Abstract The objective of this work is to investigate the conversion of spent coffee grounds (SCG) into biochar (BSC) and the ecotoxicological effects of the product obtained. The SCG and BSC were characterized by characterized by different techniques (TGA/DTG, FTIR, XRD, SEM, EDS, and EDXRF). Proton Nuclear Magnetic Resonance (1H NMR) was used to characterize the aqueous extract of BSC. The inhibitory effect on lettuce (Lactuca sativa) germination was investigated. Besides, antimicrobial activity evaluation trials were conducted with Azospirillum brasilense and Trichoderma spp. The results showed that in the BSC production process, the extractives and lignocellulosic components in the SCG were partly decomposed. Tests conducted with microorganisms did not reveal any toxic effect of BSC. However, high phytotoxicity against lettuce was recorded for rate 100 t/ha of BSC. This effect was associated with the presence of carboxylic acids identified by 1H NMR in the BSC extract aqueous.

RESUMO Devido a sua grande importância mundial, a cultura do feijoeiro requer uma produção em grande escala, tornando necessária a utilização de fertilizantes. Dentre eles, a ureia se destaca como um dos mais importantes. No entanto, observam-se perdas significativas do nitrogênio por meio de lixiviação, volatilização e desnitrificação. Para contornar esse problema, vários grupos de pesquisa têm estudado o revestimento de fertilizantes com polímeros, uma vez que, por meio deles, é possível controlar a liberação de nutrientes, bem como a sua disponibilidade no solo. Nesse contexto, o presente trabalho revestiu grânulos de ureia por meio de uma mistura simples de difenilmetano diisocianato e poliol poliéter. Foram produzidos cinco tipos de revestimentos variando as proporções dos reagentes. Todas as amostras foram caracterizadas por espectroscopia de infravermelho e microscopia eletrônica de varredura e foram realizados ensaios in vivo com Phaseolus vulgaris L.. Os espectros de infravermelho confirmaram a polimerização por meio da formação da ligação de uretana. As micrografias evidenciaram um recobrimento com espessura inferior a 30 µm. Os ensaios de liberação controlada da ureia em água mostraram que os revestimentos poliméricos retardam a liberação da ureia em aproximadamente 50 % durante um período de 200 min. Já os ensaios in vivo mostraram que a utilização da ureia com revestimentos nas proporções (em massa) de 60:40 e 50:50 (difenilmetano diisocianato/poliol poliéter) elevaram o teor de massa seca em 52 e 22 %, respectivamente. Com isso, conclui-se que é possível revestir fertilizantes nitrogenados de forma simples com eficiência, otimizando a liberação dos nutrientes no solo e tornando-os mais sustentáveis.

ABSTRACT Due to its great global importance, bean crop requires large-scale production, making necessary the usage of fertilizers. Among them, urea stands out as one of the most important. However, significant losses of nitrogen are constantly observed through leaching, volatilization and denitrification. In order to circumvent this problem, several research groups have studied the coating of fertilizers with polymers, since, through them, it is possible to control the release of nutrients as well as their availability in the soil. In this context, the present work aim son coating urea granules by means of a simple mixture of diphenylmethane diisocyanate and polyol polyether. Five types of coatings have been produced by varying the proportions of the reactants. All samples were characterized by infrared spectroscopy and scanning electron microscopy. In addition, in vivo assays were performed with Phaseolus vulgaris L.. Infrared spectra confirmed the polymerization by formation of the urethane bond. The micrographs showed coating with a thickness of less than 30 μm. Controlled release urea tests in water have shown that the polymer coatings delay release of the urea by approximately 50% over a period of 200 min. The results of the in vivo tests, in turn, showed that the use of urea with coatings in the 60:40 and 50:50 mass proportions (diphenylmethane diisocyanate/polyol polyether) increased the dry mass content in 52 and 22 %, respectively. In this way, it can be concluded that it is possible to coat nitrogen fertilizers simply with efficiency, allowing the release of nutrients into the soil and making it more sustainable.