Aplicación de técnicas de remediación en aguas y suelos contaminados por residuos de herbicidas

Resum

Three processes influence the fate of pesticides in the environment. They include: 1) adsorption, 2) transfer, and 3) degradation (photochemical, chemical, and microbiological). These processes condition their persistence (the length of time required for one-half of the original amount to disappear) of a pesticide in the soil. Several processes can move pesticides from the soil: 1) diffusion, 2) volatilization, 3) erosion and run-off, 4) plant uptake, 5) organisms accumulation and 6) leaching. Pesticide leaching is high for pesticides with weak adsorption and high persistence, in climatic areas with high rainfall regime and low temperatures and in soils with limited content of organic matter and sandy texture. Therefore, groundwater vulnerability must be assessed. Preventing groundwater pollution is the optimal solution to avoid a hazardous situation. In addition to the reduction in the use of pesticides with high environmental toxicity, there are two main lines to resolve this problem. The first one is to avoid uncontrolled releases. The second one is the use of physical (membrane filtration, adsorption, etc.), chemical (precipitation, oxidation,), and biological (activated sludge, biological aerated filters, and others) methods to enhance the water quality. In this context, the development of Solar Chemistry Applications is considered to be of preferential importance, especially photochemical processes based on chemical reactions generated after the absorption of solar photons over the surface of some reactants and/or catalysts. Among them, Advanced Oxidation Processes (AOPs) have gained considerable interest and their applications have been recently increased, especially heterogeneous photocatalysis using a renewable source of energy as sunlight. Pesticides are oxidized by “in situ” by generation of highly oxidant species such as hydroxyl (HO•) and other radicals. The main advantages of these technologies is that they achieve the removal or at least reduction of the pesticides by mineralization, in place of transferring them, as it happens with conventional processes. These technologies are especially interesting in regions characterized by an intensive agriculture and particular climatic conditions, where the annual levels of solar radiation are very high and water scarcity exists. In view of the above, the main goals of this work were the following: i) Assessment of the influence of three different composted amendments (agro-forestry, agro-industrial and animal wastes) on the sorption, degradation and mobility of eight herbicides, commonly used in Mediterranean countries and belonging to four different families (triazine, phenylurea, diphenylether and dinitroaniline compounds); ii) Appraisal of the use of solarization and biosolarization as eco-friendly tools to enhance degradation of the herbicides, and; iii) Evaluation of AOPs (heterogeneous photocatalysis and acoustic cavitation) on the photodegradation of these herbicides in different water matrix. The main findings achieved can be summarized as follows: i) Addition of organic amendments significantly decrease herbicide leaching by increased adsorption due to organic matter content, ii) Solar heating techniques (solarization and biosolarization) noticeably enhance herbicide degradation in the soil, mainly due to the increase in soil temperature, and iii). The water treatment by heterogeneous photocatalysis and acoustic cavitation using semiconductor materials (TiO2 and ZnO) in tandem with an oxidant (Na2S2O8), using natural and artificial light, drastically reduces the persistence of herbicides in water although the notorious effect of water matrix components must be considered.