Abstract
Current intensive agricultural practices, although highly successful in terms of production, have been found to be environmentally unsustainable. One of the crucial approaches to increase agricultural sustainability is the recycling of organic wastes, since these materials often contain many beneficial nutrients for soil and agriculture. Recently, pyrolytic conversion of biodegradable waste into charred material has gained global attention as an amendment to recycle nutrients while improving soil health. Increasing interest in the beneficial applications of pyrolyzed biomass has expanded multidisciplinary areas for science and engineering. The fertilizers used in this study were prepared by pyrolyzing mixtures of two abundant residues in Mediterranean areas: grape seeds and sewage sludge, in different proportions (100% GS, 75% GS-25% SS, 50% GS-50% SS, 25% GS-75% SS, 100% SS). In addition, fresh sludge was mixed with pyrolyzed grape seeds and included as an additional treatment. In this study, the positives and negatives of the application of biochars on agronomic potential and environmental risk have been addressed, taking into account P, Zn, Cu, Fe, As and Cd. In order to choose the best mixture, it is necessary to find a compromise between maximizing the beneficial elements that are translocated to the plant crop, as well as reducing the elements that are leached. Results of a 6-week greenhouse study indicated that the unpyrolyzed sludge mixture contained the largest amount of available nutrients Fe, Cu and P. In agreement, this treatment mixed with a Chromic Luvisol soil (40 ton/ha) increased the uptake of these elements in corn (Zea mays L.—LG ambitious). The yield also increased by 60% in this treatment. However, this mixture also contained more contaminants (As, Cd) which were extracted with Ammonium Bicarbonate-DTPA. According to our results, the treatments where grape seeds and sewage sludge were mixed at 50% and then pyrolyzed exhibited the optimal compromise between efficiency (nutrients uptake) and tolerable levels of potentially toxic elements in leachates.
Highlights
The FAO gives a central role to agriculture in order to achieve the Millennium objectives.By improving agricultural productivity and promoting better nutrition, the targeted reductions in worldwide poverty and hunger could be met [1]
The treatments where grape seeds and sewage sludge were mixed at 50%
Pyrolysis of materials increased the total concentration of micro-nutrients, P and potentially toxic metals (As, Cd) (Table 4) when compared to the original raw mixtures (Table 2)
Summary
The FAO gives a central role to agriculture in order to achieve the Millennium objectives.By improving agricultural productivity and promoting better nutrition, the targeted reductions in worldwide poverty and hunger could be met [1]. Intensive agriculture does generate a large negative impact due to high levels of agriculture inputs, such as chemical fertilizers. These produce the highest yield of crops at the lowest possible cost [2], maximizing food production. The real objective is to replace the linear process—based on production, consumption and disposal—with a circular economy in which the materials are reincorporated into the production process in order to create new products In this approach, waste management plays a key role, since many residues contain beneficial nutrients for agriculture [3]. It must be ensured that these fertilizers from waste do not cause negative effects on the soil and the environment
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