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The leather industry (tanneries) generates high amounts of toxic wastes, including solid and liquid effluents that are rich in organic matter and mineral content. Vermicomposting was studied as an alternative method of treating the wastes from tanneries. Vermicompost was produced from the following tannery residues: tanned chips of wet-blue leather, sludge from a liquid residue treatment station, and a mixture of both. Five hundred earthworms (Eisenia fetida) were added to each barrel. During the following 135 days the following parameters were evaluated: pH, total organic carbon (TOC), organic matter (OM), cation exchange capacity (CEC), C:N ratio, and chromium content as Cr (III) and Cr (VI). The results for pH, TOC and OM contents showed decreases in their values during the composting process, whereas values for CEC and total nitrogen rose, indicating that the vermicompost reached maturity. For chromium, at 135 days, all values of Cr (VI) were below the detectable level. Therefore, the Cr (VI) content had probably been biologically transformed into Cr (III), confirming the use of this technique as an advanced biological treatment. The study reinforces the idea that vermicomposting could be introduced as an effective technology for the treatment of industrial tannery waste and the production of agricultural inputs.

Purpose In this study, vermicomposted tannery wastes were applied in the organic cultivation of sweet pepper in a greenhouse. The effects of this organic matter addition on plant development and on the distributions of Cr(III) and Cr(VI) in plant tissues and organs were assessed. Methods In a greenhouse, organic sweet peppers were cultivated adding vermicomposted tannery to the substrate (sample VRC) and the results were compared with the samples control (dYL; only soil) and reference (NPK; adding mineral fertilizer). The growth, nutritive value and fruit production were assessed to evaluate the plant development in different types of substrate. Besides evaluating the biostimulant effect of vermicomposts, the distributions of Cr in plant tissues were also studied. Results Up to three harvested sweet peppers were obtained per plant, compared with only one fruit for the reference treatment with NPK addition. Based on the Cr dynamics in the plants, the highest concentration was found in the fruits, varied as follows: fruits > stem and stalks > leaves = root; however, the Cr concentration in the fruits was statistically the same across all treatments. Additionally, only Cr(III) was detected and quantified in the fruits. Conclusion The addition of vermicompost was biostimulating to plants and positively influenced their development. Based on the Cr dynamics in the plants, since the Cr concentration was the same across all treatments, it demonstrated that the addition of tannery residues to the vermicompost did not negatively influence the health benefits or food security of the produced fruits.

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