ABSTRACT Biochar derived from coffee waste has been reported as a promising material for heavy metal sorption. However, if the intended use is environmental remediation, knowing the extent to which desorption may occur is critical. Thus, the objective of this work was to evaluate the efficiency of spent coffee ground (SCG) and coffee parchment (CP) biochars pyrolyzed at 700 °C under laboratory conditions, in the sorption of Cd and Pb from aqueous solutions, in a pH range from 2 to 10, and their retention after an induced desorption process with a 2.9 pH acetic acid solution. Both biochars were alkaline, and the initial pH of the solution had a large effect on the sorption capacity of SCG but a small effect on the sorption capacity of CP. The Pb sorption capacity was higher for CP (18.6 mg·g–1) than for SCG (11.4 mg·g–1), while both biochars had low Cd retention capacities (1.18 mg·g–1). Coffee parchment also showed the highest Pb retention (30% to 87%), while for Cd there was no difference between CP and SCG biochars. Our results showed that metal precipitation was the main mechanism for metal immobilization and CP biochar proved to be more reliable than SCG, mainly for Pb, due to its higher sorption capacity and lower metal release by desorption than SCG. These characteristics are particularly important for the use of biochar in environmental remediation. Besides that, the biochar production represents an eco-friendly destination for these feedstocks, contributing to the circular economy.

ABSTRACT The agricultural use of biochar has been the focus of much research in the last decade due to the improvement of soil chemical, physical, and biological attributes. Nonetheless, Brazil still has no specific legislation for biochar, limiting its agricultural use. The objective of the present work is to evaluate the use of biochar produced from spent coffee grounds (SCG) and coffee parchment (CP) by slow pyrolysis at 700 °C according to the existing framework of the Brazilian Ministry of Agriculture, Livestock, and Food Supply (MAPA) legislation for organic fertilizer, soil conditioner or plant substrate. Biochar was characterized according to normative instructions No. 17, 31, 61, 7, 5 and 35. Although not required by the addressed legislation, the semitotal content of macro- and micronutrients was also determined. While CP biochar could be used as an organic fertilizer or plant substrate, SCG biochar, due to its higher Ni content and lower than required cation exchange capacity (CEC), did not meet MAPA legislation criteria to allow for its agricultural use. Future regulations can be based on the current standards, and structural attributes, such as total C content, particle size distribution, and complete macro- and micronutrient determination should be included. Further research may also indicate the viability of biochar use as a soil conditioner based on a more representative set of biomasses with a higher CEC. These considerations will help to take advantage of the benefits of biochar to soil, contributing to a circular economy, which is still at a difficult stage in Brazil.

A estimativa do nitrogênio (N) disponibilizado para as plantas, oriundo de resíduos orgânicos, é usualmente mensurada com base em experimentos em casa de vegetação ou incubação aeróbia. Esses métodos são trabalhosos, de custo elevado e pouco práticos para rotinas de laboratório, exigindo abordagens alternativas. Partindo da hipótese de relação positiva entre frações orgânicas e N disponível, este trabalho teve como objetivo avaliar a qualidade do fracionamento químico do N, por meio do método da hidrólise ácida, em dez resíduos orgânicos. A hidrólise ácida fracionou a matéria orgânica dos resíduos em compartimentos lábeis e recalcitrante de N, os quais foram comparados à quantidade de N absorvida pelas plantas obtida pelo índice de recuperação de nitrogênio (IRN). Relações significativas foram observadas entre a frações lábil 1 (R² = 0,86; p=0,008) e lábil total (R² = 0,89; p=0,004) e os valores de IRN para os resíduos película de café, estercos de frango e bovino, pó de café, turfa e cama de frango.

The nitrogen (N) available for plants from organic residues is usually estimated by greenhouse or aerobic incubation experiments. These methods are laborious, expensive and impracticable for laboratory routines, requiring alternative approaches. Following the hypothesis of positive relation between organic fractions and available N, the aim of this work was to evaluate the acid hydrolysis as an alternative method in comparison to the N absorbed by maize on a greenhouse experiment for 10 organic wastes. The acid hydrolysis fractionated the N of the wastes’ organic matter in labile and recalcitrant pools, which was compared to the amount of N absorbed by the plants measured by nitrogen recuperation index (NRI). There was a significant relationship between the labile pool 1 (R² = 0,86; p=0,008) and total labile pool (R² = 0,89; p=0,004) and the NRI values for the coffee silverskin, chicken and cattle manure, expired coffee powder, peat and poultry litter wastes.