Use of vermicompost for the removal of toxic metal ions of synthetic aqueous solutions and real wastewater

Abstract

Samples of vermicompost were used to decontaminate aqueous media containing Cd2+, Cu2+, Mn2+, Ni2+, Pb2+ and/or Zn2+ ions at concentration up to 10X higher than the limits of National Council of the Environment (Resolution 430/2011). For this purpose, 50.00 mL of synthetic solutions (pH 0.9 just after preparation) and wastewater from a chemical laboratory were stirred with dried vermicompost (~10.0000 g), without sieving or with diameter ≤ 0.053 mm. Aqueous media were treated with vermicompost, either at rest (24 to 96 h) or under mechanical agitation (2 to 10 h). All elements were spectrometrically determined in the different supernatants. In the synthetic solutions, except for Mn2+ and Zn2+, concentrations were lower than the legal limits or than the limits of detection, when vermicompost without sieving was used. After treating synthetic solutions with sieved vermicompost, Cd2+, Cu2+, Ni2+, Pb2+ e Zn2+ ions concentrations were undetectable, while Mn2+ concentrations were too close to the legal limits. In the wastewater, Cd2+and Pb2+ concentrations, which were 1.5 and 3.8X higher than the legal limits, respectively, were undetectable after treatment with vermicompost without sieving. Besides its efficiency of retaining the evaluated cations, vermicompost was able to increase the aqueous media pH from 0.9 to 6.0 ± 0.5.