Síntese de fertilizantes de liberação lenta usando os resíduos da carcinicultura como fonte de nutrientes

Abstract

Shrimp farming is one of the fastest growing productive sectors and contributes to the global fish supplies. Its solid and liquid residues are high in nutrients and organic materials from the feed, shrimp excreta and animal fragments. The disposal of this waste, in addition to generating environmental damages, such as eutrophication and soil degradation, causes the reduction of biodiversity, and produces economic problems, since valuable biomaterials are wasted. Therefore, it is of great importance to develop techniques capable of inserting waste into the production chain, strengthening the premise of sustainable development of shrimp farming, due to its economic and social importance. In this work, slowrelease fertilizers were synthesized utilizing the solid residue from shrimp farming, chitosan, montmorillonite and urea. The spheres of fertilizers were produced and characterized by means of elemental analysis (CHN), giving values of 14,4-18,4% of carbon, 5,6-6,9% of hydrogen and 12,3-19,3 of nitrogen. The infrared spectra (FTIR) showed absorption bands referring to functional groups that make up the spheres, confirming the presence of hydroxyl and carboxylate groups present in the organic matter of the residue, as well as bands typical of chitosan, amide bond, and group band Al-O, characteristic of montmorillonite. The SEM images confirmed the formation of regular spheres with a uniform surface. For the quantification of urea in water, a calibration curve was constructed by UV-Vis spectrophotometry, at a wavelength of 427nm, obtaining a coefficient of determination (R2 ) 0.9977, demonstrating the efficiency of the method for determination urea. Water release tests showed that fertilizers release urea slowly, reaching a maximum after 15 days (95-97%). The kinetic data of urea were adjusted to the Higuch, indicative that the release mechanism occurred by Fickian diffusion. In soil release study, presented that nitrogen is released slowly by the fertilizers produced, which can be classified as slow-release fertilizers. The degradation study presented the biodegradability of fertilizers in the soil, with a rate higher than 60% after 30 days of incubation in the soil, indicating their ability to be applied to the soil without generating waste. The application of fertilizers in corn cultivation showed superior root length and size compared to the control. The findings in this work show a new and important approach to be given to shrimp farming waste.