxymonosulphate, which led in the case of Valsartan to potentially less toxic products. In addition, an innovative AOP process was investigated for wastewater treatment based on the use of hypochlorite and sunlight/UVA on another emerging pollutant, Nimesulide. It has been shown that treatment in the absence of light at near-neutral pH can also degrade the pollutant in wastewater in a short time only in the presence of UVA or sunlight, resulting in sub-pipelines at an advanced oxidation stage, characterized by high-resolution mass analysis, and a clear reduction of organic carbon in solution compared to the process in absence of light. Regarding industrial wastewater, processes to reduce the toxicity of vegetation water, generated by the oil industry, were studied by means of classical chemical, adsorption and precipitation processes that showed, through ecotoxicological tests, the attractiveness of flocculation processes to decrease its toxicity with respect to a model organism. Finally, a non-destructive multivariate chemometric (partial least square regression) method via Near Infrared spectroscopy (NIRs) was developed for the on-line control of certain tanning substances used by the tanning industry such as synthetic and natural tannins, glutaraldehyde, Cr(III) and even innovative tanning agents such as zeolites. The method enables the evaluation of the concentration of substances used during the tanning process through diffuse reflectance NIRS analysis of liquid solutions. This allows for direct monitoring without the need for sample pretreatment, thereby optimizing the process by assessing concentrations in real time. Consequently, it could improve the efficiency of chemical usage, reduce waste generation, and minimize the environmental impact of the pollutants involved. This PhD thesis aims to identify and optimise more sustainable treatment approaches that are effective in abating industrial wastewater pollution. The goal is to provide a solid scientific basis and tools to support a more conscious management of water resources, to reduce the environmental impact of production processes and to ensure better protection of biodiversity and human health.

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