Assessing the efficiency of modified clays for decontaminate agricultural waste water by pesticide residues

Many anthropic activities, including the agricultural and food industries, give rise to environmental problems for which it is necessary to find solutions. The presence of undesirable substances in water, the soil and foodstuffs can pose a risk to the health and hygiene to humans and animals. It is therefore essential to study methods for removing pollutants from these matrices, as to make them compatible with the maintenance of healthy environmental conditions. This paper aims at verifying the possibility of using modified clays (or organic-clays) to remove contaminants from waste water coming from different areas. This work derives from the necessity to overcome the numerous, negative aspects of current techniques and offers new, effective, easy to use and economic methods. The adsorption of the different pesticides onto micelle-clay complexes and unmodified montmorillonite clay were measured to allow the determination of the maximum pesticide quantity adsorbed in order to obtain a dose-effect relationship for practical applications. The modified clay Cloisite 20A was showed to be more efficient for use in treatment plants for the adsorption of chlorpyrifos and penconazole from aqueous solutions whereas metalaxyl is more efficiently removed by Cloisite 30B. Adsorption tests in laboratory using Cloisite 20 A were also developed for cyazofamid and cyprodinil and the results showed a high affinity of the both fungicides for the organoclay. Therefore Cloisite 20 A was show to be the most efficient organoclay from those tested in this study. This, in part, is explained by the structure of the modifier quaternary salt which contains two aliphatic chains on the structure and determinate a higher space between the layers of the montmorillonite. Subsequently a depuration scheme was developed to test the practical applicability of the Cloisite 20A organoclay and the results showed it to be efficient for decontaminating pesticide-containing water derived from vineyards. The adsorption tests in the pilot system show a removal of three of the pesticide considered, cyazofamid, penconazole and cyprodinil, to be similar to that predicted from the adsorption tests developed in the laboratory. The recovery of the modified clay after the adsorption was shown to be dependent on the presence of surfactants in the pesticide formulation. For the adsorption test of penconazole, which contains a higher quantity of surfactants in the formulation, if compared with the formulation of cyazofamid, the recovery of Cloisite 20 A was 20% higher. For the fungicide cyprodinil, formulated with antifoaming agents, an alternative treatment of the clay-water suspension was necessary. After adsorption the suspension was passed through a compost layer which determinates the sedimentation of the clay at the compost surface. Concerning the waste disposal, for instance the organoclay composted after the adsorption, additional treatments appear to be necessary for pesticides with moderate and high persistence in soil as penconazole and cyprodinil. The fungicide cyazofamid shows a significant decrease after 90 days, in favourable conditions of compost humidity and environment temperature. The results of the modelling exercise shows that the FOCUS PEARL model, generally used for calculating leaching and drainage of PPP from open field cultivations to ground/surface water could be parameterised to simulate PPP emissions from greenhouses to surface water. For the case study, weather conditions were found to have a major role on the PPP emissions from glasshouses and the open field. The more controlled climate in the greenhouse prevented a substantial precipitation excess as was observed for the open field, which had a large effect on the leaching concentrations. Furthermore, in greenhouse cultivation it was noticed that the temperature has a slightly higher influence on CC-M emissions from the greenhouse than the irrigation excess volume. However, the main conclusion of this exercise was that there are potential PPP emissions to surface water associated with crop cultivation in greenhouses, contrary to what is stated in the European Council Regulation 1107/2009, article 3. Therefore a possible use of the outputs of this exercise is in future work to develop decontamination systems for greenhouses or for open field cultivation.